eBay for the heatsink, and I would go with an old VCR or stereo amp and gut it for the case.  You can find a busted one on eBay, or you can dumpster dive...or ask a friend who has lots of electronic junk laying around.  I got my case from an old CB radio that didn't work, $1 at a yard sale.

Wow thats a lot of good info there. 

The most important thing (to me) is the power amp.  The power amp is what actually drives the speaker and makes sound.  Most of the amps we deal with here are "chip amps" meaning that the main part of the circuit is an IC.  For instance a LM3886, LM1875 or TDA2030.  The schematic shown on the datasheet is normally what we go by for our power amps.  If you want to look at some helpful information, check out the wiki at the top of the page here, click "contents" then click on a few of the chips (IE - LM3886 etc) and read.  After you get a decent basic idea and have more questions (or if you are so confused you don't get any of it) go ahead and ask us some more questions and we'll help from there.  Good luck, it's a fun and rewarding hobby.

Yup, you sure can, we help with repairs all the time.

As far as your problem goes, does it do it only when a guitar is plugged in?

I know normally when you do a dual mono you would do two transformers, one for each PSU board...but I have a 330VA transformer running my mono LM3886 and want to add another channel.  I have the stuff for a dual mono, or I could just build the amp board and use the existing PSU board.  Would it better to use the existing PSU board to run both LM3886 amp channels, or build another PSU board and split the power from the transformer to both boards?  This is going to be for a bass rig btw.

Unless there is a new one I don't know about, that is unregulated is well.  Brian's power supply board is perfect for LM3886 application as regulation is totally unnecessary.

Brian's kits are unregulated.  The output power will be roughly 1.4 x the amount you put in.  You could, in theory, tap the power to run a 9v regulator for effects.

If you go with either of the trannys I suggested, and run your amp at 8ohms (which gives you 50w RMS) it shouldn't be a problem.  There may be a tad bit of lag running at 4ohms (yielding 68watts), but I doubt it would be noticeable.

Quote from: mydementia on January 06, 2007, 09:12:36 PM
Right on - but what about the transformer?  Do I need to buy a $50 toroidal, or can I get away with the 'el cheapo' one from Partsexpress?
Mike

On paper to get full power you should have about 150VA per LM3886, but in practice it has been proven that as low as 90VA or so has worked.  VA is volt x amps (aka watts), the one you posted is about 50VA...too small.  Also, ideally you need a tranny that puts out about 22v+22v.  But you don't have to go torroidal, if you notice on the pic of my LM1875 amp, it uses a center tapped tranny.

This one should do the trick for $23: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=120-225

Or a torroidal for $41: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=122-615

I did a toroidal for my LM3886, but in retrospect, I really should have saved my money and went with a CT tranny.  The amp I used one with it sounded fine and works great.

Well, the plan is to have it like this:


                                       |-> left channel pot -> left channel amp circuit
Input ->  Master volume pot |
                                       |-> right channel pot -> right channel amp circuit

That should be fine right?

One was huge.  The big black one here could support 4x LM3886 chips or so, even running at 4ohms shouldn't be a problem:


The minimum for a LM3886 running at 8 ohms would be like the other heatsink I posted:


Check eBay, you can normally find some good sinks, thats where I got mine.

One of these would work:
http://cgi.ebay.com/2-Aluminum-4-5-x-4-5-x-5-Heatsinks_W0QQitemZ7604653489QQihZ017QQcategoryZ66946QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

But overkill is better than a heatsink that isn't big enough.  Ask RDV about that...

Alright, my brother is getting my LM3886 setup and adding another LM3886 to make it a dual mono, he wants both channels driven by one input.  Couldn't we just tie the two inputs together?  From what I gather, we can, since they are all on the same ground and whatnot.

Yeah, if you are interested in 12v DC, you are going to have a hard time finding a good sounding chip.  Some people have had luck with LM383 chips, but I did a kit with one and it sounded horrible running on 12 volts.  It could have been that it was a Veleman kit, I had never used one before, but I don't think so, I think it was the chip.  It had a VERY hard time staying clean, and it wasn't a good sounding distortion when it started to clip.

Is this going to be running on batteries or AC?  If AC, I would suggest using a LM1875 circuit, we have a guy on here that could set you up with the PCBs/components for cheap.  I have a LM1875 amp and it's very clean, very good sounding.  I haven't used it on an acoustic, but I used it for an electric guitar, and I've also used it to play music from my computer on.

I hadn't ever heard of class t amps, how many watts does the one you are doing put out?

Several places online including (but not at all limited to):

smallbearelec.com
mouser.com
partsexpress.com

And you can also normally find them at your local radio shack, thats where I get mine.