hey guys,
i've just finished a paralleled LM3886 based power amp and i'm having a weird problem.
The two LM3886 amplifiers are on separate boards and have their inputs connected by a wire between the two boards.
One board has the zobel network and damped series inductor, the output of the other board again is connected to this one by a wire.
When i turn it on, even if the volume pot is set to 0, a weird low pitched noise, which isn't particularly loud, comes out of the speaker and the mains fuse blows after a second or two.
If I disconnect the wire connecting the outputs of the two boards however, both of them work fine. this problem only occurrs when the outputs are actually connected.
I've read that if the two circuits outputs aren't well matched, they might try to 'drive each other'? i have used 1% resistors in all places that have an effect on the output signal.
I've attatched the schems of both boards. Where it says 'to board 1' etc are the points at which the two boards are connected.

Anyone have any idea what the problem might be/ how i can fix it?

edit: forgot to mention, the series inductor is 12 turns of enamelled copper wire around the 10 Ohm resistor on the output of the first board. and the reason I have used 5 parallel resistors at the output of each is that the LM3886 documentation recommends .1 Ohm resistors but I couldn't get 1% accuracy .1 Ohm resistors with high enough power rating, so I used 5 x 1 Ohm resistors to get close. 

Hey guys, this is my first post although I've been a member of the forum for a while.
I've recently decided to design and build a discrete SS amp. So far I've built the power supply circuit and designed the power amp stage but have not yet fully tested it; it looks ok in simulation though. Initially, I intended only to build a small (~5W) practice amp, but once I started, I realized how easily I could scale the design up to be much more powerful.   
The design seems able to put out about 140W RMS into a 4 Ohm load, limited to about 100W by the rating of the power transformer I'm using.

The problem is, at the moment, I have no cab/speakers able to handle that much power. All I have available for testing is a junked 20W hi-fi speaker.
Also, I haven't fully decided on the plan for the preamp. I think I'm going to go OpAmp based with a pretty stock standard Fender or Marshall tonestack, but I want to build in a reasonable distortion circuit and possibly an octave effect as well. I'd also like to be able to switch preamps/effects without having to pull apart the whole box once I've built it. What I'm thinking of doing to get around this is initially built the poweramp in one box with a master pot to limit the output to something that won't destroy whichever speakers I happen to plug it into, and build the preamp in a separate box which I'll just plug into the poweramp, so if i want a new sound I can build another and plug that in instead.

All of this leads me to ask a few questions:

With regards to giving the poweramp a variable power output to enable me to switch speakers as i go without blowing up the smaller ones, I'm thinking of putting a pot in the feedback loop to enable me to vary the gain. Does that sound good, or would it be better to set the gain in the feedback loop to a reasonable value with fixed resistors and maybe just put an attenuator pot on the input of the poweramp?

Does anyone know a good place to get guitar/instrument speakers in Australia? I don't want to buy a cab, I want to get the drivers and build the box myself. I don't necessarily need the highest quality, at this stage I'm just looking for pretty much any guitar amp speaker that will handle about 50W.

Does anyone have any suggestions as to a decent distortion/overdrive circuit for blues rock? (I play a lot of White Stripes and Black keys type stuff)

I'm planning on running my preamp circuitry off +/- 9V or 12V for the OpAmps (so far I've been using TL072's); is it better to get this supply voltage from a separate power transformer and rectifier circuit or will voltage dividers (possibly with regulators) from the main power rails suffice? I do happen to have a small centre tapped +/-12v transformer.

Does the whole plan sound reasonable?

Anyway, sorry about the epic post, thanks for reading and any comments, suggestions or random thoughts anyone has are totally welcome!