Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: Frank Mena on March 08, 2012, 04:09:11 PM
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Somewhere i read that a 300B pre-amp was in the works. Fiction....?, yet to be finalized....? wish-full thinking? somewhere on the to-do list?
Thanks in advance.
FM
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I second the interest on the 300B pre. I would wonder what sort of character that tube circuit would have, and how complex would it have to be.
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I third it! Its on my B-day wish list. Which is fast approaching in May though. Any chance of a spring release?
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Heard it! Not ideal conditions and it was sourced by the proto DAC so I can't honestly say what was contributing what,.. but it does exist.
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There is a picture of the Bottlehead display at a recent gathering.
Here:
http://www.bottlehead.com/smf/index.php/topic,2659.0.html
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Yes, the prototype exists. PB is working on a second prototype, a finished version in the style of the Tube Phono. It is the best preamp I've had in our system at BHQ. It will be a kit, intended to work with Paramount in particular but also as a great preamp for just about anything you can throw at it. Don't have a price yet, don't have a release date yet. We still have to work out some details regarding layout and parts choices.
In conjunction with working with the preamp prototype we made a change in the system yesterday. The SR45 amps we built to run the tweeters have (relative to the Paramounts) low input sensitivity, and that was forcing us to turn down level controls on the active crossovers that feed the mid range and woofer Paramounts to the point where we just couldn't quite get the system jumping with some sources. Also I had a sense that they were running out of steam into the Raal ribbons when we really cranked it. So yesterday Shawn brought in a pair of his Paramounts to replace the SR45s. This allowed us to turn up the level controls on the mids and woofers - a lot.
This combination of all Paramount amps driven with active crossovers with the 300B preamp ahead of them is now rockin' the house with 56 watts per channel. It can go very loud and sounds very quick and relaxed doing it. It's one of those "now I have to listen to all my favorite stuff all over again" kind of changes. Plan to spend a generous portion of time listening this weekend.
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Doc,
Were the Paramounts also 300Bs?
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Yeah, all 14 of the Paramounts in the system are 300Bs - one on each tweeter, four on each midrange with secondaries wired in series, two on each 4 woofer array with each amp running two parallel wired woofers. The math says the system should now be capable of 106dB peaks. It's now time to revisit our room treatments to better tune the room to handle higher levels.
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wow! 56wpc of 300B power! Delicious!
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Will the output be transformer coupled? Are you able to give us a ballpark on input and output impedance?
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Doc - With the Tode progressing so well, will attentions be turned to the 300B preamp? Would love to hear an update on this one...
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We are making some changes to speed up the release of new products. That should start in May. So hopefully we will be able to get a bunch of new product ideas out this year - Tode, the DAC, the 300B preamp and a few other ideas I've been musing on.
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Hope one of those other ideas will be a 2-way electronic crossover with adjustable gain, frequency and phase -- maybe even a couple of different slopes? :-)
-- Jim
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Hope one of those other ideas will be a 2-way electronic crossover with adjustable gain, frequency and phase -- maybe even a couple of different slopes? :-)
-- Jim
Here's the thing that always stops me when I look at a fully-adjustable crossover:
Starting point is a first- or second-order Sallen and Key circuit with cathode followers. Two dual triodes, just like Foreplay or Seduction; possibly another tube for shunt-regulated supply voltage. With no adjustments, it would make a reasonable kit. This is basically what Doc B uses in the Big Rig (I think there are four of them).
adjustable gain: high-pass, low-pass, left and right, that's 4 knobs. For uncompromised filter accuracy, they will need buffers - two more dual triodes.
Adjustable frequency: as above, but each of them is a dual pot. You can't cover any more than an octave that way, so there's a range switch for each as well. That's eight more knobs, total 12.
Phase: Forget it, the only useful way to do this is to implement a variable time delay on each output, which is easy with digital and ridiculous with analog.
So, even without phase you have 12 knobs and at least five tubes. Now think what a b*&^%h it is to wire up the three knobs on a Foreplay or Stereomour. Think about upgrading 4 mono pots plus 4 stereo pots plus four rotary switches. Think about the cost of all those premium pots and switches...
