Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: Doc B. on March 02, 2010, 06:59:05 AM

Title: Something new is coming
Post by: Doc B. on March 02, 2010, 06:59:05 AM
The past couple of days I have been secretly working on a new project with PB. In a meeting with the Queen and PB last Sunday, PB proposed a new design that is simple and cost effective. Honestly my prejudices about the design concept were such that I didn't have very high hopes for the sonics. PB cooked up the prototype that afternoon, and after my first listen I was seriously hooked on it.  It worked far better than I expected and during dinner Sunday night we were at what is often the most fun part of the development, thinking up a name. The prototype got me hooked on its sound so fast that I thought Crack was appropriate.

Yup, you're right, I haven't said what it the heck is. You will have to wait until early next week when we have the production prototype finished and ready to show you. I can tell you that the introductory price will be $199 and you won't even have to go to a bad neighborhood to buy it. We'll have an order button up next week, with a plan to ship the first kits as soon as the chassis panels are delivered. That usually takes about three weeks.
Title: Re: Something new is coming
Post by: Paul Birkeland on March 02, 2010, 08:34:18 AM
We should also mention that using our Crack will not ruin your marriage, drain your bank account, or make your teeth/hair fall out... 
Title: Re: Something new is coming
Post by: Dr. Toobz on March 02, 2010, 10:54:17 AM
Aren't ALL of BH's products already like crack? I mean, I can't live without them, and my money seems to go towards more and more BH gear/mods to keep me getting my "fix."
Title: Re: Something new is coming
Post by: Mudhiker on March 02, 2010, 04:07:15 PM
What sort of "back door" product is this?  I am almost afraid to find out.
Title: Re: Something new is coming
Post by: ironbut on March 02, 2010, 06:06:36 PM
Gee, what can I say. Seeing the name on this new forum just about snapped my neck as I wheeled around in my desk chair.
"What have those guys been up to?"
Well, never let it be said that the folks at Bottlehead central can't create a mystery.

Looking forward to having my fancy tickled.
Title: Re: Something new is coming
Post by: Wanderer on March 04, 2010, 05:21:07 AM
Nobody else seems to be guessing so I will give it a shot.

First thought was simple, high effiency speakers (ala "Zigmahornet" perhaps??)....but the fact you don't say "pair" and metion chassis pannels argues against that.

Second thought was a Class-T or other simple chip amp as a mate to the Quickie - a chip based amp seem out of BH character however.

A simple NOS DAC with simple Quickie-ish tube buffer? Battery powered? Maybe?

A battery powered tube Phono-pre to mate with Quickie? Maybe?

I am liking the last two, but what the heck do I know?

     
Title: Re: Something new is coming
Post by: Doc B. on March 04, 2010, 07:16:05 AM
You didn't guess it, but those are some really neat ideas. We have discussed a battery phono preamp, and I think we'll give a prototype a shot. I've also had an idea for a very, very basic DAC that could fit into that battery powered concept too.

No chip amps at this time. Not necessarily opposed to them, it's just that there are a zillion of them on the market.
Title: Re: Something new is coming
Post by: xcortes on March 04, 2010, 07:51:14 AM
Car amp or preamp?
Title: Re: Something new is coming
Post by: 2wo on March 04, 2010, 11:35:57 AM
I'm thinking some sort of spud amp, maybe battery powered...John
Title: Re: Something new is coming
Post by: xcortes on March 04, 2010, 11:46:29 AM
Quote
I'm thinking some sort of spud amp, maybe battery powered

Now, that would be cool!
Title: Re: Something new is coming
Post by: Cary on March 04, 2010, 04:52:11 PM
I am hoping it is an amplifier!
Title: Re: Something new is coming
Post by: Dr. Toobz on March 04, 2010, 05:04:44 PM
My guesses: a) a passive preamp of some sort, a la "Sweetest Whispers" in a box, b) a battery-powered integrated, like a Quickie with another power stage, c) a tube buffer using a single 6922, or d) some sort of guitar amp or effect pedal.
Title: Re: Something new is coming
Post by: Air on March 04, 2010, 07:05:40 PM
A Hundred a side...how about a TVC of some sort? Chuck
Title: Re: Something new is coming
Post by: ssssly on March 04, 2010, 11:15:28 PM
I hope that it is the long awaited Bottlehead flux capacitor.
Title: Re: Something new is coming
Post by: corndog71 on March 05, 2010, 02:13:14 AM
I hope that it is the long awaited Bottlehead flux capacitor.

