need quick filter ideas at speaker-level--- bicycle generator audio generator

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lohi

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Joined
Mar 9, 2006
Messages
15
Location
Winters, CA
OK, here's what I'm doing. This coming Monday, June 21, 2010, I'll be playing an exercycle at the Chapel of the Chimes in Oakland. The exercycle runs a bicycle generator (magneto-- rough AC) which drives, directly, a speaker. I have no idea of the output impedance of a bike generator but it puts out up to 6 volts or so, very spikey, and drives an 8 ohm speaker loudly. More volume than I need, actually. I'll probably be shut down if I don't pad it down  with a rheostat. Natch, the frequency is dependent on RPM. Here are the "filters" I've tried so far, successfully: an LED, in series. I haven't looked at it on the scope but it seems to make the wave even more square-wavy than it is already. Nice.
A 10 MFD non-polarized cap, in series. Cuts out the lows. Useful.
A "choke" (an old power transformer, the 24 volt side) in series. Mutes the highs. OK. I'm thinking I'll wind my own, looping coils of wire around the (insulated) handlebars.

More ideas please. I need passive elements, I don't want to hook this up to power. Well, not to non-pedal power. Any ideas I'll try. If I use it I'll give you credit. Bear in mind that time is short.

Thanks,
Keith
 

lohi

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Joined
Mar 9, 2006
Messages
15
Location
Winters, CA
I forgot to add that I'd like any ideas for changing the sound, not just filtering. It mostly sounds like an engine or motor shifting through gears. Interesting for about ten seconds. I plan to have at least one big rotary switch with which I can exchange various elements, especially series stuff. Shunt elements will probably need a second switch.
 

tv

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Feb 22, 2006
Messages
1,459
I attached the simplest form of what would be an "equalizer"

It is far from being perfect, and the controls would be interactive so a "mid-cut" would in some extremes act as a "hi-boost" of sorts...

Also, depending on the values of what-you-have at your disposal, it may work "good" or "not work at all" (IOW it won't have the effect you're after)

You will have to use what values of the components you have at hand and "tweak" it untill it somehow works.

If you want a pronounced effect, just solder some cap across your speaker's terminals.

This is no "special-fx unit", but I doubt you will make one in time.


Note: you could experiment with adding diodes accross series filtering elements, to make it a more "fx" unit.


CONNECT IN SERIES

Good luck!
 

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JohnRoberts

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Hickory, MS
Simplest way to drop volume is a series resistor. probably needs to be a power resistor, based on how hard you pedal, and how much power you throw away.

You could also drop peak power by putting two 8 ohm speakers in series...

JR
 
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