Matching transistors for a set of moog style ladder filters.

[nizzleone]

Suppose one was trying to build a set of moog style ladder filters for polyphonic applications, what transistor matching would be most important with regards to tuning?

I assume that you'd want the "rungs" of the ladder to match up across all filters. ie would you want all Q14s and Q15s on every filter to match up to one another, and same with all Q16s and Q17s and so on?
Just for illustrative purposes referring to this image (http://home.comcast.net/~sbernardi/elec/og2/og3_moogladder1.gif)

[softfin]

Welcome to e-m nizzleone!

There are at least two recent threads on this subject:

http://electro-music.com/forum/viewtopic.php?&t=18365

http://electro-music.com/forum/viewtopic.php?&t=34402

You might find even more discussions about it by searching the forum.

[ultrashock]

http://electro-music.com/forum/post-290611.html
one more recent topic from me

[nizzleone]

Hello and thanks,
Those thread seems to be about how to match transistors, and google searching earlier about transistor matching is what actually brought me to the forum.

I am more interested in which transistors need to be matched across six of the same filter in order to get those filters reasonably in tune with each other.

I have six replacement VCF/VCA combo chips for a Juno 106 and while they sound amazing, the trim pots for filter frequency adjustment don't have a far enough range to get two of the chips in tune with the rest. I was going to try and swap out the transistors on the chips in an effort to bring things into harmony.

I was thinking about getting 100-200 of the necessary transistor from mouser and hand matching whatever size sets as close as I could.

[softfin]

Looking at the schem (you posted a link to) I think q14&q15 and q6&q7 are the most critical in regards to matching... If you match a pile of transistors, why not match all pairs

Btw, from my own adventures building moog filters I have noticed matching the filter core caps is important as well.
I matched the 'filter core' caps to 1% on one of my moog type filters and it sounds considerably better/ defined than my other similar filter which I didn't match those caps for.

Can't say more than this due to not being an expert on moog stuff, but hope this is of some help.

[Peake]

Perhaps the yusynth.net site will shed some light, particularly the minimoog filter clone.