NOW we're talking!!
Title: Re: Something new is coming
Post by: Grainger49 on March 05, 2010, 02:44:44 AM
Aahh, take me back in time...
Title: Re: Something new is coming
Post by: Jim R. on March 05, 2010, 01:55:18 PM
A.) A small, single tube, battery powered iPod dock to drive those low-z headphones.

B.) Asingle tube, battery powered white noise generator for we chronic insomniacs.  in the group. :-)

-- Jim

Title: And the winner is ---
Post by: Doc B. on March 07, 2010, 04:21:10 PM
well, nobody guessed it. But I do think this kit is going to be a winner. Crack is an OTL headphone amplifier - very simple and inexpensive - that will have optional upgrades as soon as we get the basic kits together and shipping. It's really, really good with high impedance headphones and only $199. American made power trans designed by PJ, American old stock tubes, American made chassis.

(http://www.bottlehead.com/sc_images/products/442_image.jpg)

http://www.bottlehead.com/store.php?crn=44&rn=442&action=show_detail (http://www.bottlehead.com/store.php?crn=44&rn=442&action=show_detail)
Title: Re: Something new is coming
Post by: Jim R. on March 07, 2010, 04:25:59 PM
Sign me up!

Sounds really cool and the price is right.  Any details of which tube (s)?  Hoping it will be something I have lots of :D.

-- Jim
Title: Re: Something new is coming
Post by: Doc B. on March 07, 2010, 04:32:13 PM
Tubes are 12AU7 and 6AS7/6080
Title: Re: Something new is coming
Post by: Dr. Toobz on March 07, 2010, 05:25:39 PM
After messing around with my Quickie sans OPT's, using larger (electrolytic) coupling caps and some high-impedance phones, I secretly hoped BH would someday come out with something OTL that would put out enough juice to power big headphones. Looks like my wish has been fulfilled! Count me in for this one.

I can't wait to hear what this sounds like with my Beyers - I love tubes, but am not a fan of transformers!
Title: holy smokes - that was fast!
Post by: Doc B. on March 07, 2010, 06:11:56 PM
Thanks for the orders!
Title: Re: Something new is coming
Post by: Dr. Toobz on March 07, 2010, 06:19:09 PM
PS - please add a button for the BH badge in your new ordering system. I sent an extra $6 separately for a badge since I didn't see them on the new ordering page.....
Title: Re: Something new is coming
Post by: Paully on March 08, 2010, 03:43:05 AM
I have absolutely no need for one, and yet something tells me I am going to have one.  I must, I need!
Title: Re: Something new is coming
Post by: Paully on March 08, 2010, 03:44:47 AM
By the way, I love the write up!
Title: Re: Something new is coming
Post by: Grainger49 on March 08, 2010, 04:35:12 AM
PS - please add a button for the BH badge in your new ordering system. I sent an extra $6 separately for a badge since I didn't see them on the new ordering page.....

That would be a great idea for every product page.
Title: Re: Something new is coming
Post by: Wanderer on March 08, 2010, 05:01:08 AM
I know I will regret asking, I am in danger of becoming an addict:

Has it been tried with low sensitivity AKG 240Monitor phones? The autoformer Quickie works with my 240M cans, but just barely.     

