EL84, Balanced Input, Push-Pull Amplifier

Cressy Snr · Post by **Cressy Snr** » Sun May 05, 2013 5:22 pm

IslandPink wrote:Yes , then the next step would be to put in two slightly unmatched valves, get a bit of 2nd harmonic into the mix, and enjoy the improved tone !

Sounds OK by me Mark

Paul Barker · Post by **Paul Barker** » Sun May 05, 2013 6:32 pm

IslandPink wrote:Yes , then the next step would be to put in two slightly unmatched valves, get a bit of 2nd harmonic into the mix, and enjoy the improved tone !

( - which is after all, what the harmonic equaliser does to a small extent )
Oops, maybe I'm not welcome at this party now ...

That is mainly why I am single ended on the input. The thought of every stage in the amp susceptible to odd harmonics just didn't sit right with me. I can't undertake the journey all the way to push pull.

Stephy Bench and Sukuma San both use push pull mixed with single ended either way round to good effect.

Just as the use of a pentode voltage amplifier blends harmonics in a SET amp, a single triode front end would blend in the other way a push pull amp.

Cressy Snr · Post by **Cressy Snr** » Mon May 06, 2013 12:11 pm

Paul Barker wrote:
That is mainly why I am single ended on the input. The thought of every stage in the amp susceptible to odd harmonics just didn't sit right with me. I can't undertake the journey all the way to push pull.

That's interesting Paul. I've found with the amp fully balanced PP, end-to-end, that vast differences between different recordings have been revealed, much more so than with anything else I have used, either solid state or valve powered.
This amp is quite capable of making the big Metronomes sound like a loud transistor radio with a 2" speaker on one track, yet the next track is a beautifully balanced top to bottom, uncompressed specimen of gorgeousness.

The question is do I want such a revealing sound, one that shows 60% of my 60s pop and commercial 70s soul up as AM radio fodder...all midrange compressed as if it is coming down a telephone? Well yes I do, because in spite of the bad sound in hi fi terms, the amp somehow manages to cut through the crap and reveal stuff in those old recordings that frankly, I had not heard before. By that I don't mean that the sounds were not audible, but that now those same sounds, mean something musically and contribute to the whole in a way I had not appreciated previously. In hi-fi terms those old records sound like crap, but musically they reach me in a new way.

I'm sure this state of affairs could be recreated with a single ended amp, far easier than what I have had to do in push pull by someone who knows what they are doing, but I have never really managed it. TBH

The question of tone comes up big style with balanced push pull operation. If a record is hard, compressed and engineered to sound best on the radio, then that's what you get. Whether you like it or not is irrelevant, but you still get the guitar tone for example. It is usually the voices that are the elements that go over the top on radio balanced recordings and those FT17H supertwatters will let you know that somebody hyped up the upper mids to get the record noticed.

The best stuff is sublime, the commercial 60s 70s stuff less so but still interesting to listen to as you can hear the decisions the engineers made all those years ago. You may not like what they did but you are given the full facts to deal with as you see fit. I suppose you could call balanced push pull analytical. That will rule it out entirely for a lot of people. I like it, others will find it detestable, but that's entirely down to individual choice.

Paul Barker · Post by **Paul Barker** » Mon May 06, 2013 2:33 pm

The only explanation can be that you have very low odd order harmonic distortion.

Max built a PP 300b along the balanced lines. Would be interesting to hear his experience compared to WAD 300b PP which we know sounds great.

IslandPink · Post by **IslandPink** » Mon May 06, 2013 5:19 pm

This is probably showing what I found and Lynn Olson said years ago, that PP Class A is the best at handling the reactive load of the speakers without generating too much distortion or phase shifts . So maybe if you want a little 2nd harmonic to balance the residual 3rd/5th , the thing would be to put it in up-stream, in the pre-amp that drives the phase-splitter.
That's what I'd try if I did a PP again - something along the lines of Steve's amp, but with a 6080 pre-amp with low anode loading, for example. That could be really nice. That way you keep the superior speaker-handling of the PP power amp, but sweeten the sound just a touch with the pre-amp, if you don't want it to be quite so analytical .

Hmm.....

JamesD · Post by **JamesD** » Mon May 06, 2013 7:17 pm

Back when I built 2A3 PP amps with balanced input stages I designed the OPT transformers to have up to 10% of static current as imbalance so as to add in some even harmonics to balance the residual odd harmonics - to my ear it sounded better.