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Paul,
Ok, gotcha. Figured I was asking for a bit much :-). I also don't really want to go the digital eq route either, the one exception may be to use a 4-channel dac and use the digital crossover feature in PureMusic, but I don't want to take my nice clean audio and send it into a cheap A/D converter and then to another dac which is probably not up to the same sonic standards as a dedicated source dac. I'm also trying to stay away from CF circuits as much as possible, but that isn't always practical either.
-- Jim
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If we made a non-adjustable kit, here's what I would do. Get a cheap adjustable crossover - Rane is local here and makes several models; there are many others. Play with it until I had a pretty good idea of what crossover function I wanted. Then, build a tube version with those slopes and frequencies.
For the Big Rig, we actually made measurements of the drivers and designed a crossover specifically for them, then implemented it. We've made a few small alterations since, but one or two subtle adjustments can be done by soldering easily enough. It's the initial stages, if you don't have detailed measurements of the individual drivers as installed, where you'd want to do lots and lots of experimenting and listening and therefor need a highly adjustable crossover.
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Will the output be transformer coupled? Are you able to give us a ballpark on input and output impedance?
Must have been missed by those in the know. Doc, PJ, can you answer this yet or is it still in the works?
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It will be cap output, single ended 500 ohms or so output impedance. With an option to add a 1:1 trans with CT secondary if you want to run balanced.
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Is it possible to have an approx time for when the 300b-pre will be released? Will it be an all-out kit, or will you offer various options?
Roger
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As I mentioned a few posts below, some changes will be happening in May and we should have a little better sense of a schedule for when new things will be coming out after that.
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Dan, Paul,
Do you see any issues with this preamp driving 16-20 foot ICs? That would be into SR-45s, Stereomour (built as a power amp), and possibly paramounts in the future?
Trying to get a sense of how the new room will be configured and right now I'm leaning towards keeping the main rackk next to the listening chair and running some long interconnects over to the amps which will be situated near the speakers. I'm trying to keep the space between the speakers as free of acoustic interferences as possible, but I also don't want to run 1.8 watts through 20 feet of speaker wire.
Thanks,
Jim
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Should be no problem. I estimate 50 meters of cable before you see any HF rolloff, and plenty of current margin above that. That's a theoretical estimate of course, but gives you a good idea.
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Paul,
Thanks -- that helps a lot and also solidifies my plans for the new room.
-- Jim
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50 meters! ... that is great and responsible engineering.. thank you for engineering in all that flexibility Paul...
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Just to give everyone a heads up on this project - we have another that is ahead of this one in terms of release, but we are currently working on studying the best way to heat the 300B filaments. We hear a difference in the quality of the noise floor with different schemes and need a little time to refine our approach. Which led, yesterday, to our needing to look at the noise on the scope. Which led to having to go inside the scope to figure out why the acquisition board on the scope was flaking out. Which led to PB picking up some new batteries on his way home, to solder in today. Some days doing one simple thing ends up being like building a ship! Hopefully the scope will behave and we can get some useful data and move forward.
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hi all, question for jim: what is a source for quality i/c in the 16-20 range? i have a situation where almost all of my listening is streaming from my pc to my bottlehead preamp located 16 feet away. i did locate an i/c from parts express ($70). not the highest quality. don't know where else to look. suggestions?? thanks, don
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Don,
I currently have a pair of Crimson Music Link speaker cables that are 20' long and they use the same cable with different terminations for their interconnects, so it would be a simple matter of swapping banana plugs for RCAs. Not cheap though.
You can diy a deceent pair from cat-5 or 6 by braiding the pairs and then connecting all the solid color wires together at each end, and then all the striped pairs at both ends and putting some sleeving over them -- and possibly some groud braid as a shield if you want -- or just use cat-6 as it is and do the same thing for terminations. The earlier usually requires that you use (if you can find it) cat-5 with twisted pairs that are bonded together. You could also use mogami star quad abling of various sizes, but really good quality is, for the most part, going to cost some money. Some of the DH labs cabling could be decent too. There are a zillion ways to do this, but what level of performance, shielding, etc. will vary greatly with each approach and setup.
