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Percussion EG for Hi Hat
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jumunius



Joined: Apr 19, 2010
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PostPosted: Tue Aug 23, 2011 3:34 pm    Post subject: Percussion EG for Hi Hat
Subject description: Now with schematics!
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Hi,

I have recently been working on a 3x Trigger input / Percussion EG from Thomas Henry's Electronic Drum Cookbook. (The same basic circuit appears on the Bass++ and the MPS.) I take it, build it 3 times with separate inputs outputs and pots, and I figure if I sum the 3 and run it into a single VCA with an audio source (for example Liquid Hi Hat noise when I build that) then I could use the 3 separate decays to do things like high hats, accented drums, interesting bass patterns, etc.

What I'm realizing though is that it probably won't work right for faster hi hat parts. If an open hat EG fires with a 1/2 second decay, followed an 1/4 of a second later by a closed hat EG, the CV from the closed hat would add to the existing decay of the open hat yes? In some cases this could be desirable but what if I want the open hat to cut off whenever the closed hat is fired?

I tried looking at the 808 hats circuit and didn't fully understand it -- it's somewhat muddied by the accent input, which isn't something I have built in anyways.

If anyone has suggestions of how to do this I'd appreciate it.

Last edited by jumunius on Thu Nov 03, 2011 11:51 pm; edited 1 time in total
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stewpye



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PostPosted: Tue Aug 23, 2011 7:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

You need to shut off (or pull down) the OH envelope when the CH envelope triggers. If you take a look at the DR110 schematic it may be more obvious that the 606 or 808.
http://www.theninhotline.net/dr110/

Basically when the CH envelope is triggered it turns on a transistor to discharge the OH decay capacitor. Instead of using a diode VCA you can just buffer and mix the OH and CH envelopes (mixing may be taken care of by your VCA circuit).

Stew.
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jumunius



Joined: Apr 19, 2010
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PostPosted: Wed Aug 24, 2011 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

stewpye wrote:
Hi,
Basically when the CH envelope is triggered it turns on a transistor to discharge the OH decay capacitor. Instead of using a diode VCA you can just buffer and mix the OH and CH envelopes (mixing may be taken care of by your VCA circuit).


Thanks Stew. I think I see that happening at Q4. I'll give it a try.

-Jim
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jumunius



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PostPosted: Fri Sep 16, 2011 9:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, finally got around to testing this out after monkeying around with other aspects of this module. I notice that Roland does a few things differently, most obviously they don't have what I refer to as Q3 -- a transistor for the CH EG with an independent CH out. I don't know what I'm losing here, but I prefer having separate outs that I then mix via a DC mixer -- this gives me ability to balance the CH and OH separate from Q2, the transistor that drains the OH when CH fires.

It takes some doing to actually get CH and OH to play well together -- I have to set the decays of CH just right. Too quick decay doesn't drain OH and too slow decay somehow manages to truncate the decays of all OHs, even those not followed by an immediate CH. This is one excuse for having individual output levels for CH and OH -- once the interaction between the two voices is working well, I can add or subtract CV level from one or the other.

I tried making R4/R5 variable but that rarely made a big difference in a desirable way (and when it did I never recaptured whatever winning combination I had).

When I solder this together this weekend I'll probably add a switch at R4, since I want to be able to use this module for Hi Hats as well as non-hi hat percussions, 2 independent EGs, and various synth sequencing purposes.

Anyways, thanks -- that appears to have done it. Let me know of course if I've bungled anything.


PercEG_HiHats_Schematic.jpg
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Early sketch of schematic for percussion EG for open/closed hats
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PercEG_HiHats_Schematic.jpg



Last edited by jumunius on Fri Nov 04, 2011 12:00 am; edited 1 time in total
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stewpye



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PostPosted: Sun Sep 18, 2011 7:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

I'd try feeding Q2 via its own diode from the CH trigger input instead of from the CH enevelope cap. Also reduce R4 to 2.2k and R5 to 10k. If your trigger pulse is of a suiatble length it may be fine, or you may have to stetch the pulse a bit...

