What can substitute for this kind of trigger input?

[Mark Hammer]

I had built a quartet of these units - http://www.muzines.co.uk/articles/the-syntom-drum-synthesiser/2593 - to supplement an all-analog e-drum assembly.  Had a devil of a time getting these little "syndrum"-like units to sweep or simply trigger.  The magazine article indicates use of crystal earpieces as the triggering source.  I have a couple, but they seem to be non-functional, so I tried other much lower impedance headphone cartridges, but they didn't work, either.  Finally, I unearthed some crystal mic cartridges (probably from telephone handsets) I had bought years ago, and they worked like a charm.  But I only have two of them, and would prefer to save them for other purposes.

So the question is what sort of external signal, fed to the trigger input of these drum circuits, would have roughly the save characteristics as a tap on a mic cartridge or crystal earphone?

[Strategy]

I've always wanted to try building these vintage magazine drum circuits! There are four or so different ones in this series and with PCB patterns floating around the web. But I haven't gotten around to it.

You have a lot of options> I have done a lot with drum synth circuits. Though a long time guitar pedal builder, I've been a drummer in as many projects as I have played keys or other instruments, so of course I sought out electronic DIY projects for drummers!
1. I most commmonly use use a piezo disc which wouldn't be so different from your old telephone elements. Different sizes yield different results. I modified an 8" acoustic rack tom with a piezo mounted under the drum head so I could play my DIY drum synth modules from my drum kit. But you can mount a piezo disc in/on anything. This will be very similar to what you've done so far but some of them put out a pretty big signal. These are extremely cheap and easy to get depending on your fav suppliers.

2. Sometimes synth/drum machine trigger sources, although on some vintage drum synth circuits like (like my Star Instruments Synare clones) the results are really mixed especially if it's just +5V coming from the trigger source; there's not enough voltage for some circuits that's looking for the larger spike that comes from a piezo.

3. You could also use orphan electronic drum pads, provided it's a mono/single zone (t/s) jack one. A lot of these have a piezo deep inside. Maybe $25 on Reverb or Ebay for that. The nice thing about those is you have a bouncy, drumstick friendly surface and often a mounting bracket already on it.

4. Audio sources can be made to work, but you have to be able to gain up the signal and experiment with getting it loud enough to trigger your instrument.

I hope this helps!
Strategy

[Rob Strand]

1. I most commmonly use use a piezo disc which wouldn't be so different from your old telephone elements. Different sizes yield different results. I modified an 8" acoustic rack tom with a piezo mounted under the drum head so I could play my DIY drum synth modules from my drum kit. But you can mount a piezo disc in/on anything. This will be very similar to what you've done so far but some of them put out a pretty big signal. These are extremely cheap and easy to get depending on your fav suppliers

+1

[Phend]

When I google diy stompbox I get things like this. .. see the end of this video

[PRR]

....crystal earpieces as the triggering source.  I have a couple, but they seem to be non-functional,

Stick it in your ear. Tap a 9V battery to the leads. If it don't CLICK, it's dead. Extreme drive can do that, but also just old age. The crystal is sensitive to moisture and/or temperature, and consumer-grade elements don't last.

....crystal mic cartridges (probably from telephone handsets) I had bought years ago,...

North American BellTel phones never used crystal mics. Low-Z carbon, then electret. Some post-Bell phones used piezos (fancy "crystal") for ringers/dinkelers.

....they worked like a charm.  But I only have two of them, ...

Can you post a photo? It may be super common once you have a name. (Or are there still real electronics shops in your area? The proprietor or the gnome in the back room may know whatzit and where the surplus is hidden.)

[Ripthorn]

I designed a simple analog kick from pedal that actually used a microcontroller to create my pulses with tap tempo. Easy to dial in pulse width, etc.

[Mark Hammer]

As requested...

One of the mic cartridges shown has a bit of the front "surgically removed" (I forget how I accomplished that).  Inside is actually a suspended piezo disc.  The plan was to use the cartridge as a sensor for a homebrew spring reverb system, which is why you see a spring soldered to the centre of the disc.  It actually worked pretty well in the prototype I made some years back, and is awaiting a more formal construction.



I'm thinking that the collection of piezo discs I have - ranging from about 5/8" to 1.5" across - ought to be sufficient.  I had made up some pads for triggering, by wedging discs between thin sheets of cork.  That was providing very modest outputs, and not triggering the Syntom.  When I measured the output of the bare discs, however, by placing the disc on the desktop, uncovered, it was pretty substantial.  So maybe the issue is not what I was trying to use, but the packaging it came in.

I'll try triggering with a bare disc, and report back.

