Ladder Filter for Shruthi

Won’t the THAT 300-series give you two matched pairs so that you can use it for both top and bottom of the ladder? That’s the downside of the 3046 - only one pair, all the transistors are somewhat even though.

If you can do (fiddly) surface mount then this is what you want…cheap and meets Moog matching standards.


The THAT300 series only guarantees matching within 5mV IIRC-not much better than the old 3046…

Hi, thanks, it is a good idea to use DMMT3940W.
Ok we talk about this schematics.It is not complete ready yet, wrong pins on the Opamp .
All restsiors in the cascade 1 k.
What works ? Resonancy frequency from 30 HZ to 20 KHZ , 20…30 mv pro octave.
Frequency 0…20 KHz. R12 set a pos value on the op amp 6B and gives the deepest frequency.
Vca is like olliviers, ( not in the schematics) I must measure the maximum output on Shruthi before the VCA to adjust it. I think it is 20.50 mv.
Problem: a fast Modulation let the filter give out the modulation frequency without a input signal and Q=0.
Possible mistakes. 1: no matched transistors, 2: maybe is IC 2B on the limit, because the DC input is 3,45…3,65 V. And the TL 072 is not a rail to rail opamp.



Did you use low tolerance Caps for C2 … C5 ?

no , at first not. But i will use next 1 % tolerance.

What capacity are they? Maybe i have some on stock…

Ha, i think i have ve got it. Was simply a design mistake on op amp 2.
Output Ladder 2c 820 nf and 2 Resistors in cain. 47 K. One R=1 M to ground and a second R=1 M as a feedback resistor on OPAMP 2. If i now modulate from 0 HZ to 20KHZ V out 1V ss i get a DC mod signal 10mv. This i can maybe reduced wit R and C 1 with 1 % tolerance.
It is not the matched transistors and also not the capacitors. !
I have learn much by developing this schematics…
I will update the schematics and post it.


Great work, Andre!
I can route the PCB if you haven’t made it yet.

by hand? old school möøg Style?

I’m not so masterly tracer as you. Still using Eagle :wink:

can you do it single sided? then id redraw the core for maximum fidelity by hand :wink:

Yes =)
And I have a bunch of matched transistor arrays used in soviet möøg ladder filter clones. So no problem to assemble and test it.

Hi, it is not ready yet. The filter works but i had to measure the input volume from the Shruthi oscillator and than i must adjust the filter output to the Shruthi VCA…
Here is the last schematics.
Than i will do a special OSC >>Filter FM with CV 1. And than it is maybe ready.
And i will make a better schematics with all in.


Lame question: what is the function of IC5B (first in cutoff CV converter chain)?

i have a slightly bigger machinery to etch boards, if schrab does the layout i volunteer to do some pcbs…

Andre, i confirm that! And he has pink etching gloves while my hands are yellow!

More there

My wife would kill me in a most cruel manner if i would ever pack such equipment into the kitchen…

My wife encourages me to do so…

Such equipment is the jewel of any kitchen!