Listening for Quad amplifier differences

[Craig Sawyers]

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The weird thing was the Quad did not listen to most of their designs. I good old friend joined Quad in the early 80's; the SOA protection device on the 405 was one of his.

From him I ended up visiting Quad and spending a cheerful hour or two talking to the late great Mike Albinson. He said that they really relied on design and measurement only. Perhaps the only exception was the electrostatic speakers, but that was a dedicated effort by Peter Walker and Peter Baxandall.

When I quizzed Albinson if he was a hifi buff, he said no - his interest was restoring and driving motorbikes!

So no listening panels at Quad, certainly back in the day. Design it, measure it, sell it.

Craig

[GrimJosef]

Originally Posted by Craig Sawyers

The weird thing was the Quad did not listen to most of their designs ... they really relied on design and measurement only ...

That's backed up by Ken Kessler in his coffee table book on Quad, and also by another report I read which described their tests with a subtraction comparator. This took a strong musical signal, tapped off a small amount, fed that through the amplifier under test and then subtracted the large original signal from the amp's output (with suitable correction before the amp to match the amplitude and phase). The difference was the distortion. Apparently with the Quad II going at full power the difference was just audible if sent direct to a speaker. With the 303 another amplifier had to be added to raise the difference signal to a level where it could be heard.

Cheers,

GJ

I reckon that if the real Quad survived they would have digital amplifiers now with a proper output filter.

[Radio Wrangler]

There was the famous comparison Peter Walker did between the different generations of amplifier technology. Quad are in print about the lack of perceived differences between valves and transistors of their different generations.

Also they demonstrated gear at various hifi shows (along with the famous lawnmower flex)

So they did listen to their own products.

David

[Ted Kendall]

Originally Posted by Radio Wrangler

There was the famous comparison Peter Walker did between the different generations of amplifier technology. Quad are in print about the lack of perceived differences between valves and transistors of their different generations.

Also they demonstrated gear at various hifi shows (along with the famous lawnmower flex)

So they did listen to their own products.

David

To say nothing of the first demonstrations of the ESL63 - cancelling a squarewave in air between two speakers.

[Craig Sawyers]

Originally Posted by Ted Kendall

To say nothing of the first demonstrations of the ESL63 - cancelling a squarewave in air between two speakers.

But neither of those has anything to do with listening, in the sense of having a bespoke room. Such as Wharfedale had. Quad did not have a listening room, period. Just a pent roof shop floor.

The particular Quad test was done in 1978 (attached), and was based on a Quad assertion that all adequately designed amplifiers should sound indistinguishable. They proved that, using an impressive listening panel, that the 303, 405 and Quad II were statistically indistinguishable. What is interesting is that they did not use a Quad E/S speaker, but the Yamaha NS1000M. They did this essentially PR exercise to demonstrate that the emerging review methods in the audio press were fundamentally flawed (and usually slammed Quad gear).

Then there was the famous Carver challenge with Stereophile. He asserted he could make his cheapest semiconductor amp sound indistinguishable to a state of the art valved amp https://www.stereophile.com/content/carver-challenge . He also used an acoustic null test technique.

Craig

[Jez1234]

Originally Posted by Craig Sawyers

But neither of those has anything to do with listening, in the sense of having a bespoke room. Such as Wharfedale had. Quad did not have a listening room, period. Just a pent roof shop floor.

The particular Quad test was done in 1978 (attached), and was based on a Quad assertion that all adequately designed amplifiers should sound indistinguishable. They proved that, using an impressive listening panel, that the 303, 405 and Quad II were statistically indistinguishable. What is interesting is that they did not use a Quad E/S speaker, but the Yamaha NS1000M. They did this essentially PR exercise to demonstrate that the emerging review methods in the audio press were fundamentally flawed (and usually slammed Quad gear).

Then there was the famous Carver challenge with Stereophile. He asserted he could make his cheapest semiconductor amp sound indistinguishable to a state of the art valved amp https://www.stereophile.com/content/carver-challenge . He also used an acoustic null test technique.

Craig

All adequately designed amplifiers do not sound the same though! Even Quads II, 303 and 405 sound quite different from one another. I'm very familiar with the above articles and other similar ones BTW.

All adequately designed amplifiers do not sound the same though!

SO you refute Quads testing then. Unless you call the sound what it does when dropped, Quad II a smash tinkling sound, 303 a thud, and 405 more of a clank.

[Radio Wrangler]

OK, that's got me smiling, MM. But I think there was also a phrase about being driven within their capabilities, which is quite important.

Drive them into clipping or hit them with out of the audio range signals and I don't doubt that differences may be heard. But the moment you do this, you've moved out of the realm of hifi and into performance art.

Would I rebuild a Quad II for my own use? No. They're quaint and have a certain appeal but they're far over-priced and don't do enough power for my somewhat inefficient speakers and my liking for prog rock and pipe organs.

Would I rebuild a 303 for my own use. No. I use a bit more power on peaks and they're reliant on transistor characteristics which are no longer made.

Would I rebuild a 405 for my own use? I'd consider it, if I needed another amplifier, but I feel no need to change from the thing I've been using for 41 years.

I'm quite happy to help someone who already has a Quad II, because they're nice historical artefacts from a golden period in British audio, and can make a good showing of themselves subject to speakers efficient enough to not need more power. There is enjoyment to be had.

I'm less inclined to get involved with anyone who wants Quad IIs (or other period pieces) because they are absolutely convinced that nothing later was any good. I think they've missed something.

David

Agree 100% David, I have very modest power requirements for my "stereo" I usually listen to spoken word (radio plays) and maybe a film or two. I doubt I exceed a watt, and my TDAxxxx chip does a good job. The Tannoy DC4's do a very good job for me too.

