[sdiy] Saw DCO

[Magnus Danielson]

From: Richard Wentk <richard at skydancer.com>
Subject: Re: [sdiy] Saw DCO
Date: Wed, 06 Oct 2004 19:19:51 +0100
Message-ID: <5.1.0.14.2.20041006190943.041cbfe0 at pop3.skydancer.com>

> At 19:42 06/10/2004 +0200, Magnus Danielson wrote:
> 
> >Actually, what I would do is set up another OTA and maybe an op-amp to create
> >a separate control loop for the amplitude.
> 
> Why? I don't get what the advantage of this is over using a preset 
> digitally computed curve via a separate DAC/DAC output to control level.

Just to show another way of solving it. This is what just appeared in my head
as one way of doing it. Good or bad is certainly up for discussion, but you can
do it this way to if you wish.

Oh, you don't have to make the computation in the MPU. There's one advantage.

(That I think many people are trying to do too much in CPUs such that things
barely work at the same time may have something to do with it. Why do it the
complex way when there might be alternative solutions? Some stuff is fairly
easy in analogue, some in digital and yeat some in software/CPU, do it where it
is best done!)

> Since it's a non-precise kind of application it would be easier to use a 
> spare 3080 (or use a dual OTA of some other sort for exact matching) to 
> finagle a temperature compensation current value and add/subtract this from 
> the level drive current directly. With no loop and no time constant to 
> worry about, instantaneous error will be much smaller. And for a dual OTA, 
> matching would guarantee accurate temp tracking.

I can't read your mind in advance and I don't look at problems with the same
eyes. Therefore we come to different conclusions. This is actually what makes
it more interesting. You may very well be right on this particular issue, but
don't kill other approaches as hard. Enjoy the diversity.

Actually, why do stuff with 4069UBs? They are not particularly well suited,
yeat people get them to dance very peculiar dances for being just a hex
inverter. It's a challenge and it's different, that's why. Why spend time to do
a Moog ladder, whe can quickly do a 4-pole lowpass in a CPU! :/

Cheers,
Magnus