Bottlehead Forum

Other Gear => Headphones => Topic started by: Deke609 on July 05, 2018, 01:53:30 PM

Title: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 05, 2018, 01:53:30 PM
Hi all - what Bottlehead amp would you recommend for the Audeze LCD 4 (200 ohms)?  I think I saw a post from Doc B. suggesting that the Crack, with a 5998 in place of the 6080, can be paired with cans having a input impedance as low as 70 ohms.  But I've read on other forums that the LCD 4s are power hungry - so I'm not sure if this would be a good paring.  I built a heavily modded Crack w/Speedball (w/ Tung Sol 5998) and love it, and so will try it with the LCD 4s for sure, but do others think another amp would be superior - e..g., S.E.X.? - perhaps even a Kaiju or Stereoamour if they can can be modded for output to cans?

I have no technical or theoretical knowledge about audio circuits and the like - just a guy that loves good sound and DIY soldering projects :)

thanks in advance,

Derek

Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on July 05, 2018, 01:56:00 PM
S.E.X. is a sure bet. Mainline might have enough power, but I have not tried it with the LCD4. Another sure thing would be the Neothoriator. I do have one available.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 05, 2018, 05:59:01 PM
Many thanks Doc.

The Neo is intriguing but outside my price range. So the S.E.X. it is.  But I am still concerned about driving the LCD 4s to their full potential. 

What do people think about running dual S.E.X. monoblocks, one for left channel and one for right?  Is that doable? Maybe with gross and fine attenuators on both to get matching volume?

If the dual monoblock approach makes sense, my next question is: Do I get and build 1 S.E.X. now in stereo configuration to see how its sounds, and then convert to monoblock if I think the headphones need more power, or just build the dual monoblock configuration from the get go?  Would the conversion from stereo to monoblock be an entire rebuild with newly sourced parts? If yes, I'd rather just start with the dual monoblock project. 

many thanks again,

Derek

Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on July 05, 2018, 06:41:51 PM
Start with one. It's probably plenty of power. If you feel you must have more power you could build a Stereomour II with DC filament supply and make up a binding post to whatever-your-headphone-connector-is adapter
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 05, 2018, 07:40:16 PM
Thanks Doc.  Order for S.E.X. placed.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on July 05, 2018, 08:10:22 PM
Thank you!
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 11, 2018, 01:28:37 PM
Doc - Apologies for belaboring the issue, but I know myself: even if the S.E.X. sounds great paired with the LCD 4s, I'll always be wondering what they would have sounded like driven by the Stereomour.  So I'm almost decided on replacing my S.E.X.order with an order for the Stereomour with all upgrades.  The only thing holding me back is a question about noise floor.  In a 2015 thread, Paul B. stated that the Stereomour should not be used drive headphones with an input impedance of 62 ohms b/c the noise floor would be too high.  I don't know if Paul B's answer predated the the DC filament upgrade or whether he would have given the same answer in respect of the LCD 4s.

The LCD 4s, to which the amp I build will be dedicated, are a different beast: 200 ohms impedance and sensitivity of 97dB

For comparison: the LCD 3s (which I will not be using) have an input impedance of either 100 or 50 ohms and sensitivity of 102dB

The BH description of the DC filament upgrade includes the following:

"This supply will reduce the already exceptionally low noise floor of the AC heated Stereomour II amplifier to levels acceptable for use with the most sensitive horn speakers. Its installation is recommended in particular for use with speakers above [email protected]@1M sensitivity. "

That sounds like a good match for the LCD 4s with their sensitivity of 97dB.  Am I wrong about this? I can live with a faint hum at quiet spots in the music in exchange for greater dynamics.   

many thanks in advance,

Derek

Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on July 11, 2018, 02:02:12 PM
Yes, the Stereomour II with the DC filament supply will work well and be very quiet. The comments from 2015 are about an earlier version of the kit that did not have the DC filament upgrade. You will of course have to make up some sort of adapter to connect the speaker cable binding posts to your headphone cable. Your best bet is to contact Eileen tomorrow (queen at bottlehead dot com or 206-451-4275) when she is back in the office and she can help you with upgrading the order from S.E.X. to Stereomour II.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 11, 2018, 02:08:30 PM
That's great.  Thanks a million, Doc.  I will contact Eileen tomorrow as you suggested.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on July 12, 2018, 05:20:13 PM
Those comments I made were indeed about the Stereomour I, which would work OK on a very power hungry headphone like the K1000, but would be too noisy for much else that was on the market.

The Steremour II with the DC heater upgrade will be significantly quieter and capable of driving just about any headphone you can think of.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 13, 2018, 05:39:58 AM
Thanks Paul.  I've put in my order for the Stereomour II with all 3 upgrades. 

Even if there is noticeable hum, I think it will be worth it just to hear what the LCD 4s are capable of when there is tons of power on tap.

Worst case scenarios: either (a) I thereafter engage in endless modding/tweaking in search of an even lower noise floor (which would be fun - so not that bad of a scenario); or (b) I have an excuse to get a nice pair of bookshelf speakers.

And who knows, maybe you guys at BH will come up with an upgrade that lowers the noise floor even further, or, dream of dreams, converts the SII into a headphone amp for power hungry cans.  :)


Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on July 13, 2018, 05:44:45 AM
The modifications to allow something like the Stereomour II with all the upgrades to work on a headphone like a Grado would involve adding two resistors per channel to pad the output down and keep the amp loaded.  I generally recommend a pair of 16 ohm and a pair of 1 ohm resistors to accomplish this.

For what you're doing, you may not need any resistors at all.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 13, 2018, 10:54:01 AM
Many thanks Paul. I'm really looking forward to the Stereomour II with the LCD 4s.  Once I've got the amp running and settled in, I'll be sure to post about the results. 
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 17, 2018, 05:30:59 AM
Paul - Just following up about using resistors to lower output and keep the amp loaded.  Is there an optimal range of load that needs to placed on the amp for it to sound its best?  I.e., does the amp need to perform a minimum amount of "work" before it comes into its own?

