Replacement Parts for Quad 909

So i had a 909 serviced a while back and they changed the main caps and the transformer out, and now it doesn't sound as good lol (when i was expecting it sound better).

The sound is even more laid back and flat (not good lol).

The transformer is presumably an off the shelf of some variety and the caps are Kemet/BHC.

I figure both of these things are effecting the sound negatively, rather than it just being a single bad item.

I know Naim Audio use Talema transformers, if i asked them to make me up a transformer would it likely improve the sound?

Is it possible the Naim transformers colour the sound in a pleasant way, are are they likely to be dead quiet which may possibly be a bit boring?
 
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Barring shoddy transformer construction or your existing system is in a large area and you need a fair portion of the available power, it's unlikely there will be significant difference in sound quality due to the brand of toroidal transformer.

Talema do make decent quality toroidal transdormers but then, so do many other European manufacturers using probably the same or similar cores and magnet wire. There can be lower noise and with extra features like a belly-band or inter-layer shield but such custom 1-off transformer builds are not cheap. More to the point, what was the reason for changing a major part of the amplifier like the power transformer?

Are you sure that the only change to your system is the service work? How long has it been between listening before and after servicing? Did you subsequently receive the replaced parts or at least a list of them?

The more likely and usual candidate for affecting sound quality is simply renewing capacitors (including upgrading or increasing the amount of smoothing capacitance) though there aren't a lot of them in Quad power amplifiers. The effect you describe is only what I'd expect with a re-cap; tighter, clearer sound and usually the bass is noticeably stronger too - depending on the age and relative quality of the parts replaced.
 
Hi Ian thanks for the reply.

Yes i'm quite sure those were the only changes and i do have the invoice sheet listing those parts. I originally purchased 2 new 909's back in 2007 and only had one of them serviced, so i do a direct comparison and the older/untouched unit definitely sounds better.

Kemet/BHC have a very good reputation but some say they "just don't sound good". Maybe it's the BHC caps. They do have excellent specs, but as we all know you can't really judge something from specs, you need to listen with your ears. Honestly i think it's the BHC caps.

Ian may i ask you are PSU caps considered in the "signal path"?, and what is the definition of "signal path"?
 
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....may i ask you are PSU caps considered in the "signal path"?, and what is the definition of "signal path"?
This is a real old chestnut - a long and hotly debated issue that is bound to wake up others here and start another fiery debate - like measurements v sound quality and other pointless topics. The question is a semantic one; where it all depends, as your question suggests, on what is meant by "in the signal path".

A naive view is that the signal path is just the AC path(s) drawn as a highlighted or bold line through the amplifier schematic from input to output, as you may see in some service manuals. This only identifies series components and active devices, switches etc. in those lines. In fact, it usually ignores shunt circuit components and the power supply and ground return paths for the signal. These will be just as much in the signal path, whether by series or shunt connections.

From the whole amplifier perspective, everything is in the signal path to some degree because it will have some effect on the output. It's not so simple, understanding the amplifier design because most circuits have multiple functions and the signal path carries various DC components too. What we find though, is the term "signal path" is really just a convenient category into which we place the primary forward signal path, once we've identified it.

Of course, there are also subcircuits like protection, indicator lights, remote control, microprocessors and soft start circuits that may be considered as not being in the signal path but there will always be a case for saying that if we believe it has any perceptible affect on sound, then it may be so :rolleyes:

To put the main smoothing electrolytics in a (chest)nutshell, consider they are necessary to shape the the DC supply from a rough sawtooth waveform to virtually smooth DC. Pull the caps out of circuit and just try to listen to the resulting buzz-saw sound effect. It's not audio at all. So, is the PSU in the signal path? Of course it is, since it supplies the very current for amplification that the speakers draw upon. You can't actually have a power supply (and that also means the capacitors in parallel with it) that isn't in the signal path.
 
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Opamp change for QUAD 909

Is changing the opamp in a Quad 909 worth doing?

There are some who say the standard opamp (TLC271) acts merely as a DC servo and is not in the signal path, and others who say it is in the signal path and changing it can make a difference to the sound.

I’m tempted to try OPA627 which i'm told should be safe to try, or possibly LM4562.

