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Lesser known Quad power amplifiers

Discussion in 'classic' started by NeilK, May 1, 2022.

  1. NeilK

    NeilK pfm Member

    I like vintage Quad amplification. In addition to the usual suspects, 303, 306 and a less than impressive 405 I've spent time with a 520 and a pair of 510s. These rack mount 'professional' amplifiers seem well built and perform extremely well. Currently I'm really enjoying a refurbished 240 which I purchased from Keith Snook. It seems to be based on the 306 circuit but with a beefier power supply.

    [​IMG] by ,
     
    cooky1257 and TonyScarlett like this.
  2. Grog

    Grog pfm Member

    I have a ex BBC 240, great amp.. they seem rare!
    I've just swapped it out for a 606, too early to make any conclusions but very similar sound so far.
     
    NeilK likes this.
  3. Ianp

    Ianp pfm Member

    Openly stating you're less than impressed with the 405, cool . In hindsight with this amp I agree with you, it or the synergy never worked for me. Bit dry. Love the earlier ones and the 909 though.
     
    NeilK likes this.
  4. Operajulian

    Operajulian Opera Julian

    A number of stage theatres in which I have worked in had Quad 520 as the amps driving the theatre speakers for sound effects and general sound. I would not put them to work as power amps for driving concert pa systems but they were not bad, very dependable, general all rounder etc
     
    NeilK likes this.
  5. cooky1257

    cooky1257 pfm Member

    A pair of 240's here driving a second system, great little amps that look great too.
     
    NeilK likes this.
  6. NeilK

    NeilK pfm Member

    After some serious listening I'm coming round to thinking this is one of my favorite amplifiers.

    Pretty much my thoughts exactly - mind you conventional wisdom doesn't rate the 33 pre-amp (except aesthetically) but I'm quite happy with it's sound, a properly serviced example with the 'tone controls' cancel button engaged is not at all bad.
     
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Today I have mainly been listening to a Quad 303. Recapped etc by Dada. 5600uF output caps used.

    Somewhat better than I recall of standard but not recapped (and fitted with much smaller original output caps) units.

    Overall I prefer it to the last Quad amp I had in, a 520, by a fair margin.

    A nice lack of any "nasty" "transistory", "brittleness", "chrome" etc to the mid and treble. Imaging and soundstaging very good.

    Compared to my usual Arkless Electronics 16WPC class A monoblocks (much more expensive amp if you could buy one) though it is rather lacking in dynamics, "balls", slam, "range of timbral palette", somewhat lacking in deep bass extension and a bit loose down there. The top end is a bit "soft", "rounded" by Nth degrees but no huge difference.
    Subjectively it sounds considerably less "powerful" even though it's actually 45WPC compared to the 16WPC of my own amp and "smaller" (hard to put into words but smaller will have to do). Dynamics don't "startle" as they do with the Arkless Electronics monoblocks. I can see why the aphorism of "better on classical than rock" has been used at times in relation to the 303... not that it can't do rock you understand... it's just maybe not it's forte.

    For the price you can get a S/H 303 and ease of servicing though... Recommended:)
     
    ampedup, chartz, NeilK and 2 others like this.
  8. Gervais Cote

    Gervais Cote Predator

    How long will we have to wait until a series of Arkless class A amps get for sale on the market............o_O
     
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    A good question......o_O......:rolleyes:
     
    chiily, NeilK and martin clark like this.
  10. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Update after its been on a few more hours and having taken in mainly folk and classical since last post...

    Really rather good! In terms of musicality, "tone", lack of "SS nasties".. plus previously noted very good imaging and soundstaging.. you'd have to pay a lot of money to better it with a brand new modern amp. Note that the criticisms above stand though, the biggest being, to my ears, rather a lack of slam and balls plus a touch of looseness in especially the low bass.. which is noticeably lacking anyway by Nth degree standards, but upper bass, where it's more important is OK. This with the 5600uF output caps fitted by Dada.

    On "girl and guitar" or "string quartet" etc I reckon you could put the 303 against a £1500 modern amp.

    With the original 2000uF output caps I think the bottom end would be rather unacceptable by modern standards though unless driving 15R and intrinsically pretty well damped speakers.
     
    chartz likes this.
  11. TonyScarlett

    TonyScarlett pfm Member

    Maybe one of the reasons they go so well with LS3/5As, your missing those lower bass notes anyway!
    TS
     
    NeilK and Arkless Electronics like this.
  12. Radfordman

    Radfordman pfm Member

    I understand that if C100 is increased from it's 0.68uF size, bass roll off is less.
     
  13. Radfordman

    Radfordman pfm Member

    My memory fades a bit, but I think when the 303 first came out, many Hi Fi speakers were 15 Ohm.
     
  14. Radfordman

    Radfordman pfm Member

    I quite like the 303, so I bought a spare or two

    [​IMG]DSCF2277 by A60man, on Flickr
     
    NeilK and TonyScarlett like this.
  15. chartz

    chartz If it’s broke fix it!

    I replace it with a 1 µF (no, not a Wima :rolleyes:).

    I see that Jez finally likes the good old 303.
    Honestly I compared it to the 306 again this morning (also good) and on the ‘57´s it’s better to these ears!
    I listen to classical mainly, and church organ music does sound fantastic!
     
  16. Radfordman

    Radfordman pfm Member

    A badly set up 303 can sound a bit rough in the treble, but properly adjusted, sounds fine.

    If you are using with ESL57's I have read that it's best to stay with the 2000/ 2200uF output capacitors. I'll search for the write up about this.
     
  17. Radfordman

    Radfordman pfm Member

  18. chartz

    chartz If it’s broke fix it!

    Yes, by Jim of this parish!
     
  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    In many ways it's good but I couldn't live with a standard one due to the bass lightness, lack of slam etc. Would be worse still with a 33
    I have come up with mods to get around both this limitation and to give good power into 4R load plus a fair bit less THD but it looks like I'm not going to find a 303 to try them on as they go for more than I'm willing to pay. As I'm going to be junking many of the original parts I just want a cheap one, rust, broken fins etc no problem but bizarrely although you can get a working one for £130 ish a completely knackered, rusty one advertised as "doesn't work. for spares only" generally still goes for around £90!! :eek::mad:

    I have a sorted 405-2 (standard apart from bigger smoothing caps plus it's been recapped) and I much prefer it to the 303 (and the 520, which I really don't like) but it still needs mods to put the bass right before I could live with it. As I design amps I tend to use ones I've built for daily listening duties.
     
    chartz likes this.
  20. chartz

    chartz If it’s broke fix it!

    Everything I buy is as-is (never touched, all original) but the stuff has to be mint – and dirt cheap!
    Think € 100 for a 303 or a 405. I also paid € 80 for the 306 last year (also looking like new).
    Sometimes I have to look long and hard but I always seem to get there in the end.:)
    All my Quad is therefore mint and of course fully functional after rejuvenation.
    Funny that you should prefer the 405 over the 303 though. I’ve read many posts by Alan Shaw on the HUG forum and like you, he seems to prefer the 405 over the 303 with his speakers.
    I don’t. I find the 303 brighter, more ‘fun’ with a deeper soundstage. Is it distortion doing its trick, you know as valves can do?
     
    Arkless Electronics likes this.

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