Interview with Quad's Peter Walker in 1978

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Originally Posted by DSJR

Mark, wasn't the 303 designed to sonically mimic the II's in many ways? I believe the output caps were the largest they could get back then (any bigger would have been too large and probably too expensive then as well. Mine have Rifa caps as replacements, but I think the values are pretty stock from memory. Since they're now screw-connecting, they'll be easy to replace with summat bigger in value one day..

http://i132.photobucket.com/albums/q.../DSCF1448a.jpg

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I have no idea Dave in all honesty :scratch: One thing that may lend some kind of credence to that is a certain quote:- "the closest approach to the original sound"... Effectively they were if you like attepmting to get them to sound the same or to add the least distortion :)

I think Robs post above is a rather good one indeed & he is quite correct. A good many speakers were full range drivers & 15/16 ohms DC resistance.

You are quite right about the caps as i mentioned on a thread with some Croft equipment pics only yesterday. Technology moves on & big value capacitors are much smaller in overall volume than they used to be back in the day! ;)

nice post rob, and i quite undestand where you are coming from

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- Music is complex while test tones are simple and don't truly test the amplifier.

The amplifier simply responds to changes in voltage and current. Music signals can be defined by changes in voltage and current. A music signal is no more difficult to reproduce than a handful of test tones.
Humans perceive music as complex because we separate the individual strands both audibly and visually if we look at the waveforms, but the amplifier doesn't - it has no power of perception and only sees voltage and current.
On a slightly different point, asking an amplifier to reproduce 20khz at full output is a pretty tough test, and tougher than most music signals since you are asking the amplifier to swing fully and rapidly to doth DC rails. Might look simple and easy to humans but that's tough for many amplifiers.

Returning to Quad, they made the null test a feature of their testing and would invite competitors to the factory and ask them to submit their amplifiers to this test. Quad were able to demonstrate that you could null the amplifier output by injecting a portion back into the input in anti-phase. Now, if the amplifier were materially changing the signal passing through it in any way, it wouldn't null. But it did, indicating that signal complexity wasn't causing any difficulty over and above the lab test signals.

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Its funny how my experence differs. in my opinion both these amplifiers dont so much change the signal as filter it, detail, air and realisim is removed that i know is in the signal source, much less so with the quad 11 amps(without their pre) in my experence ( i've owned /used both)

i quite take your point about impedance matching, but it can't be the whole story...

steve

I think you'll find it was the preamps which could take the most away.. the 33 in stock form could sound tight-as*ed and with a carrot up its backside. Suitably updated, and I don't mean with hundreds of pounds worth of Net-Audio replacement boards either, the sound ebbs and flows with the dynamics in the signal, the bass breathes now, which it didn't before and, even if it's not the last work in preamp-sonics, it's a darned sight better than in standard form IMO - mines a very late one by the way. The later preamps from the 44 onwards can be spruced up as well, showing how good the power amps could actually be.

The only Quad power amp I can't get on with, and that's because I don't listen exclusively to string quartets, is the 306, which to me sounds limp-wristed on anything with any percussion in it. The 405 in mk2 version is like a "grown-up" 303 to me and can be taken further these days and the 606 remains a secret bargain still, which can drive 4 Ohm loads without difficulty. The later 606 onwards had some little tweaks too IIRC, which again can be retro-fitted I understand.

Just my thoughts, obviously...

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Originally Posted by DSJR

The 405 in mk2 version is like a "grown-up" 303 to me and can be taken further these days and the 606 remains a secret bargain still, which can drive 4 Ohm loads without difficulty. The later 606 onwards had some little tweaks too IIRC, which again can be retro-fitted I understand.

Just my thoughts, obviously...

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I have a pair of modified MK1s (by me :eyebrows:) which are more than capable of over 200W RMS both channels driven with music (4ohms). They'll keep cool enough to on music signals, just don't ask them to do a continuous output as they'll get a tad warm.

The output transistors have been replaced with higher gain 200W TO3 versions that were not available back in the day & obviously the poxy current limiting has been altered to...

As long as you know what you are doing, or someone who does then they can all be brought up to a much better specification :)

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Originally Posted by SPS

nice post rob, and i quite undestand where you are coming from






Its funny how my experence differs. in my opinion both these amplifiers dont so much change the signal as filter it, detail, air and realisim is removed that i know is in the signal source, much less so with the quad 11 amps(without their pre) in my experence ( i've owned /used both)

i quite take your point about impedance matching, but it can't be the whole story...

steve

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Hi Steve,

The Quad II will have a different response to a SS amp in the loudspeaker crossover region which is where the impedance is usually quite reactive.
That's usually slap bang in the area that influences the perception of detail, presence and air to some degree. You could however replicate this on a SS amp with EQ.....

Impedance matching is certainly only one part of the puzzle but an important one that is often ignored. Distortion is the other culprit, not just the headline THD figure but the distortion spectrum beneath. How much IMD, do even or odd order harmonics dominate, how far do they extend etc.
The answer of course is to get very low THD so that you don't then need to worry about what sits beneath that headline figure. Distortion is only an issue if present in quantities that are audible. So going from say 0.005% to 0.0005% isn't going to be audible no matter what the content. Going from say 0.1% to 1% might well be audible if the latter contains lots of IMD, but it might not if it contains mainly 2nd harmonic distortion.

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Originally Posted by Reid Malenfant

As long as you know what you are doing, or someone who does then they can all be brought up to a much better specification :)

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I agree Mark, they are all products of their time and I'm sure that if PJW was still around and making amplifiers he'd do things differently. He was always happy to adapt and use new components and methods though always maintained that most of these advances simply made the products more reliable, smaller and more energy efficient, plus offering more power. He never claimed any sonic gains for successive products and would never attempt to convince an existing Quad owner to 'upgrade' if he felt there was no sonic benefit.

Sorry, I'm a bit of a Quad collector :)
The kit and all of the papers and related writings over the years.

If anyone enjoyed the Walker interview they might find this interview by his engineering assistant Mike Albinson interesting:

http://www.quadesl.org/Album/Intervi...ealbinson.html

Scary looking bloke :eek:

Rob

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Originally Posted by RobHolt

Going from say 0.1% to 1% might well be audible if the latter contains lots of IMD, but it might not if it contains mainly 2nd harmonic distortion.

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Ah yes, even harmonics sound musical, odd harmonics are not welcome here :eyebrows: