Info. Wanted On Valve Amps

[Mike Reed]

Can any of you tube rollers give me a brief run-down on the different types and benefits/drawbacks of valve amps?

EG. Single-ended, Push-pull?? Self-biassing (new thing and desirable or what?) Anything else I should seriously consider if chaging from s/s amplification (not preamplification).

Any info. appreciated. Not sure if this is the right place, but I guess I'll be moved if not.

[DHT]

I also would be interested to know the difference, between different valve circuits, Single ended, parallel and push pull, and what are the effects of feedback to the character of the sound?
btw Hello everyone ,interesting forum, I wish you all the best DHT.

[anthonyTD]

Can any of you tube rollers give me a brief run-down on the different types and benefits/drawbacks of valve amps?

EG. Single-ended, Push-pull?? Self-biassing (new thing and desirable or what?) Anything else I should seriously consider if chaging from s/s amplification (not preamplification).

Any info. appreciated. Not sure if this is the right place, but I guess I'll be


Hi mike, DHT,
I will try and outline the main differences, between types of valve operation, also, the pro's and con's of each.
Single ended was the original way of operating a valve from the very early days of electronic amplification, [1920's] and the same basic circuit topologies are still being used by some manufacturers today, with little change!!! Basically single ended is just that, a single valve coupled to the primary of an appropriate transformer, with the secondary coupled to the loudspeaker. obviously it will also have one or more gain stages prior to the output stage, which would also be coupled as single ended to the output valve via transformer, capacitor, or in some cases directly coupled! The signal therefore throughout the circuit is totally single ended...
this type of circuit is relatively simple in comparison to push-pull and is preferred by a lot of purists because of its relatively low parts count in the signal path...most traditional single ended amps use triodes because the distortion they produce is mainly second harmonic, which our ears tend to like...also, in the early days, that’s all there was... but these circuits are not without faults, far from it, because most types of single ended amplifiers are inherently class A and use triodes their efficiency is only around 20% [bit more] so not much power to be had from one output valve...
Also, the damping factor [their ability to control the loudspeaker movement] was severely low without feedback, and lastly, their frequency range wasn’t great! But despite all this, they could [and still do in some cases] sound very beguiling, and some would even say, magical in the right system!

Now to push-pull,
in a push-pull output stage there are two [at least] devices that share the original signal and current between them, this is done by using a circuit I will refer to as a phase splitter, what this does is splits the original signal into its respect negative and positive halves, this circuit is then coupled to the output valves in a similar manner to single ended, but one out put valve has the negative side of the signal applied, and the other has the positive…[if the circuit is run in true class A both halves of the signal will usually be seen at both output valves] the main advantages of push-pull over single ended in most cases are, the increase in power potential, linearity, and damping factor… also, they can be run in more efficient operating modes,, i.e., class A, class A,B class,B,etc…due to this, efficiency in good push-pull designs can be much higher than single ended, [up to around 60% in theory] there is a lot more to be said about the different types of both single ended and push-pull circuit topology, and certain things to take into account when deciding on one type over the other, but, I think I have covered the basics here, and I can always come back to you with more if needed…also, i will explain,[if needed] about the diffrent types of biasing,etc...
Anthony…

[DHT]

Anthony Hi, thanks very much for the info, very informative, can I just ask about feedback, that is taking part of the signal and feeding it back into the circuit ( as in the push pull ? ) what audible effect does adding feedback have?

[anthonyTD]

Anthony Hi, thanks very much for the info, very informative, can I just ask about feedback, that is taking part of the signal and feeding it back into the circuit ( as in the push pull ? ) what audible effect does adding feedback have?

hi DHT,
applying negative feedback, usually from the secondary of the output transformer to the first gain stage [in oposite phase] to both circuit topologies will have similar affects, ie, increased damping factor, lower distortion, lower noise, increased frequency range...although too much can lead to instability, excesive loss of gain, and loss of vibrance, and articulation, making the amp sound dead and lifeless...
anthony...

