Amp fixin.

My bass amp needs some love. It’s been a few years since anything good was done to it, the pots are scratchy and the inputs don’t always work, so it’s time to blow it open and do some much-needed surgery.

My bass amp
20 Watts of power!

About 15 years ago I found a “Fender Sidekick Bass” amp in a pawn shop and picked it up. It’s a crappy little solid state amp from the late ’80s, made in Taiwan.  It has a large sound for its size, and has taken a lot of abuse over the years without quitting.  Until recently, I haven’t had a bass that was worth anything, so I’ve never replaced my amp; I have become quite attached to it.  I’ve been going to an acoustic jam once a month since September, and my acoustic bass just doesn’t have enough volume to cut over all the guitars, so it was suggested that I bring an amp.

Now when playing along with electric guitars, I’d just crank the amp up to ten and leave it. However, setting the levels right with a bunch of acoustic guitars is a bit different, and it turns out all the pots on my amp have gotten a bit scratchy over the years, making it nearly impossible for me to set a level that would work between 2 and 3 on the dial. I got to endure a lot of “turn it up, we can’t hear you” and “I can’t hear the singer, turn it down”. Not a good impression to make on a bunch of people I’m just getting to know.

Working on a late ’80s solid state amplifier is like working on a late ’80s minivan. No matter what you do to it, it will never be “good”, and will never be classic. The best my amp will ever be is a late ’80s low power solid state amp.  But my free time is “free time”, and the cheapest comparable bass amp at Long & McQuade is probably the Rumble 15 or 30, for between $100 and $200, so even if it will never sound “good”, fixing it is better than spending $150 on an amp that will also sound like crap.

Cabinet back removed, showing the back of the speaker
Not much going on inside

When I opened it up, I remembered that I had “fixed” this amp before. Quite the ball of tape hanging from the input wires.

Amp removed, input side
I don't think those wires passed the QC

The nuts on the input jacks stripped maybe ten years ago when I was working for a friend at his guitar store. We had a dead amp there with the same jack spacing, so I swiped the inputs from it. The Fender amp had a larger circuit board with resistors on it to separate the two input signals, but the replacement didn’t, so I guess I must have found two resistors lying around and just jammed them inline.

Spliced wires and inline resistors
I'm not proud

This will have to be remedied.

NEC μPC1188H chip
The entire brain

This is what runs everything. I grabbed the Bipolar Analog Integrated Circuit uPC1188H datasheet to check it out, but I haven’t checked the little board that’s attached to see how it’s used in my amp. It is the same chip amp as the Princeton stereo chorus, and is still used a lot.

More to come, second part is on the way.

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