Use of Diodes in Filters??

John Speth johns at
Thu Nov 20 09:34:44 CET 1997

Don't designers use series diodes for the purposes of developing a higher forward voltage other than, say .7V for a single Si diode?  Maybe that's it?

John Speth
Object Engineering, Inc.
johns at

-----Original Message-----
From:	media at [SMTP:media at]
Sent:	Wednesday, November 19, 1997 12:09 PM
To:	synth-diy
Subject:	Use of Diodes in Filters??

First, I'd like to again thank everyone who has mailed me sources of VCF

I apologize if this seems an uneducated inquiry, but I am curious as to the
use of diodes in several filter schematics I've looked at.  In all cases
they seem to be common silicon signal diodes.

In several designs there seem to be three or more diodes in series.  What
different function does that serve than that of a single diode??

On the MS-50 schematic there seem to be six, three in series in each
direction, running parallel to the resistor in the negative feedback path
of an op-amp.  Even more curious, there is what appears to be a bridge
rectifier in the middle of the circuit!!

On the EMS filter also shows several diodes in series.  There are also two
rows of diodes with capacitors running across them.  The Mini-Moog VCF
schematic shows a similar structure using transistors in place of diodes.
I presume these are the famous "diode ladders" -- how do these function??

I hope these questions aren't too tiresome.  I tried looking into several
books, finding numerous non-resonant low-pass filter designs which make
perfect sense, but I am yet to find a description of these uses for diodes.



"It's like, when a band has a name like 7 Year Bitch,
 it's like, they don't have to be very good."
                                  -- Butt-Head                          

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