Not an urgent question - I'm simply trying to educate myself about what all the "stuff" in the amp actually does.  At present, I have only a very rudimentary knowledge and am trying to improve on that.

many thanks in advance,

Derek

Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on July 17, 2018, 08:39:34 AM
If the resistor values get too large, you'll lose damping of the headphones and the bass will get lumpy on you. If the resistor values are too small, you'll load the amp down and it will distort.

Using about twice the intended load seems to be a good trade-off between these issues.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 18, 2018, 12:45:33 PM
Many thanks again Paul.  The damping vs distortion issue is very helpful. I'm doing a bit of self study about these and other issues and hope to get back to you in a few weeks with what I hope at least will be the right questions. 

By the sound of things, finding the right damping/distortion balance is matter of "try and listen" experimentation.  But it also sounds like that, with enough experimentation, I should be able to get the amp nicely dialed in for the LCD 4s. My current working idea is to create a box with stepped attenuators that would plug into the binding posts and then allow connection of the headphones - so that the load at the output could be adjusted to see what sounds best.  I think this might be a bit of construction challenge as the resistors for the attenuators would probably need to be rated for 4W or so to cover off the 3.5Wpc? and would therefore be quite large and possibly expensive.  But the ability to switch loads would allow for quick A/B comparisons.  I'd try to get less expensive (and consequently noisy) resistors for the attenuators. Once I find R values that worked best for me, I assume I should get some low noise resistors (e.g., Vishay naked bulk foil?) for the final implementation?  Does that make sense? 

many thanks in advance,

Derek
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on July 18, 2018, 03:59:59 PM
I would try wiring the amp for 2 ohm output and driving the headphones straight from the speaker jacks first.  There's no need to spend money on a problem that you aren't certain you will have.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Joppa on July 18, 2018, 04:36:33 PM
I see that PB posted while I was writing. He's right; comparing the 2-ohm and 8-ohm outputs will give you two data points on the power/distortion tradeoff, at essentially zero cost, and you are likely to be happy with either. The rest of this post is in case you (or someone else reading this) wants to go into more depth to explore these variables.

You can get adjustable L-pads for loudspeaker crossovers. They are not expensive, handle plenty of power, and have wirewound resistance elements (the good kind!). If you load the output of an 8-ohm L-pad with an 8-ohm power resistor (also widely available and inexpensive), it will present an 8-ohm load to the power amp no matter the setting, and still provide an adjustable signal to the headphones (which are in parallel with the 8-ohm load resistor). As long as the phone impedance is much larger than 8 ohms, it will be dominated by the paralleled 8-ohm resistor.

This way, the damping will be excellent no matter the setting, and you can explore the distortion vs. power tradeoff in a fairly clean experiment.

Once you know your sweet spot for power/distortion, you can separately explore the damping issue. We can get into that another time - there are actually two in the case where an output transformer is involved: 1) headphone damping affected by source output impedance, and 2) parafeed circuit resonance affected by amp load impedance. The latter is usually a smaller effect, and often can be ignored, but if you want to explore all the relevant variables it might be interesting.

I recommend this approach because the results are more easily perceived, understood, and communicated.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 18, 2018, 06:14:17 PM
Many thanks to you both.  I agree that it makes no sense to problem-solve a problem that may not even materialize.  But curiosity is getting the better of me and I "just want to see what happens if ..."  This is all quite new and fascinating to me.  I've tried numerous times over the years to learn the basic principles of electronics from texts that taught the principles in the abstract or only provided boring experimental applications -- in both cases, that part of my brain that asks "Who cares? So what?" would kick in and I'd close the books after a short time. I've probably relearned "how to calculate voltage between two resistors" at least 10 times by now and never cared, and it wasn't until last night that I had an "Aha" moment when I saw that a volume pot acts as a variable voltage divider - the simple beauty of it! ... So maybe I'm getting the bug.

Regarding the premade L-pads for power amps - that is very helpful.  I will look into that.  My idea of putting together large step attenuators was my attempt to solve the (perceived) problem of how to determine the required resistance values (they could be read from the position of the attenuator). I came across a lot of discussion about the use of L-pads for guitar amps, and assumed that such devices would use a potentiometer and that this would making it difficult to determine the "good sounding" resistor values b/c I'd have to estimate the position of the knob as a point on the resistance divider range of the pot - but maybe that's not an issue.  I'll look into it.  But perhaps you (Paul J.) are suggesting that the L-pad could be part of the "permanent solution" -- i.e., that it would be good enough sonically and not need to be replaced by a fixed value resistor setup?

I had also planned to ask you (Paul J.) about capacitors, as I came across an earlier post of yours that mentioned tweaking "parafeed capacitors" and I did some initial online reading about that last night.  But I will wait until I understand more about it before asking questions.

Again, many thanks to you both for having taken the time to respond so helpfully. I really appreciate it.  I'm not sure what I'm looking forward to more: good sounding music or the learning/experimentation :)  But why choose between them?  Hopefully I can have both (barring a major screw-up that melts my amp or blows up my cans).
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 18, 2018, 06:34:02 PM
Oops. I misunderstood the L-pad point.  I think you are saying that it presents a fixed and not variable resistance load to amp - e.g., so that on the 8 ohm tap the amp "sees" an 8 ohm load.  I had in mind a device (perhaps non-existent) that could vary the load that the amp sees.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Joppa on July 18, 2018, 06:56:12 PM
In my post, I mentioned exploring the damping issues - one of them is the effect of changing the load on the amp. It's rather involved, and as I said often a small enough effect to be ignored - or postponed. In any case, a different thing from the power/distortion balance question.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 19, 2018, 04:04:02 AM
Thanks Paul J. I think I understand now: the L-pad is to take the load issue out of the equation so that power/distortion can be cleanly experimented with.   Once that is done, I can return to the load issue if I want. 
Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on July 19, 2018, 05:10:51 AM
I would hope that if you are going to explore these small issues you plan to have some equipment besides your ears to measure the results. I would suggest getting some measurement software that will work with a sound card so you can quantify frequency response and distortion. That will help a lot towards understanding what is really going on when you change the loading.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 19, 2018, 07:14:16 AM
Ha! Thanks Doc.  I hadn't thought past my ears, but that makes obvious sense (obvious, now that you've pointed it out to me).  Any recommendations?
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 21, 2018, 06:46:52 AM
OK. I've made some small progress in preparing for the load and power/distortion experimentation. Following Doc's suggestion that I get some test equipment, I've ordered a USB oscilloscope (Pico 2204A), together with banana plug terminated connectors, and a basic audio signal generator (B&K Precision 3001), for a total cost of about $250 excl. shipping. I hope this will be adequate for my limited testing purposes. (Reason for the B&K: a reviewer of the scope indicated that the built-in audio generator isn't so good for hifi amplifier testing and suggested getting an external one).