For me, the Crimson cables are some of the best I've heard, including many of the insanely priced ones, and while not exactly bargain basement pricing, aren't outrageous compared to most of the boutique cables -- figure $350 for a 1 meter pair of interconnects, and about $525 for an 8-foot pair of speaker cables. These are my favorite overall and go well with BH gear.
HTH,
Jim
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Status update please :)
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Pretty much all the circuit design issues are resolved - PB just sorted out an impedance question for his snazzy gain controls today. And we have a pretty nice-looking chassis layout. It's 10 by 12 inches, same as Stereomour, and dual-mono the hard way - two power transformers(!). Next up is to build another prototype, this time with all the production parts and component values. That may or may not be the actual production prototype (the one that will be in the manual).
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Thanks Paul :) Does the single chassis allow room for different attenuators (ladder, etc), and other user specific mods? It sounds pretty full given the single chassis layout.
Regards,
Aaron
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... PB just sorted out an impedance question for his snazzy gain controls today... and dual-mono the hard way
Does this mean there will be separate left/right gain controls? Having the ability to fine tune channel balance would be a MAJOR plus in my book. Thanks.
Gerry
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Remember that there's only one tube per channel so a 12 x 10 in chassis should have enough space. It's 120 sq in vs 60 of the FP2 and 80 of the FP3.
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There are two tubes per channel, a 300B for the voltage amp and a 6BQ5 for the shunt regulator. We were assuming the chassis would be 10" x 12" until PB started trying to fit in all the XLR jacks for balanced inputs and outputs yesterday. Those have required an increase in the layout to 12 x 12. Even though it's "just a preamp", there is a lot of stuff in this puppy - two power transformers for the dual mono supplies, big shunt regulator boards, a fairly sophisticated regulator for the filament supply, a very trick 63 step coarse/fine volume control (that in my opinion will not automatically be upgraded by putting in a different attenuator) probably optional input and output transformers for balanced operation, and all of this needs to be laid out so that there is ample room between your hand and the hot tubes when turning the knobs. My hunch is that we are close on the layout, and we will hopefully be ordering some parts for the functional prototype in the next week or so.
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Maybe you could offer the kit with/without XLR to save some people some money. I know that I'm not interested in balanced. I have too much invested in RCA cables, and I dont think balanced is needed in short cable runs.
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She's picking up speed now!!!!!!!
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Yep, I thought about the regulators after posting. Why constrain to 12 width? Go to 19!
Saludos
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Yes, at this point that plan is that transformer balanced inputs will be an option, the coarse/fine stepped stereo attenuator will be an option with the basic version being a stereo volume pot and balance control pot. We are investigating other options as well. The kit will be available with and without 300Bs. PB is shooting for an under $1K price tag for the basic version w/o 300Bs. Not sure if we will make it, but we should get close.
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Oooh Boy!
The balanced in/out sounds peachy to me!
Need any beta testers?
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Dan/PB/PJ, could you tell us a little more about this fancy attenuator you have created? My ideal attenuator would have 1dB (or less) steps where each channel can be adjusted (for balance) but overall volume increased in stereo (one control).
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Yes, at this point the plan is that transformer balanced inputs will be an option...
The following is related to the balanced option. Allen Wright stated the balanced operation only made sense if it were used in the entire system. In other words from source component to preamp to amplifier.
Putting aside the fact that the new 300B preamp may be used with other amplifiers, why even offer the balanced option if the Paramount amplifier itself is not balanced? I
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Balanced output is not necessarily from a fully differential output. As sweet and bright a guy as Allen was, he used to make me crazy by mixing the definitions. He was talking about push-pull circuits inside the amp (or as George Wright use to call it, push and shove circuits).
Balanced connection simply means that the impedances are balanced between the signal wires at both the source and load end of the cable. It's a technique for wiring equipment together with cables the improves the common mode noise rejection, not an amp topology.