[Rob Strand]

When you stick a disc piezo down on a panel it becomes a contact microphone which will have significantly higher sensitivity.  On normal mics you want to minimize handling noise hence you will suspend elements with rubber and foam so they don't touch the casing.

FWIW, to increase with the sensitivity you can increase the 1M feedback resistor.

[Mark Hammer]

I'm wondering what might be able to provide a suitable trigger pulse, if generated by a sequencer.  The article doesn't really say.  It seems to assume that one would ONLY employ manual triggering by physically striking something.  I'm not opposed to that, but it would be nice to know if the units could be harnessed to something more automated, if one wished.

[theehman]

Maybe something like the EHX Clockworks?

[Strategy]

EHX clockworks is a great idea, Korg SQ-1 but I think it won't have enough trigger outputs to run all four of your modules. The Korg SQ-64 has 8 trigger outputs and a used one is only slightly more expensive than an SQ-1! I use the Frostwave Fat Controller, and when it's not in a state of failure, I use the tom channel trigger outputs from my Roland TR-606.

There may be posts about the Syntom, Synchime etc. projects over on the electro-music forum that tease some of this out, been a while since I spent time over there but I think that's where I first encountered these circuits.

Strategy

[Mark Hammer]

Hooked up a bare piezo disc, and everything works properly.  I guess the problem was that the cork pads I was using to damp drumstick strikes was damping so much that  the disc wasn't providing enough of an output.  With the cork removed, the disc delivers the goods.

Forum member Chillums astutely drew my attention to another e-percussion project in E&MM magazine that also uses a crystal earphone to trigger the unit, BUT also provides for use of a sequencer or other electronic trigger pulse of 7.5-12V.  The circuit is easily adapted to this Syntom, so I may not have to rely on the piezo devices exclusively.

[Rob Strand]

I'm not sure how well this would work but I was thinking what would happen if you have a panel with rigid edge supports.   Then mount one piezo in the center and one (or more) near the edge.   You then for example duplicate the circuit upto IC1 pin 10.  For the edge piezo(s) you have with a faster time, different sensitivity and perhaps a DC offset.   You merge the two circuit together before pin 10.   The whole idea is you can get different pitch or decay rates by hitting at the pad at different locations.

No doubt to get it to work at all will take a lot of finessing but the strike-position dependent behaviour would be a cool feature.    The circuit will be similar in principle to what's there but will be a more complex variation.   You could scale the decay rate off a single pot using current mirrors although to start it's probably easier to have two pots.

[amptramp]

There is an interesting drum synthesizer on page 49 here:

https://worldradiohistory.com/Archive-Radio-Electronics/80s/1980/Radio-Electronics-1980-05.pdf

and the construction and use are on page 59 here:

https://worldradiohistory.com/Archive-Radio-Electronics/80s/1980/Radio-Electronics-1980-06.pdf

It allows external inputs to be applied through the J1 input jack and the J3 external input jack.  There are control pots for

sensor gain
envelope decay time
initial pitch
modulation up/down
waveform selection
noise/oscillator mix
noise filter
output level

and there is a switch for sweep/man and status lights for power and trigger detected.  There are six jacks for:

trigger input
ext CV in
ext signal in
ef/trigger out (stereo jack)
output
cancel

This is an ambitious machine but you don't need everything in a drum machine.

I do have one suggestion for a piezo transducer location:  put it on the drumstick.  I have a toy synthesizer which does exactly that - it has two plastic drumsticks with the piezo sensor on the end of each of them.

[StephenGiles]

I'm wondering if those electret mic capsules available on ebay might do the trick, might need some preamping though.

[Strategy]

that magazine article illustrates a classic remo practice pad which can be opened up and rigged with a piezo in its pad layers.
I've always wanted to try this, too. Those pads are still made all these years later in essentially that same design, and are pretty inexpensive IIRC.
I may be wrong but I think they even feature a stand mounting bracket on the bottom like a threaded insert, so you could stand and play them.
ideal DIY electronic drum pad vehicle. But again, orphan electronic drum kit pads are so plentiful that if you didn't want to DIY your own playing surfaces, you'd have lots of cheap options.
- Strategy

[anotherjim]

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[amz-fx]

From last century...



regards, Jack

[Mark Hammer]

From last century...

regards, Jack

Thanks, Jack.  I can always rely on you, Thomas Henry, or Craig Anderton to bail me out.

[amz-fx]

Thanks, Jack.  I can always rely on you, Thomas Henry, or Craig Anderton to bail me out.

The schematic I posted is from a project that I did with Tom Henry for Nuts & Volts magazine around 1997. I was going to post a link to it but a quick look around their site didn't turn it up.

Bets regards, Jack