Regards,
Stewart.
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jumunius



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PostPosted: Tue Sep 20, 2011 7:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh brilliant. And so obvious now, why didn't I just think of that?!?!? Embarassed

Thanks!
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jumunius



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PostPosted: Wed Sep 21, 2011 1:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, that works well, and it works best without having to extend my trigger pulse (which is also from the Thomas Henry Drum Cookbook). I also find interesting results adding a cap to ground at the anode. Anywhere from 22N on up to 100N (I like 47N the best) diminishes the CV even further, presumably by elongating the trigger pulse. So I'm considering one switch to toggle "hat mode" on/off, which is the OH kill feature, and then a subsequent "extra kill" toggle for effect when hat mode is on. It seems like a nice way to drop down or bump the dynamics from section to section in a rhythm loop.

One more thing I like about your solution is that it works just as well with 2 voices as 1 -- since i have 3 EGs, ideally I have 2 voices that should each kill the OH. In my original scheme I had mostly given up on that working.
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stewpye



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PostPosted: Wed Sep 21, 2011 6:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

You could reduce R4 to about 100 ohms. This will discharge the OH decay cap faster.

Stew.
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jumunius



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PostPosted: Fri Sep 23, 2011 1:35 am    Post subject: Reply with quote  Mark this post and the followings unread

stewpye wrote:
You could reduce R4 to about 100 ohms. This will discharge the OH decay cap faster.


Thanks Stew -- good to know where to adjust. After fixing a few other issues in my build I settled on 270 ohms as the best moderate OH kill level. Although 100 ohms worked well as the maximum, my board is getting crowded, so the 47N cap to ground seemed a better solution (since I can mount that cap to my panel components). They achieve similar results it seems.

I didn't quite get a chance to test the final build as I miswired one thing. Tomorrow night I suppose.

-Jim
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jumunius



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PostPosted: Thu Nov 03, 2011 11:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, so I've mostly finished putting together a 3x Percussion EG + DC Mixer module. The module borrows directly from Thomas Henry (Trigger and EG), MFOS (DC Mixer), and one from another thread, apparently adapted from a Ken Stone module (glide). As you can see, I can thank Stewpye for the hi hat functionality, which is one of the more unique things about the module. I hope I haven't stepped on any toes posting a schematic which borrows these circuits; they are all pretty readily available.

So, in essence, I did little more than paste a bunch of people's cool stuff together. But it's turning out to be a pretty handy combination of simple functions, and as a whole I don't see much like it out there, so I thought I'd post my design docs. Feel free to comment, question, or build one yourself.

What it is:

3 Percussion EGs (with Trigger conditioners) with individual or mix outs
3 Channel DC Mixer, either to mix EG or external signals
"Hi Hat Mode" for reducing overlap between the 3 EGs
Glide control, for varying attack time (say you want shakers, or to use the EGs to create a complex CV pattern to animate a filter)
1 attenuverting mix out with +/- pot
1 + mix out with no pot

8-9 pots: 3 for each decay, 3 level controls for each EG or mixer channel, 1 for attenuverting out, 1 for glide, and 1 optional control for hi hat mode.
8 jacks: 3 jacks are trigger ins, 3 jacks that can function as individual envelope out OR DC signal in (for mixer), and 2 jacks for +/- and + outputs respectively.
1-2 switches: 1 switch for switching the DC jacks to In or Out mode, and an optional switch for turning hi-hat mode on and off (the optional pot could serve this function, or you could use both pot and switch for more options for interactivity).

See attached 2-page schematic, and my preliminary MOTM-format panel design (I haven't done a proper panel yet). Note that the panel design uses the 9 pot option referred to in fine print in the schematics (adds the fine tuning control for hi-hat mode). Also I haven't built the DC mixer mode switch yet.