I've also looked into L-pad attenuators and have some questions.

(1) Which one(s) to get?

Parts Express sells 8 ohm speaker L-pads in either mono or stereo, and with 15W, 50W or 100W ratings.  Regarding mono vs. stereo: I assume that a stereo L-pad will allow me to connect both right and left speaker outputs to it - so that the single pot will attenuate both right and left earphones simultaneously and more-or-less evenly. Is this correct?  In which case I need only 1 L-pad?

Regarding wattage rating: Which is likely to be sonically better, if any? The price difference between them is small, so I'll get the 100W if that is likely to sound/work best.

Link to the Parts Express L-pad page: https://www.parts-express.com/cat/speaker-l-pads/306 (https://www.parts-express.com/cat/speaker-l-pads/306)

(2) Implementation: 8 ohm L-pad(s) PLUS 8 ohm power resistor(s), or just 8 ohm L-pad(s)?

I am confused by Paul J's suggestion, quoted below, which I took to mean that I need BOTH an 8 ohm L-pad and an 8 ohm power resistor (or possibly two power resistors - one for each pair of speaker outputs?):


You can get adjustable L-pads for loudspeaker crossovers. They are not expensive, handle plenty of power, and have wirewound resistance elements (the good kind!). If you load the output of an 8-ohm L-pad with an 8-ohm power resistor (also widely available and inexpensive), it will present an 8-ohm load to the power amp no matter the setting, and still provide an adjustable signal to the headphones (which are in parallel with the 8-ohm load resistor).


I had assumed that the 8 ohm L-pad would take care of presenting the amp with a constant 8 ohm load and that nothing else would be required to do so.  I'm not questioning the suggestion - I just want to make sure that I've interpreting it correctly and order the right stuff. So I need BOTH the L-pad and an 8 ohm power resistor?

So my questions w/r/t L-pads: How many L-pads (1 or 2), mono or stereo, and at what wattage rating?  How many power resistors, if any, (1 or 2)?

Testing -- Just to be sure I'm understanding this right, once I find the sweet spot on the L-pad pot for the power/distortion issue, I can determine the corresponding impedance value of the L-pad by (a) cutting the power, and (b) leaving the pot turned to the sweet spot, measuring the resistance between two terminals of the L-pad pot?  I.e., the L-pad would have two resistors values - one fixed (8 ohms) and the other adjustable by turning the knob (X) - and I find X by following the above procedure.


Many thanks in advance,

Derek

[edited to add missing word]
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on July 21, 2018, 08:43:05 AM
It's pretty easy and inexpensive to just use ARTA and a soundcard (the soundcard will act as both the generator and the signal measuring device) for your distortion measurements, but it looks like the Picoscope has an FFT.  For years I got away with using a $40 M-audio Fast Track soundcard, but I recently splurged on an Mtrack Plus MKII to get some extra bandwidth.

Yes to the stereo L-pad, that is the way to go.

I would not pay the extra money for an L-pad rated for higher power.

Yes, you need an 8 ohm load.  The L-pad will present an 8 ohm load to your amplifier provided the L-pad itself is loaded with 8 ohms.

As far as finding the sweet spot, if you do your measurements at 100Hz, you can easily measure the AC voltage coming out of the amp and coming out of the L-pad with your DVM, then you would have a good idea of the fixed resistor values you might want to buy.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 21, 2018, 08:53:50 AM
Awesome.  Many thanks Paul B.

Just a quick follow-up question: do I need (a) 1 or 2 L-pads? and (b) 1 or 2 8 ohm power resistors?  E.g., do i need one L-pad/power-resistor combo for the right channel and a second for the left (2x2)?
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on July 21, 2018, 12:36:17 PM
Awesome.  Many thanks Paul B.

Just a quick follow-up question: do I need (a) 1 or 2 L-pads?
One stereo or two mono L-pads.
and (b) 1 or 2 8 ohm power resistors?
Two 8 ohm resistors.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on July 21, 2018, 03:49:05 PM
Perfect.  Many thanks Paul B.
Title: Next Steps?
Post by: Deke609 on September 20, 2018, 04:35:35 PM
I just got the my SII up and running in stock configuration. That was a bit more involved than putting together the Crack! Only screwed up one thing (installed a 5W 3K instead of a 5W 2K -- but caught that mistake and fixed it). Passed all resistance and voltage checks. Fired her up and no smoke. Woohoo!

Following previous advice, I plan to compare the amp configured at 2 and then 8 ohms with my Audeze LCD 4s plugged directly into the speaker outs. It is currently configured for 2 ohms.

Question: should I install the 3 upgrades before comparing 2 and 8 ohm configurations, or compare 2 and 8 ohms first?

Observations and first impressions with zero burn-in and cold amp configured for 2 ohms (Roon -> Yggdrasil DAC -> SII -> LCD4):

(1) Slight hum when no music is playing - but mourquiet upgrade should minimize that and perhaps even eliminate it. 

(2) With the volume pot ranging from 7 (no sound) to 5 (max) o'clock, my normal listening level is between 2 and 3. I expect this will change when I try the amp configured for 8 ohms -- I assume I'll get a big jump in gain from this.

