Quad amplifier buyer guide?

[DarrenHW]

Following on from my "Opinions on Quad 405 Upgrade Boards?" thread (http://theartofsound.net/forum/showthread.php?41173-Opinions-on-Quad-405-Upgrade-Boards) I want to try other members of the Quad amplifier family, namely the 303 and 606, but I'm open to other suggestions. Can anyone direct me to some sort of buyers guide for these amps i.e. differences in generations, servicing requirements, connection changes and preferences etc...

Cheers,

[Firebottle]

Have you seen this post from Barry, well worth a read:

http://theartofsound.net/forum/showthread.php?27351-My-Life-with-Quad&highlight=Quad

:)

[DarrenHW]

I had but forgot about it, thanks Alan, I guess I'll be adding a 5 series to the list.

[Barry]

I had but forgot about it, thanks Alan, I guess I'll be adding a 5 series to the list.

My Quad article needs updating, but I might be able to help you with your interest in the Series 5 amplifiers.

There were two 'versions' of the amplifier. Both use the Quad ‘current dumping’ circuit topology. The circuit is virtually identical between the two versions and is a development of that used in the 405-2, save two output power transistors are used in parallel in each half, whereas only single power devices are used in the 405. The Series 5 amplifiers are non-inverting (unlike the 303 and 405 before them).

The first version is the 510, a single channel monoblock amplifier capable of providing up to 135W into any load of between 2Ω and 72Ω. It can do this because there is an impedance matching transformer fitted between the output transistors and the speaker terminals (a male XLR connector). This is similar to the arrangement used in the earlier Quad 50D and 50E monoblock amplifiers. The desired impedance matching is determined by suitable series and/or parallel connection of the eight secondary windings. This is achieved by plugging in the appropriate card into the back of the amplifier, which provides the correct series/parallel connections. The six output cards supplied with the amplifier are labelled with the maximum voltage swing obtainable for that setting:

2Ω - 17V rms, 4.5Ω- 25V rms, 8Ω – 33V rms

18Ω – 50V rms, 32Ω – 67V rms, and 72Ω – 100V rms.

For use with the Quad 57 electrostatic speakers the 17V card is used.

The input is DC isolated using a transformer, which allows balanced line connection to be used if desired. A useful property of a transformer-coupled amplifier is the ability to connect it in series or parallel. This is a direct consequence of the provision of a transformer-coupled input and output. It is necessary to maintain the isolation between input and output signal paths in order to capitalise on this attribute. Connection in series will provide greater output voltage swings, whilst connection in parallel will allow the delivery of greater current into low impedance.

The sensitivity is 500mV for full output


The second version is the 520, a two-channel amplifier capable of producing 105W per channel into 8Ω, and 160W into 4Ω.

The 520 themselves have a small number of variants. The basic 520 is called the 520f, since there is the provision to fit a balanced input module to provide each channel with an isolated (and hence ‘floating’) transformer input. The 521f is virtually identical save the input gain control is a dual-ganged potentiometer, allowing completely symmetrical operation. There is also the 522f, designed for the BBC, identical to the 521f but allowed DC lift of the circuit’s 0V rail from the mains earth.

Some later 520s used Neutrik ‘Speakon’ connectors for the output connection; earlier samples used XLR male connectors.

The audio circuitry for both the 510 and 520 amplifiers is virtually identical, save for the output transformer and the input transformer (if used). With the 520 the output from the power devices is connected directly to the speaker connector.

The only other difference concerns the power supplies. In the 510 the power supply is unregulated and uses a bi-limboid transformer (as used in the 405), whereas the 520 uses a regulated power supply fed by a toroidal transformer (and for amplifiers having serial number >6500, an inrush limiter is fitted), this single supply being used for both channels.


I have both a 520f and a pair of 510s amplifiers. The 520 amplifier is used in my second system for AV duties and feeds a pair of B&W DM2a speakers. The pair of 510s are my ‘summer’ amplifiers, used in my main system feeding Quad 57 speakers (so the amps are voltage limited to 17V). Each 510 amplifier is located directly behind each speaker, and uses balanced line connections back to the preamplifier.

