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Replacement Parts for Quad 909
Replacement Parts for Quad 909
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Old 7th February 2017, 08:24 AM   #11
Mooly is offline Mooly  United Kingdom
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Replacement Parts for Quad 909
The main reason is because I'm not a believer in boutique passive parts. The amps overall sonic character is determined mainly by its topology and its implementation.
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Old 7th February 2017, 10:56 AM   #12
DF96 is offline DF96  England
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In a typical SS amp almost all the resistors are 'in the signal path'. Almost any commercial non-faulty resistor type will do the job.

Resistor/capacitor swappers are basically cable swappers who have now learnt how to solder. In order to gain credibility they have to recruit others to their cause, which they seem to do quite successfully.
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Old 9th February 2017, 09:40 AM   #13
Sonic77 is offline Sonic77
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Default 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.

Last edited by jazbo8; 10th February 2017 at 10:23 AM. Reason: typo
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Old 9th February 2017, 10:28 AM   #14
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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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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Old 9th February 2017, 07:26 PM   #15
Ian Finch is offline Ian Finch  Australia
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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.
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Old 9th February 2017, 07:36 PM   #16
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Well put Ian.
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Old 9th February 2017, 07:49 PM   #17
uglykid is offline uglykid  Denmark
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hi.

i have build the 606/909 clone and my advice is the same dont touch it, its a very nice sounding amp. just my 2 cent.
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Old 10th February 2017, 10:20 AM   #18
Sonic77 is offline Sonic77
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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”.
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Old 10th February 2017, 12:28 PM   #19
Old'n'Cranky is offline Old'n'Cranky  Australia
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Yes.
This is going to end well.................
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Old 10th February 2017, 12:31 PM   #20
basi is offline basi  Croatia
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Quote:
Originally Posted by Old'n'Cranky View Post
Yes.
This is going to end well.................
I Agree.
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Less is more!!!
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