LM13700 VCF update no.2

[Tony Allgood]

Sounds like it would be better to build a Moog ladder then. Would this
be better alternative to the state variable design.? Or has anyone
tried the multiplier route like the Wireless World synth?

Further update on the 13700 VCF:

I have reduced the control breakthrough by feeding a small amount of
the control Iabc signal into the inverting input of the second OTA. It
works a treat. Mind you I have this thing about putting trim pots into
a design. I had hoped that the only pots would be the front panel
controls.

And I'm not quite sure that input offsets would cause the breakthrough
that I'm seeing here. After all, would not the offsets produced at the
input be subjected to the frequency response of the VCF? When I
modulate this VCF with a square wave I get a square wave at the output.
No sign of any ringing at the edges. Now if I put a square wave into
the audio input, the usual expected wave shapes occur. Also the
breakthrough decreases with Q setting.

Tony Allgood.

Cumbria, UK

'I may live in the middle of nowhere, but the views are nice'

Juergen wrote:
> 
> If you really want to use a gilbert VCA, the 3280 is the better
> choice by far. Or these Curtis 8-pin dual VCAs which Paul
> Schreiber sells.
> The 13700 is a great chip, nevertheless, if you want a dual
> 3080 or 3094.
> 
>