Yes, the LM386 is cool that way. You can easily use it with a single supply... I am going to the thrift shops this afternoon to scrounge up some speakers. I want to get a pretty big one (8-10 inches), but which is fairly light weight (smallish magnet). The idea is to keep the weight down for portability, but have a big surface area to make a nice deep bass drum sound. The 6" subwoofer I have is too damn heavy and actually sounds less deep than my nice vintage 8" organ speaker. I don't want to use my nice vintage speaker for this thing (save that for my next amp!), so I'm off to find a cheap one at the thrift shop. Once I get the speaker, then I can continue to fine tune the drum voice by fooling with the cap values. The idea will be to tune the drum sound to the speaker I end up buying, so that sound will be the best it can be for whatever speaker I end up using....

Here's a slapped together schematic of the circuit I'm working with so far. It's likely that the cap values on the left side (the drum side) will change a little as I fine tune. I'll upload a final schem when done...

I see now that I did not put a coupling cap between the drum circuit and the input of the lm386. Another DUH moment for me. I put one in and it all works VERY well. I'm only using one of the two "transistor drums", as I find I get a louder output that way. With an 8" 8ohm speaker, it is pretty damn loud enough. Not as loud as a real bass drum hit with a hard beat, but PLENTY loud for my application. Actually, I find it's the perfect volume. Normal kick drums are too loud for street playing unless you really amp up loud... I'm still playing around with cap values to find the best bass drum "voice", but this project is a definite thumbs up.

I will cobble together a schematic shortly, and after it is together, I'll take some pictures and post some sound clips/movies. I have a good idea for the housing and the pedal trigger.

Thanks again JM,

You are THE man!

Well, the drums circuit works fine and sounds great through a 25 watt amp, but it does not seem to marry well with the lm386. I built them together on the same breadboard, powered by the same 9volt. After experimentation, I went with the super simplified version of the lm386 that is in the "Smokey" amp. I hooked up a speaker and used a mic to confirm the amp works fine (it does!), then connect the input to the drum circuit. No sound. I check the drum circuit again through my test amp (25 watts). It works!. I test the lm386 again. It works, and is plenty loud enough to hear the output from the drum circuit. I reconnect them again. Nothing... The only thing I can think of right now is that the drum circuit does not like sharing a power supply/power ground with the amp? Would this make sense? I'm setting the lm386's negative input to the ground reference (same ground as the drum circuit, and all connected to the - battery lead). Is this wrong? I'm perplexed!

I put the drum circuit on the breadboard today, and it sounds awesome through my test amp. I'll add the lm386 circuit to the breadboard and try it out through a few potential speakers. This is a potential winner of a build!

OH! That's and even BETTER idea! I hadn't even thought about making an electronic foot drum!

If I'm going to power it, I might as well make the whole think electronic!  Duh!  :duh

This way I can make it much more compact and robust,a nd don;t have to worry about producing any kind of acoustic sound... Much easier and simpler, and much cooler! I will definitely do it this way! Thank you VERY much for pointing this out to me!

Yes, i also play didj, and I can confirm that a piezo (DIY from radioshack buzzer) will not cut it. Dynamic mics also don't cut it. Your best low cost DIY solution will likely be to use an electret element. You can buy these at Radioshack. You'll also have to build a battery-box to power it.

This link will get you going on a good design: http://www.oldbird.org/mike_home.htm

JM, thank you for the WONDERFUL reply! You are a great source of knowledge!

   I have been using my smaller "stompbox" that I made from a cigarbox and piezo transducer with great success through my lm1874 amp using a hi-fi speaker. Usually, I only use it at 1/4 of the volume because of feedback, but this is still pretty loud.
The reason I wanted to try with an lm386 is because of portability. Being powered by one 9volt makes it easy. Higher wattage amps would need bigger/more complicated battery arrays. This thing would be for street playing, so battery is a must, and volume is only secondary, I suppose.

  I read what you say about the lm386, and I agree that the variety of "poarchboard" I linked to will be probably louder just acoustically than amplified with that chip. However, what if I made a smaller variety? One that would not have too much acoustic volume? ie. just a board with a transducer, and no acoustic resonating space? So in this case it would just be the tapping on the board with my foot that would be amplified, not the resonance of this tapping as with a fully acoustic stompbox. I could then mount the speaker up front facing forward for sound projection... Something like this:

Speaker and amp

        \
        ||_      Flat board to tap on
        ||-|             
        /   ||=================||
                   ^
     Transducer will go here


  I suppose the only way to tell for sure is to try! I will go ahead with the circuit I posted below, and I will report back with my results. If I need a bigger amp, I will ask then for some more advice!

Thanks again for your great reply!

I found a schematic for that bass boost function I mentioned. What do you guys think, should i give this a try?

oh, i forgot to mention that i had read somewhere that you can get a bass boost function on the lm386 by connecting a small value resistor in series with a smallish cap between pins 1 and 5. I think like 10k and .33uf? I think you also have to leave pin 8 open.... Anyone have experience with this mod?

Hi guys,

   It's been a while since I've posted anything here, but I've definitely been lurking around and reading posts... Not to worry, I'm still doing crazy DIY audio electronics stuff in my mad scientist workshop here in Arizona!

That brings me to my latest project idea: an "self-amplified" porchboard (also sometimes known as a "stompbox", not to be confused with "stompboxes" in the pedal effects sense). If you want to understand what I mean better, see these links:
http://www.porchboard.com/
http://www.tomdukich.com/stomp%20box.html
Basically, it's a thinish wooden box with a pickup glued inside, and 1/4" jack that you run out to a bass amp or a powered subwoofer. When you stomp your foot on it, it sounds like a bass drum. It's for solo people to self-accompany themselves with a but of rhythm...

