[sdiy] Matched transistors - critical parameters?

[ASSI]

On Friday 10 February 2012, 08:18:33, Matthew Smith wrote:
> As we're talking SMDs, footprint on a PCB (mine are gold-plated anyway)
> and some sort of spring clip to hold the part down?

If you are serious about it you'll need something like this (not cheap):

http://www.emulation.com/catalog/off-the-shelf_solutions/sockets/sot/

If you just want to do a quick check, get a manipulator with vacuum tip and 
just pat them down on the test board.

However, as already said before we got carried into how closely one can 
match discrete transistors by hand: most circuits that were designed for 
discrete transistors and employ pairwise matching are fine with less 
precision (even if not trimmed) and non-monolithic duals would often be good 
enough without even checking.  Consider using a different circuit if that 
isn't the case.  If it turns out once in a while a dual is at the edge of 
the distribution, just take it off and solder the next one in.  If that 
isn't an option, use a proper matched pair transistor.  Still less work and 
expense than sitting through a matching session.

If you'd rather be in the matching business, get a used tape&reel feeder 
with at least 6 rails and build a matching robot to sort from tape to tape.  


Regards,
Achim.
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