 
Title: Re: Something new is coming
Post by: Doc B. on March 08, 2010, 05:52:16 AM
I haven't had a chance to try AKG240s, as my pair was donated to the studio several years ago. We have used 300 ohm Sennheisers and they can easily be driven way too loud. So Crack should work very nicely with 600 ohm AKGs. A high impedance headphone is the intended mate to this circuit, and my guess is you can probably deliver about 1/2W into them. The headphone mod concept for the Quickie was done simply to show how one can do some pretty unconventional stuff to a $99 kit. It works, but it's not the original intended usage of the kit. The output trans mod rather drastically reduces the relatively low gain and it's probably going to work best with low impedance headphones that are more sensitive.
Title: Re: Something new is coming
Post by: Jim R. on March 08, 2010, 06:40:20 AM
Damn.  Just bartered my last nice pair of 12au7s, and sold the last of my 6as7s over a year ago (had bought them, ironically enough, to build a headphone amp :-). )

I'll be placing my order shortly!

-- Jim
Title: Re: Something new is coming
Post by: vanofmonks on March 08, 2010, 06:46:18 AM
Just ordered mine.  Happy birthday to me.  If I can get it by 3/17 that would be awesome.  Has anyone come up with a crossfeed circuit for it yet?
Title: Re: Something new is coming
Post by: Paul Birkeland on March 08, 2010, 06:49:31 AM
I know I will regret asking, I am in danger of becoming an addict:

Has it been tried with low sensitivity AKG 240Monitor phones? The autoformer Quickie works with my 240M cans, but just barely.     

 
I managed to score some K240M's locally not too long ago.  I just plugged them into the first prototype, and you will certainly have more power than you can use.
Title: Re: Something new is coming
Post by: vuntruong on March 08, 2010, 06:52:13 AM
Would it be wise to order 2 Crack and use them as a balance heaphones amp? 
Title: Re: Something new is coming
Post by: xcortes on March 08, 2010, 06:59:43 AM
I just ordered mine! I'm getting fond of headphone listening and the coolness factor of the Crack amp is something you just can't pass on.
Title: Re: Something new is coming
Post by: Doc B. on March 08, 2010, 07:04:14 AM
Quote
If I can get it by 3/17 that would be awesome.

It's probably going to be a week or two longer than that before we can ship. This new kit has a new chassis plate design and those typically take about three weeks to receive from the laser cutter.
Title: Re: Something new is coming
Post by: Paul Birkeland on March 08, 2010, 03:37:27 PM
Would it be wise to order 2 Crack and use them as a balance heaphones amp? 

I have tried this before, and I wouldn't discourage such an attempt, but I would warn that the 6080/6AS7 is notorious for having pretty poorly matched sections. 

In a single ended circuit like the Crack, this is not particularly bothersome.  In a differential circuit, it will be far more pronounced. 
Title: Re: Something new is coming
Post by: arveedub on March 08, 2010, 04:49:42 PM
What would you recommend as the minimum impedance for a set of headphones to use with the kit?
Title: Re: Something new is coming
Post by: dmannnnn on March 08, 2010, 10:02:32 PM
Just ordered mine.  Happy birthday to me.  If I can get it by 3/17 that would be awesome.  Has anyone come up with a crossfeed circuit for it yet?

Here are a couple of projects I have been eyeing.

http://www.tangentsoft.net/audio/mlxfeed.html (http://www.tangentsoft.net/audio/mlxfeed.html)

http://www.meier-audio.homepage.t-online.de/ (http://www.meier-audio.homepage.t-online.de/)
click 'crossfeed filter' next to 'projects' at the top of the page.
Title: Re: Something new is coming
Post by: Doc B. on March 09, 2010, 06:20:20 AM
Quote
What would you recommend as the minimum impedance for a set of headphones to use with the kit?