Despite being designed for professional use, and so are reliable and protected from abuse, they have excellent sound qualities: poise, subtly and a sense of authority that some amplifiers lack. If you like the sound quality of amplifiers using current dumping (and some don’t: describing the sound as ‘grey’ and un-involving), then you will have no complaint with the Series 5 range (or indeed the Series 6 606 amplifier).

[Firebottle]

Excellent post Barry :thumbsup:

[DSJR]

The 500 series are total rubbish and not worth anyone looking at - except me ;) FFS fellas, make a noise about these and the already silly prices will go through the roof ;) Supply caps will need checking now, as on ALL Quads of this era and earlier...

The 606 and descendants are readily available and in my opinion, really good and better power wise, than the 500's which now sell for at least as much (I know, I prefer the looks of the 500's too and they're more imposing again in the flesh :)). Mk1 606's had 10,000uF supply caps and mk2 caps were 15,000uF, together with a toroidal transformer. I believe the amp boards were all but identical (I think!). The mk1 606 needed an hour or so to open up sonically, where the mk2 was 'there' straight from switch-on. The 707 was also delightful, although I hated the Speakon connectors. The 909 is potentially at least as good, but Chinese ones will need the caps looking at, as bad ones ruin noise and distortion and sadly, this affects music reproduction a little :(

As for the 303, in my view it's a wonderful, charming *period piece,* this latter emphasised for good reason. I've recently re-acquired mine (sympathetically rebuilt a while ago) and am using it sans 33 preamp, but with a passive instead. In the midrange, the sound is truly sublime, open, grain-free and beautifully 'musical,' but the treble and bass really depends on partnering speakers, as there's no 'control' at these extremes I find, together with nowadays vicious current limiting. Into my benign load IMF Compacts, everything was fine until I tried to play some remastered Depeche Mode tracks. The percussion, both electronic and drummed, really hits out and the poor 303 just couldn't hack it here, the bass becoming bloated and ill defined. One DM track that showed it clearly was 'Lie To Me' from the album 'Some Great Reward.' In comparison, the NVA and Krell allowed the bass lines to play rather better. So, if you get a nice 303 that's been sympathetically serviced rather than butchered with me-too replacement boards, with the right speakers, it'll thoroughly entertain in a similar way to the II valve amps, but won't open the window as wide as a 405-2, 520 or 606 onwards can in direct comparison.

Hope this helps - and PLEASE chaps, play down the 500's a bit? Most have been thrashed to death in pro use anyway :)

[southall-1998]

Which speakers work well with the 303?

S.

[walpurgis]

Which speakers work well with the 303?

S.

Most.

[Light Dependant Resistor]

Which speakers work well with the 303?

S.

I have a 303 used regularly with JR149, and have even used them
with Gale GS401. The 303 was designed very much for the ESL57
I think you would be hard pressed to find a speaker that did not
work well with a 303. Just yesterday connected to Wharfdales
the 303 sounded magnificent.

The 303 and 405 were often used by Gale for the GS401
Ira Gale being very aware of the ESL57 and amplifiers matching
to loudspeakers. Gale were developing an amplifier to suit
the 401 precisely, but a 303 or a 405 were what a lot of
customers ended up using. http://0339436.netsolhost.com/WordPress/gs401-speaker/

303's invert phase so for everything other than ESL57 reverse speaker connection ie
Red to Black at the speaker. This was very much intentional to suit the ESL57 where
Red to Red and Black to Black for the ESL57 is correct.

Cheers / Chris

[DarrenHW]

Barry - Thank you very much for the info on the Series 5, I've only really seen these discussed here, there's very little information about them. A little reading up suggests the Series 5 does not use OP Amps, is this true and if so what effect does this have on the sound? Looking at the photo you uploaded of your 510's here: http://theartofsound.net/forum/showthread.php?38771-Bank-Holiday-tinkering, servicing seem pretty straight forward? From the point of view of servicing the 520 has the added complication of the regulated PSU, what if any difference would you say the regulated PSU brings?


If you like the sound quality of amplifiers using current dumping (and some don’t: describing the sound as ‘grey’ and un-involving), then you will have no complaint with the Series 5 range (or indeed the Series 6 606 amplifier).

