[sdiy] What do people use for matched transistors these days?

Gordonjcp gordonjcp at gjcp.net
Mon Sep 11 12:30:54 CEST 2023


On Sat, Sep 09, 2023 at 06:35:10AM -0600, Quincas Moreira via Synth-diy wrote:
> For a long time I’ve just been using neighboring resistors from the same
> strip. Manufacturing processes are more precise these days, All my
> oscillators track well this way
> 

Here's the thing. Any transistors you buy now are likely to be the much-derided "Chinese knockoffs". So, someone will have approximated the spec of (say) a BC548, made a few million, batched them into BC548A, B, and C, and bagged them up and sold them to you on eBay at 100 for two quid.

They will not resemble your NOS BC548s, probably, but then any two given NOS BC548s are unlikely to resemble each other because the tolerances were absolute bollocks.

Today though the "BC548" that some dude in a shed in Shenzen is churning out over his lunch break is probably made with far sharper masks, far more reliable machinery, far cleaner chemistry, and in general a far more repeatable and consistent process. So, any two off the same strip will likely be off the same wafer and therefore much the same as all the others on the strip, to a far closer tolerance than "real" ones.

You can use the Ian Fritz method to check matching, and I bet you'll find they're easily within 10mV which is pretty okay for ladder filters, and you might find they're within a couple of mV which is the spec that the Moog service manuals call for in expo converters.

I can't say I've ever had a circuit fail to work at all because of mismatched transistors, although I've probably made some that could have tracked well over a wider range if I'd paid more attention.

-- 
Gordonjcp



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