DIY electret contact MIC for cymbals

Zapp Brannigan

New member
Hi,

I'm trying to copy the Zildjian GEN16 AE cymbal system. They are using something they are calling a 'direct source pickup' to amplify low volume cymbals. With this system you get true electric cymbals (instead of a trigger - sample system).

I think the 'direct source pickup' is an electret microphone configured to work like a contact microphone. So I tried making an electret contact microphone by attaching an electret to a flathead bolt with epoxy putty (see pic).

I hooked this up with a 50kOhm logarithmic potentiometer to a VM114 7W audio amplifier (velleman). For now, I'm powering the mic and the amp with a 9V battery (I could get a low noise audio power supply in the future). The contact mic is bolted trough a hole I made in an old sabian solar 16" ride (not a great sounding cymbal to begin with!).

I used the schematic in the attachment. But instead of a 10k resistor for the electret, I used a 1M resistor and I switched the capacitor for a 1000µF capacitor (it seemed to give les distortion). I also attached an small sound sample, doesn't sound that bad, but it could be better (the sound is only contact sound, there is no ambient sound picked up, which is great).

So my questions:
  • Does anyone agree that the 'direct source pickup' is in fact an electret mic hooked up to a preamp?
  • Any ideas on how to improve the sound?
  • Do I need another amp for the electret microphone?
  • I'm using a cheap electret cartridge, would it be a good idea to use a 'back' electret microphone cartridge? Any advice on which one to use?
  • Am I using the right circuit for the electret?

Thanks in advance, I'm a bit of a microphone noob, but it's an interesting project!
 

Attachments

  • Screenshot 2020-06-03 at 18.13.21.png
    Screenshot 2020-06-03 at 18.13.21.png
    699.8 KB · Views: 11
  • Screenshot 2020-06-03 at 18.13.14.png
    Screenshot 2020-06-03 at 18.13.14.png
    29 KB · Views: 8
  • 1000µ.mp3
    309.8 KB · Views: 12
OK, I discovered that the 7W amp is a really bad idea. Ik need a preamp of course. I used the following circuit
Screenshot 2020-06-05 at 23.56.14.png
This gives way better results, much less distortion when it's played loud.

If I hook this up to an equalizer I might get some decent results. I also ordered a higher quality primo electret capsule (Primo EM172-Z1), can't wait to try that one.

Any input on how to improve the sound would still be welcome :-)
 

Attachments

  • preamp.mp3
    329.7 KB · Views: 16
I used the schematic in the attachment. But instead of a 10k resistor for the electret, I used a 1M resistor and I switched the capacitor for a 1000µF capacitor (it seemed to give les distortion). I also attached an small sound sample, doesn't sound that bad, but it could be better (the sound is only contact sound, there is no ambient sound picked up, which is great).

So my questions:
  • Does anyone agree that the 'direct source pickup' is in fact an electret mic hooked up to a preamp?
  • Any ideas on how to improve the sound?
  • Do I need another amp for the electret microphone?
  • I'm using a cheap electret cartridge, would it be a good idea to use a 'back' electret microphone cartridge? Any advice on which one to use?
  • Am I using the right circuit for the electret?

A couple of thoughts...

All electret microphone capsules are back electret microphones.

If you want the best sound I'd take a look at some of the web pages describing how to modify the Radio Shack PZM mics. There's a good one at

Pressure Zone Microphones - History and other information

You will need to feed the output into a conventional balanced microphone input with phantom power.
 
I might be wrong, but wouldn't the PMZ mic also record a lot of ambient sound? I'll be hitting mesh head drums and other cymbals very close by.

I'm feeding the output of my preamp to the mic in of my roland quad capture audio interface. The phantom power is off, because the electret is powered by the 9v battery.
 
I suggested those pages because those circuits should also work with the electret capsules that you have. However, you ought get reasonable results using the simple circuit in your first post provided you use the component values shown in that circuit diagram (1M ohm and 1000uF are definitely not right) and connect the output to pins 2 and 3 of the mic input on the Quad Capture.
 
OK, thanks, I found the circuits to make the output balanced. Am I correct in assuming that the only reason for a balanced output is eliminating noise picked up by the cable from the mic to the amp? Or do balanced lines have other advantages?

Right now I'm using the circuit in my second post with a preamp in the circuit, the output goes to a behringer mx 1604a mixer (to the mic in)
I don't have any noise issues so would it be useful to convert it to a more complex balanced circuit?
 
