Little help identifying a part in an audio amplifier.

Thread Starter


Joined Oct 9, 2018
Long story short, have a powered subwoofer someone gave me years ago. Has bugged me for years and I could not solve the riddle..... It had a hard short but I could not find anything in circuit that was shorted. I am revisiting the project.

I think due to my "testing", I have fried both the front end power transistors. They are reading around 2ohms between legs. They certainly were not before. Anyway, there is a small daughter board by them that appears to be the driver for them. There is no oscillator chip or anything, just a bunch of resistors, diodes, and a single T0-220 bipolar transistor. The collector side of that couples to a couple resistors, then a small component that almost looks like a ferrite bead. It is an axial leaded, shiny black barrel the size of a 1/4W resistor. There are no markings at all on it, but the board shows it as "D11", but I am not sure we can call it a diode or not. It does not show voltage drop, capacitance, or resistance. It is effectively open.

There are a couple zeners on the board, marked with "Z", and a couple others marked with "D". The markings on those were rather odd. They looked just like a zener, clear glass, etc, but not marked like a zener.

This was on one of them.

I cannot yet be certain what happened to this circuit but I guess i plan to replace what I can find and soft start the amp to see if I can detect what is going on with it. You would think a hard short would be easy to find.....

As well, I determined a main transformer on the board has about 14 pins. one of the pins that connects to the + lead from the rectifier doesn't ring out with any other pins. I never see those damaged but scratching my head on that one.


Joined Oct 2, 2009
Welcome to AAC!

A picture is worth a thousand words. Post a picture.
Give us the make and model number. Post a link to circuit schematics if you have a link.

Thread Starter


Joined Oct 9, 2018
My apology. No pics yet. The amp is a Bash. I am looking for numbers.

However, I did find some posts on another site showing pretty much the same issues and failed parts. SMPS with minimal protection it seems.

One has indicated the part in question is actually a diac. a DB4, 40V diac. I think the main questions in my mind now are, how do I want to go about testing that, and should the glass barrel be black? I am guess that means she is toast but I should probably make sure.

My thought was just to put a resistor in circuit with my DC lab supply to tune the current limit, then just put the diac in series with the resistor. As I read it, it should trip at 40V and output 5V and a max of .3A. Should work in both directions.

See any issues with that?