Quad 34 - Clicks and pops when playing

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22-Apr-2019 09:39 PM

zbyszek

zbyszek

Posts: 3

Hello,

I have recently bought a used Quad 34. 16XXX serial number with RCA sockets.

I upgraded it using the instructions from the DaDa manual.

I left all the original ICs intact and replaced all electrolytic capacitors (Elna Silmic II and Nichicon FG). I put wire links for C48, C54, C89, C90, C91, and C92.

I also switched the resistors in the output voltage divider to get 1.1V output (as per the instruction book).

Last, I put 4,7kOhm resistors in place of the CD flags, to attenuate CD input a bit more as I noticed that it sounds better when the output voltage is higher (less attenuated), which required me to attenuate CD input futher.

My 34 runs together with a 405-2, which I also revised with OPA604, new electrolytics, and decreased input sensitivity to 1,5V.

When listening to CDs I notice a peculiar behaviour. From time to time, every couple of minutes there are quiet ticks or spikes, sounding like those from a vinyl record. What is even more odd, they are not limited to one channel, but appear in various places of the stereo image.

I can't really tell if it also happens on the Dics input, because these ticks are impossible to differentiate from genuine vinyl ticks.

Everything looks okay when I hook up the 34 to a signal generator and an oscilloscope.

Have any of you come across similar behavior?


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08-May-2019 04:05 PM

Stefaan

Stefaan

Posts: 601


It looks like HF oscillation.

Did you install the 100nF capacitors to decouple the power supply of the opamps as described on page 7 of the Revision-manual?

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09-May-2019 03:22 AM

EJP

EJP

Posts: 1617

I had this recently on another device. It turned out to be bad PSU capacitors. Check the polarity, and check for bulges at the ends where the crosses are.
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12-May-2019 10:34 AM

zbyszek

zbyszek

Posts: 3

I did not decouple the opamps, because I left the original ones intact.

In the mean time, I decoupled the C77, C78, C30, and C31 elcos with 1uF Wima MKS2, and clicks and pops are gone now.

I don't know if the WIMAs fixed the problem, or if the components have "settled in", but the problem seems to be gone.

I will be replacing the opamps in the future with OPA604. Hopefully, this will improve the dynamics a bit, because right now I am under an impression that the 34 is a bit of a bottleneck in my system.

I used the 405-2 with an airport express plugged in directly (I don't have any other source with variable output), and the dynamic range was really impressive. The sound was effortless with huge headroom.

When I plugged the 34 in between, the magic is gone.


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12-May-2019 11:58 AM

EJP

EJP

Posts: 1617

You didn't 'decouple' those capacitors, you replaced them. Decoupling consists of shunting a circuit node to ground. The capacitors you mention are allcoupling capacitors.
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12-May-2019 12:27 PM

zbyszek

zbyszek

Posts: 3

What I meant is that I put 1uF Wima MKS2 in parallel with the 100uF elcos. Sorry for the misunderstanding.

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