(3) Overall sound presentation is remarkable for an amp with no burn in or warm-up - Marvin Gaye's album, What's Going On, sounds wonderful: "human" and spacious.

(4) Bass is muffled -- like someone strapped a pillow to the bass drum: "whumphh".  Rush's "Tom Sawyer" lacks punch.

(5) Details are there if I listen for them, but a bit veiled -- opening guitar on "Roundabout" from Yes' Fragile Album missing the micro details and clarity that make you believe you're in the recording studio with the band.

I expect installing the upgrades and switching to 8 ohms (or possibly 4 if 8 goes too far in the other direction) will take care of (4) and (5) above.  That, and letting the amp warm up and burn-in  ;D

If the 3 upgrades are even half as good as others have described them on this forum, the SII and LCD 4s are going to be a helluva match!

Liking what I'm hearing so far!

Derek






Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on September 20, 2018, 05:43:49 PM
I would recommend installing the DC filament upgrade first, then evaluating the various impedance taps.  There isn't going to be any hum at that point, and you can focus on listening to what you get at the various impedance taps in a more qualitative way rather than focusing on noise floor.

With the reduced noise floor, there may be a bit more bass bloom at higher impedance taps, but this will also depend a little bit on break-in as well.

To complicate matters further, you can technically get deeper bass out of a Stereomour at reduced power levels by converting it to run the #45 tube.  I would go ahead and do all your analysis without considering that, then maybe explore that more at a later date.

-PB
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 21, 2018, 02:13:15 AM
Many thanks again, Paul.  I'll install the Mourquiet DC Filament next as you suggest.

Regarding the bass: based on reviews, it sounds like the Shunt Regulation upgrade will give me more slam and oomph as well.  But I'll wait to install it and the DC Filament Mourquiet upgrade until after I'm done playing around with output impedances.

And after all of that, I will build the L-pads and try to figure how my new oscilloscope works. Some suggest reading the manual first - I may try that this time  :D

[edited in line with correction from JH and PB below]
Title: Re: Audeze LCD 4 - Which amp?
Post by: fullheadofnothing on September 21, 2018, 06:33:41 AM
Why is the attenuator upgrade being perceived as reducing hum, rather than the DC filament upgrade, which measurably reduces hum?
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on September 21, 2018, 06:40:53 AM
Oops, yes, that's a typo.  Do the DC filament upgrade first, not the attenuator.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 21, 2018, 07:19:46 AM
Many thanks guys - I was just about to start on the Mourquiet when I saw this.  So I will do the DC Filament instead.  I suppose there'd be no harm in doing the MQ too.  But I'll wait on that as suggested.
Title: Re: Audeze LCD 4 - Which amp?
Post by: fullheadofnothing on September 21, 2018, 08:11:27 AM
I was about to post about the hum balance, and then I saw that the instructions are missing from the manual. I'm getting that fixed in the manual, and I will post a sticky thread to the forum, but the basic process is:

( ) Connect the black lead of the meter to the black binding post of the right channel. Connect the red lead of the meter to the red binding post of the right channel.
To find the lowest possible position on the hum pot, you will also need to connect a speaker to the binding posts

Set the meter to read AC volts. If you meter does not autorange, set it to the lowest AC millivolt (mV) scale. Turn the trim pot all the way down to short the input. This will help keep outside electrical interference from affecting the reading on your meter.

( ) Install all tubes into their respective sockets.

( ) Turn the amplifier on let it warm up for a minute or two. Then slowly adjust the hum balance potentiometer behind to the four pin tube socket to get the lowest reading possible on the meter. This should be 0.8 - 2 mV depending on the tube used.

( ) Repeat this process for the left channel tube.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 21, 2018, 10:55:46 AM
The DC Filament is in and the SII is DEAD SILENT through the headphones. Wow.

Joshua: thanks for the hum pot instructions - On initial setup I simply set the pots to approximate mid-point on the dial. I hear no hum now with the DCF upgrade, but that may change when I switch to 8 ohms. In any event, I will follow the instructions you provided, if only "just to see".  Is it possible to use an o-scope in place of a speaker? I don't have any speakers - My house is "semi-detached", meaning I share a wall with my neighbor and so speakers are a no go since I prefer to listen at loud-ish levels - that's the reason for the LCD 4s and building a system around them - for headphones, they are very "speaker-like".  But I can probably borrow a speaker if necessary.

Listening impressions with the DCF installed are essentially the same as before, minus the hum with maybe a bit more detail. Based on my initial impressions I figured that my SII, as currently configured, would excel with classical -- strings in particular.  So I am listening to Yo Yo Ma's The Cello Suites. Wonderful.

If the Shunt Regulation and Mourquiet upgrades give me some more detail and bass, I will be in heaven.  But even as is, my SII with DCF upgrade is great with the LCD 4s.

I am now going to rewire the OTs for 8 ohms to do a quick comparison. Here's hoping I don't have to undo too much the DCF install I just completed!




Title: Re: Audeze LCD 4 - Which amp?
Post by: fullheadofnothing on September 21, 2018, 11:06:47 AM
Once you get the DC upgrade in, the hum pots aren't going to do much. With AC filaments, tiny movements of the pot can cause shifts of several mV, so it's worth carefully checking. It was your post that made me realize it was missing from this manual, so thanks for making me go looking for it...

The reason for attaching a speaker is the loading will affect the performance, so you want to set the hum balance with something besides the meter loading the amp. The load doesn't have to be a speaker, it could be a dummy load (a high power rated 8Ω resistor (ask a smarter person than me how high rated it needs to be.))

Also, more than throwing upgrades at it, give it some hours and see how the sound opens-up with break in.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on September 21, 2018, 11:56:59 AM
To be more specific about the loading, the reason for it is to establish a point of reference for the suggested level of 0.8 to 2mV of hum. If there is no load on the amp that number will be higher and thus not relative to the ~8 ohm loading method we used to establish the 0.8 to 2.0 mV reference. And by the way that is specifically 0.8 mVrms to 2.0 mVrms.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 21, 2018, 12:00:11 PM
Yup. Sound advice. Couldn't pull myself from listening - the sound is opening up quickly and the bass has gotten MUCH tighter - the amp was just cold.

