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-   -   amp for bike stereo (http://www.diyaudio.com/forums/chip-amps/117919-amp-bike-stereo.html)

notrobb 21st February 2008 08:30 PM

amp for bike stereo
 
Hi, I'm brand new here, but searched around and didn't see this question anywhere else, so here goes..

I'm wondering if anyone can recommend an amp for me to build that would be good for a bicycle stereo, i guess like a diy sonic impact t-amp, but i'd rather build it myself (not because i'm cheap, it's really more of a pride thing)

- stereo output (from what i understand i might build 2 identical amps?)
- portable (ideally fit into a cigarette tin, which is slightly larger than an altoids tin)
- battery powered (might convert to solar eventually)
- output to 2 small computer speakers that will be mounted on my bike
- input from my ipod

I'm fairly new to electronics, so the theory is still hazy, but i'm learning. And i can follow schematics and instructions well (i just built an APC from scratch).

Thanks in advance for any input!

Bearman 21st February 2008 09:50 PM

You might try a small Amp3 from the 41hz website. They are basically a better sounding T amp that runs on 12 volts. Using a 12v 3amp SLA battery should last for a couple of days.

At Jans site also, he has a AMP9 that is 4 channels that can run on 12v too. A bit higher wattage amp, so the battery life is not as long. Thay are all class D amps so the efficiency is much higher than the chipamps are.

They both require soldering small SMD resistors and caps so they do need a steady hand and a pair of tweesers and a soldering iron that has a small tip.

Good forum for ideas and help over there too.

danielwritesbac 25th February 2008 04:31 PM

What kind of bicycle is it, and is "lightweight" a primary factor?

Edit: I meant to ask if its the sort of bike that zooms over rocks, or if its the sort of bike that's expected to climb tall pavement hills at near-racing speeds?

xiphmont 25th February 2008 04:36 PM

Quote:

Originally posted by danielwritesbac
What kind of bicycle is it, and is "lightweight" a primary factor?

Edit: I meant to ask if its the sort of bike that zooms over rocks, or if its the sort of bike that's expected to climb tall pavement hills at near-racing speeds?


... or are we talking 'Gold Wing'? :-) OK, I know we're not, those come with surround stereos, but some other big bike...

[edit: oop, never mind, he did eventually say 'bicycle'.]

danielwritesbac 25th February 2008 05:05 PM

Unlike the motorcycle, the bicycle has limited flywheel capacity, which is the rear wheel. With the cyclist (even if skinny), there's already an insufficient flywheel. This causes the propulsion to be in "micro-pulses" so that the weight of the bicycle is a limiting factor on its speed.

That's why I was thinking that a smallest size canvas handlebar bag could contain the amplifier as well as serve for speaker enclosure. There's a little "can shape" model from SunLite, and it has round, speaker-size, nylon canvas ends, as well as a sturdy hard plastic sheet that covers the insides, except for the ends. Ah! A speaker enclosure. ;)

One could fetch a pair of "grandma kitchen" type portable plastic radios from the local thrift store, and remove the hyper-efficient speaker drivers. Those are about 3 inches, 8 ohms, with over 100db efficiency (typical). They're better than usual computer speakers. These could be somewhat waterproofed with polyurethane for furniture, or the prosound speaker waterproofing compound.

A disc of super-light waterproof material could be made to assist in gluing the now water-resistant speaker drivers inside the ends of the above handlebar bag. Its cutout for the drivers would be slightly smaller than the drivers so that it could press them into place. Siliconized construction adhesive (nail pro) is strong enough to hold the described disc in place (which holds the speakers in place). That will keep the backwave from eating up the bass response.

Then a miniature class-D amplifier could run this pair of speakers; however, one would want to increase its efficiency by selecting input filter caps (very small polyester) that are able to remove bass that couldn't come out of that size speakers.

Some of the 1 to 3 watt class-D are able for sufficient power on 3x AA batteries, and could run all day long with more than enough volume, considering 103db speaker as a resource. Those amplifiers will be over at the Class D forum.

notrobb 25th February 2008 05:15 PM

well, i ride a fairly light roadbike. mostly around the city and not in a racing sort of way. a pocket sized amp is definitly what i'm hoping for.

i'm considering doing a CMOY in a tin and getting some cheap battery powered computer speakers. it's more for me to hear music than to be blasting it to the whole block anyway.....

notrobb 25th February 2008 05:15 PM

thanks for the advice daniel,
that sounds like the sort of setup i'm going to shoot for.
R

xiphmont 25th February 2008 06:19 PM

Batteryspace.com semi-regularly has sales on LiIon + charger combos. I don't think they have a sale going on now, but that's how I got the batteries for the lights on my bike. 5g per watt-hour... mmm.... I can run low beams for a whole day for only 250g. :-)

danielwritesbac 25th February 2008 08:17 PM

On the Oklahoma Freewheel (amost 500 miles with no outlets available), I take a Kodak digital camera (2gb card), an RCA Pearl, a Serfas 8 led light, and then some. All of these can work with rechargable (usually), lithium, or standard--And, if the music quits, you can get back to the music fast with a quick stop at the Quick Shop for ordinary size batteries. ;)

Or, if using lIon, you could plug it into the nearest electrical outlet and wait. . . and wait. . . This is usually fine for the mountain bike, because they usually return to home base, and that's a more seemly location for it to nurse upon electrical outlets.

However, on the road bike, travel bike, and new turbo-hybrid (traditional Dutch comfort on an otherwise racing bike), they follow a $1 (us) per gram performance to weight ratio, in general. They also cover long distances, usually 80 miles with very little effort. Although the effort involved is mostly reliant on a good fit (like good clothes fit), still any increase in the effort could decrease its range.
Remember, these bicycles repeatedly accelerate rather than use a flywheel, so the machine weight is a vital consideration when designing an audio system for it.

So, that's why I suggested the miniature (postage stamp size) Class-d amplifier (small batteries) and hyper-efficient speakers. ;)

Some athletes maintain 2 bicycles, both with an identical fit, but one is much less efficient for extra exercise (the workout bike). So, if the audio system is for a "workout bike" then by all means tape a hi-fi to it. ;)

P.S. For a small Class-D amp, its possible to cause it a slight power boost by running the speakers as a capacitive load. Perhaps a 10v, 1000uf cap or smaller (its small anyway) in series with the speakers, could help. Polarity is usually the same as connecting speakers in series. Capacitive loads can perform a soft-clip instead of the usual Class-D hard clip. So, while that isn't really more power, it will sound like it. ;)
That's good for an exuberant moment with the Ipod. Specifically, I mention this because some MP3 players have a terrible sound at the EQ Flat setting, but the other settings may cause a miniature amplifier to clip. If your source has the variable 5 band EQ instead of the fixed selections, then you probably don't need the output cap. Otherwise, its worth a try. ;)

Andersonix 4th March 2008 02:13 PM

Quote:

Originally posted by notrobb
well, i ride a fairly light roadbike. mostly around the city and not in a racing sort of way.
Safety Nazi Say:
DON'T RIDE YOUR BIKE IN TRAFFIC WHILE PLAYING MUSIC. If you look it up, you'll find that it's also illegal (for a good reason). Come on, you're extra vulnerable as it is on a bike, so why add to the distractions?
Carry on...


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