I have another question:

I want to power multiple preamp + electret circuits with the same power source. Would it be possible to send the mono audio signal and the V+ power supply with a stereo jack connection?
I would try the following circuit, with multiple mic + preamp circuits in parallel connected to the same power source, each with it's own output to the mixer (only one mic + preamp circuit is shown).
+9V through the ring connection, ground through the sleeve and the audio signal through the tip.
preamp-supply.png
 
Most contact microphones that I've seen are piezo microphones. Piezo microphones use a thin ceramic element that is metalized on each side. WIres are connected to each side and the microphone produces an electrical output when the ceramic element is deformed by sound vibration. These mikes have a very high impedance and sometimes have a matching preamp, but should work when plugged into a direct box. They are usually attached to your sound source with a removable adhesive. They can be cheap, I just saw a set of 5 mics on Amazon for $14. (Search for contact microphone) For the price, it might be worth experimenting and seeing how the sound compares with your electret microphone. Play with positioning, the sound will likely be different depending on where you place it on the cymbal. Have fun!
 
Most contact microphones that I've seen are piezo microphones. Piezo microphones use a thin ceramic element that is metalized on each side. WIres are connected to each side and the microphone produces an electrical output when the ceramic element is deformed by sound vibration. These mikes have a very high impedance and sometimes have a matching preamp, but should work when plugged into a direct box. They are usually attached to your sound source with a removable adhesive. They can be cheap, I just saw a set of 5 mics on Amazon for $14. (Search for contact microphone) For the price, it might be worth experimenting and seeing how the sound compares with your electret microphone. Play with positioning, the sound will likely be different depending on where you place it on the cymbal. Have fun!

$3 apiece is pretty expensive fore piezos unless they come with some cool extra features/circuitry.

You can buy the mic part of their setup as a standalone: GEN16 DIRECT SOURCE SENSOR KIT At $25 it's cheap enough to consider trying to dissect one to see what's going on. You can also get it with the power supply

Your samples sound cool in a lo-fi kind of way. They seem to be missing a lot of high-end tho.
 
Thanks,

Both are interesting ideas. I've meddled a lot with piezo's as triggers for my DIY edrum (and indeed, I buy them for less than 1$), but I never used them as contact mic. But they are Lo-Fi and will alter the sound of the cymbals quite a lot I think. Also when you attach them to the cymbal, they already have an influence on the sound. But I might use them in the future to add depth to the sound.

The direct source sensor kit is a great idea, In Europe they are more like 45$ a piece. I might buy one and plug it in to my preamp to see if it works. I won't dissect it though, I'm pretty convinced it's an electret by now: I've found the patent: https://patentimages.storage.googleapis.com/3a/e9/fb/cd93f56d3c1aa9/US8872015.pdf
 
...Your samples sound cool in a lo-fi kind of way. They seem to be missing a lot of high-end tho.

Yes, the question is: why are they lo-fi, why am I missing the high-end?
  • is it the preamp? should I work with an opamp instead of a transistor? it seems the gain is enough with the transistor preamp.
  • is it the mic? its a very cheap electret mic, I'm waiting for the primo EM172.
  • Is it inherent to the recording technique?
  • I guess the roland quad capture should be up to the task.
  • Is it the connections or the cables, I'm not using shielded cables but I don't think there's a noise issue.
 
It could be the mic. Do you have the frequency response graph for it?

Cables seems unlikely. As you said, that would mostly just introduce noise rather than attenuating frequency.

I think getting the kit will probably be your best route for exploring the difference between that and your DIY solution. I suspect there's a lot of "magic" in their software too, but I'm sure they won't tell you that.
 
So I hooked up the contact mics with preamps to the fazley mute cymbals. The output is going through a Berhinger MX1604A (cheap second hand version ) and is mixed with SSD5 free hugo edition drum sounds controlled by my roland-TD6V module. The sound is not perfect and there's some distortion going on, also muted cymbals will always sound thinner and higher than the real deal. In the previous samples, I made a mistake with the preamp: I introduced a trimpot before the electret mic, to control the volume. This has an effect on the frequency respons of the mic, now I removed the trimpot and the sound is much better.

This is me playing around on the kit: drumkitfull.mp3 - Google Drive
(I'm not a studio drummer :-)

The preamp fits on a small breadboard:

Screenshot 2020-06-11 at 20.42.51.png

Everything attached to the ride cymbal (tie wraps rule !):

IMG_20200611_142323 (1).jpg

I also had to use a rubber o-ring to dampen the mic, otherwise I would get insane distortion. Maybe the distortion that's left will go away with proper dampening, but now it's time to play the drums :-).

Screenshot 2020-06-11 at 21.06.31.png

In fact, the hardest part was (is) finding a decent 9V power supply for the mic and preamp, all the one's I tried give to much noise. For now I'm using a 9v battery.

I'm still waiting on the High quality electret mic (Primo EM172-Z1), wonder what the effect will be. In the future I will also try to run this through an effects processor to get some reverb or delay.
 

Attachments

  • IMG_20200611_142448.jpg
    IMG_20200611_142448.jpg
    318.2 KB · Views: 6
Back
Top