[DHT]

Anthony ,thanks so a little feedback is not always a bad thing, you will have to excuse my ignorance but would/could increased 'damping factor' lead to a tighter better control over bass?
Also, will an amp with greater output ie 50 watts to 20 always control a speaker with more authority ? Or is the current delivery of the amp ,or other factors more important, thanks for taking the time to answer my questions very kind of you.

[anthonyTD]

Anthony ,thanks so a little feedback is not always a bad thing, you will have to excuse my ignorance but would/could increased 'damping factor' lead to a tighter better control over bass?
Also, will an amp with greater output ie 50 watts to 20 always control a speaker with more authority ? Or is the current delivery of the amp ,or other factors more important, thanks for taking the time to answer my questions very kind of you.

EXACTLY, feedback when used correctly, and in the right amounts can be an asset, it will definitely tighten the bass characteristic of any amp.
more power is always an advantage to a degree, not necesarily for better control of a loudspeaker, but with more power, you have more headroom, which is esential for driving inefficient real-world speakers and for realistic reproduction of loud passages of orchestral music and the likes...

anthony...

[DHT]

Anthony really very good of you, does it then follow that single ended amps will have a beautiful mid at the expense perhaps of bass and treble performance, and that a push pull may have more drive and extension to the detriment of the mid?
I suppose I am asking is it possible to have the best of both worlds in one amp?

[anthonyTD]

Anthony really very good of you, does it then follow that single ended amps will have a beautiful mid at the expense perhaps of bass and treble performance, and that a push pull may have more drive and extension to the detriment of the mid?
I suppose I am asking is it possible to have the best of both worlds in one amp?
hi DHT,
it is possible to have most of everything from either topology, but not using old conventional circuitry alone,[in my opinion] each topology has its gains and pitfalls in its primitive form, but if you have been on my web site,[in my profile] you will see that i deliberately chose single ended toplology to show what could be achieved if you combine valve circuitry with the best of modern technology, ie, the soul range of amplification...
anthony...

[Steve Toy]

Anthony,

You have a private message (see top of the screen where it says Welcome, anthonyTD) :)

[Mike Reed]

Thank you, ANTHONY, for your in-depth dissertation on different valve amp. design approaches.

I have been following DHT's questions and your very helpful answers, especially regarding feedback, which, in practical terms, I roughly understand. To encapsulate, less is better but none is a bit tricky!

Single-ended (triode valves, mainly, I guess) are renowned for their euphonious sound but lack balls and dynamic extension.

Push-pull have more grunt (watts) and extension but lack the 'ambience' and naturalness of the single-ended.

I have had a few valve amps in the past (Jason, Quad, RCA, Armstrong etc) which were fine for the prevailing state of the art then (60s), but I believe things valvish have come on a lot since.

In your opinion, which manufacturers (models?) from the past five of so years would you consider for a highish-end system (to replace Naim monoblocks) and be run from the top Naim pre? I've looked at ARC, Conrad-Johnson and Art Audio, among others, which must all have their strong/weak points or rather, sonic biasses, but have been a bit non-plussed by the choice.

Even Prima Luna, with its self-biassing circuit and very affordable price looks tempting on paper, but this may well be a bit of a red herring in my quest for 'a blast from the past' and a 'return to my roots' (excuse cliches).

Speakers are ProAc Response 4s (developed with ARC) Sources are vinyl, cd , tuner and TV/video.

Bet you'd wished you'd never started.........

[anthonyTD]

Thank you, ANTHONY, for your in-depth dissertation on different valve amp. design approaches.

I have been following DHT's questions and your very helpful answers, especially regarding feedback, which, in practical terms, I roughly understand. To encapsulate, less is better but none is a bit tricky!

Single-ended (triode valves, mainly, I guess) are renowned for their euphonious sound but lack balls and dynamic extension.

Push-pull have more grunt (watts) and extension but lack the 'ambience' and naturalness of the single-ended.

