noise: [Noisebridge-discuss] Dynamo Regulator Help Needed

jim jim at
Sun Jul 21 21:43:25 UTC 2013

A different approach, assuming AC from the 
"dynamo", is to feed it to a transformer, 
even a 1-1 tranny, and feed the audio amp 
with the tranny secondary (with recitfier 
and conditioning circuitry between the 
secondary and the amp's power input stage). 

On Sun, 2013-07-21 at 14:24 -0700, Dennis Gentry wrote:
> 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 handle.
> 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!
> Dennis
> P.S.  Anyone know a good way to quickly draw and send circuit diagrams
> in email?
> 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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