Pedal power

[PedalPower]

Hello all. I've seen quite a few postings about using the amps on bicycles but haven't found anything about powering them from bicycles. I hurredly cobbled together a pedal-powered generator for the electric piano for a recent outdoor choir concert and it worked really well: http://www.youtube.com/watch?v=Cq6JQwIftvk. Powering the piano even at full volume only required very little effort: I reckon I could get quite a few more watts out of it for a small amount of sound reinforcement. I use a 24V DC 250W scooter motor as recommended by http://www.magnificentrevolution.org/. The piano needs 12V for which I bought a very efficient switching regulator: http://uk.farnell.com/texas-instrume...060/dp/1109705.

It looks like the best amplifier is Amp 4 - single-ended supply, right sort of power, relatively high voltage. I realise I might have to protect it from excessively enthusiastic pedalling, which I could do efficiently with a normally-closed relay which is activated at 30V. And I realise I might need "rep coils" (audio transformers) as the piano will be operating from the same supply, but if I keep the ground leads short I might be OK without this. Any other thoughts? Pointers towards robust and efficient but reasonably-priced speakers would be helpful. Thank you.

[krilli]

That ... is ... so cool!

Did you have a driver size in mind? Have you seen the the DIY Boominator boombox? ... it's a bit on the heavy side w.r.t. what you're doing, but it's an exercise in efficiency.

[PedalPower]

Thanks krilli! They also put this one up but unfortunately you can't see the generator: http://www.youtube.com/watch?v=Nrr9sTiVBHw.

I haven't thought much about speakers so far. I'm tempted just to buy some complete units, but that would be admitting defeat to a certain extent. I did find the Boominator which looks like a great device, but a conventional stereo pair of speakers, probably on floor stands, would be more suited to this application.

[krilli]

OK, so the speakers themselves don't need to be all that portable?

[V-bro]

Super cool!

About 25 years ago I was connecting a Sony tape ports walkman to my bicycle 6Vac generator and made a rectifier and shunt regulator circuit to make it all work... This has always been a dream for me...

I also once saw this comic drawing of a guy sweating his balls off pedalling on a generator to power his TV. On the screen it said:"Patience please"...

------X-max. can be several meters on any driver, too bad it can be done only once...------

[PedalPower]

No, the speakers don't need to be that portable - we've got a 20kg piano, 3/4 of a bicycle and a heavy training stand to lug around so we're into vehicle transport territory already unfortunately. They shouldn't be normal domestic ones though - however careful you are it's impossible to avoid damaging those.

V-bro: I used to do similar sorts of things to you with your Walkman. I've still got some C-sized NiCd cells irretrievably wedged into the seat tube of my old bike. A colleague told me one of his friends actually did power his children's TV with pedals, to keep them fit! Come to think of it, the Nintendo Wii consumes less than 50W at 12V, and modern large LCD monitors don't take more than about 40W, so you could hang a rather good portable gaming setup off this generator. You'd need a battery or some sort of reservoir though to allow quick changes without interrupting power. Magnificent Revolution uses enormous capacitors (1 Farad+) designed for antisocial car stereos, but they're only rated at 20V or so max.

[krilli]

Consider getting special PA speakers. They should be more rugged, and they're usually more sensitive than domestic speakers, so you'll get more loudness for less pedaling. Also, they're more geared toward dispersion etc..

[PedalPower]

Yes I think I'd get PA-type speakers - the question is which ones. Oh well.

[krilli]

Yes

[PedalPower]

For interest, a colleague has recommended various speakers:

Skytronics 952.990: very small and very cheap; not very sensitive (89dB)
Studiospares Forte: 93dB
Studiospares Fortissimo: 96dB; a proper PA speaker with stand mounting
Toa F2000: pricey

I'm a bit worried about clipping destroying tweeters if the supply voltage starts to fall. I don't know if it's feasible to use the OVRLDB output of the TC2000 to open the output relay. Come to think of it, what controls the output relay? (I haven't bought one yet so don't have access to the instructions.)

And also on varying supply voltage, I notice from the data sheet that there's a resistor which you are supposed to select based on supply voltage. I wonder if I could replace this with an active circuit to adjust it automatically?