I have had a few valve amps in the past (Jason, Quad, RCA, Armstrong etc) which were fine for the prevailing state of the art then (60s), but I believe things valvish have come on a lot since.

In your opinion, which manufacturers (models?) from the past five of so years would you consider for a highish-end system (to replace Naim monoblocks) and be run from the top Naim pre? I've looked at ARC, Conrad-Johnson and Art Audio, among others, which must all have their strong/weak points or rather, sonic biasses, but have been a bit non-plussed by the choice.

Even Prima Luna, with its self-biassing circuit and very affordable price looks tempting on paper, but this may well be a bit of a red herring in my quest for 'a blast from the past' and a 'return to my roots' (excuse cliches).

Speakers are ProAc Response 4s (developed with ARC) Sources are vinyl, cd , tuner and TV/video.

Bet you'd wished you'd never started.........

hi mike,
i do try!!!
as for recomending a valve amp, i dont really think i am in a position to give an un-biased opinion on what to go for, so forgive me if i dont, but if you were to ask me to recomend an amp that would almost certainly better anything you have mentioned above, and money was not an obvious problem, [within reason] i would recomend amps like macintosh 275 etc, [the re issue]
hope this helps.
regards,anthony...

[NRG]

Sorry to butt in, if you are looking for a valve amp moving from Naim amplification I would recommend a listen to the Audio Research VS55 or VSi55. Superb build with great dynamics and sound quality.



Single-ended (triode valves, mainly, I guess) are renowned for their euphonious sound but lack balls and dynamic extension.

Push-pull have more grunt (watts) and extension but lack the 'ambience' and naturalness of the single-ended.

As most things you can't pigeon hole valve amps like this, it very much depends on implementation and the valve used.

For instance the best valve amp I've heard is a DIY SE design based on the 211 transmitter valve with over 1KV of HT. It only produces 20W / channel but has such control and dynamics you would not believe it. Unfortunately it's so large and heavy it needs two men to lift it and another two to lift the PSU!

[Mike Reed]

; i would recomend amps like macintosh 275 etc, (the re issue)

Thanks, Anthony. A surprise recommendation, and not one I would have thought of. I believe Mackintosh are Canadian, aren't they? Apart from that, I know absolutely nothing about them; even whether they were valved or s/s. I shall, however, bear that in mind.

NRG Butt in ad infinitum with tips like that! I've seen a few of these come and go on E-bay, the forums or in dealers. I believe ARC's 'V' range may be developed from their flagship model of old.

You speak as of someone who has first-hand experience of this transition, but possibly you changed the entire amplification system. I wish to only throw out the bathwater, but keep the baby, as it were (or maybe that should be transposed!).

However, should you have any other hints borne of experience, please butt in again. The VS55 and its sibling would have ample power into my speakers, and I shall keep my eyes peeled.

[anthonyTD]

Sorry to butt in, if you are looking for a valve amp moving from Naim amplification I would recommend a listen to the Audio Research VS55 or VSi55. Superb build with great dynamics and sound quality.




As most things you can't pigeon hole valve amps like this, it very much depends on implementation and the valve used.

For instance the best valve amp I've heard is a DIY SE design based on the 211 transmitter valve with over 1KV of HT. It only produces 20W / channel but has such control and dynamics you would not believe it. Unfortunately it's so large and heavy it needs two men to lift it and another two to lift the PSU!
This is exactly the reason why i was reluctant to recomend any thing in the first place, all systems, and listening inviroments are diffrent, as for audio research,well, i have had extensive experience with a lot of their models over the years being a valve amp techi, and although as you say the build quality is very good, [in my opinion] their circuits leave a lot to be desired...
at the end of the day, it all comes down to individual taste, but some amplifier designs are consistently embraced by a wide audience, hence my recomendation...
anthony...

[Mike]

For instance the best valve amp I've heard is a DIY SE design based on the 211 transmitter valve with over 1KV of HT.

A NickG design perhaps?

:)

[NRG]

A NickG design perhaps?

:)


;) You got it!