Can mute pin on LM3886 (etc.) eliminate popping?

cm961 · 5th October 2004, 04:22 PM

Hi guys,

I have a 4 channel gainclone that I love, but when powering up and down the speakers, a lot of odd noises are heard. If I put a capacitor across the mute pin resistor, will this help?

What I'm looking for is an easy way to eliminate turn on/off thumps. I've investigated using relays, but it looks overly complicated and the datasheet says it has controlled turn on/off. So I'm probably doing something wrong. It would be nice to fix this problem with one capacitor. Do all other gainclones without relays thump on turn on?

Thanks,
Pete

P.S. In the LM3886 datasheet its listed as Cm. "Mute capacitance set up to create a large time constant for turn-on and turn-off muting". Sounds promising! Can anyone confirm this?

peranders · 5th October 2004, 05:26 PM

Using the mute function may do the trick. My LM3886 amp is totally silent, especially the "model 1" (of 6). The file below contains 6 different versions where only model 1 and 4 are tested. Model 4 isn't totally silent but pretty much.

http://www.sjostromaudio.com/hifi_fi...qrp01r0xls.zip

Peter Daniel · 5th October 2004, 05:34 PM

Quote:

Originally posted by cm961
Do all other gainclones without relays thump on turn on?

Properly wired GC will not produce thump at turn on.

cm961 · 6th October 2004, 01:09 AM

Seriously? Wo. Well I'm using a 4 channel gainclone I made, I believe 2 are LM3886 and 2 are LM3875. I'm pretty sure all 4 pop on turn on. Pretty bad pop too, makes me concerned about the tweeters. The star grounds it are terrible. Yeah I said grounds. It's not that I did not know how to wire properly, just that I've never had a soldering iron which could actually melt solder until now.

Thanks for the tips.

Pete

Peter Daniel · 6th October 2004, 01:24 AM

The popping may be caused by improper grounding, PS wires routing. I had it at one time too, but later it disappeared when I changed layout.

cm961 · 6th October 2004, 01:34 AM

Ok, well now that I have an extremely hot (but crappy) soldering iron, I'm going to rewire it. I believe I gave each amp a "local" star ground, and then ran those to the main star ground. I know, terrible, but my iron couldn't melt the joints.

So I'll rewire and also add capacitors across the muting resistor.

Thanks again.

Pete

xplod1236 · 6th October 2004, 02:38 AM

I never had success with the turn on delay. I have the mute pins of 4 LM3886s connected to one resistor and a 470 uf cap. The datasheet says to use a 100 uf cap for each chip, so 470 uf should take care of that. When I turn the amp on, I get sound immediately. Also, I don't get any turn on/off thumps.

What's the equation for figuring out the length of the delay?

cm961 · 8th October 2004, 01:06 PM

I tried I think 470uF as well and it didn't seem to help.

I have a question about the grounding though.

My amp channels are all point to point wiring with everything connected right to the pins of the amp. Then the grounds are connected to one wire (where the +ve and -ve caps connect together) and then a thick wire runs to ground.

Also the speaker outputs -ve are connected to the main ground as well. Perhaps they should be connected to the channel's ground?

Do all grounds need to go to the star ground? If so, what happens when you use a PCB?

All four channels exibit the turn on, turn off thump (its a DC offset that fades away. Positive on amp start-up, negative on amp shut-down).

Pete

5th October 2004, 04:22 PM	#1
cm961 diyAudio Member Join Date: Jun 2001 Location: Peterborough, Ontario	Can mute pin on LM3886 (etc.) eliminate popping? Hi guys, I have a 4 channel gainclone that I love, but when powering up and down the speakers, a lot of odd noises are heard. If I put a capacitor across the mute pin resistor, will this help? What I'm looking for is an easy way to eliminate turn on/off thumps. I've investigated using relays, but it looks overly complicated and the datasheet says it has controlled turn on/off. So I'm probably doing something wrong. It would be nice to fix this problem with one capacitor. Do all other gainclones without relays thump on turn on? Thanks, Pete P.S. In the LM3886 datasheet its listed as Cm. "Mute capacitance set up to create a large time constant for turn-on and turn-off muting". Sounds promising! Can anyone confirm this?

5th October 2004, 05:26 PM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Using the mute function may do the trick. My LM3886 amp is totally silent, especially the "model 1" (of 6). The file below contains 6 different versions where only model 1 and 4 are tested. Model 4 isn't totally silent but pretty much. http://www.sjostromaudio.com/hifi_fi...qrp01r0xls.zip __________________ /Per-Anders (my first name) or P-A as my friends call me

6th October 2004, 01:24 AM	#5
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	The popping may be caused by improper grounding, PS wires routing. I had it at one time too, but later it disappeared when I changed layout. __________________ 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

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6th October 2004, 01:09 AM	#4
cm961 diyAudio Member Join Date: Jun 2001 Location: Peterborough, Ontario	Seriously? Wo. Well I'm using a 4 channel gainclone I made, I believe 2 are LM3886 and 2 are LM3875. I'm pretty sure all 4 pop on turn on. Pretty bad pop too, makes me concerned about the tweeters. The star grounds it are terrible. Yeah I said grounds. It's not that I did not know how to wire properly, just that I've never had a soldering iron which could actually melt solder until now. Thanks for the tips. Pete

6th October 2004, 01:34 AM	#6
cm961 diyAudio Member Join Date: Jun 2001 Location: Peterborough, Ontario	Ok, well now that I have an extremely hot (but crappy) soldering iron, I'm going to rewire it. I believe I gave each amp a "local" star ground, and then ran those to the main star ground. I know, terrible, but my iron couldn't melt the joints. So I'll rewire and also add capacitors across the muting resistor. Thanks again. Pete

6th October 2004, 02:38 AM	#7
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	I never had success with the turn on delay. I have the mute pins of 4 LM3886s connected to one resistor and a 470 uf cap. The datasheet says to use a 100 uf cap for each chip, so 470 uf should take care of that. When I turn the amp on, I get sound immediately. Also, I don't get any turn on/off thumps. What's the equation for figuring out the length of the delay?

8th October 2004, 01:06 PM	#8
cm961 diyAudio Member Join Date: Jun 2001 Location: Peterborough, Ontario	I tried I think 470uF as well and it didn't seem to help. I have a question about the grounding though. My amp channels are all point to point wiring with everything connected right to the pins of the amp. Then the grounds are connected to one wire (where the +ve and -ve caps connect together) and then a thick wire runs to ground. Also the speaker outputs -ve are connected to the main ground as well. Perhaps they should be connected to the channel's ground? Do all grounds need to go to the star ground? If so, what happens when you use a PCB? All four channels exibit the turn on, turn off thump (its a DC offset that fades away. Positive on amp start-up, negative on amp shut-down). Pete

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