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Old 3rd November 2014, 02:42 PM   #1
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Default "blameless" standard for tube amplifiers?

I was wondering about this
Lets say that we want to create from scratch an "entry level" 10-15W PP amplifier.
Do You think it will be useful to put together a set of design/construction rules that will .."Remove all the builder/assembler mistakes
to improve the audio performance to a standard for which the builder/assembler cannot be blamed." ,
i.e in a similar way D. Self do for solid state circuitry?
Or, the valve input-driver stage topologies are simply too many to redact such a set of rules?
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Old 3rd November 2014, 10:24 PM   #2
Bigun is online now Bigun  Canada
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It's worth a try maybe.

My thought - LTP input / phase splitter, 6V6 PP output ?
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Old 3rd November 2014, 10:58 PM   #3
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Back in my "Sand Pit" days I built quite a few of Doug Self's "Blameless Amplifiers".

It was very interesting to note which of his blameless mods actually improved my enjoyment of the sound and which did not.

For example the bootstrapped load on the VAS gave the amp a lovely tube like sound which the CCS load "blameless mod" killed stone dead. So that "blameless mod" was deleted.

I went from a version of that amp (Hugh Deans AKSA55N+) to the Baby Huey tube design.

Cheers,
Ian
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Old 4th November 2014, 12:00 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

Its doable for a mullard 5-10 type design, details are in :
30W Push Pull amplifier designed by Claus Byrith, Royal Academy of Music in Aarhus, Denmark. | Lundahl Transformers

rgds, sreten.

FWIW "a lovely tube like sound" is the very antithesis
of the "Blameless" concept and is a nonsense critique.
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Old 4th November 2014, 12:07 AM   #5
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Quote:
Originally Posted by gingertube View Post
the Baby Huey tube design.
There's one for the list. I'll add:

The Red light District
The "El Cheapo"
Tubelab Simple PP
Dynaco ST-35

There must be more.....

jeff
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Old 4th November 2014, 02:38 AM   #6
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Well, for starter I can think of two basic features:
It will not present any audible hum
It will be able to drive any competently designed , passive crossover, three way loudspeaker.

Last edited by Mosquito; 4th November 2014 at 02:42 AM.
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Old 4th November 2014, 05:00 AM   #7
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Acc. Your requirements, You need omnivorous amp, that, IMO, is with big power and not expensive tubes like 5881, EL34, 6P3S-E. Every PP is suitable for Your needs. HiEnd SE doesn't enough to drive Your speakers with heavy and big filters.
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Old 4th November 2014, 05:04 AM   #8
Keit is offline Keit  Australia
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Poor old Doug Self was much misunderstood by many, even though his writing style is very clear. And like me he didn't like people dumping unfounded criticism on him. And he really didn't like people building his designs, making mistakes & changes, and then complaining the performance was not good.

His major concept was not that his circuits were especially good (though they ARE pretty good); it was that by scientifically investigating EACH SEPARATE cause of distortion, and properly understanding each cause, you are then in a position to optimise a given amplifier topology for the lowest overall distortion.

His work has its limitations in these ways:-
1) He limited his work to only one type of topology. There are others.
2) He focussed on THD. THD has only a rough correlation to the pleasure in listening, there are other factors, and the THD of almost any amp these days is well below what you can hear.
3) He used SPICE as his primary analytical tool and thereby misled himself on the performance of power FETs.
4) He didn't appreciate that the ear's sensitivity to distortion corresponds to the time average probability density function of the music. What this means is that a step in the transfer characteristic (say due to cross-over distortion) at the quiescent point (instantanous zero volts to the loudspeaker) is a lot more unpleasant than the same size step at say +5 volts or at -5V. That's because music and natural sounds cross zero more often than they cross higher voltages.

It ought to be readily possible to do the same for tube amps - that is, select a topology (say triode input amp, concertina phase splitter, tetrode push pull output, or whatever takes your fancy), and analyse it & test it to understand the various causes of THD, transient intermod, or any other type of unpleasantness, and then produce the best possible performance that particular topology is capable off.

But I have never seen it done in one series of articles or in one book like D Self did for his selected solid state topology. It most definitely HAS been done bit by bit in a considerable body of 1950's literature - professional journals, tube manufacturer applications lab reports,etc. Trouble is these are not "accessible" to non-professionals without a lot of work.

I've given serious thought of producing a couple of Doug Self-style "blameless" article series for topologies for tubes and FETs. Four things inhibit me:

a) kit sellers see no money in it. And kit sellers have a considerable influence on what magazines publish;
b) The editors of the few remaining electronics magazines like Silicon Chip don't like detailed engineering. What they do like is projects that newbies can succesfully put together.
c) It would be a lot of work with little scope to bring in something really new
d) The example of Doug Self. He did truely outstanding work and got pilloried for it.

I've built Class A solid state amps. The D Self style topology used by Silicon Chip for ss Class A is good, very good, but it is not the best for Class A.

I've engineered and built FET based amps for professional test purposes. A reference amp for evaluating other amps must have perfomance comfortably exceeding the amps under test. And I got that performace with FET's, depite Doug repeatedly asserting, with some good arguments, why that should not be so.

Perhpas people should tell the editors of Silicon Chip, Elektor, and the like, that blameless amp articles for different topologies is what they want. Lobby for what you want. If editors see a strong need, they find someone to do the job.

Last edited by Keit; 4th November 2014 at 05:27 AM.
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Old 4th November 2014, 05:48 AM   #9
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Have you considered Linear Audio? When you write a good article about systematically improving performance of valve amplifiers, I would be surprised when Jan Didden would not be interested in it.
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Old 4th November 2014, 06:34 AM   #10
BigE is offline BigE  Canada
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Quote:
Originally Posted by Keit View Post
4) He didn't appreciate that the ear's sensitivity to distortion corresponds to the time average probability density function of the music. What this means is that a step in the transfer characteristic (say due to cross-over distortion) at the quiescent point (instantanous zero volts to the loudspeaker) is a lot more unpleasant than the same size step at say +5 volts or at -5V. That's because music and natural sounds cross zero more often than they cross higher voltages.
.
Could you explain this differently for those like me that don't understand.
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