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In Reply to: RE: So many 300B schematics...which one? posted by Audiodyssey on October 03, 2009 at 15:05:00
Just so your list of schematics is complete before you make your final choice...
the T-Rex (John Broskie and Dick Olsher and Steve Bench)
I have some modified Welbourne DRD monos but if I had the need I would go T-rex.
cheers
paba
Thanks for this, I hadn't seen it. I kind of like the idea of the 5687 in front. Do you know of anyone that could give me any feedback on performance?
I would have to dispense with the use of Plitron TX's. That is one hell of a regulated supply. How often do you suppose those tubes in the PS would need replacing?
"I KNOW you can hear it, but are you REALLY listening?"
Edits: 10/03/09
I think the power supply is so often neglected in 300B set that I have seen. I would say that the order of impact on the sound is:
1) topology (2 stages or 3 stages or interstage transformer etc.)
2) quality of the iron
3) power supply
choices like AC or DC heaters and how clean your B+ is will play big because you are probably using high eff speakers (95dB and more if you can find some) with your 7-8 watts and hence you will hear the power supply effects.
cheers
paba
Hi paba,
Intersting post. I would say it differently, from my experiences:
1) Topology, two stage vs: three, AND topology, 300B vs 2A3.
(On efficient speakers, a 2A3 is the superior tube choice, and a good two stage amp performs better than ANY good three stage. KISS rules.)
2) Power supply
(The chokes and inductor(s) have to be 20 Ohms DCR or less, or you are wasting your time, money, and badly deluding yourself). The SE amp's wiring and lay out needs to be optimized also!!
3) Output Transformer quality
(Yes, it is certainly a factor, but it is "totally trumped" by doing 1) and 2) above. With 1) AND 2) done as best as possible, and a wire-modded Transcendar will very easily outperform ANY of the highest quality outputs you, or any one else, may choose.
The output transformer is the LEAST important of the three, on the basis of overall audio performance, when the amp is built correctly. Very few SE amps are !!
Jeff Medwin
Hi Jeff,
not sure I get all of your post. So I will state what I understood.
I place Transformer last on my list as you so we agree there.
By two stage and three stage I mean to stay two different tubes before the 300b (to me means 3 three stages) and 1 tube before the 300b means 2 stages. (Even if the one tube is double triode which some might argue that it is two tubes in one envelope). Interstage transformer is obvious. I believe in KISS but blind KISS is not always the best. We can make something simple but not too simple. My 300b amps are two stage by my definition but I've never heard the highest end 300b implementations.
Power supply. Here is what I was trying to say... design choices like AC or DC heaters and the quality of those supplies feeding the tubes before the 300b will have a big impact on the sound of that amp especially if using high eff speakers.
thanks
Paba
Hi paba,Using both sections of a dual triode, for different functions, ie: input function and another section as a driver function - the 300B amp has a three stage topology. We are talking about the SE amp's number of stages doing differing functions, not number of tubes employed.
Using a single stage, functioning as a input AND driver, powering a 300B, is an amp with a two stage topology. Even if the first stage is a dual triode, sections connected in parallel, performing the same functions, it is a two stage amp !!
If two and three stage topologies are done (each to the best possible execution), the two stage will outperform the three stage, and that is why I build them. The three stage WILL be less transparent, due to the extra (third) stage.
So, proper KISS rules, and when each topology is optimized, less is more !!
Jeff Medwin
Edits: 10/08/09
Get any one of those three factors wrong (topology, PS or OPT) and no amount of improvement in the other two will save you.
Ray,
In practice at the highest possible build and design level, not at all, the SE OP XFR is truly last of the three, but it is nice to have a good one, of course.
Jeff
Jeff:
The question of 2 or 3 stages is dependent upon if there is an active preamp upstream or not. In my experience, you need 3 gain stages, be they all in the amplifier or 1 in the preamp and 2 in the power amp.
No doubt, the choice of output tube is significant. So is topology: cap or transformer or direct coupling between stages.
As for output transformer quality/construction, I can assure you: You will heard a marked difference between a standard copper wound, M6 EI core and a silver wound, nickel double C cored transformer. :) I would not put it at the bottom of the list. To me it is equally important.
Donald North
Hi Donald,
I totally believe you about C Cores, and I have NOT had build experience with them, hard to source in the USA.
