Final LM3886 GC Schem

meta · 21st July 2004, 07:36 PM

Hi...

I really wanna get this built, but as its my 1st amp project and I'm laying out and makin my own pcb I gotta make sure the fikker will work...

Here's the latest schem (for 1 chan) based on the datasheet circuit and info given for the 'DESIGN A 40W/4X AUDIO AMPLIFIER' bit...

Are the values of components ok? Is where I've put either S or P gnd ok?

I'll be using a stepped att instead of a pot...

Thanks > again.

carlmart · 21st July 2004, 08:56 PM

Why are you using an INA134 balanced chip? Are you going to feed a balanced signal?

If not you should do better with an OPA627 or similar, used as a buffer or line amp. The main purpose and design of a differential chip is to keep CMMR high, so other specs are not as good as non-differential chips.

Then you can put your pot, stepped or not, before that chip. Putting a pot before a differential chip may invalidate its advantages. Putting it after that stage would be foolish. So, again, why do you need a differential stage?

Carlos

meta · 21st July 2004, 09:19 PM

because Im feedin a balanced input

Upupa Epops · 21st July 2004, 09:34 PM

You must get to + input resistor to the ground ( 100 kOhm ) and AC separed pot by cap 1 micro. If you don't do it, pot will be rattle and output offset will be slide depend on turning of pot.

meta · 30th July 2004, 01:45 PM

Well, got one of these GC's built then

I ended up using this the pcb from this site: http://www.dpaton.net/audio/3886amp/3886.shtml with a few alterations. The rest (balanced rcv/psu) was done with stripboard and p2p - this was my 1st amp afterall so I thought I may as well bodge it...

The housing I used is from a old 40s radio I found under the stairs - a sand n varnish and came out quite nice. the vol att is 22k 12Pos...

Sounds fantastic I gotta say.

platenspeler · 1st August 2004, 10:00 AM

It looks good in any case, I like these wooden cases. Unfortunately I'm not that good in woodwork.

The attenuator switches incl. mod look quite familiar

Looking at the photo it seems you use the same switches as I do, but you seem to have found switches with more than 2 decks if I see right?

regards,

Maarten

21st July 2004, 07:36 PM	#1
meta diyAudio Member Join Date: Nov 2002 Location: London	Final LM3886 GC Schem Hi... I really wanna get this built, but as its my 1st amp project and I'm laying out and makin my own pcb I gotta make sure the fikker will work... Here's the latest schem (for 1 chan) based on the datasheet circuit and info given for the 'DESIGN A 40W/4X AUDIO AMPLIFIER' bit... Are the values of components ok? Is where I've put either S or P gnd ok? I'll be using a stepped att instead of a pot... Thanks > again.

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21st July 2004, 08:56 PM	#2
carlmart diyAudio Member Join Date: Mar 2001 Location: Brazil	Why are you using an INA134 balanced chip? Are you going to feed a balanced signal? If not you should do better with an OPA627 or similar, used as a buffer or line amp. The main purpose and design of a differential chip is to keep CMMR high, so other specs are not as good as non-differential chips. Then you can put your pot, stepped or not, before that chip. Putting a pot before a differential chip may invalidate its advantages. Putting it after that stage would be foolish. So, again, why do you need a differential stage? Carlos

21st July 2004, 09:19 PM	#3
meta diyAudio Member Join Date: Nov 2002 Location: London	because Im feedin a balanced input

21st July 2004, 09:34 PM	#4
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	You must get to + input resistor to the ground ( 100 kOhm ) and AC separed pot by cap 1 micro. If you don't do it, pot will be rattle and output offset will be slide depend on turning of pot.

30th July 2004, 01:45 PM	#5
meta diyAudio Member Join Date: Nov 2002 Location: London	Well, got one of these GC's built then I ended up using this the pcb from this site: http://www.dpaton.net/audio/3886amp/3886.shtml with a few alterations. The rest (balanced rcv/psu) was done with stripboard and p2p - this was my 1st amp afterall so I thought I may as well bodge it... The housing I used is from a old 40s radio I found under the stairs - a sand n varnish and came out quite nice. the vol att is 22k 12Pos... Sounds fantastic I gotta say.

1st August 2004, 10:00 AM	#6
platenspeler diyAudio Member Join Date: Jan 2003 Location: Netherlands	It looks good in any case, I like these wooden cases. Unfortunately I'm not that good in woodwork. The attenuator switches incl. mod look quite familiar Looking at the photo it seems you use the same switches as I do, but you seem to have found switches with more than 2 decks if I see right? regards, Maarten

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