My Life with Quad

[MartinT]

Bigger power amps rarely have anything to do with requiring more power, Dave. It's about gaining control by better damping factor - giving you deeper and tighter bass; and authority by not capping those rare but mighty transients that only occur infrequently in music.

The overall effect of a bigger amp with similar circuit is of structural authority, more realistic dynamics and greater insight into the music.

[Rare Bird]

I use 90db speekarse with 12 watt amp, loads of power on tap..

[synsei]

Bigger power amps rarely have anything to do with requiring more power, Dave. It's about gaining control by better damping factor - giving you deeper and tighter bass; and authority by not capping those rare but mighty transients that only occur infrequently in music.

The overall effect of a bigger amp with similar circuit is of structural authority, more realistic dynamics and greater insight into the music.

The thing is Martin the 306 shows a clean pair of heels to just about every other power amp I've used, including the Valhalla, although this amp has its own charms, especially in the midrange. What has become apparent is that the Hafler DH220 I ran for a couple of years was not a good amp, despite all the money I spent on it to 'improve' it. Even though it could heft 110wpc into the DM2's it did not control the bass or offer anywhere near the extension this little Quad does, which makes me even more curious about the 606

[The Black Adder]

Magnificent write up... What a corker!

[MartinT]

The thing is Martin the 306 shows a clean pair of heels to just about every other power amp I've used, including the Valhalla, although this amp has its own charms, especially in the midrange. What has become apparent is that the Hafler DH220 I ran for a couple of years was not a good amp, despite all the money I spent on it to 'improve' it. Even though it could heft 110wpc into the DM2's it did not control the bass or offer anywhere near the extension this little Quad does, which makes me even more curious about the 606

Oh yes, I recognise such statements. I once constructed a huge MOSFET power amp with 1.3kW power supplies based on the Hitachi circuit. It sounded flat, lifeless and frankly dull. So did the Hitachi.

It isn't about power, it's about delivery. Two key factors are damping (how low is the impedance such that it controls the cones with a vice-like grip); fast voltage swing (how quickly does it respond to requirements for transient current demand, while delivering the required voltage). Of course, it must be of low distortion in its basic circuit.

It's not for nothing that so many circuit topologies have been tried. To bring things back on topic, Quad's current dumping circuit as introduced in the 405 is a fascinating study into the use of cheap transistors in order to achieve its aims.

[DSJR]

The '500' power amps were a development of the 405, whereby the single output transistors of the 405 were doubled up in the 510 and 520. Incidently the circuits of the 510 and 520 are identical, save the 510 is a single channel amplifier, employing an output transformer to couple to the speaker load (as did the Quad 50s), whereas in the 520 (a two channel amplifier) the coupling is direct. The 606 went one step further and employed 3 output transistors in parallel.

I *think* the 520 series used the revised input circuit of the 606 and onwards, with the op-amp outside the signal path, unless I'm very much mistaken That's why I have this sneaky longing for one

The 606 IS a great amp, especially with the supply caps taken to the later values (15k instead of 10k). I think the other difference was the mains transformer changing in the mk2 models. Either way, warm-up time seemed reduced in the mk2 onwards and the sound retained that lovely non-harsh 'velvet' quality the 303 and II's have in abundance. The HFW review of the 909 sums the family 'Quad' sound up beautifully IMO

[JJack]

What a great post!

[Barry]

I *think* the 520 series used the revised input circuit of the 606 and onwards, with the op-amp outside the signal path, unless I'm very much mistaken That's why I have this sneaky longing for one.

Yes, you are right Dave. I have just had a look at the circuit diagram for both the 510 and 520. The low-level Class A amp is now composed of discrete transistors. The op-amp to which you refer is part of the feedback loop, where it is used to preserve DC control.

[Barry]

Hi Barry,

I'm very new to Quad having only just got a pair of ESL 2805s a few months ago so forgive my johnny-come-lately impertinence and I haven't heard ESL 57s so don't know how they compare to the 2805s.
However everything that you say about how wonderful the 57s are resonates with my short experience of the 2805s. I would say though that I have not experienced any of the first 3 negatives you mention. Bass is deep and powerful and they play *loud*, certainly in my attic anyway. A blast of Daft Punk at volume soon shuts up any ESL skeptic that has visited. I also don't get the beaming with the 2805s.

I'm so smitten with them that I can't ever imagine being without them (or one of their successors). Once you hear ESLs it's hard to compromise with anything else.

Anyway, my point is, what am I missing - why haven't you moved up the ESL range? 2805s for example can be got used mint for about £2k, which for an exit level speaker isn't outrageous.

Excellent post by the way - very informative.

Hello Jason,

I'm pleased to hear you are delighted with the Quad 2805s. Both the 2805 and it's bigger brother, the 2905, built on the strengths of the 988 and 989 respectively; themselves being a development of the Quad 63. The 63 was a fairly radical change of design of electrostatic speakers: consisting of a series of concentric annular electrodes sequentially fed via a delay line to mimic a point source.

I did hear the 63 when it came out in 1981, and recognised that it could reproduce deeper bass than that of the 57, and could play louder. I was not particularly convinced of the 'point source' scheme (I had my doubts about the contribution of the delay circuitry to the sound). Put simply, I saw no reason to replace my 57s.

Of course the 2805 and 2905 are the latest incarnation and one presumes they have improved on the 63. I would expect the bass to be better still, and for them to play louder (what is the sensitivity of the 2805?), be free of beaming, along with the advantages gained through an increase in the rigidity of the speaker frame.

So why haven't replaced my 57s with them? That's difficult to answer, but in the first instance I haven't heard a pair, or even sought out a Quad dealer who could demonstrate them (or better still, A/B them against the 57s). Second, I have got so used to my 57s, they do everything that want from a loudspeaker: their strengths are very, very important to me, conversely their weaknesses are not that important to me. I suspect that maybe I'm one of those people who just like vintage equipment - my turntables, and cartridges are 'vintage', so too are my tape machines.

But if ever I find a Quad dealer who can demonstrate either the 2805 or 2905, I will give them a listen.

Regards

[Rare Bird]

Nice Barry
I would always choose the '57' over any of the other of their models, however if i was in the market for a set i would try my hardest to locate a pair of Braun's 'LE1'..