Yet Another Transistor Matcher - my version

 I found an article or a blog post on how to match transistors with a bit of slick interface. Matching transistors is pretty essential for exponential converters and ladder networks for filters on synths. Now you can do it manually with precision measurements, or you can use this circuit to show a quite groovy method. 

YATMA

I adapted it slightly - I have a whole drawer of old LF13331 analogue switches which I have used with an Arduino to sequence through, and a x1000 amp on the back side. It takes up to 8 NPN or PNP transistors, and plots their Vbe on a scope. Now since I am an old git and I like to be able to see the components I am soldering,  I am using pretty much all PTH components. How quaint, I hear you say. 

So, I have a small KiCad PCB made by Seeed Studios: 

The small Arduino Pico on the top just runs a small loop that switches two of the 16 switches on, connecting a current source (a chosen resistor) to one of the eight transistors in the ZIF socket on the other side. I had to put the ZIF socket on the back, so I can mount the board backside to the front panel with the socket sticking through. 

The jumpers can be moved to allow either NPN, or PNP (or simpler devices) to be selected. Then, the big BNC socket on the board is used to connect to a scope - I found the small old world scope managed to hold a sync much better than the digital one. 

The net effect is in this bit of a scope picture. I have AC coupling on so the tops of each step slope slightly in this picture - but you can easily see how you can select pairs of transistors with similar characteristics. 2 and 4 in this case are really close, 6 and 8 quite close and so on. It's surprising how quickly the levels change with a finger on the tranny - so it takes a bit of time to settle once the transistors are put in the sockets. 

And it works!  Quite pleased to be honest.