Noob ? BrianGT Lm 3875 with 10k pot?

bender460 · 5th November 2004, 07:54 PM

Sorry for the noob question but I have built the amps Lm 3875 basic kit witch work good with a 100k "radioshack pot". I have some 10k pots I would like to try but do not get much volume. What do I need to change? I did try to search for it but all the formulas concerning gain

I am lost. Any help would be great.

carlosfm · 6th November 2004, 12:34 AM

You don't get much volume with a 10k pot because you have a 22k resistor on the PCB, from NI input to ground.
Change that resistor for 100k.

You will have better results with a 10k pot than with a 100k pot IMHO.

bender460 · 6th November 2004, 02:25 AM

Thanks for the response

. The 22k is where I have the pot (R2) no resistor just the pot. R1 is a 220ohm. Do I need the pot wired in different?

mcs · 6th November 2004, 02:27 PM

How is it wired now?

You should have one end to the input, the other end to ground and the wiper to the chip input pin.

Best regards,

Mikkel C. Simonsen

bender460 · 7th November 2004, 04:58 PM

Mikkel , that is how I have it wired in. I still havn't figured it out.

Vikash · 7th November 2004, 05:08 PM

I'm using a 10k pot and I've left the 22k from NI to ground as is without any volume issues.

Link to pot wiring just in case.

carlosfm · 8th November 2004, 01:11 AM

I suspect there may be a mistake with the gain setting resistors on the chip.

bender460 · 8th November 2004, 07:36 PM

I'm using the pot as a preamp, with my cd player connected directly. If I leave the 22k to ground I get no control with the pot. VERY loud (like full volume), works fine with my preamp with the 22k but not with the pot alone. If one of you could post a diagram that would be great "pics are worth a thousand words

espacialy for newbies like me.

Thanks again guys.

Vikash · 8th November 2004, 08:23 PM

have you connected something in place of the removed 22k resistor?

carlosfm · 8th November 2004, 09:15 PM

There's definitely (or so it seams) a mistake with the way you wired the pot.
Can someone make a sketch, as I don't have the time now?
A new amp is calling me, it's sounding good.

5th November 2004, 07:54 PM	#1
bender460 diyAudio Member Join Date: Sep 2004 Location: MT	Noob ? BrianGT Lm 3875 with 10k pot? Sorry for the noob question but I have built the amps Lm 3875 basic kit witch work good with a 100k "radioshack pot". I have some 10k pots I would like to try but do not get much volume. What do I need to change? I did try to search for it but all the formulas concerning gain I am lost. Any help would be great.

6th November 2004, 02:27 PM	#4
mcs diyAudio Member Join Date: Aug 2003 Location: Denmark	How is it wired now? You should have one end to the input, the other end to ground and the wiper to the chip input pin. Best regards, Mikkel C. Simonsen __________________ My personal electronics website Remote control kits website

7th November 2004, 05:08 PM	#6
Vikash diyAudio Moderator Emeritus Join Date: May 2003 Location: UK	I'm using a 10k pot and I've left the 22k from NI to ground as is without any volume issues. Link to pot wiring just in case. __________________ "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.)

8th November 2004, 08:23 PM	#9
Vikash diyAudio Moderator Emeritus Join Date: May 2003 Location: UK	have you connected something in place of the removed 22k resistor? __________________ "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.)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

6th November 2004, 12:34 AM	#2
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	You don't get much volume with a 10k pot because you have a 22k resistor on the PCB, from NI input to ground. Change that resistor for 100k. You will have better results with a 10k pot than with a 100k pot IMHO.

6th November 2004, 02:25 AM	#3
bender460 diyAudio Member Join Date: Sep 2004 Location: MT	Thanks for the response . The 22k is where I have the pot (R2) no resistor just the pot. R1 is a 220ohm. Do I need the pot wired in different?

7th November 2004, 04:58 PM	#5
bender460 diyAudio Member Join Date: Sep 2004 Location: MT	Mikkel , that is how I have it wired in. I still havn't figured it out.

8th November 2004, 01:11 AM	#7
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	I suspect there may be a mistake with the gain setting resistors on the chip.

8th November 2004, 07:36 PM	#8
bender460 diyAudio Member Join Date: Sep 2004 Location: MT	I'm using the pot as a preamp, with my cd player connected directly. If I leave the 22k to ground I get no control with the pot. VERY loud (like full volume), works fine with my preamp with the 22k but not with the pot alone. If one of you could post a diagram that would be great "pics are worth a thousand words espacialy for newbies like me. Thanks again guys.

8th November 2004, 09:15 PM	#10
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	There's definitely (or so it seams) a mistake with the way you wired the pot. Can someone make a sketch, as I don't have the time now? A new amp is calling me, it's sounding good.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
NOOB! Thinking of building a 4 ch 3875 amp - questions..	quickshift	Chip Amps	7	7th August 2005 01:57 PM
One more finished BrianGT 3875	ejn327	Chip Amps	4	3rd March 2005 12:47 AM
LED for BrianGT 3875 Kit	dsavitsk	Chip Amps	4	27th February 2005 05:35 PM
BrianGT 3875 parts changes	dsavitsk	Chip Amps	3	25th February 2005 01:34 PM
BrianGT 3875 kit troubleshooting	ejn327	Chip Amps	18	18th February 2005 02:46 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read