Ibanez IBZ-20 Amplifier schematics

I got a Ibanez IBZ-20 guitar amplifier, that had some issues that needed to be fixed. All potentiometers were dead, and jacks were badly corroded, but in addition amplification was not working correctly. I could not find any schematics for this old amplifier, so I decided to reverse-engineer the whole circuit board.

Here is the schematic that I made:


It turned out that problem with the amplifier was that one of the two 2SD313 power transistors was gone open. This in turn caused smaller transistors on PCB to act as power stage, and whole speaker current was passed trough small 270ohm resistor that could not handle that kind of dissipation.

Burned resistor due failed power transistor

I also decided to replace all capacitors, and removed that brown glue, which turns into corrosive and conductive mess when it ages and attracts moisture from air.

Recapped and glue removed
Bottom side of the PCB. Old hand taped layouts look kinda funky.

2 thoughts on “Ibanez IBZ-20 Amplifier schematics”

  1. Hi there! Random find, but since you seem to be the only other person that owns one of these, I would like to ask you something, related to the Speaker Output in the back. What kind of speaker does this little amp take? I have an 18″ bass cabinet lying around and a 2×10 cabinet with some Celestions (don’t recall the models) and I would like to see if it works with either of them. Cheers!

    1. Original speaker in the amp is 8″ one rated at 20W and 8 ohms, if I remember correctly. Amp is not powerfully, so driving larger cabinets could be problematic. 2×10 could work if speakers are wired in series, but don’t expect it getting loud unless the speakers are exceptionally efficient. Enough for practice or really small venues.

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