Electronic Bongos

[FUZZZZzzzz]

I wanted to build something fun today and found this schematic. To my surprise it actually works. The potmeters set the decay. Too high and it will oscillate. When you turn it down a little its a pretty convincing bongoset (as in cheap drum machine) as the two oscillators are tuned differently. My only trouble with it is that it's not loud enough. Could be the design? Is there an easy way to raise the overall volume or should I build some kind of booster? Would it help to take out the two 10k resistors before the 100n output cap? If I get the volume right I will share the layout

[Kipper4]

If you scale down the 10k you'd have to change the output cap also.
It forms part of an rc. cr network.
Maybe tack on an amp instead.

[anotherjim]

Those 2 10k's are a passive mixer. They have to be there to stop the 2 generators fighting - although that could be another sound too, I expect that could get messy.
What I'd do is replace the output with an opamp 2 input mixer, then you can add as much gain as you want.

[snk]

Nice !
Did you make a veroboard layout for it yet ?
It should fit nicely with your russian clap machine

[FUZZZZzzzz]

Well.. here it is. I've combined it with a 741 preamp circuit. I had a 741 laying around. I left out the input cap.  I also drew a layout, but as I later added the preamp I had to change a couple of things. It's looks a bit weird now. A lot of open spaces .  Hope its ok and working as is. Enjoy! I made a video!!!!

[FUZZZZzzzz]

[snk]

Thank you !
Can the touch plates be regular piezos ?
Is there any way to change the tuning with a pot ?

[FUZZZZzzzz]

I think the tuning has to do with the caps around the touchplates. the potmeters only set the decay. mind you this is very simple circuit and very much a one trick pony.

"This circuit consists of twin-T sine-wave oscillators. Each oscillator has a filter in the feedback loop. If the loop gain is greater than unity, the circuit will oscillate. Gain is adjusted to be just less than unity. Touching the touch plate starts the oscillator, but the moment your finger is removed from the touch plate the oscillations will die away."

Anything metal or copper will start the oscillation. I dont think a piezo will contribute anything special to this circuit. But, I could be wrong.

[Strategy]

I tried to build this once from an old magazine article pcb layout and could never get it working in spite of the low parts count! Great to see one in action!

[Mark Hammer]

Nice job.  There's a ton of such twin-T ringing bandpass "drum" circuit out there, many of which appeared in Electronic Musician magazine (finger drums and a Craig Anderton circuit), Popular Electronics (see James Barbarello's "Cabonga"), Electronics Today International, and Elektor, not to mention the various compact non-sampling drum machines from Roland, Korg, PAiA, and others.

The vast majority of those units, however, relied on an external trigger, from a "brain" or simple clock-sequencer, rather than a touch-plate, as in this example, so construction is that much simpler.  Note that , with the addition of an active mixer stage, there is no limit to the number of "drums" one could incorporate into this  arrangement, apart from the ability to differentiate them, sonically.  So, a 3 or even 4-drum assembly is quite feasible.

[Rob Strand]

You gotta love those old analog circuits.

A better/separate trigger circuit would give a more convincing bongo sound.   Sounds like when you touch the pads the background Hum and Buzz comes through the audio.

[FUZZZZzzzz]

You gotta love those old analog circuits.

A better/separate trigger circuit would give a more convincing bongo sound.   Sounds like when you touch the pads the background Hum and Buzz comes through the audio.

I agree. theres a small amount of hum and buzz in the signal. the best 'bongo sound' you can get is when you put the pots on the edge of elf oscillation. All in all a fun circuit, but nothing I would use on stage live

At least now theres a video for anyone to decide if its worth the effort of building or breadboarding.

[duck_arse]

I'm not in this thread yet. from the video, there is enough for someone to breadbord it.

I did today, wasn't getting much touch action going, but only had a wire as a contact. doesn't sound like the vid, yet. I did try a piezo element - it works, but damps the tee some, changes the action.

[mozz]

Actually I had a set of electronic bongos, late 60s early 70s.  Probably my dad bought them from either Lafayette electronics or Allied.  Maybe even radio shack sold them  Most likely in their catalogs.  They did have a boining ringing sound.