The output impedance of the 6080 cathode follower is around 100 ohms. So in theory the most ideal load will be 300 and 600 ohm headphones. You could push this down to 100 ohms and just expect somewhat increased distortion - in fact we tried it with 32 ohm phones and it sounded pretty darn good, but that is not the intended usage. The current wisdom seems to be that a S.E.X. amp with the 120 ohm resistors removed from the jack works best with low ( like 32 ohm)  impedance headphones. The curves of some 6080 relatives might give a little lower output impedance in the given circuit, but I have not pursued that yet. Remember, this kit is only about 10 days old.
Title: Re: Something new is coming
Post by: Jim R. on March 09, 2010, 06:30:47 AM
You can also try increasing the output coupling capacitor value to get a little more mileage out of some borderline cans.

So Doc, where you expecting so many orders for a kit that is only 10 days old and has not had a lot of pre-release anticipation built up around it?  Pretty cool if you ask me.

-- Jim
Title: Re: Something new is coming
Post by: Doc B. on March 09, 2010, 08:06:29 AM
Definitely cool. It's interesting to see more and more folks go for higher impedance cans these days. Since PB brought up this idea I been looking for precedents and in the process had noticed that there had been some attempts to revive a similar but different kind of 6080 based OTL headphone amp by some folks over on Head-fi that ultimately weren't able to happen for reasons of cost. The fact that we could use mostly parts that are already in stock (including an existing, great power trans design by PJ that we have made in quantity) allowed us to put together something for a really low price. Perhaps the word will get out over there that we are offering something for a very low price that is easily tweaked and could fill the bill.
Title: Re: Something new is coming
Post by: ironbut on March 09, 2010, 10:02:48 AM
Hey, funny you should mention it.
I started a thread over there yesterday. You should get a few early adopters from there. I've noticed an undercurrent of interest in DIY on Headfi lately and I think this'll be a dandy kit for those folks to get their feet wet.

https://www.head-fi.org/forums/f5/crack-bottlehead-otl-476650/

Title: Re: Something new is coming
Post by: mrarroyo on March 09, 2010, 02:44:33 PM
Hi, my name is Miguel and I saw the post in Head Fi on the Crack and came over to read about it. I have soldered in the past, most of the time successfully but I have had a couple of mishaps w/ circuit board type of amps. Anyways I am looking forward to this new amp but I have a few questions if I may.

1. Will the aluminum plate be pre-drilled to accept the components, plus will it be sized to fit in the wood base.
2. Will the wooden boards be pre-cut and ready for assembly?
3. How much work to finish the wood? I like to use beeswax w/ a lite stain on many of my projects.
4. Does the wood bass come in pine or just alder?

Thanks.
Title: Re: Something new is coming
Post by: Paul Birkeland on March 09, 2010, 03:07:24 PM

1. Will the aluminum plate be pre-drilled to accept the components, plus will it be sized to fit in the wood base.
2. Will the wooden boards be pre-cut and ready for assembly?
3. How much work to finish the wood? I like to use beeswax w/ a lite stain on many of my projects.
4. Does the wood bass come in pine or just alder

The aluminum plates are laser cut and ready to go.  No machining is required. 

The wood pieces for the base are cut and have a groove for the top plate to rest in. 

Finishing the wood is completely optional.  Plan on maybe a little sanding, then stain away. 

The wood bases are alder only.  A Google search may find wood workers who have made Bottlehead bases in other finishes, and sometimes they offer custom bases for a fee. 
Title: Re: Something new is coming
Post by: roger_s on March 09, 2010, 05:55:38 PM
Having only four headphone amps (including my S.E.X.) I went ahead and ordered a Crack.  It only makes sense with three pairs of Grados, a pair of HD650 Sennheisers, and a pair of AKG 702s lying about...

Good work, Doc.

Title: Re: Something new is coming
Post by: Grainger49 on March 10, 2010, 12:22:52 AM
 .  .  .      4. Does the wood bass come in pine or just alder?

Thanks.

Just to add a little.  Think of alder as Pacific Northwest pine without the pitch.  It has prettier grain than the pine I am used to in the South.
Title: Re: Something new is coming
Post by: jpstereo on March 10, 2010, 04:20:36 AM
I am very interested in purchasing this kit up but, alas, I have ZERO kit building experience.  How long would something like this take to build and what are the minimum basic tools required?  I would not in all likelihood be building on a regular basis or even infrequently.  I do not mean to ask if this info exists elsewhere but I am new to this forum.  Is there a sample manual available to download?

