An automated transistor tester, as well as matched pair finder, for DIY synthesizer projects.
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Credit where credit is due:
This project is based on the automatic "pass/fail" transistor matching circuit by the late and much lamented Ray Wilson.
Which, in turn, was based on the transistor matching circuits developed by Bob Moog, who needs no introduction.
If it turns out that my only innovation in this project was "have a microcontroller do it," well, maybe that's enough.
For the prototyping of this project (and presumably many others), I had actually planned to use the benchtop DC supply that I had ordered, the Rigol DP832, but it isn't going to be delivered on time, and I really wanted to get going on this project. The usual solution for needing a bipolar power supply, two 9-volt batteries in series, wouldn't work here because I need at least 12V supply rails. So I put together a circuit that splits a +24VDC supply into ±12VDC supply rails, using a TL431 voltage reference and LM317/337 adjustable positive/negative linear voltage regulators:
(Sorry for the ugly hand-drawn schematic, but I didn't feel like drawing it into a CAD program.)
Anyway, after a bit of messing around with things, I finally got it to where at least it looks stable on my meter:
Not a perfect split, but it was never going to be. I'm going to check the supplies for noise before I go ahead with using it, but at least I now have a way of moving forward on this project.
Oh, and just for giggles, this is how the circuit ended up looking:
It sure is ugly! And it sure does work! Function over form, people...
Kuri P. Yon
Desreverteg
bigbat
Adam Jensen
Peter Walsh