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Old 18th March 2012, 02:12 PM   #1
kumori is offline kumori  Europe
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Angry DC on Lightspeed-attenuator possible

Hallo,
I have two questions about DC on volume pots.
1) I read a few times that DC potential on a line level volume pot is a bad thing and should be avoided. Why is it a bad thing and what happens when you apply DC on your line level pot?
2) Does this limitation also apply to the lightspeed attenuator? I thought that it might be different here since there is no whiper on a lightspeed. But this is just a guess (hope)

I'm asking, becuase I have a Naim-style preamp, which is basically a buffer followed by a volume pot, followed by the gain stage. Since the buffer already has an output cap, I would like to omit the input cap of the gain stage. My problem is that my power supply is not perfectly symmetrical, resulting in an DC offset of about 0,1 Volts at the gain stage input. Without the input cap this potential would be applied to the pot. I guess that this is not acceptable, using a regular pot. Would the lightspeed attenuator be an alternative? Or are there other possibilities?

Thanks for any help
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Old 19th March 2012, 12:16 AM   #2
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Quote:
Originally Posted by kumori View Post
I would like to omit the input cap of the gain stage. My problem is that my power supply is not perfectly symmetrical, resulting in an DC offset of about 0,1 Volts at the gain stage input. Without the input cap this potential would be applied to the pot. I guess that this is not acceptable, using a regular pot. Would the lightspeed attenuator be an alternative? Or are there other possibilities?

Thanks for any help

The Lightspeed will handle 100mV dc offset, but the poweramp after the Lightspeed may not, if it is dc coupled as well with dc servo's, 100mV may be out of range of the servo's to try to correct, the Lightspeed is dc coupled and will pass everything to the poweramp from the source, be it music or dc offset.
I say up to 20mV of dc offset from the source is ok, but 100mV is way too much source offset, put the blocking cap back in. Also if you poweramp is dc coupled it will make a nice hefty thump through the speakers, at these offset levels, especially if the Lightspeed volume is left up.

Cheers George
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DC on Lightspeed-attenuator possible kumori Analog Line Level 35 20th March 2012 07:31 PM
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