But I'm going to need more gain - I can max out the vol pot on Rush's Tom Sawyer and some other "rockin'" tracks.  In fact, the last bit of dial doesn't seem to do anything, so I wonder whether I've hit the max that the amp can put out at 2 ohms and am experiencing "soft" clipping?  In any event, I don't have much headroom on the 2 ohm setting and am going to try a higher setting.  I'd like to find an ohm setting where I'm listening around 11-12 o'clock on the dial.

Question: Does you think 4 ohms will be enough of a jump in gain, or should I try 8 next?


I may still go ahead with the other upgrades this wknd - only because I have the time now and won't again for a while.  While this will deprive me of experiencing the impact of the upgrades on a fully broken-in SII, I can live with that.  In the end, I won't care whether the amazing sound is attributable 70/30, 60/40 or some other ratio of stock to upgrades.  I just want the amazing sound!

Re hum pot setting: I have a 8 ohm dummy load!  I think it's 100W or 200W - can't remember. Picked it up earlier in the summer as parts for playing around with L-pads for the SII. 


Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 21, 2018, 05:39:47 PM
Well, curiosity got the better of me and I installed the Shunt Regulation upgrade tonight.  IT IS AMAZING. This $89 upgrade just gave me sound quality improvements that I would expect to pay AT LEAST another $1K to $2K for were I buying retail and looking to upgrade models.  WOW.  The sound is superb: detail, coherence, punchier bass, "realness", "spaciousness" -- it's all here.  Unbelievable.  This is not a subtle "tweak" - it's a night-and-day obvious improvement.  The amp I am listening to now is not the same amp that I was listening to 5 hours ago.  I am floored.  And I haven't even installed the Mourquiet yet!

Many thanks to all of you at Bottlehead for making such an incredible piece of audio equipment available,

Derek







Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on September 21, 2018, 08:04:35 PM
Quote
The amp I am listening to now is not the same amp that I was listening to 5 hours ago.

Just keep running it in. It will get even better.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 25, 2018, 10:32:37 AM
A question about voltage output and testing

The amp is still in the early stage of burning in, but already sounds stellar with the LCD4's.

I want to start playing around with my o-scope.  I have a set of BNC probes that will allow me to connect both the scope and the headphones to the speaker posts.  My thinking is, if and to the extent that the load the headphones put on the amp affects frequency response, distortion, etc., it make sense to measure the amp under the load of the headphones.

The scope has an input sensitivity of +/- 20V (with overage protection at +/- 100V (DC and AC peak)).  My DAC puts out 2V rms from the rca outs.  I have the amp configured for 2 ohms. I don't want to exceed the input sensitivity of the scope, but I haven't gotten to the point in my self-directed learning about amp electronics to make sense of the voltage gain formulas or their relationship to dBs (all I remember is that it's logarithmic).   

Is there an ideal and scope-safe volume setting, in dB, that I should use for playing around with my scope?  I am assuming that an increase in dBs translates to an increase in output voltage.

Many thanks in advance,

Derek

Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on September 25, 2018, 10:48:56 AM
Most scopes will handle a considerable amount of AC voltage, generally far more than you're going to see on the speaker jacks of a single ended tube amp.

For measuring distortion, a scope isn't going to tell you all that much unless it has FFT functionality built in.  A $50 soundcard and some free software will though!
Title: Re: Audeze LCD 4 - Which amp?
Post by: Tom-s on September 25, 2018, 10:01:21 PM
Derek, keep up the good work.
Keep posting about the upgrades and how they affect the Stereomour II with your headphones.

If your still planning on a 45 conversion; be sure to let us know how it worked out!

And could you perhaps test/compare with other headphones?

I'm very happy to learn that there's more after Mainline for headphones (and speakers 8) ).


Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 26, 2018, 05:30:09 AM
Most scopes will handle a considerable amount of AC voltage, generally far more than you're going to see on the speaker jacks of a single ended tube amp.

For measuring distortion, a scope isn't going to tell you all that much unless it has FFT functionality built in.  A $50 soundcard and some free software will though!

Thanks again Paul.  I have a cheapish usb scope (Picoscope 2204A), which I figured wouldn't be as robust as as a benchtop model.  But it apparently has FFT (although I have no idea how to access that functionality for reasons made clear by what follows).

I may need to go the soundcard and software route, at least initially -- I spent about 6 hours last night trying to figure out how to get the o-scope "working" and cursing it for not being immediately intuitive (I'm sure it works just fine - it's my brain that's the problem).

To a more technically adept onlooker my last night's misadventure in oscilloscoping would have looked like a scene from Zoolander: "The files are in the computer?" ... Smashes computer on floor and looks for physical files.  I couldn't even figure out how to connect its output to the amp - solved that this morning by soldering some banana posts to a rca plug and connected to the right channel input of the amp.  So far I've managed to get a frequency sweep from the scope to play through the right headphone, with the scope input connected to same speaker taps that connect the headphones, but I have no idea (yet) how to get the scope to measure and plot dB's by frequency.  Sheesh ... plug-and-play has ruined my ability to figure things out.

I'll look into the soundcard/freeware option this evening.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on September 26, 2018, 06:25:47 AM
Derek, keep up the good work.
Keep posting about the upgrades and how they affect the Stereomour II with your headphones.

If your still planning on a 45 conversion; be sure to let us know how it worked out!

And could you perhaps test/compare with other headphones?

I'm very happy to learn that there's more after Mainline for headphones (and speakers 8) ).

Thanks for the encouragement Tom!

