[sdiy] MS 20 FILTER

[Colin Raffel]

Hey Diago,

That symbol, the two circles, signifies the OTA's current-based  
amplification feature.
Vr is the reference voltage, in a single supply circuit such as this  
one, this means 1/2 of V... by using Vr as ground and ground as V-,  
it simulates a dual supply system.  Vr in this case is around 4.5 v,  
and is generated by the top right little circuit there with two LEDs.
That buffer circuit is built into the LM13600.
Read up more on the LM13600, it is a very useful chip!  You can refer  
to the LM13700 datasheet-it is the same in structure with a slightly  
different built in buffer.
http://www.experimentalistsanonymous.com/diy/Datasheets/LM13700.pdf

A note about the circuit you are referring to-I have found that it  
clips very ugly, the MS20 filter I think is supposed to sound nice  
clipping... I believe that's because Tim E's implementation is  
designed for 9v (pedal use) and makes some sacrifices.  I have never  
tried this circuit, but this one supposedly reflects the real MS20  
filter more.
http://www.uni-bonn.de/~uzs159/rs20.png

-Colin

On Dec 17, 2005, at 11:02 PM, synth DIY wrote:

> hi! i have this MS 20 filter project to do and i've been have some  
> problems:
>
> in this schematic i don't really understand the meaning of the  
> symbol in the output of U1a and U1b.
>
> "Vr" voltage is the ground voltage?
>
> between pin 7 and 8 ( and 10 and 9 ) it's a buffer circuit. should  
> i use any specific kind of buffer?
>
> Lm 136000 datasheet is not available, but i found a  http:// 
> www.datasheetcatalog.com/datasheets_pdf/L/M/1/3/LM13600.shtml.
> is it the same?
>
>
> thanks
> Diogo
> <sk.gif>