You state:
"The question of 2 or 3 stages is dependent upon if there is an active preamp upstream or not. In my experience, you need 3 gain stages, be they all in the amplifier or 1 in the preamp and 2 in the power amp."
If you go to the Serious Stereo web pages, you will see a two stage DC 2A3 amp and audio system that requires NO active preamplifier stages in front of it, but rather, a passive attenuator.
I have had lots of listening experience to this system, at four RMAF shows, and I can tell you the gain works out fine and it is NOT dependent upon an active preamp upstream at all.
Hence, my comments on loss of transparency with a three stage amp. With a three stage, you can pick out a delicious sounding input stage, and or a beefy low Z driver stage, but they will not together quite do what a well designed two stage will do, transparency-wise. This is my experience.
Jeff Medwin
Hi Jeff,
Yes, I've read through that site before. Do you know is the gain input-output of that amplifier? I estimate around 22dB. In my experience using passive preamps and true 95dB efficient speakers, 22dB is not enough. I've found 30dB or slightly higher provides the best micro dynamics and life to the musical presentation and listening experience. I like to use transformer volume controls like the Silver Rock. From my measurements, they're best performing at their lower settings (-40 to - 60dB), requiring 30dB+ gain amplifiers.
Donald North
I had that trans-pot and I sold it. It lost energy like a Yugo with a fuel system leak.
I then tried every passive attenuator out there-- regardless of price, and I finally got Tribute's trans-pot, and built my own box and wiring around it. Jay Fisher has this one and he loves it. It is very dynamic, has great dynamic shadings, and gets all levels and layers of the midrange out there very well.
I wanted more bandwidth for my own systems, and set about building a Ladder type out of Shallco 45 position switches, and then I built a L-Pad unit out of military-style wirewound pots with the same strict attention paid to low-loss wiring. I love the thing, and also the LADDER.
You can forget about losses and needing more gain with these the way I build them. You have gain and dynamics to burn because the losses are minimized before the amp sees the signal.
What's left of it after it goes thru the attenuator is-- in this case-- MOST of it!
---Dennis---
It lost energy like a Yugo with a fuel system leak?! That's not what I and my friends have heard. Of course with TVCs, they're particular about system synergy and specifics like output impedance driving them, cap or direct coupled, input impedance, etc.
Donald North
Two different worlds here.If you've got an active preamp driving it and you have excess gain from an extra stage in your amp, then you'll not notice the attenuator losses.
What I've found is that taking that 3rd stage out of an amplifier and replacing it with a single one of high gain, doesn't yield quite the total gain of most 3 or 4 stage amps, but that is a moot point because those amps can't compare in overall fidelity to music and what some refer to as "jump factor"-- rhythm, pace and accurate event timing.
The simple two-stage amp simply walks all over amps with more active stages.
If you then merely add the 3rd stage back-- say, into an active preamp, then you're back to the same topology-- too many active stages.
So, if you're going to run the simple 2-stage amp and use a passive attenuator for a volume control, you will definately notice losses which occur in that attenuator.
I've noticed that, and since I'm not willing to go back to too many amp or preamp stages, I have built an attenuator that really rocks-- has almost unmeasurable signal losses or signal changes in character.
This approach has produced a system that excels in dynamics, correct rhythm, pace and event timing, and fine introspection into music's many attitudes, player's intentions and intents during a musical performance.
Today, the difference is just too great. I could never go back.
---Dennis---
Edits: 10/09/09
Dennis,It seems to me that there could be scope for trying a suitable pentode to drive the 2A3 in your amp, as per the original L-W. (I know that was actually a tetrode but you know what I mean.)
You might hopefully get the improved performance that others have discovered from such an arrangement. Maybe you could offer such a topology as an alternative to those who prefer the sound?
Edits: 10/12/09
Hi Ray,
Having just spent three full days listening to Dennis' amps at a show, (as I have done these last four years at RMAF) any change as you suggest would likely be a degrade.
They are superbly balanced, superb sounding, totally honest amps, just as they exist !! It is probably the best sounding low powered amp ever available as a manufactured product. At least, this is my own opinion, from all my own listening experiences in various systems.
Jeff Medwin
People's tastes differ and there are those who say they really like pentode drivers. I'm not suggesting it necessarily as an improvement, just an alternative that might be interesting to try.
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