lm386-powered amplifed porch-board bass drum idea

[darwindeathcat]

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

[darwindeathcat]

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?

[darwindeathcat]

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

[J M Fahey]

Hi darwindeath.
Great idea making this instrument. :tu:
I'd *Love* to hear an MP3, because YouTube quality sucks big way, specially on this which is a very deep bass drum, much deeper than a regular one.
Now on to he amplification side:
to begin with you can't put a speaker on the same case where you have a vibrating board which is the actual instrument, and its pickup, no way.
The original makers did not do it for a good reason.
On the other side, you need *a lot* of power, forget the LM386 (well, if you need headphones for monitoring while the line out goes to a big PA, it may do for that)
The amp/speaker suggested "officially" is a biamped system, by no one less than Bose, an acoustic Genius and I'm not joking, with 60W RMS to drive the 6 or 8 speaker column, plus an undefined power but certainly no less than another 60W driving a dedicated subwoofer, in a substantial box (look at the pictures, it's larger than the Bass Amp, the Powered Speaker and the 100W 2x6" Jazz amp).
With a hand over my heart, and speaking to a Friend,  I'd suggest at least an LM3886/TDA7294 driving the woofer (8" to 12")
For the midrange, which you'll need to have a clear, definite "kick", will be a couple 6" or 8" (or a column of 4x4" or 6" or a couple 6x9") driven by a similar amp.
Unfortunately you are in the territory of a drum, which not only is LOUD, but being percussive needs very high sound peaks; biamplification eases that somewhat.
The acoustic level produced by an LM386 will be buried by the *acoustic* sound of the instrument.
Anyway don't believe me, test it since it's easy and cheap, so you can later go on to a larger project with a clear mind.
That thing produces a 33 Hz sound, no kidding.
Since they know that neither bass amps nor big PAs reproduce that well, they already mix a 3rd harmonic (that's to say 100 Hz) to make it audible.
The "light" setting is 100 Hz, and the " medium" some frequency in between .
Just for comparison, the chest thumping bass drum in a drum set, is tuned from 90 to 100Hz; this instrument goes much lower, that's why they compare it to a marching band drum, which is *huge* and larger than what's used by the baddest Thrash/Heavy/Death metal drummer, go figure !!
I did make some amplifiers specifically for drummers who went electronic, with pads, modules, Midi and all that stuff, and a 3 way box, with a 15", an 8" midrange and 4 Tweeters, 100W powered, was no match for a regular drum. Close, but no cigar.
I had to upgrade to biamplification, 100 or 150W for the woofer, 60W for mid/high to reach it, and use 2 such boxes, one on each side of the drummer, to beat a regular drum set.
I repeat it; drums are loud.
Post some pictures and MP3s.
PS: the schematic you posted is correct, but we are talking clock radio/walkman/MP3 player here. Not even a TV set.
Good luck and congratulations on your project.

[darwindeathcat]

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!

[J M Fahey]

Then go all the way and fake it ... ahem! .... sorry .... "emulate" it
Try: http://www.talkingelectronics.com/projects/200TrCcts/200TrCcts.html#40
as-is (you have two drums there), you can send frequency up/down changing the capacitors, all in the same percentage; duplicating all three on each oscillator will lower you one octave.
I built them ages ago, and the bass drums were impressive and earth shaking.
You can trigger them as simply as laying 2 strips of wood 2 or 4 mm apart , each with some brass or aluminum paper contacts, and stomping them lightly with your foot.
Experiment, tune them a useful interval apart for a richer sound.
Cost and time is nil.

[darwindeathcat]

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!

[darwindeathcat]

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!

[J M Fahey]

Good. :tu:
Now, where did I put those plans about a *digital* Didgeridoo?
That funny crocodile hunter guy who came yesterday to my shop said he'd pay well for one of those. :lmao:

[darwindeathcat]

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!

[J M Fahey]

Draw what you actually built, maybe you are missing some coupling cap somewhere.
You do not need any fancy schematic drawing package, just draw it clearly on a sheet of paper and scan it.
Save it as a greyscale .gif .
.JPEGS are meant for color pictures, small detail becomes fuzzy and unreadable and letters and thin lines have "ghosts" around them.

[darwindeathcat]

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!

[darwindeathcat]

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...

[phatt]

The experts will know more bout this but,, I'm sure the pos input terminal of Opamps needs to see a DC path to ground ?  (In this case a single supply rail needs a half voltage refference)

Hey good idea though and it obviously works :tu:
Phil.

[tonyharker]

LM386 isnt really an Op amp but a small power amp.  It has an internal reference to earth of 50K.