I'll admit it, I've not been following this thread too closely, but let me
add my two cents worth. I had thought someone was having trouble with clock
bleed through in the output, but maybe it's just a case of slew across 3
octaves in the interval of a few ms. So I did the following experiment:
1) white noise to input of S/H
2) use internal clock at about 4 Hz (not critical)
3) output of S/H to 1V/OCT input of either VCO or VCF
4) output of VCO (or VCF) directly out (i.e., no VCA)
5) start with the S/H level at 0 and slowly move up until you hear popping
(occasional pops between 3 and 5, significantly more popping between 8 and
10, all dependent on the size of the interval)
With the VCO, I don't hear any popping until the intervals start getting
reasonably large (bigger than a fifth), and I wasn't surprised at the module
doing this. I did get more popping earlier with the VCF. In fact, I found a
very cool patch as well:
1) S/H as above
2) S/H output to the 1V/oct input of the 420
3) nothing at the inputs of the 420
4) bring the RES pot of the 420 to where it hangs on the edge of oscillation
Great tuned percussion patch -- very similar to "ringing" a Serge VCF -- very
"marimba" like.
Normally, I would use some kind of gate and an EG on the VCF and therefore
wouldn't notice the popping.
JB
In a message dated 10/6/99 9:53:30 PM,
goku@... writes:
>Hi everyone,
> I've been getting annoying S&H pops on my MOTM-100 also. This is very
>noticeable when patched to the VCF. At first I thought this was part of
>the
>"badness" of the '420 design. But I get audible clicks on my Minimoog filter
>as
>well. So I investigated further. Tried two other type S&H units but no
>popping.
>There had to be an explanition. So I tried running the '100 through the
>Mini
>keyboard circuit, instead of straight to the VCF, and the popping went
>away.
>Interesting! Apparently the '100 changes voltage so fast there is a click
>when
>routed directly to the VCF or VCA. The keyboard circuit seemed to smooth
>the
>transition between voltages ever so slightly and kind of morphed the
resulting
>output wave. No more pops or metronome like clicking.
>Here is a sample wave of the S&H filter sound first through the Mini keyboard
>circuit(no pooping), then straight to the VCF (loud popping).
>
>http://www.geocities.com/SunsetStrip/Frontrow/4877/sh02.wav
>
>If you look at this wav in Sound Forge and Magnify 1:1 you can see the
>smooth
>transition between samples in the first part. The changes have nice rounded
>edges
>between samples. On the second part the changes are very abrupt. Harsh
>straight
>transitions between samples causing pops.
>
>OK, so the circuit needs some kind of lag to be musically useful. But how.
>I'm not a tech so I tried a few things by "ear". I came up with a 1uF 25v.
>electrolytic across the output jack. Negative connected to ground and
>positive to the output. Seemed to work? I substituted larger values but
>got an audible lag, like a "wah" on the filter or glide on VCO. I didn't
>have
>any smaller values, but 1uF seems an inaudible amount of lag. I also
>tried loading up the output with the 1uF installed, ran to the VCA,VCO,
>2 filters simultaneously to see if I got more lag, but seemed OK.
> Can you help here Paul? Should I have a 741 follower after this. Is there
>a
>better way? I don't want to use a full blown lag module for this simple
>task.
>Could put a switch on the '100 panel to put it in and out of the circuit.
>A
>"soft/hard" switch? Or is there something wrong with my '100? Didn't anyone
>else notice this?
>
> Anyhow the S&H filter sound is one of my favorites. And this S&H really
>kicks ass when running other instruments through the filters.
>Here's a small zipped MP3 of last weeks jam session with the popping
>S&H filter sound. Next week no popping!
>