Bottlehead Forum
General Category => General Discussion => Topic started by: Mistertaz on October 31, 2011, 04:05:19 PM
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Hi!
There was some talk of new Bottlehead preamp designs... What's happening with them? Is a new Foreplay in the works?
Taz.
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We're working on something. It's not finalized yet.
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A directly heated triode otl preamp would be spectacular.... in the future someday....
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That is one of the things we are working on. I am in the throes of finishing the Smack assembly manual at the moment -
"Cut and strip back 1/4" (6mm) a 3/4" (19mm) red Teflon wire and attach one end to terminal 15L, do not solder yet"...AAUUUUUGGGHHHH! I'll sign your f***ing confession! Just make the assembly instructions stop!
When we have that wrapped up we will start working on the DHT version of the IDHT POC prototype preamp we have had working for a few months now. Might try to have it done for the meet on the 19th.
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n.b. POC is Proof Of Concept, not what you think it is... :^)
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Is it going to be an affordable Foreplay replacement, or a high end (ie. expensive) preamp?
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And the I
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n.b. POC is Proof Of Concept, not what you think it is... :^)
Back in the 70's it was the Infinity POS.
Xavier, I think it is "indirect."
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Is it going to be an affordable Foreplay replacement, or a high end (ie. expensive) preamp?
Our latest thinking has been that our entry-level amps (S.E.X. and Stereomour) are integrated and do not need a preamp, so we're thinking something to match Eros and Paramount. But we're looking for a really high end product as well. Eros is the "trickle down" technology from the high end Repro tape preamp, so a similar path is not out of the question.
In fact, nothing is out of the question until we finish trying out different concepts. At one point I was investigating a very low cost preamp, between Foreplay and Quickie. It and many others were never tested, but we have built and listened to 4 or 5 quite different designs so far.
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Is it going to be an affordable Foreplay replacement, or a high end (ie. expensive) preamp?
Yes. ;^)>
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my own humble opinion..... with careful matching to the amp, which, of course, you guys will do, I can't think of a BETTER preamp than a DHT OTL pre...... that should be as "high end" as it can get and a brilliant partner for the premium BH gear.... ok exciting news!! thank you D & P...
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...I can't think of a BETTER preamp than a DHT OTL pre......
I could not pass up remarking on this post. Obviously we agree in principle, or we would not be experimenting with it (!) I have a couple examples of the difficult boundary between principle and practice though.
1) A DHT preamp means a really quiet filament power. There is no known theoretical reason why DC filament power should have any sonic problems, but it is widely accepted that it does unless it is done really really carefully. Our previous designs were quiet enough for power output tubes, but can't possibly cut it for a serious preamp - there will have to be some development work!
2) You want a DHT OTL pre? Quickie is a DHT OTL pre. And you can buy a hundred of them for the price of a commercial high-end preamp. One hundred! (Batteries not included.) OK, it's really a triode-wired pentode. For ten grand, I'll make you a version that uses a Type 31 real triode. I'll even supply batteries!
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With the PJCSS and more expensive capacitors in the cathode bypass and coupling positions, the Quickie is already a pretty darn good DHT preamp. A really quiet, higher voltage power supply, stepped attenuators, a metal plate, a rotary selector switch and extra set of input jacks, and some way of floating the tube sockets on the plate (to reduce micophonics) would be a nice upgrade kit. This still would probably cost less than the IDHT Foreplay III.
Of course, give me a 01A, 76, 10Y, or 30 preamp (maybe even battery operated, off lantern batteries, for some of the 5V or 2V tubes?) and then I'm in!
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Part of my design requirement is that the tube should have a very low output impedance to get the bass performance optimal, like 500 ohms or less. The 3S4 is of a little higher output impedance than my design goal, but it does indeed make a rockin' little DHT preamp. We have a high school intern working with us these days, who just started building a Quickie for his final presentation. I think he's going to blow some minds at his school.
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Re Dr Toobz's concern about floating the tube socket in a way so as to really decrease tube microphonics, this can easily be done by mounthing the sockets on a piece of 1/4" teflon. This works very well.
Bernie.
