LM3886 DC servo PCB

mravlca · 15th December 2009, 08:34 PM

Hi!

Recently I bought LM3886 with DC servo from Arresting audio and I was so impressed by its sound that I decided to draw my own board single sided. It is made this way so that it can be home etched, but before I publish this project I have to make shure that there are no errors, so if you would be so kind enough and check out the board and tell me what could I do better and what should be repaired.

Regards Aleš

Redshift187 · 16th December 2009, 04:59 AM

Hi Aleš! Glad you liked.

Going over your design, looks good but I noticed a couple of things:

- R7 appears to be connecting the + input to the output. I think you want that connected between the - input and the output.

- you need a resistor between LM3886 pin 8 and C19 (part of the mute circuit).

- you should probably not use a trace for connecting input ground to the output ground, you should use a jumper and connect it back to between the power input and the capacitors C15 and C17. You don't want to combine the speaker return path to ground with the signal ground.

Out of curiosity, did you use a zobel or output inductor with the boards I designed?

mravlca · 16th December 2009, 02:42 PM

Hi!

I removed R7, it was feedback resistor to +in, the resistor on pin 8 to V- was already there(R5) and I did connect the input ground as you suggested.

On your boards I have used output inductor and zobel filter and the sound got a bit more relaxed on highs.

Regards Aleš

Redshift187 · 16th December 2009, 04:12 PM

There are two resistors in the mute circuits I've used. A 15k from pin 8 to the capacitor, then a 8.2k from the capacitor to V- (your R5). This is a delayed unmute to further avoid noises on power up. You can find details on the circuit in the LM4780 document on page 15.

Redshift187 · 16th December 2009, 04:15 PM

Upon further research, the extra resistor may not be necessary. I wonder why they have 2 different unmute delay circuits for the LM3886 and the LM4780.

mravlca · 18th December 2009, 02:14 PM

Here it is my prototype board just to check if everything is working properly.

Regards Aleš

mravlca · 28th December 2009, 01:21 PM

First prototype has been made and works great although I haven't use Zobel filter and ouput filter.

Regards Aleš

p.s. Project files will be published after new year.

Redshift187 · 28th December 2009, 02:05 PM

Very nice work!

mravlca · 28th December 2009, 05:15 PM

Quote:

Originally Posted by Redshift187

Very nice work!

Thank you! Well I see it very ugly, it was just made to see if it works.

Regards Aleš

Redshift187 · 29th December 2009, 02:03 AM

I don't think it's ugly at all. The copper traces are well done, as are the solder joints.

16th December 2009, 04:59 AM	#2
Redshift187 diyAudio Member Join Date: Aug 2008	Hi Aleš! Glad you liked. Going over your design, looks good but I noticed a couple of things: - R7 appears to be connecting the + input to the output. I think you want that connected between the - input and the output. - you need a resistor between LM3886 pin 8 and C19 (part of the mute circuit). - you should probably not use a trace for connecting input ground to the output ground, you should use a jumper and connect it back to between the power input and the capacitors C15 and C17. You don't want to combine the speaker return path to ground with the signal ground. Out of curiosity, did you use a zobel or output inductor with the boards I designed? __________________ Tyler

16th December 2009, 04:12 PM	#4
Redshift187 diyAudio Member Join Date: Aug 2008	There are two resistors in the mute circuits I've used. A 15k from pin 8 to the capacitor, then a 8.2k from the capacitor to V- (your R5). This is a delayed unmute to further avoid noises on power up. You can find details on the circuit in the LM4780 document on page 15. __________________ Tyler

16th December 2009, 04:15 PM	#5
Redshift187 diyAudio Member Join Date: Aug 2008	Upon further research, the extra resistor may not be necessary. I wonder why they have 2 different unmute delay circuits for the LM3886 and the LM4780. __________________ Tyler

28th December 2009, 02:05 PM	#8
Redshift187 diyAudio Member Join Date: Aug 2008	Very nice work! __________________ Tyler

29th December 2009, 02:03 AM	#10
Redshift187 diyAudio Member Join Date: Aug 2008	I don't think it's ugly at all. The copper traces are well done, as are the solder joints. __________________ Tyler


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