Would it be worth purchasing the tools/equipment needed (thinking I may not use the much in the future) or should I just have it built?

Thanks in advance for any help.

JP

Title: Re: Something new is coming
Post by: Grainger49 on March 10, 2010, 04:42:42 AM
The description says two evenings.  Make that three and you can be safe.

This is a list of tools:

Suggested Tools (http://www.bottlehead.com/smf/index.php/topic,173.0.html)

The manuals mention these as a must:

Eye protection, slotted tip screwdriver, needle nose pliers, wire cutter, wire stripper (12 Gauge and smaller), soldering iron (40W is ok), volt-ohm meter, light source, sharpie marker 7 a towel to keep the top plate from being scratched.  (this list lifted from the Eros manual, I bet Crack is the same)

I bet the kit starts with the power supply, and ends with the audio circuit.  This gets you used to soldering before you get to the most critical circuitry.  
Title: Re: Something new is coming
Post by: Doc B. on March 10, 2010, 05:00:03 AM
Hi jp,

Yes, build it yourself! Crack is what we used to call a Skill Level I kit, intended for first time builders. Two things happen when you build it yourself. First is that you gain confidence to look a little more deeply into all of your gear and make more educated decisions about future equipment purchases, because you gain a little more understanding of how the stuff goes together (and how much gets spent on the parts inside vs. the fancy face plates). Secondly you will experience a very neat thing I call Proud Papa Syndrome. Because you have built gear yourself it automatically sounds a little better to you than it would if you bought it built.

When we figure how long it takes to build a kit we usually look at how long it takes one of us techs and then multiply that by some factor. Not including the cosmetic stuff like chassis paint or polish and stain and varnish on the base ( which you can either leave plain and simple like the product shot or go crazy with like some of the cool kit builds you can see in the forum gallery) the actual assembly is easily doable in a couple evenings and folks with a kit or two under their belt will probably finish it in one evening. Another interesting phenomenon is what I call post construction let down. Some folks hurry to get sound only to realize they really should have slowed down and savored the pleasure of building the kit. You get lots of listening time with the finished kit, but you can't really go back to the assembly phase.

We really understand the first timer here, and I think the community here have an unprecedented reputation of support for newbs. If you get stuck on some step and post about it here you will usually get an answer to your question within a couple hours.
Title: Re: Something new is coming
Post by: Paully on March 10, 2010, 05:12:13 AM
Let me add that I am a Latin teacher with little technical knowledge and I have built a lot of these kits.  The easy ones and the complex ones.  You can do it.  Just practice soldering on some spare parts or some cheap parts from Radio Shack.  Watch a soldering tutorial online, its not hard. 

The manuals are the best in the business, truly.  If you can tell a resistor from a capacitor you can easily do this, and from looking at the underside of the Crack amp, this is the one to cut your teeth on.  The manuals have great instructions and Doc's hobby of photography makes the manuals incredibly well illustrated.  The pictures are clear and let you see if you have done it correctly.  You need a soldering iron, solder, needle nose pliers, wire stripper, some screw drivers.  Can't think of anything else off the top of my head.  It really is fun to do and being able to have people listen to it, be amazed, and then you say you built yourself and it only cost $200.  Well, its about as much fun as you can have in audio.
Title: Re: Something new is coming
Post by: Grainger49 on March 10, 2010, 05:14:11 AM
Someone should post a link to the soldering tutorial online.  We lost the animation we had at the old site when the poster (can't remember who) closed his site.  It was a good animation.

And I will echo Paul's support of the manuals.  I have built kits since the mid 60s.  These are the best I have even seen.  The pictures almost tell it all.

