LFOs

[Magnus Danielson]

From: "Mike I." <mirwin1 at istar.ca>
Subject: Re: LFOs
Date: Tue, 04 Jul 2000 20:00:07 -0400

> Hi Magnus,

Hi Mike,

> I've looked at the Small Stone LFO a few times over the past year (and 
> even breadboarded one using the CA3094 and another using an LM13600 + 
> Darlington) but I'm still rather uncertain of how the circuit actually 
> works!

Ah. OK.

> Using a voltage drive for the OTA Iabc pin is an interesting 
> technique, but I still don't know how the LFO itself works!

OK.

> Would you be  able to shed some light on this for me (maybe post it
> to the list if you think it's worthwhile?).

I think it could be an interesing thing for a wider group of people to
maybe meditate over...

The OTA acts like a current source to load and unload the
capacitor. The trannies in the CA3094 acts like output
buffer. However, the OTA input trannies can be a bit confusing. They
act like a Schmitt trigger such that the OTA will rise or fall
depending on which state it has. The switch will alter the hysteresis
such that the output range will change, as a result will also the LFO
frequency range be altered. This curcuit gets somewhat confusing due
to the design need to keep components down and cheap. Anyway, the
trannies can be replaced by the standard op-amp setup if you so request.

> I built a 16-stage phaser using the Small Stone allpass circuit with
> LM13600's, but used a standard expo current source and LFO to drive
> the Iabc pins.

Ah, how interesting. 16-stages, that's quite alot!

Let us know how it all works out!

Cheers,
Magnus