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Quad 909 upgrade/mod list

Chris88

Chris88

pfm Member
Hi people, i'm a relatively young chap who's never done anything like this before, but i would like to try and upgrade my Quad 909 amp to make it the very best it can possibly be. I would really appreciate some feedback regarding the following possibilities;


1./ Replace input coupling cap C2 with 470nF Kemet SMR (Quad used MKT).

2./ Introduce decoupling caps (100nF MKT) for Zener diodes D1, D2 & D12 (although i think i read somewhere that D12 may already be decoupled by C15?)

3./ Replace small signal electrolytics (C7, C9, C11) With Nichicon KZ. Is it ok to use 100V here? (Quad used 63V). The Nichicon is only available in 100V.

4./ Replace PSU caps with either "Kemet" or "Mundorf Mlytic". Has anyone heard these? Some say Kemet are a little bland sounding? Would the Mundorf Mlytic be superior?

5./ Possibly replace opamp TLC271 with OPA627 or LME49710? The opamp is a DC servo but some claim it still impacts the sound?

6./ Bypass the circuit breaker and hard wire directly to the IEC inlet. Is this ok to do?

7./ Is there anything worth considering to upgrade wirewound resistors R16 and R17? (possibly non-inductive wirewound?)

Thankyou in advance : )
 
1) Replace C2 (330nF) & C3 (1uF) with Panasonic ECWF polypropylene caps from RS components. They fit nicely in place of the originals.

2) Replace the feedback cap C7 (47uF 100V) with a Nichicon KZ from Hi-Fi Collective.

3) Replace C9 and C11 (220uF 63V) with Panasonic FC or Vishay 136 types.

The combination of the above gives - subjectively - more 'punch' and improved treble detail. As always, do these things one at a time and evaluate the results.

- John.
 
Chris88 said:
4./ Replace PSU caps with either "Kemet" or "Mundorf Mlytic". Has anyone heard these? Some say Kemet are a little bland sounding? Would the Mundorf Mlytic be superior?
Click to expand...

I haven't used Kemet but I used Mltyics when I recapped a power amp a few years back and I thought they were excellent.

F&T capacitors are worth looking at too, as far as I understand it they actually manufacture the Mundorfs.
 
5) a 'faster' opamp like those is useless in a servo. Easier to RC filter the servo's output if fed-through noise is a worry (it isnt, in this case)
 
Ok now were talking, thankyou all for the input much appreciated : )

* Is it ok to increase the capacitance of C7, C9, C11 or is that a bad idea?

* I've searched high and low but can't find polypropylene in the correct 10mm 100V size. Is it really better than Kemet SMR?

* How about bypassing the circuit breaker and hard wiring direct to the IEC?

* How about decoupling caps (100nF MKT) for Zener diodes D1, D2 & D12? (is D12 already be decoupled by C15?)
 
Not looked again at the circuit. But *in general* I'd avoid changing the type or value of items within a feedback loop of an established design unless you're going to check things like stability margins and how the THD varies with output loading, etc. Current Dumping designs in particular need care with the 'bridge' components, etc, that share out the work.

I've also found in the past that adding a cap across a zener or 'rubber diode' can actually cause odd problems. the outer of the cap can act as an electrostatic 'antenna' to couple to nearby in the circuit and add parasitics. And the capacitor types people rate as being 'good' often tend to be physically larger, and thus more prone to this kind of thing.

However TBH my approach to amp design is to fix identifiable problems rather than change component types in search of a 'sound' I might think 'better'. If it doesn't sound right but measures OK, I'd change the design or find out why.
 
* Is it ok to increase the capacitance of C7, C9, C11 or is that a bad idea?

I'd go with John's recipe since that has been tested and known to work (I haven't checked the circuit to see what larger values will do, if anything)

* I've searched high and low but can't find polypropylene in the correct 10mm 100V size. Is it really better than Kemet SMR?

Theoretically yes, but in this application I doubt it. SMRs really do measure very very well, with excellent linearity - better than MKT (search for Cyril Bateman's capacitor measurements on line).

* How about bypassing the circuit breaker and hard wiring direct to the IEC?

NO benefit there and it protects the amp (instead of a fuse) - a circuit breaker is a decent spring contact, probably a a better internal contact than poxy IEC sockets...

* How about decoupling caps (100nF MKT) for Zener diodes D1, D2 & D12?

Probably not very effective. Zeners - when run at a decent current as these are, c 10mA - are actually very quiet (contrary to much nonsense you'll read on audio sites ;)
If you wanted to bypass them, use something like 10uF (say tantalum bead - check polarity when fitting!) - so that with the series resistance feeding them you have enough capacitance to help knock-down low frequency and midrange ripple usefully. Don't go too large on this capacitance else you may end up with odd thumps when you turn the amp off.
 
Chris, what issues/problems have you identified with the 909 where a modification is required?
 
I'd also point out that one of the most attractive aspects of Quad amps is they are very stable and, due to rather clever design, tend to fail-safe. An amp I am happy to use day to day with rare, collectable and valuable speakers, unlike certain 'hair-shirt audiophile' stuff that can destroy a speaker if a component fails, short occurs or whatever. As such removing the protection circuit is about the last thing I'd do!
 
