Arp filters. Re: [sdiy] WP LM3900 VCF

[Louis van Dompselaar]

> I built one on the breadboard. Based on an EFM schematic. I didn't match 
> any transistors. In fact,  a few were 2N3906 and the remaining were 
> BC557. Still sounded very nice.

Probably the EFM VCF7?  I recently built that one as well, recreating
the PCB from the component layout and a photograph that is on the
Yusynth website.  I, too, didn't have enough 2N3906 lying around
when testing and partly used BC559's.  When I later got all 3906's
it didn't sound that different to me.  So I don't think these
transistors are too critical.

This is what my test-version sounded like (with the 559's in):
http://www.casia.org/modular/efmvcf7.mp3


Off topic:
Yusynth correctly suggest that the EFM PCB contains errors.
Q4/Q6 and Q8/Q10 are wired incorrectly.  It's easiest to fix if you take 
Q4 to be Q6 and vice versa, that only requires two traces to be 
rerouted. The same goes for Q8 and Q10.  Odd enough, Yusynth go on to 
suggest corrections that are in itself wrong (you'd end up with the 
emitters of Q8 and Q9 connected).


Louis