Help with a drum synth

[Heemis]

I know this isn't the usual stompbox question, but I know I've seen some similar posts here, and was wondering if anyone can point me in the right direction.

Basically I'm looking to do a simple drum synth, 2 sounds:  Kick (probably just a triangle wave with some envelope control?) and snare (another wave with some noise?).  I've got a 4017 sequencer a la the vanishing point set up.  I'm wondering if this will work to trigger the drum sounds? 

I've found a couple of drum synth schems but they seem overly complicated for what I'm looking to do... I want this to sound pretty lo fi... I'll be running it through a lot of effects after the fact.  I'm wondering if anyone has any simple analog drum synth schematics, or any ideas about where to start.  Also wondering if anyone knows If I can use the output of the 4017 to trigger these sounds, or if I'll need additional circuit.

Any help would be vastly appreciated!

[Ry]

There is a Thomas Henry book all about making electronic drum sounds using noise and gates. 

It has been recently converted to PDF and is for sale here:

http://www.magsmoke.com/thomas_henry_drum_cookbook.asp

[frequencycentral]

Some gold dust for ya: http://www.cgs.synth.net/modules/gate_sequencer2.html

[choklitlove]

let me see if i can remember some off the top of my head: syndrum, syntom, synbal, cabonga snare, some of the old EH boxes like sonic boom and space drum.  if you google those followed by "schematic", you should be able to get them.  ok, now i'm going to look some up that i couldn't remember: Coron DS7, DS8, CGS drum, drumulator, alpha, there are a lot.

and to answer the other part, yes a sequencer will trigger them just fine, and i don't think you'll need to add anything.  especially if you're thinking more of a lo-fi solution.  any piezo element can be left and a jack can be added in parallel to it.  i hope this helps!

[Heemis]

Wow guys, thanks so much, this is exactly the kind of stuff I was looking for.  Looks like I've got some reading to do!

I'll try to post a schematic of what I finally come up with in case anyone is interested.

Thanks again!

[Heemis]

So I'm checking out this schematic:  http://www.cgs.synth.net/modules/pic/schem_cgs18.gif

Looks like I should be able to mod this to fit my needs... Only thing I don't quite understand is the bipolar capacitor on the output of both channels.  Can I simply use a polarized electrolytic for these?  Or is there a reason for using a bipolar cap?

Also... what are the chances I can run this off a 12v single sided supply?  I haven't dabbled much into bipolar supplies yet...

[Heemis]

Ok, I went ahead and put one of the drums together from that schematic.  I set up a virtual ground of +6vdc using a voltage divider and hooked up all ground connections to that, and all -15v connections to 0vdc.  I am getting the oscillations to come through, until I set the resonance trimmer as stated on the project page, but I'm having trouble with the trigger.  I am running the output of the vanishing point into the trigger input of this circuit.  I have also tried running the output of the hex inverter i'm using to pulse the 4017, neither will trigger the drum.  I wonder about the portion of the schematic that has the - inputs of both trigger op amps tied together... since I was only testing one drum sim, I just hooked it up as if the second op amp was not there.  Could this have any effect on the triggering?  Last thing is that I used a TL072 for the trigger op amp, since I only have one LM358 right now.  Any ideas?

[choklitlove]

not sure, but before experimenting with the sequencer, i would build the drums and trigger them with a piezo just to make sure they work, know what i mean?

[Heemis]

That's probably a good idea, however, I don't have a piezo to work with right now.  Would I be able to maybe use a mic into a pre and the output of that as a trigger?  The schem page says the trigger simply requires an input voltage of approximately 3 volts...

[Heemis]

Ok, so I feel a bit like i'm talking to myself here, but I'm making progress.  I've plugged in a mic through a pre to the trigger input, and it's definitely triggering the drum sound.  Now all I need to do is figure out why the output of the vanishing point won't trigger it.  I measure ~5.5 volts after the LED on one output of the 4017... this seems like enough voltage to trigger the drum... any ideas as to why it isn't?

[Heemis]

More progress.  Got the sequencer to trigger the drum, but I'm having strange issues.  I think they relate to running the vanishing point on a bipolar supply.  Before I was trying to run the vanishing point off a 9v battery and the drum sim off a 6v bipolar (12v wallwart).  Once I hooked the VP up to the bipolar supply it started triggering. 

The issues I'm having are that the speed of the VP changes based on my proximity to the circuit... sounds strange, but it definitely speeds up/slows down as I get closer or further away (theremin sequencer??).

Also I'm getting a rather large impact sound that isn't softened by reducing the 2.2k resistor as the schem mentions... I'm thinking it's some clock ticking seeping through... anyone have any recommendations for isolating the two a bit more?

[Heemis]

Anyone out there?

I was able to stabilize the rate, but I'm still getting this clicking at the beginning of each trigger.  I actually kind of like it... gives the kick sound some "snap"... but I'd rather be able to control that.  So I'm still looking for a way to better isolate the sequencer from the drum... possibly a different sequencer arrangement?  If anyone has any ideas, I'm all ears!

[frequencycentral]

It's kind of hard to know what's happening exactly without knowing what drum unit you're using.

On a slightly tangential tack, I have this idea for a 4017 drum machine in which the summed outputs of the sequencer drive a LM3914 bar graph driver. The position of the pot for each step is set would dictate which output of the LM3914 goes high, so just by dialing the pot you could dictate which of up to 10 different drum units gets triggered. I'll get around to it eventually...........

[Heemis]

I guess it was quite a few posts ago, but I am using this schem:  http://www.cgs.synth.net/modules/pic/schem_cgs18.gif

Although I think the issue at this point is stemming from the sequencer... I think the click is coming from the seq, but it's hard to tell if it's part of the integral drum sound or not.  The "impact" pot I've wired up does change the sound a bit, but the click is always there.

I realize I also make reference to a bit of the info on this page: http://www.cgs.synth.net/modules/cgs18_drum.html

[choklitlove]

i had the same problem a while ago when i was sequencing the sonic boomer.  i'm trying to remember what i did....

i'm gonna have to get out the stuff and let you know when i get a chance.

[choklitlove]

sorry man, haven't had time to look into it further.  i REALLY think you should post over here: http://electro-music.com/forum/forum-112.html

i used to post on their old DIY sub-forum but it's all re-arranged now.  but they're great people over there.  come back, let us know when you get the answer because i'm curious too!

[sean k]

I did some drum module stuff too and got into problems with sequencers and finally figured it out but didn't follow it up and finish the stuff.

I was using 555's into 4017's and the crux of the matter is that the pulse lengths are really important. You have to make the high going pulse small and keep it that way and only lengthen the low pulse otherwise the modules have a hard time doing their stuff. I spent alot of time reading up on the 555 and I think I got it right just before I gave up...