Volume control for lm3875 amp

Arx · 3rd February 2006, 06:00 AM

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

lineup · 3rd February 2006, 07:36 AM

Is it inverted gainclone or noninverted?

You have a link to schematic?

filholder · 3rd February 2006, 08:13 AM

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

Destroyer OS. · 3rd February 2006, 04:46 PM

How does inverted change the use of the pot?

Arx · 4th February 2006, 01:23 AM

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

Vikash · 4th February 2006, 01:29 AM

10k is fine. Unless you intend to law fake it.

Arx · 4th February 2006, 09:55 AM

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?

Nordic · 4th February 2006, 11:14 AM

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.

Wynand · 4th February 2006, 11:36 AM

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.

Nordic · 4th February 2006, 01:54 PM

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.

3rd February 2006, 06:00 AM	#1
Arx diyAudio Member Join Date: Aug 2003 Location: North Vancouver, B.C.	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

3rd February 2006, 07:36 AM	#2
lineup diyAudio Member Join Date: Dec 2005 Location: the north	Is it inverted gainclone or noninverted? You have a link to schematic? __________________ lineup

4th February 2006, 01:29 AM	#6
Vikash diyAudio Moderator Emeritus Join Date: May 2003 Location: UK	10k is fine. Unless you intend to law fake it. __________________ "The human mind is so constituted that it colours with its own previous conceptions any new notion that presents itself for acceptance." - J. Wilhelm. (But I still think mine sounds better than yours.)

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3rd February 2006, 08:13 AM	#3
filholder diyAudio Member Join Date: Jan 2005 Location: london	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

3rd February 2006, 04:46 PM	#4
Destroyer OS. diyAudio Member Join Date: Nov 2005	How does inverted change the use of the pot?

4th February 2006, 01:23 AM	#5
Arx diyAudio Member Join Date: Aug 2003 Location: North Vancouver, B.C.	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

4th February 2006, 11:14 AM	#8
Nordic diyAudio Member Join Date: Sep 2005	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.

4th February 2006, 11:36 AM	#9
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	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.

4th February 2006, 01:54 PM	#10
Nordic diyAudio Member Join Date: Sep 2005	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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