Re 45 conversion: I hadn't actually planned to do it, b/c I'm concerned the drop in wattage (from 3.5 Wpc to I think 1.75 Wpc) would leave me with an amp too quiet for the LCD4s.  But that may change depending on: (a) the results of my future experiments with the other impedance configurations for the SII (4, 8, 16 ohms): and (b) whether I can resist getting a Kaiju next year.   ;D

As currently configured (2 ohms) and in its present state (not even burned in), the SII is just stunning.  The DCF upgrade completely eliminated the hum, and the Shunt Regulator upgrade was mindblowing - among other things, the bass is now punchy and precise.  A good test track for slam (to my ears) is ZZ Top's "Master of Sparks" from their Tres Hombres album - the opening drums out of the SII through the LCD4s are incredible.

Re other headphones: I only have 3 pairs: the LCD4s, Focal Elex and HD6xx.  I am listening to the the Elex as I write.   The Elex is a Massdrop/Focal collaboration that is essentially the Elear with Clear pads, and reported lowering of the Elear's original bass response (I've never heard the Elears, so can't comment on this).  They are easier to drive and much more sensitive than the LCD4s, so I think they make a nice comparison. 

Some specs for the Elex (from the Massdrop website):

Impedance: 80 ohms
Sensitivity: 104 dB SPL / 1 mW at 1 kHz
THD: < 0.3% at 1 kHz / 100 dB SPL
Frequency response: 5 Hz–23 kHz

Specs for the LCD4s (from the Audeze website):

Impedance:   200 ohms
Sensitivity:   97 dB/1mW (at Drum Reference Point)
Voltage sensitivity:   95 dB/1V
THD:   <0.1% @ 100dB
Frequency response:   5Hz – 50kHz

Both pairs of headphones sound great out of the SII configured for 2 ohms.  I prefer the LCD4s, but only because they are for my tastes a superior headphone. There is no hum that I can notice through either pair of headphones - but that may change when I configure the amp for 8 ohms - particularly, I imagine, with the more sensitive Elex.

My (loud-ish to loud) volume listening ranges on the Mourquiet Attenuator upgrade for the 2 headphones:

Elex:  -27 dB to -22.5 dB
LCD4: -9 dB to -3 dB

So, my tentative conclusion is that a fully upgraded SII is a stellar option for a wide range of headphones.  I'll try the HD6xx later this week.

cheers,

Derek








Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 13, 2018, 01:18:39 PM
Switched the OT configuration from 2 Ohms to 8 Ohms this afternoon and, my oh my, it is GLORIOUS. 

The SQ change is immediately obvious.  Most noticeable: bass is A LOT MORE detailed, present and authoritative. At 2 Ohms I felt I could still use a bit more bass (even after the Shunt Regulation upgrade, which gave the bass a lot more punch and precision). But at 8 Ohms, the bass is perfect for my tastes (and I like a fair amount of bass - I like my music visceral). Overall, at 8 Ohms music is both more precise and more fluid - which I would have thought contradictory, but that's the best way I can think of describing it.  Everything is more coherent.  And the added gain has given me a good deal of headroom. I went from regularly listening at 2 Ohms with the course attenuator at 0 dBs to listening at 8 Ohms withe course attenuator at -9 dBs. Sweet!

There are no downsides that I can hear.  No hum with the DC Filament even at 8 Ohms.

Conclusion: A fully upgraded SII configured for 8 Ohms is a SUPERB match for the LCD4s. 

Many thanks to everyone at BH who played a role in creating this fantastic amp.

cheers,

Derek

Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 18, 2018, 02:38:42 PM
@Doc, PJ and PB - I'm considering putting a BeePre between my DAC and the SII, for use with my LCD 4s. The preamp gets rave reviews here for soundstage, detail, fullness, and other wonderful sonic qualities. My only holdback is a concern about noise. I suspect I'll be ok, but want to check with you guys first in case this is a "no way, it'll be way too noisy" pairing for my headphones. 

The SII has been dead silent since I installed the SR upgrade [oops, I meant the DCF upgrade], even configured for 8 ohms.  Doing the hum pot adjustment/testing, I am down to 0.1 mV on each channel. But even if I adjust the pot to allow 1+ mV, I still hear nothing.  The LCD 4s are not that sensitive (97 dB) and have 200 Ohms impedance.  And they can take a fair bit of current and voltage. At 2 Ohms, I could max out the volume on some tracks, and the headphones seem to love the added gain at 8 ohms (the bass really opened up and everything sounds both more fluid and controlled). And at 8 Ohms I haven;t had to turn the volume attenuators down that much - just one turn of the coarse attenuator (-9dBs for loudish and -18 dBs for normal/quieter listening). So I think I found a winning combination with the LCD4s and the SII.  But if I can get even more of the BH sound with the BeePre ...

Thoughts?

[edited to correct error]
Title: Re: Audeze LCD 4 - Which amp?
Post by: Doc B. on October 18, 2018, 02:44:26 PM
You don't need a preamp with the Stereomour II. The BeePre is super quiet in terms of power supply, but there is the potential issue of microphonics in the directly heated 300Bs if you can't put the preamp somewhere where it will be isolated from external vibration.

OK, the disclaimers are out of the way. Sonically it could be a very nice combination. Let us know when you are ready to order.  ;)
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 18, 2018, 03:18:19 PM
Thanks Doc.

Ready!

Microphonics, if it becomes an issue, are something I can probably fix.  My rack rests on spring-loaded self-leveling feet.  I've read the threads you started about sorbothane feet and lead tube rings. And Jamie R's recent posts about his vibration control box using an inflatable cushion and heavy plate.  So there are lots of potential, stackable solutions.

cheers and thanks,

Derek
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 19, 2018, 08:54:23 AM
Order for Beepre and BeeQuiet placed  :)  I had originally earmarked this money for a SS amp, also American made, but canceled my order of same after hearing just how good the SII is.  The SS amp was for greater bass extension - but now I'd rather focus my efforts on getting more of the BH sound from my system. (That said, if BH ever makes the Kaiju iron upgrade for the SII, I will be the first to order - I bet there are enough SII owners on this forum that would jump at the upgrade to make it do-able).
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 25, 2018, 03:07:09 PM
Guys - Now that the amp has 100+ hours on it, and I've experimented with all 4 output impedance configurations, I'd like to return to the power/distortion and damping issues.  And just to be clear, I'm not trying to "correct" anything. I am perfectly happy with the amp - it sounds stellar at 4, 8 and 16 ohms configurations (in comparison with which, 2 Ohms sounds a bit dry and lifeless - but I was perfectly happy with 2 Ohms before hearing 4, 8 and 16  :D). So this is just for fun and education - if I somehow manage to squeeze out a bit more SQ improvement from all this, that's just a bonus.

