A few thoughts on the wasp clone

Rene Schmitz uzs159 at uni-bonn.de
Thu Jan 29 02:45:11 CET 1998


Hi everyone,

Today I completed the construction of a wasp filter clone!
Its on a 100x100mm matrix board. I powered it up, and ... 
...it immediately worked :->

Here my thoughts about it.

First I have to say that the sound of the unit is quite pleasant,
it was really worth building it!
I do not attempt to describe the sound, since it is hard to describe.
Only one word, the overdrive section produces a distortion that remembers
me the names of various guitar stomp-boxes.
I'm really surprised how much sound is into a logic IC!

The compactness of the filter makes it probably a good candidate for a 
formant filter section. 
Four of the filters (then fairly without the notch and overdrive)
two in BP one HP and one LP in parallel would make a nice formant module.
Needless to say that this module would be CV-able.
(this would take 2x 4069s and 8x 3080s)
The overdrive/speaker simulator section should be a seperate module then!

For stand-alone use one can easily power it with a battery, operation is at best
at 5V, but the unit works from 15V down to 3V! (Ok, the frequency scaling gets 
messed up when varying the supply, but that could be cured)
It draws max. 6mA @ 5V. Maybe one can even "feed" it with partially used 
batteries. I added a second input to the unit, with higher input sensitivity, 
to use it with my bass, and I could set the filter so that I got nice guitar 
sounds with the overdrive when playing in the higher octaves.

One thing that *should* be added is exponential control voltage. 
The advantage is one could use it as a tracking filter.
A little NPN/PNP expo converter will probably work even at +/-5V, and the 
expo current could be added at the Iabc pins, so one has linear and expo
control 
as well. I prefer a filter with expo *and* linear cv inputs, since with an
exponential decay EG, the filter sweeps sound better to me with a linear
response 
on the filter, since the time that it takes to sweep the filter from one
harmonic 
to the other is equal, for basic waveshapes, and the filter is longer in a
frequency 
range where it effects the harmonics.

Anyway, the cutoff pot would go to the expo summer of course. 
(For accurracy reasons I'd prefer a "real" opamp here...) 
The negative supply that it would require is no real drawback in a 
synth-environment.

Bye
 Rene




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