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[Marks DTM Calib]

Mark, I always like your well-presented and reasoned input, so I'm not sure if I'm disagreeing with you here or not.....
"The old electrostatic speakers setups I always found worked best on a valve amp and vinyl source mainly due to the rich (read even harmonic distortion) of the amp"
...but my understanding is that even harmonics are cancellelled in the push-pull output transformer of a valve amplifier, leaving only the fundamental (of course!) and the nicer-sounding odd harmonics which do not spoil the enjoyment like the harsher even harmonics. Psycho-aural experts will be able to explain why: I can't!

Ron.

The problem is Ron that it will only cancel at certain frequencies due to the real world fact that the transformer has inductance and hence a far from linear frequency response. Consequently it still gets through 

[Bigron]

Mark, I am fearful of hi-jacking this topic for an esoteric debate on a non-Omega topic, but the THD produced by a good vale amplifier, especially if it has an Ultra-Linear output transformer configuration, would be better than 1% across the spectrum - unless overloaded!
My greater concern regarding the effects of non-linearity in the output stage(s) would be the creation of IM products, which even to my old ears would be more noticeable.

However, I think I hate you because you have got me considering making a Mullard 5-20 valve amplifier! Now, where will I get the valves, decent transformer....where did I put my old Q-Max cutter?............

Ron.

[Kevin Wood]

Watford Valves
Langrex
etc.

Canterbury Windings
Sowter (deep breath as you open your wallet!)
Danbury
etc...

Can't help you on that one.

In that order.

I built a pair of 5-20 clone monoblocks about 15-20 years ago. They are still languishing in the loft. THD was about 0.05% at 1KHz and rated output, IIRC.

[Bigron]

Thanks Kevin. Um, I'm guessing my pension won't run to those items AND keep my Omega alive! Ah well...........

Ron.

[Marks DTM Calib]

Mark, I am fearful of hi-jacking this topic for an esoteric debate on a non-Omega topic, but the THD produced by a good vale amplifier, especially if it has an Ultra-Linear output transformer configuration, would be better than 1% across the spectrum - unless overloaded!
My greater concern regarding the effects of non-linearity in the output stage(s) would be the creation of IM products, which even to my old ears would be more noticeable.

However, I think I hate you because you have got me considering making a Mullard 5-20 valve amplifier! Now, where will I get the valves, decent transformer....where did I put my old Q-Max cutter?............

Ron.

No no, its all good and interesting, its been a flipping age (read to long!) since the grey matter considered audio design!

The distortion and harmonics are obviously very dependent on the output stage as you stated earlier, a push pull with (overpriced) top notch output transformer will cancel many of the even harmonics problem. Trouble is that the THD is not a great measure of performance as its does not allow for the reality of higher order harmonics sounding bad when compared to the lower order portions (I noted many moons ago some companies adding a square law type approach to the weighting but, I suspect it got a bit difficult for many to understand).

If your considering building an amp, there are some reasonable kits out there for not to much money which are good starting points plus, the Russians are still building reasonably quality valves.

A did knock together an amp with a Valve (2A3) based pre-amp stage followed by a nice rugged Mosfet output stage which worked pretty well.

[chrisgixer]

Aaaah a nice technical thread


If only I understood even 1/5th if it

[Bigron]

Some say that nostalgia is best left in the past, but I cut my teeth on valve circuits so this topic has given me a warm, cuddly feeling! 
I do agree with your comments, though, especially concerning the unbalnced ratio between orders of harmonics. so we ARE on the same page, basically. Still in regard to the Quads, unless you spend that fortune that we don't have of top-notch transformers, I reluctantly admit that a decent MOSFET amplifier would win on transient response, which the ESLs would capitalise on.

Chris, I can only apologise that you feel left out; I used to teach Electronics, so I could start a fresh class for you? I dare not waste any more Forum time explaining harmonics, distortion, non-linearity and intermodulation products, all of which are factors affecting audio quality - please accept that good values in each of these parameters cost lots of beer vouchers to achieve! 

Ron.

[Marks DTM Calib]

They certainly do on valve amps!

Less so on solid stage thankfully where a good PSU will cost double that of a good output stage.

I have in the loft an S5 K12M which, despite some of its short comings (which make it interesting as they can be improved on), was reasonable money for what it is.

[Bigron]

Yes, and really nudging into another area - valve amps for guitarists....perfect?
We both know the reason, but I'm not expanding on that for fear of alienating most of the membership....apart from Essex Big Al, who is a fine player. My Tannoy Yorks would suit him down to the ground, but he ain't 'aving 'em!

Ron.

[Marks DTM Calib]

Give the softer 'clipping' characteristics of a valve compared to the hardness of a solid state version, they clearly have a key place on a hard driven guitar amp or a distortion unit (although a good old diode in an opamp feedback loop is pretty reasonable!)

[Kevin Wood]

Back when I was still at school our window cleaner was a guitarist. Something he spotted in my bedroom window (probably the bloody great Tektronix 546 oscilloscope or the ham radio gear!) prompted him to ask if I was any good at fixing valve amps.

Well, how hard can it be, so I said yes. The next week he turned up with a 100W Marshall stack, much to my parents' delight. An hour or two probing around identified the faulty valve and off it went.

Cue a phone to my mate who, unlike me, actually had some musical talent, and a guitar.

"Guess what I've got here?..."
"Right. I'll be over. I'm bringing my guitar"

 

[chrisgixer]

Oh that's quite alright Ron. The other guys know full well, there's no point explaining these things to me in such detail as I need to be hands on, from scratch, to take these things in properly and understand them. Sadly I have had so little need for electronics in my life that I have sub zero experience of it. Explaining to me would need another server in TB's office I think.

But I do trust the end results of these conversations so please, fire away

[chrisgixer]

...although I'm sort of picking some of it.

[Bigron]

Marks, it's not the clipping characteristics that guitarists love - so I'm told, anyway, I ain't a musician, I can only play the fool - it's the massive reserve for short durations as when a string, particularly bass string, is plucked. Because of the space charge in the output valves, the peak-to-average power ratio is very high and allows for a high dynamic range and hence an impressive performance.
I hope any guitarists on here will chip in and confirm or deny the above, please?

Kevin, what a day for nostalgia! In my early days as a design engineer, those Tektronix 'scopes were like Rolls Royces; we had TWO of them, but we still fought over them!

Thanks for your forbearance and comments, Chris. I do understand your difficulty from what many of my students have said, along the lines of - "Well, we can't see what's going on insude electronic things like we can in the mechanical workshops".

Ron.

[Rods2]

Marks, it's not the clipping characteristics that guitarists love - so I'm told, anyway, I ain't a musician, I can only play the fool - it's the massive reserve for short durations as when a string, particularly bass string, is plucked. Because of the space charge in the output valves, the peak-to-average power ratio is very high and allows for a high dynamic range and hence an impressive performance.
I hope any guitarists on here will chip in and confirm or deny the above, please?

Kevin, what a day for nostalgia! In my early days as a design engineer, those Tektronix 'scopes were like Rolls Royces; we had TWO of them, but we still fought over them!

Thanks for your forbearance and comments, Chris. I do understand your difficulty from what many of my students have said, along the lines of - "Well, we can't see what's going on insude electronic things like we can in the mechanical workshops".

Ron.

Always a central part of my life, when designing computers working for the MOD. Storage scopes were really useful for capturing and analysing what was going on.