Is there anything worth considering to upgrade wirewound resistors R16 and R17? (possibly non-inductive wirewound?)
 
You still haven't given any clear reason for making any of these changes. Saying "it *might* sound better" in isolation isn't really a rational reason. If you want something 'better' then look for a different amp that may do whatever it is you have in mind.

Otherwise you'll end up wondering about every component, the layout, the wiring loom, the box, connectors, .... i.e. everything anyway.

Trig's broom effect. 8-]
 
I can understand swapping out the apparently poor quality and unreliable Chinese caps and maybe removing the Quad Bus connections. IIRC that is what Dada Electronics recommend and they seem to know what they are doing.
 
Why mess with the 909?

Because to my ears the 909 is overly smooth and bland sounding, mellow and boring. I purchased this amp while i was a student several years ago because at the time it was all i could afford.

What the 909 does have going for it however is raw power on tap. I have done extensive research regarding 909 mods and with some basic upgrades it can be made to sound noticeably better.

Critisism of this amp often involves lack of treble ect, and MANY people have mentioned replacing C7, C9 C11 can make a BIG difference here. Using high quality caps from quality bands such as Nichicon ect.

The reality is Quad used many cheap components inside this amp, and replacing some of these parts with better quality types can make the amp much better.

Don't tell me "if you don't like Quad go and buy something else ect". Why would i want to spend crazy amounts of money for a Cyrus or Naim when for a the cost of a few capacitors i can be very satisfied with my Quad?

And please don't tell me that a Quad is a Quad and that it will never be a Cyrus or a Naim ect, because i'm not expecting it to be.

What i am expecting is to make it sound better than it currently does and based on my EXTENSIVE research i think that is realistic.

I am in this hobby for best results at affordable costs.
 
Chris88 said:
What i am expecting is to make it sound better than it currently does and based on my EXTENSIVE research i think that is realistic.
Click to expand...

At the same token, you did start out by writing "I would really appreciate some feedback"...
 
Q. Have you heard (with your own ears) one of these 'improved' Quad 909? If you can find a member with such an animal, perhaps a bake-off would be possible.

Best to do that before taking the covers off. I read this thread and I think I get that you do not have any electronics experience or knowledge.... are you really going to start on your precious 909?

If you are going to start - I would start (after several hours of soldering training - replacing stuff is harder than just building / soldering it) with just the 3 capacitors mentioned and then put the covers back on and see what you think. DO NOT try to run without covers - safety for a newbie and too many other variables at play if you looking to hear the difference.

Others will play with these sort of things because it is their hobby and they can afford to play - perhaps they have several amplifiers. Messing around with your only amplifier is risky - it is your only one. Same happened to me years ago when I was a poorer person and messed up some stuff Had to wait till i saved bigger money to fix or replace!
 
Hi Jensen thankyou for your advice and safety tips, good advice i intend on taking for sure.

You are indeed correct i have no prior electrical knowledge whatsoever, but i have become very passionate about this project and intend to see it through to completion.

I am currently enrolling in a basic electronics course so i can learn to solder and i will certainly practice extensively before ever attempting to work on the Quad. I do actually have several 909's (long story) so i can compare results easily. My preferred option would have been to pay someone to carry out the work for me, but the last time i did that my amp came back damaged and covered in scratch marks.

To answer your question, no i have not heard anyone else's modded 909 amp, but i have read many people's comments on how the sound changed after certain mods were carried out ect. I have also researched the sonic characteristics of many capacitor brands and types over the last several months or so (copying and pasting people's comments as i went), and genuinely feel i have grasped consensus views about how some of these sound (Elna, Nichicon, Panasonic, ect ect). Of course there's no way to know how a given part will sound in your amp until you've tested it yourself, but having some generalisations about how certain parts generally sound is a great place to start.

Def will not run the amp with the lid off ect, thanks again : )
 
If you have several 909's then it would be a great to send one off to Quad for a standard service (at a fixed & very reasonable price), then you'd have the perfect reference to compare a modified/upgraded one to.

My gut feeling is that the modified one would only be subtly different if you're mainly replacing the standard components for 'better' or more expensive ones (couldn't say whether that's the same thing), but I'm happy to accept that I might be wrong there.

I've got a single 909 and three different pre-amp options (ss/valve/passive, none of which are exotic), and what I would say is that swapping between the pre's certainly affects how my system sounds!
 
Chris88 said:
To answer your question, no i have not heard anyone else's modded 909 amp, but i have read many people's comments on how the sound changed after certain mods were carried out ect.
Click to expand...

I have also researched the sonic characteristics of many capacitor brands and types over the last several months or so (copying and pasting people's comments as i went), and genuinely feel i have grasped consensus views about how some of these sound (Elna, Nichicon, Panasonic, ect ect).
Click to expand...

As you state that you have no prior knowledge of electronics, what do you base your judgement of sonic characteristics on? Anecdotal comments from non-experts?
 
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