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Old 10th June 2003, 10:25 AM   #1
Zombie is offline Zombie  Sweden
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Default Quad 44 PSU - improvements?

Hello experts!
Sorry to bother you guys, but I would appreciate any help...I'd like to try to use OPA627, but suspect that the psu isn't good enough.
Or is it better as suggested in the opamp decoupling thread to use 100uF+0,1uF close to the psu pins of the opamp is better?

Anyway, what would be the simplest way to improve this regulator output noise-wise?
(Yes, I have followed the threads about psu regulation, but I don't want to rip this board out as it contains other functions, too)

Cheers
tom
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Old 10th June 2003, 12:10 PM   #2
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Tom

This isn't what you're looking for but honestly: sell the Quad and build something from scratch; it's got so many issues that upgrading opamps/psu won't cure it fully. Otoh, years of marketing and image building guarantee some resale value, especially unmodified.


cheers
peter
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Old 10th June 2003, 12:28 PM   #3
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Thanx Peter!
That's always an option, especially a valve preamp, or a passive...
Have you got smth cheap, good and easy to suggest?
Rgds
tom
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Old 10th June 2003, 12:36 PM   #4
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Hello Tom,

Have you meassured the actual ripple on the line outputs???
I have earlier had a 34 in for repair. The ripple on the line outputs was lower than the background noise-level of my scope....

QUAD has always made very good PSU's, and I even though that the opamps in the preamp is old, you would gain more by changing all the capacitors to new and better types, and remove the AC-coupling caps on in and outputs (I did that on my old 34, and the change was amazing)...

Good luck what ever you decide to do.
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Old 10th June 2003, 01:04 PM   #5
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Thank you Jan!
I have shorted out the output caps (100uF green drops, right?) - that made a significant improvement.
I have also put shottkys instead of the Graetz bridge, new elcos (1000uF and 47uF) in the PSU and bypassed them with 0,1uF polyprops.
"AC coupling caps", do you mean the 100nF and 680nF (0.1 and 0.68UF) caps on the in- and output of every audio module, including the 100nF after the balance control?
What caps would you recommend for the filter and tone control circuits, 1% polyester?

Peter: I am interested in how far I can bring this amp, too... ;-) on the expense of all the kind people coming with advice, of course

Cheers,
tom
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Old 10th June 2003, 02:10 PM   #6
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Quote:
Thank you Jan!
I have shorted out the output caps (100uF green drops, right?) - that made a significant improvement.
I have also put shottkys instead of the Graetz bridge, new elcos (1000uF and 47uF) in the PSU and bypassed them with 0,1uF polyprops.
"AC coupling caps", do you mean the 100nF and 680nF (0.1 and 0.68UF) caps on the in- and output of every audio module, including the 100nF after the balance control?
What caps would you recommend for the filter and tone control circuits, 1% polyester?
Ok! You have allready taken care of the PSU and outputs... And yes! This makes a significant improvement to almost all "older" preamps.

Yes! I mean the 100nF and 680nF that connects the different stages. ALWAYS MEASSURE for high DC-level before bypassing any caps. Not all amp are suited for this!!!!!

I can't renember if we bypassed the 100nF after the balance control. Meassure the DC from balance. If below 0.5 mA - remove the cap.

I didn't make any changes in the filter and tilt controls. As I recall, the caps there was of a really good quality. However, changing to
newer and "better" caps can improve the sound..... I like polyester and polystyrene caps. The choice depends on the value needed. Try it and let me know the results.....

Regarding the QUAD filter and tilt control, I have become so found of these special controls, that I have adopted them into my new preamp design, which I am designing at the moment.
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Old 10th June 2003, 02:27 PM   #7
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OK!
I am going to short out all those caps. Maybe there's a trade-off with shorting all "internal" DC blocking and putting good 100uF at the output (Black Gate or smth)?
Got below 1mV DC from the "Radio" card.
Have a nice evening!

Is there any link to your new preamp NON-COMMERCIAL of course ;-)?
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Old 11th June 2003, 06:27 AM   #8
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Hello again Tom,
Yes... Maybe there is a trade-off there

From the beginning of next week, you will find my new homepage
at: www.audio-circuit.dk .

I fully understand why you are making jokes on the "non-comercial" part, (you are not the first one).
ACD is only formed to ease the access to get informations from manufactures, and to be able to buy components and parts from
the major suppliers. This will be clearly stated on the website.

Enjoy your day, and let me know what happens
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Old 11th June 2003, 06:34 AM   #9
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Hej Jan!
Jag tänkte mer på en annan tråd där Per-Anders fick reprimand för att nämna sina produkter...
Mvh
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Old 11th June 2003, 07:33 AM   #10
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Ok..
Jeg mener ikke at der er nogen grund til at kritisere Per-Anders eller andre der nævner sine produkter.
Som diy'er er vi vel alle interesserede i at vores ideer bliver udbredt......
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