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Hello Aaron,
We plan to offer the stepped attenuators as an upgrade, and so far they have outperformed all other attenuators that we have used.
-Paul
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PB, I don't doubt that it is a great attenuator but can you tell me if it will allow for stepping of each channel individually to comp for balance? It's a PITA to move 150 lbs speakers to get a good center image.
Thanks,
Aaron
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It's a stereo attenuator, one switch for both channels. My suggestion for balance trim would be to put trimmers in the amp inputs. That will allow for changes in gain throughout the system as tubes age.
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Team BH, what is the attenuator resistance range for this preamp? Hopefully 10k or 50k will work? I really would like a remote, (for once) and have an ideal in mind.
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The input resistance of the level controls should be high enough for the sources you will use with it. For use with Eros or Seduction, that means 30-50K minimum so that's our criterion. Other sources will have their own requirements - a few tubed components would prefer to see 100K or more, while most solid state sources are happy with anything above 10K.
The output impedance of the level control should be low enough for the input capacitance of the tube; in this case 50K maximum. For a normal setup with a single potentiometer, its output impedance is never more than 1/4 of the pot's total resistance, so a 200K pot would be the maximum.
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Team BH, what is the attenuator resistance range for this preamp? Hopefully 10k or 50k will work? I really would like a remote, (for once) and have an ideal in mind.
The stock configuration, at least as it is drawn now, is about 57K. The upgraded attenuators, as planned, would have a variable input impedance that would vary, but be no less than 50K at any position.
For aftermarket attenuators, you can kinda use what you like, but I would stay closer to 50K if possible. Also, there is a pair of ~12V DC rails in this preamp with the negative end grounded and some surplus current, so you likely won't need a wall wart to add a remote attenuator (though you might if it has a motorized pot).
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Thank you PJ and PB, that's what I was looking for. I'm considering building mine up with the Bent Audio 50k shut modules, input selection, display and remote units. It's a little pricy but very convienent :) I had one of John's TapX preamps for a while and really enjoyed the ease of use though the sound didn't work well with my system at the time.
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Hi:
Will the contruction manual or purchase options include a one input only option (no source selection)? Due to less switches, wiring, etc., can a single input be beneficial? Thanks.
Gerry
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Hi:
Will the contruction manual or purchase options include a one input only option (no source selection)? Due to less switches, wiring, etc., can a single input be beneficial? Thanks.
Gerry
No. Just leave that stuff out if you want to, but it isn't going to change the sound much.
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Hmmm, I got to thinking again which is dangerous. What are you thoughts of using a set of Mikey's 10k/10k transformers on the input side to further isolate the ground and use my fancy 10k P&G pot? Would this potentially offer any futher input noise reduction? I have a three way Gold Point switch for use also.....
Thanks!
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In our experience, Mike's transformers have been the best sounding (I think it was a 15395 clone). But there is always some bandwidth limitation from transformers, so no transformer always sounds a hair better. Transformers do provide ground isolation and hence lower noise (hum and buzz); they allow balanced lines, also good for hum and buzz. The downside is hum pickup from magnetic fields; usually you want at least one and up to three concentric mumetal shields on an input transformer. (Normally they will have copper Faraday shields between each mumetal layer ...). This starts to get expensive and difficult!
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Thanks PJ, worst case I put some double sided tape on them and move them around for the least hum pickup from the power transformer. One in theory could just get some of that Mu metal tape/shield and wrap the transformers well too correct?
So the 10k/10k B7's would work well then? Anything else I would need to do? I see it as input>switch>B7's>pot correct?
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The tape is not as effective as a fully-enclosed can, and you must be careful to not manipulate it more than necessary. I think you can get around 15dB from careful taping, vs 30dB per can shield. Hopefully a combination of careful placement and tape will make things good.
You circuit is correct. The pot provides the correct loading for the transformer so that it performs optimally.
