Whats a GOOD LM3875 chip amp circuit?

matt_uk · 14th November 2003, 08:47 PM

Does anyone have any tried and tested circuits for this amp? I like the look of GregCC's 'Ultimate gain-clone' because of it's simplicity, maybe add some DC protection on the output.

In this type of amplifier application does the pot have to be wired the opposite way around to usual, so when the volume is down there is maximum resistance between the line in and chip in?

Also, is it really worth going for super components (as there aren't many), high audiograde pot, caps? How critical is the PSU design? How much VA rating for the transformer (230V AC)?

Looking at the 'Ultimate Gain-clone' design the max gain is 22 (i think!)? so with an input voltage of 1.5-2V, so should I be looking at around 40V supply voltage?

Matt

JOE DIRT® · 14th November 2003, 08:50 PM

Matt...this topic is explained very well on the forum...take a look

DIRT®

matt_uk · 14th November 2003, 08:57 PM

forgetting my +/- supply. Can a 2 x 40V transformer be wired into +/- 40V? I'm sure it can but don't know much about PSU design.

Does anyone have a PSU circuit? As I know nothing about bridge rectifiers or anything related to volatages greater than 3.3!

Matt

Peter Daniel · 14th November 2003, 09:11 PM

Some specific info can be found here http://www.diyaudio.com/forums/showt...921#post261921

Otherwise do search in a Chip Amps forum

GregGC · 14th November 2003, 09:12 PM

One of the many good places to start:
http://home.ca.inter.net/~cfraser/Gainclonehome.htm
http://www.euronet.nl/~mgw/diy/amps/uk_geenkloon_1.html

Check this on general Power supplies, but please pay attention to the 1000uF in the Gainclone case. It's important.
http://www.zero-distortion.com/techn...ly/powersi.htm

theChris · 14th November 2003, 10:23 PM

i guess this all depends on how much you want to put into it. i mean in the bare form the chip still works well. some people like the more expensive components and all, but when it comes down to it, they only matter if you can tell a difference. if your putting the speakers in an area with a high noise floor, well...

as for PSU design, remember that your transformer output will be about 50% higher then the ratings, as you are going to get a DC voltage close to the peaks and not close to the RMS value. this means that a +-24V transformer will be closer to +-35V on the output. there are discussions on power supply theory, and there seems to be some indication that a small resistance between the rectifier diodes and the filter caps is beneficail as it forms an RC network and enhances the lowpass filter effect.

14th November 2003, 08:47 PM	#1
matt_uk diyAudio Member Join Date: Nov 2003 Location: Northants	Whats a GOOD LM3875 chip amp circuit? Does anyone have any tried and tested circuits for this amp? I like the look of GregCC's 'Ultimate gain-clone' because of it's simplicity, maybe add some DC protection on the output. In this type of amplifier application does the pot have to be wired the opposite way around to usual, so when the volume is down there is maximum resistance between the line in and chip in? Also, is it really worth going for super components (as there aren't many), high audiograde pot, caps? How critical is the PSU design? How much VA rating for the transformer (230V AC)? Looking at the 'Ultimate Gain-clone' design the max gain is 22 (i think!)? so with an input voltage of 1.5-2V, so should I be looking at around 40V supply voltage? Matt

14th November 2003, 09:11 PM	#4
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Some specific info can be found here http://www.diyaudio.com/forums/showt...921#post261921 Otherwise do search in a Chip Amps forum __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

14th November 2003, 10:23 PM	#6
theChris diyAudio Member Join Date: Dec 2001 Location: SIUE, Illinois, USA	i guess this all depends on how much you want to put into it. i mean in the bare form the chip still works well. some people like the more expensive components and all, but when it comes down to it, they only matter if you can tell a difference. if your putting the speakers in an area with a high noise floor, well... as for PSU design, remember that your transformer output will be about 50% higher then the ratings, as you are going to get a DC voltage close to the peaks and not close to the RMS value. this means that a +-24V transformer will be closer to +-35V on the output. there are discussions on power supply theory, and there seems to be some indication that a small resistance between the rectifier diodes and the filter caps is beneficail as it forms an RC network and enhances the lowpass filter effect. __________________ if only it could be used for good, not evil...

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14th November 2003, 08:50 PM	#2
JOE DIRT® diyAudio Member Join Date: Apr 2003 Location: Brantford, ON	Matt...this topic is explained very well on the forum...take a look DIRT®

14th November 2003, 08:57 PM	#3
matt_uk diyAudio Member Join Date: Nov 2003 Location: Northants	forgetting my +/- supply. Can a 2 x 40V transformer be wired into +/- 40V? I'm sure it can but don't know much about PSU design. Does anyone have a PSU circuit? As I know nothing about bridge rectifiers or anything related to volatages greater than 3.3! Matt

14th November 2003, 09:12 PM	#5
GregGC diyAudio Member Join Date: Oct 2003 Location: Toronto	One of the many good places to start: http://home.ca.inter.net/~cfraser/Gainclonehome.htm http://www.euronet.nl/~mgw/diy/amps/uk_geenkloon_1.html Check this on general Power supplies, but please pay attention to the 1000uF in the Gainclone case. It's important. http://www.zero-distortion.com/techn...ly/powersi.htm

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