Back on topic a 100V line to 'speaker impedance seems a good idea, I just wonder what the ratio should be?

[Trevor]

Its all about musicality if thats a word I used to know George Hadcock of the tone arm fame ! He has a pair of stacked ESL57 these were driven by a pair of quad 2's
the sound was very musical and dynamic
I have heard indeed owned far more powerful systems but I would still prefer George's
Trev

[Jez1234]

Originally Posted by merlinmaxwell

SO you refute Quads testing then. Unless you call the sound what it does when dropped, Quad II a smash tinkling sound, 303 a thud, and 405 more of a clank.

I certainly do! I have worked on numerous examples of all three units over the the years and listened to them on many occasions and through various speakers and they sound very obviously different.

Those who know me will be aware that I'm bordering on "infamous" for fighting against audiophoolery and snake oil but I certainly do not agree that "all competently designed amplifiers working within their limitations sound the same".

In the case of these Quad units the huge differences in output impedance will mean actual FR anomalies due to the way this interacts with the speakers impedance curve for a start.

When it comes to correlating measurements with subjective results there is much that remains "here be dragons" as I've heard two amplifiers which both have 0.01% THD or less, damping factors of >100 and flat FR from 10Hz - >50KHz sound bizarrely different from each other on many occasions in spite of theory suggesting that both are so close to "a piece of wire with gain" that they should sound identical.

This "there's obviously a lot we still don't know about amplifiers/we must be measuring the wrong things" aspect of audio has maintained my fascination with the subject thus far

I certainly do!

Risking getting a bit far for this thread, have you results from a double blind ABX test you have performed?

[Synchrodyne]

I recall that at the time the report on the Quad comparative amplifier tests was published, there were some hi-fi magazine writers who refuted the results, sometimes with speculative reasons as to why the conclusion was – in their view – flawed. But what I never saw was a rigorous treatment that demonstrated that statistically significant differences did exist, nor any rigorous rebuttal of the Quad testing outcome. Perhaps, in the intervening 43 years someone has done the work and published the results?

Insofar as proving that something (in this case a difference) does exist is generally thought to be easier than proving that it does not, then those who would challenge the Quad results might be expected to have had an easier pathway than did Quad.


Cheers,

[GrimJosef]

Originally Posted by Jez1234

All adequately designed amplifiers do not sound the same though! Even Quads II, 303 and 405 sound quite different from one another. I'm very familiar with the above articles and other similar ones BTW.

I agree. 'Sound' is a perception created in our brains. The brain takes inputs from many sources (that's what helps to keep animals with brains alive in environments where other animals fancy them as lunch). If our brains have any indication of which amp we're listening to then we'd have to damage them (the brains) very seriously indeed to stop that knowledge affecting the sound we hear.

Whether adequately designed amplifiers operating within their design limits produce distinguishable physical differences at our eardrums is a very different question. So far we have only come up with one generally accepted way of answering it, and that's with rigorously conducted, independently observed, double-blind testing. This is sufficiently hard to do properly that it's rarely carried out, but when it has been the people who insisted they could distinguish the amps turned out not to be able to. They were more surprised and shocked about this than anyone else.

Cheers,

GJ

[alanworland]

After my Rogers Ravensbrook amp I have always been a Quad guy and must admit I love them! Had a lot of other amps over the years but always kept and use the Quad gear.
Worst sounding tuner amp was a Leak (3200?) basically a Rotel design I believe - sounded absolutely dead.

Alan

[Refugee]

I regard an amplifier as good if moving the speakers around the listening room makes them sound different.
Anything more than that is down to real estate acquasition and acoustic insulation.
As far as amplifiers go it is down to build quality.
Time to go house hunting...

[Kentode]

I've had a Quad 34/405 ll combo for a few years now, but I don't listen to it!



I listen to the music.

Oh, I also alter the bass lift and tilt whenever I want.

[Jez1234]

Originally Posted by GrimJosef

I agree. 'Sound' is a perception created in our brains. The brain takes inputs from many sources (that's what helps to keep animals with brains alive in environments where other animals fancy them as lunch). If our brains have any indication of which amp we're listening to then we'd have to damage them (the brains) very seriously indeed to stop that knowledge affecting the sound we hear.

Whether adequately designed amplifiers operating within their design limits produce distinguishable physical differences at our eardrums is a very different question. So far we have only come up with one generally accepted way of answering it, and that's with rigorously conducted, independently observed, double-blind testing. This is sufficiently hard to do properly that it's rarely carried out, but when it has been the people who insisted they could distinguish the amps turned out not to be able to. They were more surprised and shocked about this than anyone else.

Cheers,

GJ

I couldn't disagree more strongly. I cannot offer any explanations for the bizarre results of the Quad tests beyond those already extant from the time but you would have to be completely deaf for the difference between a Quad II and 405 not to be as obvious as the differences between many speakers.

FWIW I consider only a very few power amps to be truly excellent. Almost all fail at the subjective hurdles in one way or another.

[GrimJosef]

Originally Posted by Jez1234

... you would have to be completely deaf for the difference between a Quad II and 405 not to be as obvious as the differences between many speakers ...

I own several Quad IIs and a couple of Quad 405s and as long as I'm not over-driving the Quad IIs or kneeling, with my ear up against the speaker, listening for hum, they sound very similar to me. As they did, of course, to Peter Walker (who designed and built and sold tens of thousands of them). And all the people who sat the tests. I think they'd be as surprised as I would be to find that every one of us was/is 'completely deaf'. To tell us that we are is a ridiculous exaggeration, isn't it.

Cheers,

GJ