Good to know I think my audition list is now Series 5 & 6 as;


As for the 303, in my view it's a wonderful, charming *period piece,* this latter emphasised for good reason. I've recently re-acquired mine (sympathetically rebuilt a while ago) and am using it sans 33 preamp, but with a passive instead. In the midrange, the sound is truly sublime, open, grain-free and beautifully 'musical,' but the treble and bass really depends on partnering speakers, as there's no 'control' at these extremes I find, together with nowadays vicious current limiting. Into my benign load IMF Compacts, everything was fine until I tried to play some remastered Depeche Mode tracks. The percussion, both electronic and drummed, really hits out and the poor 303 just couldn't hack it here, the bass becoming bloated and ill defined. One DM track that showed it clearly was 'Lie To Me' from the album 'Some Great Reward.' In comparison, the NVA and Krell allowed the bass lines to play rather better. So, if you get a nice 303 that's been sympathetically serviced rather than butchered with me-too replacement boards, with the right speakers, it'll thoroughly entertain in a similar way to the II valve amps, but won't open the window as wide as a 405-2, 520 or 606 onwards can in direct comparison.


I'm concerned the Series 3 wouldn't be a good match for the Celestions?


The 606 and descendants are readily available and in my opinion, really good and better power wise, than the 500's which now sell for at least as much (I know, I prefer the looks of the 500's too and they're more imposing again in the flesh :)). Mk1 606's had 10,000uF supply caps and mk2 caps were 15,000uF, together with a toroidal transformer. I believe the amp boards were all but identical (I think!). The mk1 606 needed an hour or so to open up sonically, where the mk2 was 'there' straight from switch-on. The 707 was also delightful, although I hated the Speakon connectors. The 909 is potentially at least as good, but Chinese ones will need the caps looking at, as bad ones ruin noise and distortion and sadly, this affects music reproduction a little :(

Thanks Dave, I've done a little reading up on the 606, also sans OP Amp I believe? It looks like the MK2 is the one to go for?

[spendorman]

Just a point on the 303, I have four of them but the latest one has the IEC mains connector, which I find a bit more more convenient, compared to the Bulgin connector of the older models.

[DSJR]

The 500 and 600 current dumpers (possibly the 306 as well?) took the op-amp out of the signal path - to advantage I think - and should drive anything out there within reason. I had my wake-up call at KJ in the late 90's when a customer brought a mk1 606 under his arm in because he thought it was faulty. Connected 'cold' into Wilson Witts it sounded amazing and better than a Chord 1200e, let alone the Krell KAV's we used often. Go figure.....

Shane, the 303 is just fine, it's just that I played music with very powerful bass lines that are quite out of keeping with the era in which the amp was designed. Average bass levels on contemporary recordings have increased quite a bit since the 60's and 70's and the 303 used with a wide open source and passive pre couldn't quite handle it. One reason why the 33 preamp is so heavily low-filtered (roll off starts at 35Hz I believe) is to help the 303 do its job better with then wayward vinyl and tape sources..

Here's my 303 naked... It started life as a late model in all-over green, as the last ones were apparently. I suspect it did it's working life in Our price records, who bought hundreds apparently...

http://i132.photobucket.com/albums/q8/DSJR_photos/DSCF2252_zpsddoqp5s6.jpg (http://s132.photobucket.com/user/DSJR_photos/media/DSCF2252_zpsddoqp5s6.jpg.html)

[Juha]

I am running a Quad 522 here.
This is a version with balanced inputs and input transformers.

The input transformers add a special shene and texture.
Like the great U.K. audio guru Rupert Neve has said: "The sound is in the iron"

Also, friends that have heard this amp have praised the authoritative bass on Quad 522.

[r100]

Just a quick question...

is there a fundamental sound / technical difference between the Quad 606 and 909 ? There is a 909 for sale here.

Thank's
Ru

edit: Just saw Dave's comment about the 909..