Okay, so my "big idea" to improve the idea is to incorporate the bass amplifier into the porchboard itself. I've built a small one from a wooden cigar box with a piezo pickup, but I'll go much bigger with this one. I've got a subwoofer speaker (taken from a defunct, but high end, computer speaker set), a range of pickups to try out (piezo, dynamic, etc.), and the heart of the matter: an lm386 chip. The idea is to have the pickup fed right to a simple lm386 circuit that's house IN the porchboard itself. The lm386 will drive the subwoofer, which will also be housed IN the poarchboard.

So, I wonder if anyone has any advice about building an lm386 circuit that will sound good in this application (ie heavy, thuddy, bass tones). I want to avoid as many problems with feedback, muddyness, fartyness, etc. that I can. Can anyone point me to a good lm386 circuit that sounds good with bass tones? I'm worried that using a stock ruby/little gem/noisy cricket circuit will be too trebly for this application?  I'd like something with a simple but effective one knob tone control that I can use to change the timbre of the kickdrum sound a little bit, but the minimum control will just be an on/off switch and volume (I've got plenty of pots with integral switches, so I'm good there)

Any advice would be appreciated!

Cheers,

DDC

There are three very simple preamps I know of that would fit your description. All are variations on the same theme. They are easy to find, just google them. First and most classic is the Tillman one-fet preamp. This is super easy and has been around a LONG time. There are even instructions for how to fit one in a 1/4" plug on a cable. The classic uses a J-201 FET, but there is a version for an mpf-102 as well. I've built both. Next is a derivative called the "piezo pre", which is basically a tillman pre someone tuned for use with piezo pickups. I have not built this. Next is the "fetzer valve" from runoffgroove.com. This is a well like one. I've built several.

All these are super simple, one-transistor builds, run off 9 volts, and are small enough to be easily mounted on board a guitar. There are others out there too, but these are good starting places.

Good to know that the amp is working! Sounds like you will definitely need a preamp though, and perhaps one with significant gain. Maybe even a lm386-based one? I know Armstrom on this form had success building a harp amp with a lm386-based pre. Look for the "smokey", "Ruby", "little gem", and "noisy cricket" schems. Those'll do ya well.

The best solid state harp amp I have currently is one I constructed from an old radioshack PA amp I bought for $8 at the Goodwill. It's a "Realistic" brand, model number MPA-20. Very importantly, it's an older one, and the circuitry is 100% discreet (ie. it uses power transistors in the poweramp section, not a chipamp). The newer MPA-20's use a chipamp, and don't sound nearly as good. The only modification I did was to remove the "phono" section (I'm not feeding it input from a record player!), and to change how the negative feedback loop get's tapped to the output transformer. Originally, the NF loop was connected to the 8ohm tap of the OT. I removed this tap, and added two new leads, one to the 16ohm and one to the 4ohm tap of the OT. I made it switchable. When you go to the 4ohm position, it get's crunchy and breaks up early. It's also a bit louder. When you go to the 16ohm tap, it's a little quieter, but MUCH cleaner, even cleaner than it originally was. Both settings have their purposes, and I think both sound really good. This amp also has two input channels (with two separate pre's and two separate volume controls), so it's a really versatile amp. I can plug both harp and guitar into it, or harp and a footdrum (porchboard). BTW, this amp also sounds killer with my cigar box guitar (it's an acoustic with a piezo pickup).
I built this PA into a custom cabinet I threw together with singe 25 watt 8" paper-cone speaker with a smallish magnet. It's one of a pair that came from an old organ. The BEST harp speakers that I've ever found.
Anyway, the point of all this is to say that PA amps are a really great place to look for nice solid state Harp amps. PA amps have been used for years for harp (eg. look how everyone loves those old Bogen PA heads), and a nice solid state one will work as well or better than a tube one. That amp you are buying (the Lapai) is basically a PA amp. I'm not very familiar with those tripath chips, but everyone seems to think they sound good for instrument amps. You are probably on the right track. If you don't get THE sound you want out of it at first, then you'll need to start experimenting with Preamp circuits until you find one that works well with that particular chip. I suggest starting with something like the Fetzer Valve or the Tillman pre (both very simple one-transistor designs), and then move on to something like the Peppermill or Blue Magic (relatively simple two-transistor designs). Any of these preamps should let you dial in a relatively clean tone, or get a nice mild overdrive.

I found a reply direct from Adam from his own Modern Blues Harmonica forum where he discusses why he likes smaller speakers for harp:

Isaac:

The only thing I need to add to your interesting post is that some of the distortion--for the best overdriven amp sound, I mean--needs to come from the speaker cone. It's generally easier to get this from smaller speakers (6", 8", 10") rather than larger speakers (12", 15"), but the key thing is that the magnets need to be relatively small. A Hartke 4 x 10" bass speaker cabinet will sound like crap for harp because the speakers have huge magnets, precisely so that they WON'T distort when you're running loud low frequencies through them.

Amplified harp sounds best when the various sorts of overdrive--preamp, power amp, speaker--accentuate a certain high-mid frequency range. One reason old tube amps sound great, I suspect, is because they (ideally) have original speakers, with old paper cones. I remember playing through a tweed Champ, mid 50s, with the original speaker. Incredible sound.

I have two Mouses. They're identical, except that one has a plain capped speaker and the other has a speaker with a projecting lip of some sort--about 1" high. A mini-loudspeaker coming off the cone. Much, much better sound.

I didn't know that the ideal in a solid state amp, for harp, is to overdrive the preamp but not the power amp. That's interesting.