MIMF

by **phil donovan** » Tue May 01, 2012 10:21 pm

Hello. My friend is building a series of basses that he designed. He would like to experiment with installing an amp/speaker system inside some of his basses and asked me to inquire about possibly pre-made circuit boards to look at that may work for him. I told him that I would be happy to do so and I look forward to your feedback!

Thank you,
Phil

by **Greg Robinson** » Tue May 01, 2012 10:29 pm

I don't know of any pre-made circuit boards, unless you were to buy an amp, but there are a number of products like Smokey amps, and Ruby amps that run on the venerable LM386 chip, and you can quite easily get a half-watt (which is plenty loud with an efficient loudspeaker) out of one chip, two capacitors, and a 9V battery. There are all sorts of variations you can make to the circuit for different sounds, but this is about as easy as it gets.

Let me know if you want to know more.

EDIT:
I just remembered I'd seen an amp/headphone driver over at GuitarFetish, (sorry, I'm browsing from my phone, so it'll probably take you to the mobile site). I don't have any experience with this product, but it sounds like it would be perfect for your application.

by **Alan Peterson** » Tue May 01, 2012 11:48 pm

Not sure what kind of sound to expect from a speaker inside a bass instrument. It may well put out more of the higher harmonics than a nice rumbly fundamental. A larger speaker with a lot of throw is needed to adequately reproduce bass frequencies, and the power needed to run the driver is kinda steep.

On the other hand, the Bose "Acoustic Wave" radio can get piles of bass with a small speaker because the interior of the radio is a labyrinth which creates a long "organ pipe" which reinforces the bass frequency range (Cool cutaway view at http://www.bose.com/controller?url=/pop ... e_awms.jsp). With a little creative lunacy, he might be able to construct such a path inside an acoustic bass body.

If the project proves too irresistible to ignore, I might suggest an amp circuit with some legs... like the 3886 power amp used in the "Gain Clone" hi-fi amplifier. A battery can't adequately power it, but with an external 26V power supply its got power to spare. See details at http://www.eeweb.com/project/circuit_pr ... er-project

by **Mark Swanson** » Tue May 01, 2012 11:59 pm

Like Alan says, I don't think you'd get much useful sound out of a smaller amp and speaker built right into an instrument. A guitar is one thing, even that has many challenges but a bass has a whole different set of needs and it would be very hard to make that work out.

by **Rodger Knox** » Wed May 02, 2012 1:05 pm

Alan's idea has some merit, but I'm inclined to agree that an internal amp and speaker is not viable for a bass.
No doubt it can be made to work, but it won't sound as good as a $20 practise amp.

by **Greg Robinson** » Wed May 02, 2012 3:52 pm

I kinda figured Phil was going for the novelty factor of an in-built amp/speaker combo, I mean, sure it might not work as well for bass as for guitar, but the guitars aren't serious instruments either, are they?
Really, I'd just go with a Smokey circuit based on the LM386, or the GuitarFetish speaker amp, and find the best efficiency small speaker with decent response down to 40Hz (the frequency of the low E on a bass), something like this from Digikey, and call it good. You could increase the headroom to the circuit by using two 9V batteries, or use a charge pump like the MAX1044 which is cheap and designed for audio applications if you only want a single battery.

I've played around with some stuff like this and it can be some fun.

by **phil donovan** » Wed May 02, 2012 8:21 pm

thank you all for your generous responses. this is just the stuff Pete will be looking for, doesn't have to be too good, just enough for some novelty on some basses. I have built some things with the LM386 chip, and that might even do. Ill get this over to him, he'll be very happy. by the way, my friend Pete, who is one of the most brilliant people I've known, will be checking out MIMF very soon. He's coming straight out from the Alaskan depths and just entering into the world of computers, well, digital anything world. I told him how great this site is and he's very excited about the prospect of meeting you folks and learning/sharing.

thank you all!

Phil

by **Alan Peterson** » Thu May 03, 2012 10:14 am

Fun, absolutely! That's what music is all about. Just dont feel bad if that 5 cm speaker doesn't deliver as you hoped.

Even if it can give you 40 Hz, it will be several dozen dB lower than the range where the speaker works best. And you'll be popping batteries like Pez to keep things rolling.

You want to really get nuts? Try passive amplification --- do a search for a Stroh Violin. If Pete wants a novelty instrument, things don't much crazier than this!

by **David King** » Sat May 05, 2012 4:32 pm

If you can stand having a 12V supply (8 AA cells) you can't beat the tone and efficiency of a Class-T (tripath) amplifier. Sonic Impact sold them for a while, they were cheap and very small with a stereo input and 15W/channel. They can drive a 2 Ohm load and produce no heat to speak of, better than 85% efficient.

Here's one that looks similar (but without the battery compartment) http://distressedinventories.com/lepai- ... 12%2019:35

This looks even better as a built-in http://www.amazon.com/gp/product/B002IA ... =486539851

You can get decent bass out of an infinite baffle transmission line driver which could be built in miniature inside a bass body. I looked into it seriously about 10 years ago but decided it was a dumb idea when considering feedback potential.