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Combo Amp Build

I'm building a Combo Amp for someone.

The cabinet is Pine 13" wide x 15" tall and 11" deep. All glued together and used a 1/2" roundover bit in my router for the edges.

The speaker is a vintage 10" Utah 15W 8ohm. The amp is my dual Im386 chip bridged amp design. Can run on 9volt battery or walwart and output is 1 to 2 watts.

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Replies to This Discussion

Permalink Reply by Paul Craig on May 1, 2016 at 8:13pm

Thanks, I hope it works out too. Should be better than the N1.

Permalink Reply by Scott aka Farmer Ted on May 1, 2016 at 2:28pm

Nutz, yes. Price? I recently finished building a tube amplifier. Every capacitor, resistor, etc. was installed correctly. All solder joints were great. Continuity was fluid. All grounds were centrally located to one point (no ground loops). Both transformers were high quality brand new units.

Fired it up...nothing but a humming noise.

Took it to my local electronics repair shop...discovered the brand new input jacks had shorted when tightening them.

Cost...$50

Nutz? Oh yeah, nutz.

Permalink Reply by Ron "Oily" Sprague on May 1, 2016 at 3:32pm

I think this is why the original electronic amplifiers were built with very simple circuits. Anything more than two wires and a knob, and bad things can happen. I have learned a lot from this discussion.

Permalink Reply by Paul Craig on May 1, 2016 at 8:14pm

Glad we could be of help Oily. Haha

Permalink Reply by Ron "Oily" Sprague on May 1, 2016 at 9:05pm

No, really. I'm already nuts. I just learned several new ways to avoid increasing the squirreliness in my life:

1) Don't rebuild / repaint anything yourself
2) Don't mess with anything more complicated than a single throw switch
3) Let others make the mistakes.
4) Resist the urge to say "Oh, that's EASY!"
5) Avoid boastfulness; your ass WILL be bitten.
6) Go get a beer, scratch yer head and other body parts, and philosophically contemplate the follies of modern man. This may take two or more beers.

Permalink Reply by Paul Craig on May 1, 2016 at 8:25pm

Had the same thing happen on my motorcycle.

Took the old paint down to bare metal, made sure there wasn't any rust and put a good coat of primer on it. Painted a coat of bright Copper/Gold, waited for it to dry a couple days, then painted a Candy Red Metalflake(Large flake like 70's paint), let that dry a couple days and then put 3 coats of clear on that. The whole process took 2 weeks because I had to wait for good weather for spraying.

Looked great. Went for a ride came back and parked it in the drive out in the sun. Went back out to put it up and had cracks and bubbles in the paint. I wasn't in a good mood.

Permalink Reply by Paul Craig on May 15, 2016 at 5:38pm

Got my chips Saturday from Jameco. Will try to get back to this tomorrow.

Permalink Reply by Paul Craig on May 17, 2016 at 9:25am

Got it working.

Ended up using 10uf caps in the output wires to the speaker.

All I have left to do is cover the speaker baffle, affix it to the cabinet and wire the speaker. Then it's done.

Permalink Reply by Paul Craig on May 18, 2016 at 5:28am

It was all in the chips. I just replaced those crappy N1's with the N3's and bingo.

I opened up my original amp that I made, replaced the chips and added the caps to the output line and it works fine now.

Permalink Reply by Paul Craig on May 18, 2016 at 11:29am

Correct. The first chips were IM386N1's, now we have IM386N3's.

Permalink Reply by Paul Craig on May 18, 2016 at 11:32am