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Moog VCHPF pole's NPN/PNP matching
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jpdesroc



Joined: Dec 05, 2007
Posts: 31
Location: Canada

PostPosted: Tue Apr 22, 2014 7:43 am    Post subject: Moog VCHPF pole's NPN/PNP matching Reply with quote  Mark this post and the followings unread

Did anybody build a Moog 904B VCHPF circuit?
The schematic states that all the NPN/PNP pairs
used in the 4 poles chain (Q13,14 Q17,18 Q21,22 Q25,26)
needed to be matched pairs.
See the circuit here:
http://www.freeinfosociety.com/electronics/schemview.php?id=944

I read lots of threads on the list about this issue
with no findings ..
Well I matched a lot of NPN pairs (2N3904)
and PNP pairs (2N3906) last weekend using Bob Moog's
little matching setup with very good results
(better than 2mv in matching values !) but I'm having
a hard time to match NPN/PNP pairs in my lot..
The 2N3904 batch are around .600v @ 100uA
but the 2N3906 batch are around .650v @ 100uA.
Anybody knows good complimentary pairs available
or a way to compensate for the vbe differences ?
I'm considering specialised NPN/PNP IC matched pair.

JP
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gdavis



Joined: Feb 27, 2013
Posts: 161
Location: San Diego

PostPosted: Tue Apr 22, 2014 2:44 pm    Post subject: Re: Moog VCHPF pole's NPN/PNP matching Reply with quote  Mark this post and the followings unread

jpdesroc wrote:
Did anybody build a Moog 904B VCHPF circuit?
The schematic states that all the NPN/PNP pairs
used in the 4 poles chain (Q13,14 Q17,18 Q21,22 Q25,26)
needed to be matched pairs.


I think you're misinterpreting this spec. There's a matched set of four NPN (Q13, Q17, Q21 and Q25) and a matched set of four PNP (Q14, Q18, Q22 and Q26). NPN and PNP aren't matched to each other in pairs, each transistor in a set of four is matched to the other three in the same set.

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My synth build blog: http://gndsynth.blogspot.com/
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jpdesroc



Joined: Dec 05, 2007
Posts: 31
Location: Canada

PostPosted: Tue Apr 22, 2014 5:22 pm    Post subject: Moog VCHPF pole's NPN/PNP matching.. you are right ! Reply with quote  Mark this post and the followings unread

You are totaly right !!!!
I mixed up the sense of these spec lines.
In fact without knowing I just did the right thing,
I just matched 4 pairs of NPN/PNP which have
all their NPN's closely matched and also all their PNP's
closely matched too (within <.001v) but their is a
.050v difference between the NPN and PNP vbe values.
So according to Moog's 904b schemo I'm must be ok.
Many thanks for pointing out !!!
JP
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