[sdiy] Matching transistors in "diode ladder" filters

[yves usson]

Hi Aaron

In my recreation of the EMS diode ladder filter I used simple 1N4148 and 
I selected
within the same batch those which forward drop voltages were similar 
within a range
of 3mV. If you take diodes from the same batch you will see that the 
tolerance is quite
good indeed and in order to have 7 matched pair you need not to test 
more than 20 diodes.

http://yusynth.net/Modular/EN/EMSVCF

Cheers

Yves Ussson
http://yusynth.net



Aaron Lanterman a écrit :
> One of my students is working on building a variant of the Roland 100 VCF:
> 
> http://fa.utfs.org/diy/roland100/101_op27.jpg
> 
> See lower half, 3rd "block" from the left.
> 
> I've heard that in the Moog ladder, it's important to match the top 
> transistors and the bottom transistors, but the ones in the middle 
> aren't so important to match (and some schematics of various Moogs bears 
> this out.)
> 
> Does anyone have advice of what is important to match in a "diode 
> ladder" filter? We're doing the Roland 100, but I the same question 
> could apply to TB-303, EMS, and Sonic V (IIRC).
> 
> I told my student to use CA3046s to get some cheap pairs (since I have a 
> bunch), but if he could use garden variety diodes for some that would be 
> convenient.
> 
> - Aaron
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