Back to my Amp

I hooked up my camera, now I have pictures!  Well, more pictures.

Small bottle of Contact Cleaner. Alcohol in a spray can

This stuff is magic.  Sprayed my scratchy pots with it, spun them back and forth a bit, and the loosened right up.  At first I thought I’d wrecked them, they got so loose.

These are the "Sealed" potentiometers

There is a small indent in the top of the cases of these pots.  I think it’s for the mechanical stop for the knob.  Since they’re stamped through the case, they left nice little holes to flood with contact cleaner.

No more electrical tape

I grabbed a variety pack of heat shrink tube.  On sale for like $4!  I don’t know if it works better than tape, all my old tape joints are still holding out, but it sure looks cleaner.

I have lots of these

Computer power supplies are a good source of decent wire.  This particular unit is barely-atx out of a PII 300ish.  20 pin MB connector and no PCI-E.  Will make a good bench supply, since old ATX supplies have more power on the +5V, where newer ones focus on the +12V rail(s).

Nice long, heavier-gauge wires

I’m sure I’ll use the molex connectors later, not so sure about the berg connector.

Separate grounds

The two signal lines have colours, the two ground lines are black.  This is going to cause problems later.  But I’ll get to that later.

Lumpy connections

The resistors that were on the signal lines when I took the amp apart were re-used  Soldered in-line before the signal lines join up.

Tinned and soldered

I de-soldered the old wires this time instead of just splicing into them.  Tinned the new wires, soldered them in, and trimmed them.  The pic is pre-trimming.  I also de-soldered the pilot and clip LEDs.

Turbo goes in everything. And contact cleaner is no good for the skin 🙂

I scavenged some LEDs from the bottom of my old computer toolbox.  The last computers that came with “turbo” modes were 486’s, but these LEDs came out of a 386 SX Desktop (when desktop was the opposite of tower, ie. it sat flat on your desk).  That means the computer this came out of was made between 1988 and 1992.  The youngest this LED could be is 18 years.

Sounds soft

I jammed everything back together, tossed in the old pillow, and fired it up.

Can you spot the difference?

Okay.  So I had some success and some failure.  First, the pilot light doesn’t come on.  Maybe it’s from using 20-year-old LEDs, maybe I got the polarity wrong.  Either way.  Fail.  I’ll switch the legs around later (I used connectors on the LEDs just in case, but hot glued them to the chassis.)

What the jacks used to look like

Second, I’ve got a ground loop somewhere.  Buzzes something fierce.  When I touch a patch cord to the handle brackets on the top, it stops.  What to do?  Well, when the amp came apart, the two ground leads from the input went different directions.  One to the circuit board, one to the chassis, with a jumper across the jacks.  I removed the jumper and ran both to the board, and none to the chassis.  I guess my old hack was better than my new one.  Live and learn.

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