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Effed up Quad 909 (UK made)

Thomas,

Only looked at one channel, but I've found the reason for your Mains hum, the audio input screen cable was missconnected to the amplifier PCB (shown here in its corrected orientation) :-

https://dl.dropboxusercontent.com/u/86116171/909 Audio IP.JPG

Also, the Boot strap resistor is Open circuit (R16 in the picture, the large Grey resistor you can see the damaged "white patch" on its body), the resistor has been physically damaged.

https://dl.dropboxusercontent.com/u/86116171/909 Bootstrap Resistor.JPG

More to follow...
 
The good news is that it appears the unit is a UK built amp :) or atleast no sign of cheap Asian components (maybe the PCB).
 
Yup, it even has the names of the persons that built and tested it on a card. I am thinking about getting new PSU caps, they are 10 years old now.
 
Zombie said:
Yup, it even has the names of the persons that built and tested it on a card. I am thinking about getting new PSU caps, they are 10 years old now.
Click to expand...

Well, I have some DNM Silt foil caps that might fit, or if you can order the parts, I'll fit them for you while I have the unit open.
 
If they are as good as the BHC and the same capacitance, why not try them? I also wanted to replace the elcos on the Ampbus board if that is necessary...they have never been replaced. Please let me know the cost of the caps and other parts and I will compensate you.
 
AMPBUS board? did you still want it in place? (I've removed it, but no problem to reinstall).
 
I am confused as I have never heard the amp without it. If it really degrades the sound I would not use it, if it just sits there transparently, why not keep it...what do you think?
Oor put it back like it was when you received the amp and shut off the power to the ampbus board?
 
The AMPbus board adds a significant increase in signal path complexity which is not required if you use the RCA's. Personally the first thing I'd do is to get rid of the PCB.

The problem is that having the Ampbus board still connected to the rear of the RCA's is that it still loads the signal bath (even when non powered, in fact its worst as the load becomes highly non linear without power to the PCB / Opamps) - so its best to totally remove the PCB from the rear of RCA's lugs.
 
OK, please chuck it out, but leave it in the box in case I sell and must provide the ampbus card to the new owner...and may I be so bold to ask you to add a resistor to the power diode on the front and connect it to a suitable spot on the PSU board?
 
Dada eh???

In Australia people should be very very careful indeed. Overseas office weren't much better.

bit late sorry but YOU NOW HAVE BEEN WARNED
 
Thomas,

So channels working, typical Quad perfromance:-

https://dl.dropboxusercontent.com/u/86116171/QUAD909 1W 0.0068% -76.79dB Awtd.jpg

In the above FFT you can see the spread of the Mains hum components (typical of Quad amps).

1W 1KHz, 8 Ohms, THD 0.0068% (With spread of higher order crossover distortion).

SNR Awtd -76.79dB Ref 1W 8 Ohms (Input signal level 40mV).

I'd like to improve the performance if its OK with you? - what system do you use with the AMP as its input Gain is very high?
 
Great. I use the Elite preamp and have Quad ESL-988/JBL L100 speakers, please see what you can do to improve performance.
 
This is incredible to watch... JohnW what experience have you with the 99 preamp ? I have replaced all electrolytics with low esr types and also double screened the toroidal psu. Would appreciate your opinion.

Thks

Steve
 
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