Title: Re: Something new is coming
Post by: Paully on March 10, 2010, 05:21:48 AM
Just go to youtube and type in solder.  There are a bunch of videos.
Title: Re: Something new is coming
Post by: jpstereo on March 10, 2010, 05:29:53 AM
Many, many thanks to all for the encouragement.  I still don't know if I am up to the task (certainly all thumbs here) but I am starting to think otherwise what with all this wonderful support!  As the owner of several tube amps - IMHO - there is no other way to go!

Regards,

JP
Title: Re: Something new is coming
Post by: Grainger49 on March 10, 2010, 05:30:23 AM
Yeah, but we ought to have a link here to help the new guys.

Ok, JP, where are you?  There might be a Bottlehead near who would look over your shoulder.
Title: Re: Something new is coming
Post by: jpstereo on March 10, 2010, 05:39:36 AM
Southern NH but I work in Boston ...
Title: Re: Something new is coming
Post by: jpstereo on March 10, 2010, 06:25:23 AM
Is it safe to assume that this will play nicely with my Beyerdynamic DT880s (250 ohm?)
Title: Re: Something new is coming
Post by: Doc B. on March 10, 2010, 06:39:05 AM
Should work great with 250 ohm cans.
Title: Re: Something new is coming
Post by: vladimirwolfe on March 10, 2010, 06:57:25 AM
Go for it JP. You might think you won't build another kit, but I'd be willing to bet otherwise. It's habit forming!

The forum members are extremely patient and helpful. This has to be one of the friendliest places on the web.

Doug
Title: Re: Something new is coming
Post by: jpstereo on March 10, 2010, 07:30:11 AM
It certainly does appear that way.  Thanks Doug.

JP
Title: Re: Something new is coming
Post by: Paul Joppa on March 10, 2010, 09:46:50 AM
Alder is a hardwood, unlike pine, fir, spruce, etc.
Title: Re: Something new is coming
Post by: mrarroyo on March 10, 2010, 09:57:28 AM
Thanks for the response, I would use this opportunity to obtain a better soldering station as well as magnifying glass. ;)
Title: Re: Something new is coming
Post by: Grainger49 on March 10, 2010, 10:15:37 AM
Alder is a hardwood, unlike pine, fir, spruce, etc.

PJ, I just meant that there was a lot of Alder in the Pacific NW.  Like pines in the South.  Alder is the best wood for smoking salmon.
Title: Re: Something new is coming
Post by: Todd R on March 10, 2010, 11:20:46 AM
Quote
What would you recommend as the minimum impedance for a set of headphones to use with the kit?

The output impedance of the 6080 cathode follower is around 100 ohms. So in theory the most ideal load will be 300 and 600 ohm headphones. You could push this down to 100 ohms and just expect somewhat increased distortion - in fact we tried it with 32 ohm phones and it sounded pretty darn good, but that is not the intended usage. The current wisdom seems to be that a S.E.X. amp with the 120 ohm resistors removed from the jack works best with low ( like 32 ohm)  impedance headphones. The curves of some 6080 relatives might give a little lower output impedance in the given circuit, but I have not pursued that yet. Remember, this kit is only about 10 days old.

Doc,
I have a Wheatfield HA-2 which also uses a 6080 tube. They suggest using a 6528A for low impedance phones, would that work with this kit?

BTW, how does it compare to the SEX amp when driving high impedance phones like Sennheisers?
Title: Re: Something new is coming
Post by: Doc B. on March 10, 2010, 11:53:47 AM
Hi Todd,

I mistakenly said that the amp might work with a 6528A, but the 6528A heater draws twice as much current as the 6080, so it is not a possibility. So far I like Crack better with high impedance cans, and S.E.X. better with low impedance cans.
Title: Re: Something new is coming
Post by: Dr. Toobz on March 10, 2010, 12:41:14 PM
Wouldn't a 5998 tube work here? I think the current draw is a little less than the 6AS7/6080 and the plate impedance is supposedly lower, too. I've seen it recommended in 6AS7 OTL circuits where a little lower Z-out is needed for 32-ohm phones.
Title: Re: Something new is coming
Post by: Todd R on March 10, 2010, 04:01:56 PM
Hi Todd,

I mistakenly said that the amp might work with a 6528A, but the 6528A heater draws twice as much current as the 6080, so it is not a possibility. So far I like Crack better with high impedance cans, and S.E.X. better with low impedance cans.