The 606 and descendants are readily available and in my opinion, really good and better power wise, than the 500's which now sell for at least as much (I know, I prefer the looks of the 500's too and they're more imposing again in the flesh :)). Mk1 606's had 10,000uF supply caps and mk2 caps were 15,000uF, together with a toroidal transformer. I believe the amp boards were all but identical (I think!). The mk1 606 needed an hour or so to open up sonically, where the mk2 was 'there' straight from switch-on. The 707 was also delightful, although I hated the Speakon connectors. The 909 is potentially at least as good, but Chinese ones will need the caps looking at, as bad ones ruin noise and distortion and sadly, this affects music reproduction a little :(:)

[Barry]

Barry - Thank you very much for the info on the Series 5, I've only really seen these discussed here, there's very little information about them. A little reading up suggests the Series 5 does not use OP Amps, is this true and if so what effect does this have on the sound? Looking at the photo you uploaded of your 510's here: http://theartofsound.net/forum/showthread.php?38771-Bank-Holiday-tinkering, servicing seem pretty straight forward? From the point of view of servicing the 520 has the added complication of the regulated PSU, what if any difference would you say the regulated PSU brings?

Your correct in that no op-amps are used in the signal path. There is an IC used to provide DC control, but this is not in the signal path. I'm not an electronics expert, but common opinion is that descrete circuitry is better as regards sound quality. Certainly a large improvement in SQ can be made in the 405 amp by replacing the op-amp with a better quality item.

Servicing ought to be straightforward and Dada have some ideas for upgrading/fettling these amps.

Again, I can't really comment on the desirability or otherwise of using a regulated power supply. Some say that an unregulated supply, being simpler, can respond more quickly to sudden current demand and thus the amp has a better dynamic response.

[Barry]

I am running a Quad 522 here.
This is a version with balanced inputs and input transformers.

The input transformers add a special shene and texture.
Like the great U.K. audio guru Rupert Neve has said: "The sound is in the iron"

Also, friends that have heard this amp have praised the authoritative bass on Quad 522.

That's good to know Juha.

The 522s are quite rare. Most of them being used by the BBC, so appear on the market infrequently.

[DSJR]

It's also countered that a good op-amp is better than an equivalent discrete layout due to the miniscule signal paths and so on... The end of the day, I think that correct supplies are fundamental and in my current NVSA work, I've been shocked at how a couple of chips can be made to sound 'better' by hugely increasing the size of the power supply amongst other things. So I don't think it's as cut and dried as some would make out.

The 909 can be a very fine amp indeed and maybe all the hoo-ha about capacitor quality was confined to a small final batch for all I know. There's no doubt that a good one is one of the best 'fit and forget' options out there in my opinion..

Interestingly, I heard the Elite 909 replacement with the matching preamp and the pair, run for some hours at hifi dave's place, did everything I don't remember vintage Quad amps doing as well except for the most important thing of all... Everything was so controlled, precise and 'matter of fact' it was almost as if the 'soul' in the recording had gone. A Croft integrated didn't have anywhere near the headroom, but vocal diction seemed so much better and you could hear what the acoustic guitars were actually strumming musically, rather than just being backing instruments that were 'there' in the recording. 'My' 33/303 also did this musical 'thing' with ease in direct comparison and I know from past experience that the 405-2 in good fettle can do it too, as well as the 66 and 77 series...

Interesting thing, this 'subjective' vibe.....

[Barry]

How does the Elite 909 differ from the stock 909? Are there any changes to the circuit and/or components?

[Martyn Miles]

Which speakers work well with the 303?

S.

LS3/5as.
I run them from a 34/303 and it all works superbly.

[Arkless Electronics]

I was just having a listen to a pair of Quad II monoblocks which I rebuilt for a customer... Much better than I remembered! A touch bass light maybe.... Closer to my Leak Stereo 20 than I expected and remembered the last ones I heard to be.

[walpurgis]

I was just having a listen to a pair of Quad II monoblocks which I rebuilt for a customer... Much better than I remembered! A touch bass light maybe.... Closer to my Leak Stereo 20 than I expected and remembered the last ones I heard to be.

Sounds about right. That's what my last pair were like. OK, but I prefer the Leak.

[southall-1998]

Below are both pics and description of the sale (From the seller). This 303 sounds very nice!

