[sdiy] Synth & LEDs

[Paul Schreiber]

>
>     I guess I will have to go get that issue.  I stopped my subscription
when
> the DIY articles started to disapear (they even printed a letter to the
editor I
> wrote quite a while back lamenting the demise of DIY, good thing the
internet
> has brought it back :-) ).

The comment was made that the designer (that would be me) does not believe
it tossing
wheelbarrows of LEDs in a synth, bcause it injects noise into the *power
supply rails*.

Driving LEDs in a -90SNR system is non-trivial. You have to use
constant-current
drivers with certain design rules to keep the current spikes out of the
lines. You had better
REALLY watch your grounding.

It's not a matter of 'distortion'.  Here is the quote:

"..each LED adds noise to the system in the form of added current drain and
switching transients."

Now, just how *much* noise is a point for the system itself: most likely,
you need a $30,000
Audio Precision 2 test set to even *detect* it. But, it some cases, you
could have a situation
such that you hear 'strangeness' like VCOs FM modulated without LFOs patch
in. Conversely,
lots of pro audio gear (ie compressors) have a boatload of LEDs.

This is just one of my little personal quirks. MOTM does have LEDs. Just not
everywhere.

>
>     The reviewer must have been somewhat technically oriented, but had
never
> experienced an analog synth before...

Errr...you couldn't be farther from the truth. The reviewer has 20 analog
CDs out on 4 labels,
has a degree from Stanford in music and did gratuate work with John Chowning
at CCRMA. :)

Paul Schreiber