BPA-200 w/ six chips working w/ pics!

[Mattyo5]

Well, my bpa-200 is working. I haven't done extensive listening yet, but there is power in this amp! I used 6 of the lm3886 chips and 2 of the buyout pe tranny's per monoblock amplifier...i only have one monoblock up and running so far. I used my lm3875 amp on the R channel and this one on the L channel just for giggles, and the bpa is quite a bit more sensitive.... maybe 6db + more gain. Anyway, here are the pics. I'm still getting a bit of ground hum. Not much, but a bit. I get it when I turn the amp on (switch switches AC to tranny's)... i get hum, and when i turn the amp off (even though music still plays for a bit), the hum goes away immediately. The only things that aren't tacked down are the input gnd and input wires which are still in clip leads. I'll eventually solder everything better and make it more pretty. Comments suggestions? I also get a turn-off snap...which is not nearly as apparent if I flip the switch slowly. Hmm. Enjoy the pics

-Matthew K. Olson

[Mattyo5]

another

[Mattyo5]

last one, email me for bigger pics

-Matthew K. Olson

[MWP]

Hum is a killer.
Ive battled with many of my DIY amps to remove it.
You sure the unshielded audio source wires are not causing it?

[Mattyo5]

they could be causing it...who knows. Its one wire...rather than 2.. if I move the wires the hum doesn't change. It almost seems that the hum of 6 chips is the combo of whatever hum is in a single chip amp hehe. I'll keep playing w/ it and see whats up. Thanks for lookin though

i haven't seen many of these amps here on the forum, i figured I'd build one and see if it could really be done

-Matthew K. Olson

[Faber]

Have you tried to put your trafos away from the amp case?
shure that GND is exempt from any kind of loops?

I had some hum problems with some undesired connections of the AC power to the amp case (and so the GND). Some chips where not perfectly isolated from the case and this was causing hum.

Actually I prefer to use the lm3886 with plastic case, and I have the a quieter amp.
HTH

[carlosfm]

Looking at the pics, it seams that those two trafos are single voltage, that's fine.
But I only see one rectifier board.
What diodes are you using on the PSU?
Because the MUR860s are not enough to feed 6 chips.

Now the hummmmm...
You have 3 chips in each side of the amp.
That's not the way to do it, you have a big ground wire that travels from side to side.
Actually, you should have the 6 chips toguether, and the layout should be as tight as possible.
Otherwise... hummmmmmmm...

[Mattyo5]

No i'm not sure the gnd is exempt from loops. The amp case is grounded to earth, but the power gnd is not attached to the case...the hum gets much much worse if I do that. I could try moving the tranny's away, but that defeats the purpose of the amp...i was going for something small...just for the heck of it. I am using the lm3886's w/ plastic case.

thanks for the suggestions though

-Matthew K. Olson

ps, i think the switch is causing the popps... its only a 6A rated switch... i'm using a 3A inrush current limiter though... who knows

[Mattyo5]

Yes, i'm only using the mur860's. hehe fire just seemed like a more elegant solution than a big fat bridge ... oh well.

As for the 6 chips being together, yes, I aggree...but the heatsinks I had didn't exactly uh, warrant that. But its a good point. The schematic and pcb I designed for this (which is still on the drawing board) had all 6 in a row. Anyway, guess I'll get em next time!

-Matthew K. Olson

[MWP]

BTW... what voltage are you running them at?
Because those heatsinks look far too small and are orientated the wrong way to remove any decent level of heat.