noise: [Noisebridge-discuss] Dynamo Regulator Help Needed

Dennis Gentry dennis.gentry at
Sun Jul 21 21:24:13 UTC 2013

Maybe the simplest thing is to get a speaker that can directly handle the
amount of power that the dynamo can put out, and get rid of the audio amp.

Barring that, do you have a series capacitor (say 100 uF) between the
dynamo output and the audio amp input to block DC?  You shouldn't be
feeding any constant (DC) current into the audio amp, lest it blow up.

Another way to get it to blow up would be to feed the audio amp (or the
aforementioned 100 uF cap) too high a voltage.  Instead, load the dynamo
with a (relatively high valued so it doesn't get hot) resistor across its
terminals to keep the voltage in a sane range, then use a voltage divider
to bring that maximum output voltage down to whatever your audio amp can

Less critical issues:  Do you want it to get louder as (the dynamo rotates
faster and) it gets higher pitched, or do you want to keep the volume
somewhat constant?   You might find that the dynamo will make a lot more
power at high RPMs, so when you scale down the voltage as needed to not
blow things up, the audio might not be audible at low RPMs without
amplification.  (This is easy to fix, if it is what you want.)

Hope this helps a bit!
P.S.  Anyone know a good way to quickly draw and send circuit diagrams in

On Sun, Jul 21, 2013 at 11:14 AM, Johny Radio <johnyradio at> wrote:

>  Hello
> Can anyone suggest how to limit the voltage and/or current coming out of a
> dynamo, before audio amp?
> Actually, I'm not sure if this is a dynamo or alternator-- i'm cranking
> the shaft of a DC motor, and tapping the electric terminals. I'm trying to
> amplify the AC sine coming off the terminals through a loudspeaker.
> It basically works-- i can hear the motor oscillation from the speaker
> driver, which is my goal. But i've blown two audio amplifiers doing this.
> The motor is not large (about 2" long, 1" diameter), but i'm spinning it at
> thousands of cycles per second. According to one article, as frequency
> increases, so does output current.
> I'm not sure if the issue is too much current or too much voltage. i
> believe i'm not getting clipping, so i suspect the problem is too much
> current. A couple fat resistors in series with one of the terminals did not
> prevent the amp from blowing. Also, the speaker driver heaves, which
> suggests to me either an impedance issue, grounding issue, or low-frequency
> content.
> I've found a couple ways of possibly handling too much current, using
> circuits mostly designed for charging batteries off a generator. I found
> solutions based on BJT transistors, CMOS, power regulator chips, or diodes.
> Links below.
> I'm not charging batteries, so i wonder if i can eliminate the reverse
> current protection? Actually, the motor no longer spins when i apply
> voltage to it's terminals, so i think i blew the motor in some way.
> Strangely, it still outputs a sinewave when i turn it's crank. So maybe the
> reverse current protection IS needed.
> One solution employs a pair of diodes, wired back to back, between the
> motor terminals (i think). This is intended to clip the voltage, resulting
> in a square wave. This solution is not desirable, because i want to
> preserve the sine shape coming off the DC motor.
> How can I limit current (or is it voltage?), without squaring the original
> sinewave? As always, seeking a lowest-parts-count solution, passive if
> possible. Any help is appreciated!
> --
> Johny Radio
> Stick It In Your Ear!
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> Noisebridge-discuss at

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