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Quad 909 upgrade/mod list

Discussion in 'classic' started by Chris88, May 7, 2017.

  1. Chris88

    Chris88 pfm Member

    Sorry to hear about your experience, sometimes these things can take a toll emotionally. I actually purchased x2 909 amps brand new circa 2009 and they still sound great to this day. I have never had them serviced and they are still going strong (the lid has never been off either of them).

    Incidentally these 909 amps have the "capXon" Chinese caps which get a lot of criticism, but they still sound really good to me regardless. Originally Quad used BHC Kemet. When i purchased some second hand 909's in more recent times (the ones i ahd Quad service for me), i requested they install the original BHC Kemet PSU caps, which they did, but amazingly when i got my hands on those amps it they didn't sound as good as my new original 909's (with Chinese caps).

    My initial thought was that despite the BHC caps being undoubtedly superior in regards to build quality, perhaps they might have a more laid back and smooth sonic signature compared to the Chinese caps (which i'm not really into), however i am nnot able to draw that conclusion, because that very same amps that now have the BHC caps also have non original and sub-standard (terrible) caps for C7, C9, C11 (not sure what the brand is though) and it's quite possible that could be taking a lot away form the sound quality.

    If i had instructed Quad to change the PSU caps only (with BHC Kemet) i would have been able to do a direct comparison with my original 909's (directly comparing BHC Kemet and capXon).
     
  2. fatmarley

    fatmarley Registered User

    Have you thought about a Dada service/upgrade kit? I found It gave a bit more life to the music with my 306.

    Replacing all the carbon film resistors for metal film (MRS25) In my 306 gave a bit more life to the highs, but without sounding harsh. Does the 909 have carbon film or metal?

    Replacing the Input coupling cap (C2 on the 909) made the biggest Improvement In my 306. I used a HUGE Audyn true copper max. It was a tight squeeze to fit It, but well worth the effort.

    I also made an air-core Inductor (L4 on the 909). Mine both measured 1.35u, so that's the value I replaced them with. 1.4mm enamelled copper wire, wound 11 times round an AA battery and carefully squeezed together with cable ties until they measured 1.35u. They also measure the same as the original ones In capacitance and resistance but without reverting back to the old ones I'm not sure If there was an Improvement.
     
  3. Chris88

    Chris88 pfm Member

    Cheers for that, yes i've gone over all the dada stuff and they have some good ideas.

    Don't think i'm bold enough to mess with the inductors lol (i had considered it previously), but hats off to you for your success there ; )
     
  4. Chris88

    Chris88 pfm Member

    Has anyone tried wire-wound resistors with Anton Perry Windings? (so called non-inductive)
     
  5. russel

    russel ./_dazed_and_confused

    I would have thought caddock thick film would be better.
     
  6. Chris88

    Chris88 pfm Member

    When searching for film caps on mouser and selecting the various values, under the heading "Voltage rating DC" i can find 100V, but directly beneath 100V it also lists 100VDC, are these different values or the same thing?
     
  7. Zombie

    Zombie pfm Member

    Don't worry about it. Just differently entered text.
     
  8. Chris88

    Chris88 pfm Member

    Thankyou : )
     
  9. Arkless Electronics

    Arkless Electronics Trade: Arkless

    You don't need to worry about thermal coefficient of resistance at all. Changes due to this are infinitesimal in the context which you are using them.
     
  10. Chris88

    Chris88 pfm Member

    Is there any sonic advantage to lowering the gain of an amp like this, or does that only concern the volume level? I have read about some people lowering the gain of their 909, does this change or improve the actually sound quality in any way?
     
  11. Arkless Electronics

    Arkless Electronics Trade: Arkless

    Never attempt to change the gain of an amplifier unless you really know what you are doing! It is set in negative feedback amps by...yep the amount of NFB, and this effects all sorts of things including whether or not the amp is stable or is likely to go unstable, quite probably blowing itself up and taking out your speakers in the process.
     
  12. Chris88

    Chris88 pfm Member

    ok thankyou for that i'll leave it well alone lol.

    How about the opamps? I know its not supposed to make a difference here with the Quad 909, but if i wanted to try something such as LME49710 or even OPA627 is that likely to damage the amp or cause harm?
     
  13. martin clark

    martin clark pinko bodger

    Complete waste of time - the opamps in the 909 are just the DC servos they operate only below the audioband, and do not handle the audio signal directly, but 'steers' the output to remains close to 0.00x V at DC - eliminating dc-offset at the output, on other words.

    The part fitted is an excellent choice for this (hint: slow and stable is good - the very opposite of dropping opamps like those you mention into anything without great care)
     
  14. Arkless Electronics

    Arkless Electronics Trade: Arkless

    Unlikely to make much/any difference. Servo op amp needs to be a fet input one and all need to be unity gain stable. If you don't know what I mean by these terms then you shouldn't be messing with it!
     
  15. Chris88

    Chris88 pfm Member

    ok gents, cheers for that.

    I would however like to change the input coupling capacitor (C2).

    The original MKT is approx 13mm in length, and the smallest polypropylene i can find is 20mm.

    Is using a larger cap (20mm) likely to cause any problems?
     
  16. martin clark

    martin clark pinko bodger

    Wima MKP4 caps are outstandingly good for this kind of thing - the 330nF/100v DC part (Wima part no. MKP4D033304C) or even the 250vDC part, has a 15mm pin spacing, likely a drop in. Don't sweat a few mm on an input coupling cap: it's a high-impedance input anyway, adding 20mm of flying lead just.does.not.matter.

    Banzai are a good source if you can't find others more local or convenient - range: example specific equiv: 330nF cap with 15mm lead spacing.
     
  17. John_73

    John_73 pfm Member

  18. martin clark

    martin clark pinko bodger

    Nice and compact suggestion!
     
  19. Chris88

    Chris88 pfm Member

    Thanks John, what differences did you notice with the Panasonic PP? Is it possible to describe?
     
  20. Chris88

    Chris88 pfm Member

    Wow a perfect drop in replacement, those caps are perfect for input coupling C2, thanks again John!
     
    Last edited: Nov 12, 2017

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