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Thank you Paul, yep a high end DHT OTL pre "The Nooner" (So good , you have to return home for lunch, not for the misses, but to listen to your BH GEAR!!!) is not an easy task do well, but IF you guys decide to do it, it will be superb I am sure... good luck , take your time.... thanks guys... and I can just hear the H.S. intern explaining to the class, "and yeah after a Quickie, my next project will be to work on my Extended Foreplay with Enhanced Sex of course"..... Doc, you are going to send the poor kid straight to the principals office!!.... :)
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One channel of the 300B preamp is up and running this afternoon. Wow. The system is gettin' some hair on its balls. Shawn will be cranking out another channel, hopefully to be completed by tomorrow so we can listen to them at the meeting on Saturday.
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Awesome!!
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Wow, wish I could make it to the meet just to hear this!
Transformer coupled output?
-- Jim
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Direct out, no transformers. :^)
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Holy Cow, exactly what I had in mind as my ultimate preamp, a 300B DHT OTL.... just a question, will the 300b's last longer than if they were in am amp?
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The 300B plates are dissipating only about 6 or 7 watts. They ought to last a long time.
We have noticed a bit of microphony, but it seems like it will be controllable as we only hear it when we thump the chassis. Doesn't seem to be picking up enough vibration from the speakers to be a problem. Shawn had the second channel about 30% built by last night, so I hope to report about the stereo pair this afternoon.
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Second channel had this mysterious hum, that sounded to me like a ground loop. Shawn and I spent two hours trading out nearly every part of the bad channel with the good channel in frustration and then, finally, I realized that one of the three traces I was supposed to cut on the power supply PC board in order to mod it for this application was not cut and hence causing - you guessed it - a ground loop. Palm print on forehead. Before we left tonight we got it fixed and fired up both channels, playing some our favorite vinyl demo tracks with the Tube Phono and active step up prototype.
Holy s**t! It's not just a bigger badder lower midrange as one would expect. The bass is big and bad too, the midrange resolution is crazy good and it's like the power output of the system has gone up maybe a factor of 10. This is a keeper, and a very satisfying result of my spending the last year or so trying to come up with the ultimate version of my "low output impedance/no transformers/no cathode followers" line stage. Thanks to PJ for putting up with my theories over the past year and cooking up circuits based upon them, including this one.
You guys who have Paramounts, start saving your pennies. This circuit is a match made in heaven.
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I just unwrapped a new piggy bank... :)
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OK, so now you are telling me I need to save for the DAC, the Paramounts, AND the 300B pre amp? Done...I'm officially saving for all three....I don't need to shop around anymore for anything! Congratulations, Doc!!!
John
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This will be a great addition to my Paramount set up! Can't wait, the saving has begun!
Cheers
mike
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Will this preamp have any provision for headphones as well?
I assume it's unlikely unless they're high-impedance cans?
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Yeah the output impedance is a bit high relative to most headphones. And adding an output transformer to lower the output impedance is going to reduce the gain, so you might find you need a second stage to get enough gain from your source. Next thing you know, you have designed Paramount instead of this preamp.
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Some very cool stuff brewing up in Poulsbo!
I can't wait to check it out.
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Sounds like the "ULTIMATE Foreplay" to me...... I know we are only talking about matching it up with BH gear, and I know amp matching with a DHT OTL pre can be difficult, what amps (impedences etc.) would be a bad match do you think, in other words, could this amp be used as a "generic" reference pre with SS amps, OTL tube amps, I even have a 1000 watt OTL hybrid amp... I know the best combo is to match it to YOUR amps, I guess i just want to know how flexible it would be as a generic reference pre also? thank you very much.....
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Output impedance is quite low, about 600 ohms. It should be able to drive pretty much anything.
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OK... sounds wonderful.. a preamp of this magnitude just begs to be used as a reference standard in anybodies system, and i am very happy i will be able to mate it with ALL my amps.. Thank You Paul
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When will this be announced? Has a price ballpark been identified?
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When will this be announced? Has a price ballpark been identified?
Long time yet. This was just the proof of concept - testing whether a directly heated triode actually sounds better than indirectly heated, given similar operating conditions. It's cobbled together from a pair of Crack chassis plates, Eros power supply parts, and some duct tape (just kidding!) Would a 2A3 sound as good? Don't know yet. Still undecided on the best filament power arrangement and bias method - right now it's just a chip regulator for the filaments. Also, we have two other quite different designs that also sound really good. But we already have two preamps, can't see adding three more!