Doing this with a transformer not designed for some static current offset tends to hurt the OPT performance and increase the total distortion level more than expected.

I learned this as a teenager from valve audio hobbyists who regarded KT66 and KT88 and their ilk as modern and reactionary! Funnily enough EL84 and EL34 were OK...

Its also true that balanced into SE output sounds good and makes a good driver for rf power tubes - I used an 845 driven by a 6C45pi balanced front end and I'm sure we have all heard the SE front end into 45/2A3/6B4G/6C4C at some stage - great little amps!

I'm more and more convinced that getting the harmonic distortion profile into a natural shape helps the 'correctness' of an amplifiers sound...

I'm with Steve on simple circuits but the harmonic equaliser can work extremely well - it needs careful setting up and resetting as the amplifier ages as its Gm dependent - Steffie has pointed out that this means it needs to be tweaked with output level as well and, being her, designed an amplifier to do this as well - this was not a simple amplifier once she had finished but, by all accounts, it sounded superb...

James

Post by **Nick** » Mon May 06, 2013 7:29 pm

IslandPink wrote:This is probably showing what I found and Lynn Olson said years ago, that PP Class A is the best at handling the reactive load of the speakers without generating too much distortion or phase shifts . So maybe if you want a little 2nd harmonic to balance the residual 3rd/5th , the thing would be to put it in up-stream, in the pre-amp that drives the phase-splitter.
That's what I'd try if I did a PP again - something along the lines of Steve's amp, but with a 6080 pre-amp with low anode loading, for example. That could be really nice. That way you keep the superior speaker-handling of the PP power amp, but sweeten the sound just a touch with the pre-amp, if you don't want it to be quite so analytical .

Hmm.....

Well, what I am using at the moment is the 6080 with a el84 as the load preamp driving an F5.

ed · Post by ed » Mon May 06, 2013 8:09 pm

JamesD wrote: Steffie has pointed out that this means it needs to be tweaked with output level as well and, being her, designed an amplifier to do this as well - this was not a simple amplifier once she had finished but, by all accounts, it sounded superb...

James

please forgive this slightly OT post, but here is an example of something that has bewildered me for a long time................I was familiar with Steve Bench a long time ago, and had a copy of his original website when it was taken down......to the best of my knowledge he is/was a man..he had a wife(who sadly passed) and a son. Then PB started referring to him as Stephie or Steffie. This has proliferated to the point where James is referring to she/her. So, is this the same Steve Bench from way back, or have I got my wires crossed..again? Or, has Steve Bench had a sex change?

JamesD · Post by **JamesD** » Mon May 06, 2013 8:56 pm

Hi Ed,

Yes, Steve Bench has had a sex change and is now Steffie Bench... She has several Youtube videos explaining why/what/how etc.

ciao

James

Post by **Nick** » Mon May 06, 2013 8:58 pm

Or, has Steve Bench had a sex change?

Yes, Steve == Steffie

Cressy Snr · Post by **Cressy Snr** » Wed May 08, 2013 9:23 pm

Hmmm... looking at the last few posts, it seems I am going about things all wrong again

Paul Barker · Post by **Paul Barker** » Wed May 08, 2013 9:59 pm

Hopefully Nick will still have his EL34 push pull to bring you and I have one each so we have a good variety to listen to.

Mine isn't built but it is on the way. Family life is such that I can't devote much time. A few people rely on me.

Post by **Nick** » Wed May 08, 2013 11:51 pm

Paul Barker wrote:Hopefully Nick will still have his EL34 push pull to bring you and I have one each so we have a good variety to listen to.

Mine isn't built but it is on the way. Family life is such that I can't devote much time. A few people rely on me.

Hmm, much of it is still there (I think).

JamesD · Post by **JamesD** » Thu May 09, 2013 1:09 pm

Steve,

I think you are doing things All Right! You build things, try things, think on things and end up with superb amplifiers! That 6B4G amp at Owston was a dream come true and I have heard that magic very few times in my life...

And you share evreything with us all

Boy, do you do things right!

James

Cressy Snr · Post by **Cressy Snr** » Thu May 09, 2013 7:08 pm

JamesD wrote:Steve,

I think you are doing things All Right! You build things, try things, think on things and end up with superb amplifiers! That 6B4G amp at Owston was a dream come true and I have heard that magic very few times in my life...

And you share evreything with us all

Boy, do you do things right!

James

Well I had good teachers in your good self, Nick and Paul.

Cheers James

audio-talk

EL84, Balanced Input, Push-Pull Amplifier

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