noise: [Noisebridge-discuss] re Dynamo Regulator

Dennis Gentry dennis.gentry at
Mon Jul 22 22:04:44 UTC 2013

> >>[If you limit the voltage with a voltage divider] You might find that
> the dynamo ...might not be audible at low RPMs without amplification.
> (This is easy to fix, if it is what you want.)
> --how?

An audio compressor -- the kind that reduces the dynamic range of a sound
(not the digital kind that reduces audio file sizes).

Here's a passive one that I found through a quick search:
(That same site has other fancier ones listed which use transistors
require power supplies, but) this one claims to have a pretty wide input
range (up to 10 v) and outputs an average 70 mv signal, which should be
suitable to feed into an audio amp.

It calls for 4 AA119 diodes, but I bet any germanium diode (1N34A and 1N60
is what I have lying around, although I haven't tried to buy a germanium
diode in years) would work fine, or probably a small-signal schottky (1N5711
or BAT54) would work even better.  The 1N5711s are 11 cents each from
Mouser.  Hey, do you know about octopart?  I've found it to be much more
helpful than Google when shopping for parts:

Here's how I'd put it all together:

Dynamo/motor/thing making sine signal -- voltage divider if required --
dc-blocking cap -- compressor -- audio amp -- speaker.

The first thing I'd do is figure out what kind of signal the dynamo/motor
is making at the maximum RPM you'll be running it.  If it's 40 volts
peak-to-peak, you'd want to scale the signal down by a factor of 4, so a
voltage divider ( where the
top resistor (Z1) is 100K and the bottom resistor is 22K would do that.

I can come in to Noisebridge this afternoon/evening (it is Circuit Hacking
Monday, after all) and we could dork around with this if you like.


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