Any thoughts?
 
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Opamp is DC servo and it should not influence subjective performance to a degree that you can call it "improvement". I am sure that QUAD chose adequate OPamp for the job and that any replacement is absolutely unnecessary. Even ordinary TL071 is enough for the required function, as one can see from Doug Self's power amp book. Limitations of 909 are in the topology of the power amp stage and if you are nopt satisfied with it changing DC servo opamp will not make it any better.
 
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I’m tempted to try OPA627 which i'm told should be safe to try, or possibly LM4562.

Any thoughts?

No no no !

What is fitted is perfect for the job and is not in the audio path as such. Its function is to act as an integrator which means it removes all the audio and simply produces a DC correction voltage to bias the amp.

The 4562 isn't even pin compatible (its a dual) and being bjt isn't really suited to this duty anyway.

The OPA627 is a splendid opamp, but one that would be wasted here. Whether it would function as intended isn't guaranteed 100% guaranteed either.
 
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Many of the resistors are in the signal path, but very few would benefit from being changed (if at all).

R1, R2 and R24 would be the classic 'ones to replace' and you could argue R5 and R24.

However in my personal opinion there is no point doing this for this amplifier.
 
Quad 909 numerous IC's

Hello everyone.

Some people say for the 909 amp, TLC271 is good and don't touch it.

But what about the other numerous IC's?

Is there any benefit to change LM393M, LM317LZ, LM337LZ and OP275GP? for better types?

All these reside in the 909 too.
 
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The Quad 909 is a 606, power stage wise.
What do you think will improve on one of the best designs ever?
LM393 is a comparator. No signal is sent through the standby control, no improvement can be achieved.
LM317/337 are regulators. Replacement is not an advantage.
They don't get much better in this design than the OP275. Leave as is.
The TLC271 is what it is and the negative feedback relies on its characteristics, replacing it will upset the stability of the amplifier. Leave alone!
 
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Some owners of commercial products want to be DIYs too. Even if their gear ain't broke, it probably will be suspected of being so from reading repair threads here.

However, I agree with leaving a 909 alone - at least until it was 20+ years old and due for a service or in the unlikely event of a failure.

What I would encourage though, is building a 405 or 606 clone kit for yourself and learning how it works without screwing up an existing good product, even with the greatest of care, intentions and trustworthy advice. The good thing about this is you have the mistakes already made here so you can avoid them and get a good result that might not have happened otherwise.
 
Trust me i don't want to service my Quad, but the reality is some of the original components are sub-standard, and it can be made to sound much better with a few relatively simple changes. The 909 is a good amp for the money, but it just doesn't do very well in the frequency extremes. I can live without extra base, but if the treble quality isn't there it quite simply detracts a lot from the music.

High end manufacturers Cyrus Audio and also Naim have stated in the past that the sound of a product, to a significant extent, is due to various capacitors "sonic signatures". I always found the 909 to be a bit flat, so if i can achieve a noticeable improvement in the sound with relatively small effort, why wouldn't i want to try? Sure the current dumping topology is genius, but at the end of the day, the final sound of a product is due to various components, and Quad chose some components that weren't the best quality. I have read about people changing out certain capacitors and having great results with more extended highs and improved bandwidth ect, sounds good to me!

Despite people saying TLC271 only serves as a DC servo, there have been numerous people who achieved superior sonics with different opamps in the 909, but the problem was it did create switch on and off thump sounds (OPA134 OPA237 ect). I would like to try out OPA627, because i have a hunch it may function without any issues and also provide a better sound. When i do i'll post my findings here to share (good or bad). To finish off on a note from one of the other members here;

“TLC271 adds a signature to the output, not because of intrinsic weaknesses but because it is supplied by the crudest power supply imaginable. Series dropper resistors R3, R4 (3K3) supply 6V8 Zener diodes D1 & D2 respectively from the main voltage rails. There are no decoupling capacitors around the Zeners and adding a 22uF across each diode improves the sound by an order of magnitude. Decoupling D3 & D4 similarly but with 2u2F tants (larger values create switch on thumps), will pay dividends. Replacing the 100n input cap C2 by a 470n SMR also reaps rewards”.