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I did some experimentation with shielding small signal transformers a while back. It is very tricky. I ended up using a combo of moly perm tape, mu metal can, copper tape, aluminum box. The final step was to try putting it all in a steel can to fend off the stronger magnetic fields. And it still picked up hum.
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Wow.... So you are saying it's worth a try but expect hum..... Are there other 10k/10k input transformers out there that would work well in this application and is it even worth persuing for a non-balanced configuration?
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Altec 15335s seem to work well. I'm sure they aren't as nice sounding as Mike's, but they do come with well worked out shielding. You would have to come up with a way to mount them, since they have octal bases.
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Thanks Dan. They are 15k transformers and the P&G pot is 10k, not an ideal match if I understand things correctly?
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No, not ideal - but pretty darn close. I wouldn't sweat it - the lower resistance will reduce the Q of the HF rolloff resonance and the greater damping may well actually sound better. You can always put 5K in series with the pot; you'll only lose 3-4dB. Try it and see if you hear any actual difference.
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Thanks Paul. I've got both sets of transformers and will give them a shot. Please post if you guys find a set and position that ideally match the pre-amp.
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Sorry if this question has been asked! - I dont remember seeing it mentioned but, how long are the 300B's expected to last when being used in a preamp circuit? Similar to other preamp triodes or are they run at full power?
Thanks - Eric
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They are run at very low power, about 6 watts plate dissipation. They are not likely to die from excess temperature. The filament is run at the full rated voltage and current, so it would probably have the same life expectancy with regard to breakage. The plate voltage is low, so any loss of emission due to cathode poisoning should be much slower than under power-amp conditions. Loss of emission due to exhaustion of the cathode coating from causes other than poisoning will probably be the same as under power amp conditions since the cathode current is high.
I think those are the Big Four for guessing the lifetime. Which one is most important depends on the tube's detailed construction and can be known only to the manufacturer - and if I'm not mistaken, only a few of them actually know very much along these lines.
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Thanks Paul
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That means??? If you could guess.... 3,000... 5.... !0,000 hours? depending on quality like JJ or WE type....
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At one time, WE said 20,000 hours except half that at maximum ratings. I think they stopped saying anything at all long before the tube was discontinued - there are just too may variables. Probably they were getting calls like "I only got 18,500 hours" or "my power line is only 140 volts, yet my tubes blow out after only 5000 hours"....
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Yeah, I can imagine... But with this being a preamp, I would imagine maybe 5 ish at least.. Anyway, should last a heck of a long time.... Thank you Paul
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Just an update on where the Bee Pre is, the Bee Pre in the photographs on the website is constructed and running, and we received the incredibly important blessing from PJ.
We also observed a reasonable decrease in the noise floor between the prototype and the production prototype.
We made a few tweaks to the PC board design and the parts that go on them, and those will go into production shortly.
Lastly, the chassis plate layout will be ever so slightly tweaked to provide a little more space for some parts that ended up being a tighter squeeze than we thought.
When the revised chassis plates and PC boards roll in, we'll be in manual writing mode, but in the mean time, I will install the attenuator upgrade into our second production prototype for evaluation (we are using nicer switches than we used in the prototype).
-PB
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PB,
What are the specs for the coupling caps?
Thanks,
Jim
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Howdy Jim,
There are four 10uF coupling caps and two 0.22uF power supply caps that could be upgraded. Voltages should be no less than 250V.
-PB
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Two of the 10uF caps are not used unless you are using the balanced output.
These are ourput caps, and if you are driving a really low impedance load, (under 1K ohms) you would want to increase them; 27uF is (IMHO) the point of diminishing returns.
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Howdy Jim,
There are four 10uF coupling caps and two 0.22uF power supply caps that could be upgraded. Voltages should be no less than 250V.
-PB
Yikes! That's gonna be a painful but I'm sure satisfying upgrade.
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The kit is coming with some pretty nice caps the attenuator upgrade may be a better investment.
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Speaking of attenuators... anyone have experience or heard the Lightspeed attenuators? Wonder if they would work with an active preamp...Could be interesting...
