My LM3886 Integrated Amp

panson_hk · 8th September 2007, 12:45 AM

Want to have an easy to build integrated amp for bed room, reading/working room ...; samples of LM3886 available, samples of various op-amp available. Okay, lets build a LM3886 integrated amp. Simple configuration: input source selector (all line level), buffer amp, vol control, LM3886+DC servo and output delay and DC protection.

Here we go the overall schematic.

panson_hk · 8th September 2007, 12:54 AM

And the bare PCB just received!

panson_hk · 9th September 2007, 12:16 PM

First round test passed. I simply assembled the amp section w/o DC servo (a large E cap temporary inserted in feedback) and fed it a 1 kHz signal. The output was an amplified 1 kHz signal.

However, I found layout errors: a missing resistor in DC servo and a short circuit. Luckily, easy to fix!

panson_hk · 9th September 2007, 12:25 PM

Next test with DC servo assembled. However, no FET input op-amp available, OP27G was used. The output DC offset is kept below 1 mV. The input 1 kHz sine/square signal was amplified nicely.

banana · 9th September 2007, 03:55 PM

Hi Panson,

Nice. Looks like you used a ground plane finally

panson_hk · 10th September 2007, 12:30 AM

Hi banana,

Thanks! It looks more pro with ground plane.

I mainly put ground plane to small signal section.

altor · 10th September 2007, 05:59 AM

Panson, try to exchange RPA_IN @ R1 and AGND @ R2.
The input impedance will be lower, but the sound - much better...

panson_hk · 10th September 2007, 06:12 AM

Quote:

Originally posted by altor
Panson, try to exchange RPA_IN @ R1 and AGND @ R2.
The input impedance will be lower, but the sound - much better...

Hi Alex,

Do you mean to make LM3886 an inverting amp? I have been reading posts saying this is the best. Is there any reason behind? Or just experimental result?

altor · 10th September 2007, 08:30 AM

Quote:

Originally posted by panson_hk

Hi Alex,

Do you mean to make LM3886 an inverting amp? I have been reading posts saying this is the best. Is there any reason behind? Or just experimental result?

Yes, I meas exactly inverted amp. Experimentaly - 3886 sounds better in INV.
The second thing - driving the mute pin with the curent source, it is better, but not mandatory.

panson_hk · 10th September 2007, 01:22 PM

Thanks Alex!

Polarity of D8 and D2 of DC offset detection circuit is reversed.

10th September 2007, 05:59 AM	#7
altor diyAudio Member Join Date: Oct 2003 Location: Europe-Asia	Panson, try to exchange RPA_IN @ R1 and AGND @ R2. The input impedance will be lower, but the sound - much better... __________________ Regards, Alex

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9th September 2007, 03:55 PM	#5
banana diyAudio Member Join Date: Feb 2003 Location: Hong Kong	Hi Panson, Nice. Looks like you used a ground plane finally

10th September 2007, 12:30 AM	#6
panson_hk :) diyAudio Member Join Date: Aug 2005 Blog Entries: 10	Hi banana, Thanks! It looks more pro with ground plane. I mainly put ground plane to small signal section.

10th September 2007, 01:22 PM	#10
panson_hk :) diyAudio Member Join Date: Aug 2005 Blog Entries: 10	Thanks Alex! Polarity of D8 and D2 of DC offset detection circuit is reversed.

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