OK, good to know.
Guess I'll go buy some, I mean a Crack
Title: Re: Something new is coming
Post by: Todd R on March 10, 2010, 04:25:11 PM
Hey Doc,
Just paid for a Crack.
Couldn't see where I could order the official Bottlehead badge, do you still offer them?
Title: Re: Something new is coming
Post by: Doc B. on March 10, 2010, 06:01:32 PM
Yes, we do have badges. My bad, I will get an order button up tomorrow.
Title: Re: Something new is coming
Post by: corndog71 on March 10, 2010, 06:49:39 PM
Hey Doc,
Have you thought of producing a nice heavy foil type sticker as a cheaper alternative to the badges?
Title: Re: Something new is coming
Post by: vanofmonks on March 11, 2010, 02:16:10 PM
Is there enough overhead in the heater circuit to use a 7n7 instead of the 12au7?  Curious because they are cheap and I have some nice teflon sockets.
Title: Re: Something new is coming
Post by: Paully on March 11, 2010, 02:28:35 PM
I would be curious to know that too, I have collected a bit of a stash of those.
Title: Re: Something new is coming
Post by: Doc B. on March 11, 2010, 03:33:41 PM
I had my transformer current capability figures confused and you should be able to use a few more different tubes than I originally said. I'm not going to figure every tube out that you guys ask for, but here's the general scoop:

The power trans can deliver 3.8A AC to the 6.3V heaters. Right now the 6080 draws 2.5A and the 12AU7 draws 0.3A. So right now the total draw is 2.8A. One could change to a 6SN7 (0.6A heater) by punching out the socket mounting hole and wiring in an octal socket. Or just do it the easy way and use a 6CG7 in the existing socket with the heater pins rewired from 9 and 4/5 tied to 4 and 5. 12BH7 should be pretty easy to do as well.

The 12AU7 is running at 75V and about 3.8mA - the FPIII operating point. You could also rewire the heater to 4 and 5 and use a 6922 without any other changes - essentially the Seduction operating point. Gain will be higher, which I don't necessarily consider an improvement.

One could also bump up the current through the 6080. However we are designing a C4S load for the 6080 that will work great at the present operating point, but will be running very hot if we increase it. So we will stick with the current point we have chosen (150V plate, 100V cathode, 30mA) and let builders play with hotter points if they want to.



Title: Re: Something new is coming
Post by: Jim R. on March 14, 2010, 03:16:26 PM
Is the input stage directly coupled to the output, and if not, what's the value of the coupling caps?

Thanks,

Jim
Title: Re: Something new is coming
Post by: Paul Birkeland on March 14, 2010, 07:34:13 PM
The two stages are directly coupled, there are just 100uf caps at the output.
Title: Re: Something new is coming
Post by: Todd R on March 15, 2010, 12:25:56 AM
Yes, we do have badges. My bad, I will get an order button up tomorrow.

Don't see the link yet. Is it under parts?
Title: Re: Something new is coming
Post by: Jim R. on March 15, 2010, 03:23:39 AM
PB,

Thanks.  No interstage coupling caps -- have to love that too.  This is sounding like a really sweet design... congratulations.

-- Jim
Title: Re: Something new is coming -- Semi Insane idea for 32 ohms.
Post by: VoltSecond on March 15, 2010, 05:15:51 PM
Use the C4S that uses the 2N2907. Use a POT for the current set resistor. Put the OTL cap to the wiper.

At one end you'll get a standard CCS fed cathode follower.
In the middle you'll get a hybrid push-pull amp with a reasonably low output Z.
At the far end, the solid state handles all the drive current and the cathode follower pretty much sees a high impedance.

The pot can be tweaked for tone.