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Wonder if they would work with an active preamp
We did consider this option, but hand-matching LDR's didn't seem to be such an attractive option, and the active circuitry options to keep them matched would require quite some development and additional costs.
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I understand... Have you heard one in a passive configuration before?... in your opinion, if someone was to tackle it as project, post bee pre build, as just a personal thing, do you think they are superrior to a dact2 type attenuator?? I think this bee pre kit, design wise, could be one of the very best sounding preamps on the market in decades. DHT OTL 300B type design , i think a design like that can use the very best type of attenuator possible.... It doesnt have to come from you of course.. I am just saying if someone wants to go to all the trouble, is an LDR attenuator possible (practical) for the bee pre, feasible and worth it for the bee pre?? Thank you for your reply...
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The LDRs that have been published are quite low impedance, making them less than universal with respect to sources (e.g. Seduction and Eros for example). They also appear to have tracking issues, usually approached by ruthless sorting and rejecting a large majority of devices. Both make them mostly useful to DIYers who have the time and patience, and who understand the impedance issues and can work around them.
That said, we haven't tried any yet.
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Hey Chris - here is a post on that topic.
http://rockgrotto.proboards.com/index.cgi?board=m&action=print&thread=4066
I would agree with Paul. Opto pots are not without their own problems. I would go stepped attenuator if you are looking at optimal sound quality.
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For what it's worth - while we decided not to try LDRs we did listen to a lot of different attenuators before deciding on the coarse/fine one that will be the upgrade option. That would include TVCs, Alps Blue, PEC, Goldpoint, Sweetest whispers, some old Davens, etc., in various configurations - stepped, shunt and ladder.
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At last year's Linestage Competition, I threw in a Lightspeed. If I recall, it didn't make it into the final round of listening.
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Will the upgraded fine/coarse attenuators be available when the preamp ships or will it be an upgrade available sometime in the future.
Deb
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We just got the high grade switches in to try today. Looks like they will require an adapter to mount them, so the release of the attenuator may follow the shipment of the preamp kits by a bit while we work out the details.
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Wow, superb stuff from all of you!! My question was answered in spades... and dbishopbliss' comment for me says it all... If LDRs were that great and worth using, Paul and Doc would have recommended them... Thank you guys...
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Any update on the attenuator upgrade?
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There are different configurations for the fine/coarse controls that I have seen. Right now, I am using a mono (two controls per channel), but I have yet to try one that adjusts volume normally,both channels at once-coarse, and then one fine tune volume, per channel. What type might you be using?
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The plan was to work on the prototype today, however we have a very large order of finished amps that needs to be completed a couple days before we had anticipated. Hope to get to the attenuator by Friday. It is stereo, both coarse and fine.
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Ahhh, Yet another combination. Sounds practical to me. The two mono coarse/fine adjustments per channel is a bit much unless you are using it to set volume from say, a buffer amp to an integrated amp. That is how I am using mine, but it would drive crazier with that much on a pre-amp. The beauty of the arrangement is that there are many more volume positions possible with the c/f setup than a typical 12 step attenuator.
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Yes, there are 36 steps. Steps are 1.5 dB apart.
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Does the new Bee Pre use a solid state power supply?
Dave
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The power supply is solid state. The high voltage shunt regulator is a tube/SS hybrid, using an EL84. The filament supply regulator is SS, and uses a special "noise shunt" circuit that PB and PJ cooked up.
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Was the previous incarnate the foreplay was it...........was that a solid state power supply too?
Thanks Dave
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Yes, all of our amps and preamps have solid state power supplies. One of the issues in getting a tube circuit to sound good is getting the bass to be tight and punchy. A good SS supply can help a lot in getting there. I'm sure you can find people who will dispute this. Lucky for me I don't have to listen to them.
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Yes, all of our amps and preamps have solid state power supplies. One of the issues in getting a tube circuit to sound good is getting the bass to be tight and punchy. A good SS supply can help a lot in getting there. I'm sure you can find people who will dispute this. Lucky for me I don't have to listen to them.
Hah Hah EXACTLY, thank you!