You previously suggested building a stereo L-pad that would present a fixed 8 ohm load to the amp.  I have the required parts, but I don't know whether I should proceed because I'm unsure whether my headphones need the amp output to be "padded down". I suspect not, given that I can comfortably listen to them with the amp configured for 16 Ohms with the volume attenuators at -18 dB, at -9 dB when configured for 8 ohms, and pretty much wide open at 4 Ohms. 

But I may well be missing something - so maybe it's helpful to return to something PB wrote a month ago in reference to using an L-pad:

If the resistor values get too large, you'll lose damping of the headphones and the bass will get lumpy on you. If the resistor values are too small, you'll load the amp down and it will distort.

Based on some reading I've done, my understanding is that the damping/lumpy-bass issue is a function of a headphone's impedance curve across the audible frequency bandwith. My guess is that if the headphone impedance dips appreciably at certain bass frequencies, a high output impedance could result in loss of damping at those frequencies and the bass will be loose and boomy. Do I have it right?

If my understanding is correct, then I don't think I need to worry about damping. The LCD 4s have an input impedance of 200 Ohms and the impedance versus frequency plot is dead flat - literally a straight line parallel to the x-axis for all frequencies.  This has been tested and verified by various reviewers (Inner Fidelity, Stereophile, etc.). My understanding is that this is a common characteristic of planar magnetic headphones.

So my current thinking is that (a) no padding down is necessary, and (b) headphone damping is not a problem.  BUT I have come across numerous references in online forums about "keeping an amp happy" by putting a resistor in parallel with each headphone channel -- e.g., 2 8 ohm resistors for an amp configured for 8 ohm speakers.

1st issue: Does the SII need to "see" the resistance for which it is configured to be "happy"?  If so, is this what PJ was referring to when he mentioned "parafeed circuit resonance affected by amp load impedance"?  And what PB meant when he mentioned too little resistance "loading the amp down" and causing it to distort?

One other thing I don't understand is how power hungry headphones can be be driven fully if resistors having a value much smaller than the headphone's impedance are placed in parallel with the headphones. While the headphones will still get the same voltage, wouldn't most of the current flow across the parallel resistor, bypassing the headphones?  My thinking is that if voltage is fixed by the OTs and the amp cannot exceed 3.5 to 4 Wpc, then current is necessarily limited such that, with the parallel resistors in place, the headphones may not be able to draw as much current as they need.  But maybe I misunderstand this too.

2nd issue - Distortion. I've tried to read up on this, but there are so many different types of distortion and I don't know which one or ones I should be educating myself about - what kind(s) of distortion are we talking about? And is it produced at the amp or the headphones?

Many thanks,

Derek
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on October 25, 2018, 06:22:55 PM
I suspect not, given that I can comfortably listen to them with the amp configured for 16 Ohms with the volume attenuators at -18 dB, at -9 dB when configured for 8 ohms, and pretty much wide open at 4 Ohms. 
Yeah, no reason to pad things down.  If you were all the way down on coarse and fine and things were loud, then you'd want to pad down the output a bit.  If the general noise floor of the amp was too high, the padding would also remedy that.

Based on some reading I've done, my understanding is that the damping/lumpy-bass issue is a function of a headphone's impedance curve across the audible frequency bandwith.
When load impedance gets lower than output impedance, fluctuations in the load impedance become very audible.  For example, an 8 ohm rated speaker that dips to 4 ohms and up to 50 ohms will have the potential for lumpy bass issues unless run from the 4 ohm setting (or lower).

If my understanding is correct, then I don't think I need to worry about damping. The LCD 4s have an input impedance of 200 Ohms
Yeah, plenty of damping on any impedance setting.

I have come across numerous references in online forums about "keeping an amp happy" by putting a resistor in parallel with each headphone channel -- e.g., 2 8 ohm resistors for an amp configured for 8 ohm speakers.
Our amps remain quite happy with just about anything you want to load them with.  They are unconditionally stable.

1st issue: Does the SII need to "see" the resistance for which it is configured to be "happy"?  If so, is this what PJ was referring to when he mentioned "parafeed circuit resonance affected by amp load impedance"?  And what PB meant when he mentioned too little resistance "loading the amp down" and causing it to distort?
What PJ is describing and what I brought up are two different issues.  There's no harm in putting loading resistors in parallel with the headphones, I wouldn't pretend to be able to predict whether you'd like the outcome or not.  A load that is too low in impedance relative to what the amp is expecting will generate extra distortion and a little more power.  You don't need either.

One other thing I don't understand is how power hungry headphones can be be driven fully if resistors having a value much smaller than the headphone's impedance are placed in parallel with the headphones. While the headphones will still get the same voltage, wouldn't most of the current flow across the parallel resistor, bypassing the headphones?  My thinking is that if voltage is fixed by the OTs and the amp cannot exceed 3.5 to 4 Wpc, then current is necessarily limited such that, with the parallel resistors in place, the headphones may not be able to draw as much current as they need.  But maybe I misunderstand this too.
The resistor L-pad reduces the power available to the headphones.  Putting an 8 ohm resistor in parallel with each headphone driver will slightly reduce the output of the amp, so you will see slightly reduced power to your headphones as well. 

2nd issue - Distortion. I've tried to read up on this, but there are so many different types of distortion and I don't know which one or ones I should be educating myself about - what kind(s) of distortion are we talking about? And is it produced at the amp or the headphones?
We don't really go into a whole lot of discussion here on distortion generated by transducers.  The distortion we are mentioning is harmonic distortion. 
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 26, 2018, 07:45:13 AM
Many thanks again, PB.