S.

http://i602.photobucket.com/albums/tt104/TDL-STUDIO/_57_zpsjkmvenlg.jpg (http://s602.photobucket.com/user/TDL-STUDIO/media/_57_zpsjkmvenlg.jpg.html)

http://i602.photobucket.com/albums/tt104/TDL-STUDIO/_57%204_zpswshjskpi.jpg (http://s602.photobucket.com/user/TDL-STUDIO/media/_57%204_zpswshjskpi.jpg.html)

http://i602.photobucket.com/albums/tt104/TDL-STUDIO/_57%205_zpscz9q0c1r.jpg (http://s602.photobucket.com/user/TDL-STUDIO/media/_57%205_zpscz9q0c1r.jpg.html)

http://i602.photobucket.com/albums/tt104/TDL-STUDIO/_57%207_zpstlk2unbh.jpg (http://s602.photobucket.com/user/TDL-STUDIO/media/_57%207_zpstlk2unbh.jpg.html)

http://i602.photobucket.com/albums/tt104/TDL-STUDIO/_57%206_zpso3fjpkcz.jpg (http://s602.photobucket.com/user/TDL-STUDIO/media/_57%206_zpso3fjpkcz.jpg.html)

http://i602.photobucket.com/albums/tt104/TDL-STUDIO/_57%208_zpshi124ajq.jpg (http://s602.photobucket.com/user/TDL-STUDIO/media/_57%208_zpshi124ajq.jpg.html)


My recently serviced QUAD 303 is for auction. I have a new project to fund.

It was sympathetically serviced, in late January, to retain that classic Quad 303 sound.
It is in good condition for its age, with just a few light scratches and chipped paint on the fins, as is normal. Please see the pictures.

You can also see it has new electrolytic capacitors, input capacitors and new multi-turn pots, in place of the original types which are poor quality and less reliable. Out of specification resistors were replaced too. The regulator board has had up-rated diodes and resistors fitted for reliability and stability. You will also see the new main reservoir and output capacitors have been installed inside the original capacitor cans to retain their original appearance.
A mains lead and an RCA to DIN lead are included.

[dantheman91]

Hi Guys

Just giving mine a run after a few months in hibernation :rolleyes: Still sounding like it should i absolutely love my series 3 quads.:D

[walpurgis]

Hi Guys

Just giving mine a run after a few months in hibernation :rolleyes: Still sounding like it should i absolutely love my series 3 quads.:D

How do you find it compares to the PMA-350SE? The Quad is pleasant, but can it match the lucid presentation of the Denon?

[dantheman91]

Hi Geoff

I think the Quad is warmer in presentation its suits most types of music but not all, The denon is a strong performer and have used it up until last week the denon in a contest would win for performance and sound quality and can beat most higher rated amplifiers of the time such as Rotel , Cyrus ETC but it does not have the finesse quality of the quads so therefor i think both have their pros and cons but both are staying in my collection for foreseeable future :)

[walpurgis]

Hi Geoff

I think the Quad is warmer in presentation its suits most types of music but not all, The denon is a strong performer and have used it up until last week the denon in a contest would win for performance and sound quality and can beat most higher rated amplifiers of the time such as Rotel , Cyrus ETC but it does not have the finesse quality of the quads so therefor i think both have their pros and cons but both are staying in my collection for foreseeable future :)


Yeah. That's more or less what I thought you'd say. :)

I just love the PMA-350SE. It amazes me that you can pick up such a good sounding and punchy amp for less than £100 on the second hand market. I used one with my big Tannoys for a while and it sounded great with them. Even compared to my Class A stuff.

[dantheman91]

Hi Geoff

I have used the with both the DC 1000 and 615 MK2 and both have had excelling results but i dont get why the market is so cheap for denon gear its like say to a mate you own denon kit they say "Its Crap" then your like have you heard the PMA 350SE and then they say thats a good bit of kit for the money i payed £10 for mine at a car boot 2 years ago and still use it in my main system and others i cant say that for many amplifiers that have been and gone in this hobby but the bay prices are ridicules as kit thats good goes for peanuts and they items that are poor go for x amount.

[southall-1998]

Bought another Quad 303 last week- http://www.ebay.co.uk/itm/181952345402?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I still haven't tried it yet!

S.