I Repaired My Bass Amp and Now I Feel Like a Wizard

It All Started With a Broken Bass Amp

I think it’s safe to say that I’m fairly handy with a soldering iron. No, I’m not designing circuits from scratch and turning the world of audio hardware on it’s ear, but I can follow instructions, put parts on a board, and troubleshoot things when it doesn’t work right. I’m not only competent at it, I actually enjoy it.

Repairing things is a different matter. I’ve never replaced a burnt out or malfunctioning part on a device’s circuit board. Strangely, I’d never made the connection between building a device and repairing one. It’s really the same thing, but potentially easier as you may only need to replace one part to get the device working again.

I was forced to consider this connection on a trip to the thrift store. I was scoping the electronics section, as I always do, and found an Acoustic B20 bass amp. I was priced at $19.99, but marked “as-is” which we all know is a euphemism for “broken”. The screws had been taken out of the head, so I pulled the head out and inspected it. The fuse was obviously blown, but the rest of the board looked OK. It was a long shot, but maybe the fuse just needed to be replaced. A quick Google and a few clicks later informed me that Acoustic released a batch of these amps with faulty capacitors. Replacing the capacitors would fix it. A Craigslist ad showed that these amps go for $90-$100 so $19.99 was a steal. I decided to roll the dice and get it.

Down to Business

The first thing I needed to do was locate parts. Since I usually build from kits, I don’t have a lot of extra parts lying around to to use in a repair. So I had to find a parts store. Well guess what? It’s 2014 and not many people do through-hole electronics anymore. Austin is a pretty creative place, but the neighborhood parts store is gone and Fry’s electronics is the only game in town. My other option is to order from the internet, which can be cheap, but shipping cost and ordering in such a small quantity would make the price difference about the same. So I went to Fry’s and bought a box of 315mA 250v slo-blow fuses and a 2200uF @ 25v capacitor. Actually, I got a 2200uF capacitor, but at 35v (which I’ve been assured is fine). They didn’t have the 25v one.

Back at the workbench, armed with my new parts, I pulled the head from the amp and got to work. The first thing I did, and I recommend this to anyone doing any sort of repair work or trouble shooting, was take a picture of the current state. This is so if I hit any snags I can reverse my work. I installed a new fuse and powered it up. The light came on! And then the light went out and the fuse blew. Looking closer at the two capacitors on the board, I noticed they looked a little bulged and oozing (not a healthy part). The next step was to take the board out of the head and remove those busted caps.

As usual, there are millions of little screws, nuts, and washers. I put them all in a little cup and after a little fumbling, I was able to flip the board over and desolder the caps. Amazingly, the solder was really tough to melt. When it was melted, I removed the caps and installed the new ones. They were a bit bigger than the old ones, but bit of a bending and they were soldered in.

I installed another fuse and powered it on. The light came on and stayed on. Encouraging! So I plugged in a bass and nothing happened. I was less encouraged. Before I freaked out, I plugged in a pair of headphones to see what would happen. I could hear the bass in the headphones! So maybe I had a blown speaker.

I took off the grill (which is nicely held in place with strong velcro) and examined the speaker. It looked pristine. At least it wasn’t blown. I decided to check the connection on the back. The wire was completely disconnected. Aha! So I plugged it in, powered it up, and my bass was booming (probably to the annoyance of my neighbor).

My total outlay? $30, but I’m going to count $10 of that as repair education tuition. I learned that disassembly and reassembly are the hardest part of repairs. I learned that it pays to have cheaply acquired common parts on hand. I learned that I can do this. I learned that it’s not magic, but I do feel like a wizard.


Comments

I Repaired My Bass Amp and Now I Feel Like a Wizard — 7 Comments

  1. Thanks for the post! It has been awhile since I played around with my B20 amp. I was greeted with an amp that didn’t work. After reading your post, I noticed a blown fuse and a bad capacitor (it had split at the bottom). Instead of buying a new amp, I decided to purchase all the necessary parts at Fry’s. Your advice and hint’s were greatly appreciated as I completed the install. My only hiccup was installing one of the capacitors backwards (+/-). Once I saw what I did, it was an easy correction of rotating it around. All said and done, a few hours of labor and $15 in parts. I agree with you, taking everything apart and putting everything back together is the hardest part of the job. It feels good to have it working again especially since my electrical knowledge limited at best.

  2. Thanks for your post! I too have a B20 that went bad on me the other day after tipping over in the car on the way to practice. Turned it on, power light worked but no sound. I hoped it was something simple like a loose speaker wire but I had no idea how to get inside the cab until I read your post. Got the grill off, pulled the speaker and VOILA: a disconnected speaker lead! I slipped it back on and was surprised at how loose it fit so I tightened it and the other lead, which was also loose, by crimping slightly with pliers. Put it all back together and I’m good as new. Thanks again!

  3. Hey Gents, I have an acoustic b20 and I’m having similar problems. I took it apart and it looks like the capacitors are fine. I replaced the fuse and the blue light went on and then the fuse blew. I have no idea what might be wrong. Any ideas?

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