It's good to know that my SII is happy no matter the load. 

If I were to play around with parallel resistors, what value(s) would you suggest?  I think you previously stated that twice the intended load was a good starting point.

And thanks for clarifying that it is harmonic distortion that we are talking about.  That might be something fun to experiment with. In a 1972 paper for the AES (see link in "Why do I like tube amps" thread under "General Discussion), Russell Hamm suggested that it may actually be harmonic distortion that is responsible for why many people find tube sound to be fuller bodied and punchier than SS. As Hamm explained:

"Transistor amplifiers exhibit a strong component of third harmonic distortion when driven into overload. This harmonic produces a "covered" sound, giving a recording a restricted quality. Alternatively a tube amplifier when overloaded generates a whole spectrum of harmonics. Particularly strong are the second, third, fourth, and fifth overtones, which give a full-bodies "brassy" quality to the sound. The further any amplifier is driven into saturation, the greater the amplitude of the higher harmonics like the seventh, eighth, ninth, etc. These add edge to the sound which the ear translates to loudness information. Overloading an operational amplifier produces such steeply rising edge harmonics that they become objectionable within a 5-dB range. Transistors extend this overload range to about 10 dB and tubes widen it to 20 dB or more. Using this basic analysis, the psychoacoustic characteristics stated in the beginning of this paper can be related to the electrical harmonic properties of each type of amplifier."

In the 1972 article, Hamm noted that significant/audible distortion only occurs when the amp is overloaded - which might lead one to think that at normal listening levels, harmonic distortion isn't an issue and that tube and SS should sound pretty much the same.  However, Hamm points out that transients -- the attack of a note, drum hit, etc. -- often overload the amp, if only momentarily - which suggests (to me) that tube amps should sound more dynamic even at normal (non-overloading) listening levels -- which is something that I find.

I can't claim that this is a definitive explanation of the difference between tube and SS, but it is very interesting. 

I wonder whether through tweaking the amp, it is possible to reduce 2nd harmonics that produce a "covered" sound, while leaving the other harmonics undisturbed?  And would this be a good thing? Or is the 2nd harmonic only detrimental to SQ when out of balance with the other harmonics, such that removing it or lessening it from the full range of tube harmonics would remove some of the body of the sound.  Dunno. But it would a very interesting to experiment with, were it possible to do so.

cheers,

Derek
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on October 26, 2018, 07:49:28 AM
The methods for reducing harmonic distortion in a zero feedback directly heated SET amplifier are generally more detrimental to the sound than they are helpful. 
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 26, 2018, 08:31:02 AM
Thanks PB. I think I'll stop with the tweaking for a while.  With the impedance switching board, balanced speaker outs, and some signal wire shielding, I've pretty much scratched my tweaking itch. Maybe down the road a bit I'll play with capacitors.

But for now I have the BeePre on order.  I plan to do the flux band mod you discussed on another thread, and go a little crazy with shielding the signal wire with grounded copper and where possible some MCF5 film - just for S & G's. And I'll cover with non-conductive tubing/wrap any shielded section that could possibly come into contact with a component.
Title: Re: Audeze LCD 4 - Which amp?
Post by: Paul Birkeland on October 26, 2018, 10:23:01 AM
I'd be a little cautious withe modifications on our higher end kits.  The signal wiring and a fair amount of the AC wiring is shielded already and arranged reliably and out of the way. 

The copper tubing I put in the Neothoriator did double duty as a shield and as a support for a bunch of less than rigid twisted pairs of our solid core Teflon jacketed wire.  In the BeePre, these wires are secured to the chassis and won't move.  These wires also take a gentle curve down the center of the amp that won't be so easily done with copper tubing. 
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on October 26, 2018, 12:46:45 PM
Thanks PB. Wiring paths will not be changed - for the main section through the middle, I'll be using refridgerant copper tubing, which is very soft, unlike regular copper plumbing, and I will form it to match the specified curved path.  For trickier spots, I'll use 1/8 or 3/16 OD copper braid, depending on the width of wire to be shielded.  I will be very careful in the build process and take my time. 

cheers,

Derek
Title: Re: Audeze LCD 4 - Which amp?
Post by: Deke609 on December 13, 2018, 10:30:55 AM
You don't need a preamp with the Stereomour II. The BeePre is super quiet in terms of power supply, but there is the potential issue of microphonics in the directly heated 300Bs if you can't put the preamp somewhere where it will be isolated from external vibration.

OK, the disclaimers are out of the way. Sonically it could be a very nice combination. Let us know when you are ready to order.  ;)

So, the BeePre w/ BeeQuiet has been up and running for a week. Caps and JJ 300Bs are nowhere near to broken in, but from the first switch on it has sounded superb paired with my SII.  Build is stock except for (1) teflon 4 pin sockets, (2) copper shielding around as much of the signal wire as I could manage and some sections of the power wiring (refridgerant copper tubing for long sections, and copper braid everywhere else -- sometimes both), and (3) copper flux bands on the transformers. Flux band and shielding is wired to chassis ground. 

It is still early days, but the change in SQ is dramatic.  Doc is right, the SII doesn't need the BeePre, but boy do they ever get along well. For me, adding the BeePre in front of my SII has already had as much of an impact as the Shunt Reg upgrade (my favorite of the 3 Stereomour upgrades). With the Shunt Reg upgrade added, the SII really started to punch.  With the BeePre, it is punching harder and now has SERIOUS BITE! The dynamics are incredible. This is in addition to greater clarity/detail and "openness".

So far, I mostly prefer to listen with the BeePre wide open. This may be pushing it into distortion - but if so, it is a very euphonic distortion, particularly for rock. For classical and some jazz I turn down the Coarse attenuator by a click.

I am impressed by everything about the BeePre, including the very clever layout and implementation of the schematic.  There's a lot of stuff going on in this amp -- it not only all fits, but does so in a way that makes amateur assembly possible and fun.  Bravo!

cheers,

Derek