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Old 6th April 2012, 10:20 AM   #1
Koenjer is offline Koenjer  Netherlands
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Default Volume Control Clicks

My Rotel RSP-1068 surround processor uses a Toshiba electronic volume control.

The volume control works fine but on louder volumes you can hear small click/pops when you change the volume.
I assume this has something to do with the topolgy of the volume control IC. (stepped ladder maybe?)

I allready added a 100n capacitor on the +/- 18V lines (directly soldered them on the pins of the IC)

The internal PSU of the rotel is based on the 7818/7918 and the offset is quite small (100mV).

Used volume control:
TOSHIBA, SYSTEM ELECTRONIC VOLUME CONTROL - TC9482F

Does anybody know if there is a way to minimize the clicks/pops?
Or is it something I have live with
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Old 6th April 2012, 04:35 PM   #2
fotios is offline fotios  Greece
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Quote:
Originally Posted by Koenjer View Post
My Rotel RSP-1068 surround processor uses a Toshiba electronic volume control.

The volume control works fine but on louder volumes you can hear small click/pops when you change the volume.
I assume this has something to do with the topolgy of the volume control IC. (stepped ladder maybe?)

I allready added a 100n capacitor on the +/- 18V lines (directly soldered them on the pins of the IC)

The internal PSU of the rotel is based on the 7818/7918 and the offset is quite small (100mV).

Used volume control:
TOSHIBA, SYSTEM ELECTRONIC VOLUME CONTROL - TC9482F

Does anybody know if there is a way to minimize the clicks/pops?
Or is it something I have live with
Hello Koenjer
I don't know exactly what happens with your preamplifier, but this offset of 100mV is not so small. Can I suppose that you have measured it on main outputs? For example, in power amplifiers the max permissible output dc offset was years ago less than 50mV and today is less than 20mV and many modern designs have just 0.3 to 1mV output dc offset.
Consequently in preamplifiers dc offset should be... unmeasurable.
I hope this will help you by some way. Check all ICs in the signal path for possible dc offset.
Happy Easter
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Old 6th April 2012, 05:37 PM   #3
Koenjer is offline Koenjer  Netherlands
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Quote:
Originally Posted by fotios View Post
Hello Koenjer
I don't know exactly what happens with your preamplifier, but this offset of 100mV is not so small. Can I suppose that you have measured it on main outputs? For example, in power amplifiers the max permissible output dc offset was years ago less than 50mV and today is less than 20mV and many modern designs have just 0.3 to 1mV output dc offset.
Consequently in preamplifiers dc offset should be... unmeasurable.
I hope this will help you by some way. Check all ICs in the signal path for possible dc offset.
Happy Easter
Wrong description from me.

What I meant is that there is a +/-100mv difference between the +18 and -18v.
It's actually +18.07 and -17.96.

There is also a capacitor on the audio input of the Volume IC to elliminate any DC.

Last edited by Koenjer; 6th April 2012 at 05:38 PM. Reason: add info
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Old 6th April 2012, 06:28 PM   #4
AndrewT is offline AndrewT  Scotland
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But is there a similar DC blocking cap on the output of the vol pot and/or selector?
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Old 6th April 2012, 06:39 PM   #5
Koenjer is offline Koenjer  Netherlands
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Quote:
Originally Posted by AndrewT View Post
But is there a similar DC blocking cap on the output of the vol pot and/or selector?
after the volume IC there is an buffer opamp and then a dc blocking cap to the output sockets.
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Old 6th April 2012, 06:58 PM   #6
Leon08 is offline Leon08  Germany
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This is probably a design flaw, although Rotel has good reputation, they can make errors too.In the datasheet of TC9482F is mentioned that noise from digital signals can mix with analog signals if digital lines are not properly shielded.
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