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Old 3rd February 2006, 06:00 AM   #1
Arx is offline Arx  Canada
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Default Volume control for lm3875 amp

I bought one of the kits from Peter Daniels, and am curious what value of pot will work best as a volume control. I'll probably pick up a PEC Dual. It looks like I can get 1k, 5k or 10k in linear, and pretty much the full range in log.

Any advice?

-Nick
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Old 3rd February 2006, 07:36 AM   #2
lineup is offline lineup  Sweden
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Is it inverted gainclone or noninverted?

You have a link to schematic?
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Old 3rd February 2006, 08:13 AM   #3
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I think the normal value for a LM based chipamp it somewhere between 10k and 25k log, dual obviously. You would also probably find that the best option would be a stepped attenuator such as this very good value offering:-

http://www.diyfidelity.com.au/produc...products_id=32


Regards,

Phil
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Old 3rd February 2006, 04:46 PM   #4
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How does inverted change the use of the pot?
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Old 4th February 2006, 01:23 AM   #5
Arx is offline Arx  Canada
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It's non inverting.
thanks for the suggestion on the stepped attenuator, but I've got easier, faster, and cheaper access to good pots. I'll keep it in mind for future experimenting though, if I can find a reasonably priced one in Canada.

-Nick
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Old 4th February 2006, 01:29 AM   #6
Vikash is offline Vikash  United Kingdom
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10k is fine. Unless you intend to law fake it.
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Old 4th February 2006, 09:55 AM   #7
Arx is offline Arx  Canada
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Quote:
Originally posted by Vikash
10k is fine. Unless you intend to law fake it.

I'm assuming to law fake it I would need a higher resistance linear pot?
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Old 4th February 2006, 11:14 AM   #8
Nordic is offline Nordic  South Africa
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Yeah around 100k, above and below that you run into problems... for this application though a simple dual 10K log pot is the answer.... short of going for a stepped or digital attenuator.
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Old 4th February 2006, 11:36 AM   #9
Wynand is offline Wynand  South Africa
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I've previously used a 10K pot with a TDA2050 amp (pdf's layout) and it worked fine, When I tried it with a LM3876 IC (own layout)it would generate noise.

My question is can you use the volume pot alone with no other components, like a buffer?

I rekon that it was probably bad PCB layout that caused it to make a buzz when attenuating the input signal.

If I can use only the pot it would make my amp way easier.
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Old 4th February 2006, 01:54 PM   #10
Nordic is offline Nordic  South Africa
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Wynand, something tells me you didnt use a thinner wire to connect the ground from that pot.... Also was the LM3876 inverted or not, inverted its going to have issues without a buffer whatever you do, in terms of volume control.
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