Moog filter clone question

[John Speth]

I looked over this schematic and, yep, it's a ladder filter.  It's my first look at a ladder design using diodes.  First, just a general question to those who know: How would a ladder filter using diodes sound different from one that uses transistors (assuming optimal designs for both)?

Anyway, (referring to Romeo's circuit) I'd think the key to such a circuit is the "matchness" of the transistors at the lower rung (looks like a diff amp?).  I'm certainly no expert at the finer points of circuit designs but other designs I've seen always use an integrated multiple transistor package for the lower rung (N2-V3/V4) as well as that current amplifier (N2-V2).  Furthermore, some even use a pair from the transistor package for the top rung.  What else could it be.

Is there any matching requirements for the diodes?  Will Ge diodes work as well or better than Si diodes?

John Speth
johns at oei.com

-----Original Message-----
From:	R.Fahl [SMTP:8brain at spiritone.com]
Sent:	Thursday, September 18, 1997 2:35 PM
To:	synth-diy at horus.sara.nl
Subject:	Moog filter clone question

I've built another filter, this time it's a Moog inspired clone that uses a
diode ladder instead of transistors.  Problem is that it calls for a
transistor DIP package that I've never heard of before (B 340).  I took the
liberty of subbing it with dirty old 3904s, but that doesn't seem to work.
The schematic can be found under this URL:

http://www.spiritone.com/~8brain/ddrmoogvcf.gif

If anyone would care to look at it and give me some pointers as to how to
make it work, I'd be very grateful.


Romeo