Lastly, I won't post any stripboarding info. Sadly my stripboarding work is nothing worthy of copying.... I sort of designed it as I went, so it's kind of a mess. Hey, but it works.


3xPercEG_BuildDocs.zip
 Description:
3x Percussion EG and DC Mixer schematics and front panel concept

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 Filename:  3xPercEG_BuildDocs.zip
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prgdeltablues



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PostPosted: Fri Nov 04, 2011 9:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, this looks really interesting. Just wondered about a couple of points on the schematic, page 2 - the mixer part. Shouldn't there be a 100k resistor between the opamp buffer after C8, and the inverting unity gain opamp following (the one with C9 in its feedback loop)? And again between that and the second inverting opamp?

Also, it looks as if the input stage of the mixer is actually a non-inverting averager rather than a summer. That may be intentional?

Peter
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jumunius



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PostPosted: Fri Nov 04, 2011 8:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

prgdeltablues wrote:
Hi, this looks really interesting. Just wondered about a couple of points on the schematic, page 2 - the mixer part. Shouldn't there be a 100k resistor between the opamp buffer after C8, and the inverting unity gain opamp following (the one with C9 in its feedback loop)? And again between that and the second inverting opamp?


Thanks Peter, I appreciate the feedback. As with most of my DIY stuff, I don't fully understand what I'm doing, I just wing it and hope it works out. The missing 100k resistor between the inverting op-amps was an oversight in the schematic. The one between the glide circuit and the first inverting opamp (C8 and C9 in terms of the nearby caps) may be an oversight when I grafted all these circuits together. I'll have to check my board and see if I can add it.

Quote:

Also, it looks as if the input stage of the mixer is actually a non-inverting averager rather than a summer. That may be intentional?


Not intentional, and honestly, it might not even be what's in my build. I added the glide at the end of this project and I thought I put it there, since glide appears on both the +/- and + outputs. But it's possible I put it elsewhere. That was one place I was hazy on when writing the schematic and I only did a cursory look at my build. I'll give another look.

The concept was to use the DC mixer as described in the MFOS schematic I saw (which is a pretty common DC mixer schematic, also resembles CGS, etc). And possibly due to ignorance I just assumed I could jam the glide between the resistor summing point and the op amp without affecting the circuit. Now that I read the difference between an averager and a summer I see your point!

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richardc64



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PostPosted: Sat Nov 05, 2011 8:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Q2 would do a better job of shortening the Open decay if it took its base voltage from C5&R12 and C7&R19, as shown in the earlier, hand-drawn schematic.

I don't see what C3 is supposed to do. It's so much smaller than C2 I doubt it has much effect.

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stewpye



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PostPosted: Sat Nov 05, 2011 2:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Q2 would do a better job of shortening the Open decay if it took its base voltage from C5&R12 and C7&R19, as shown in the earlier, hand-drawn schematic.


He was having some problems doing it that way. Still, there should really be a smallish capacitor on the cathode of D2 to stretch the pulse a bit.
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jumunius



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PostPosted: Sun Nov 06, 2011 1:25 am    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Q2 would do a better job of shortening the Open decay if it took its base voltage from C5&R12 and C7&R19, as shown in the earlier, hand-drawn schematic.


Do you mean remove the diodes D2 and D4 entirely as well? Wouldn't the 2 CH voices interact in that case?

Quote:
I don't see what C3 is supposed to do. It's so much smaller than C2 I doubt it has much effect.


I assumed it elongates the trigger pulse a little, which means Q2 is activated for longer, but now I'm confused about whether I put it in the right place. I think maybe it really was intended to go at the cathode of D2/D4. Better check that it even works as I remembered it. Smile

When I was testing it initially, it had the same effect as a smaller value of resistance at R7 (Stew's suggested 100 ohms), further shortening the cutoffs. And for whatever reason it was easier to layout/wire.

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richardc64



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PostPosted: Mon Nov 07, 2011 4:58 am    Post subject: Reply with quote  Mark this post and the followings unread

jumunius wrote:
richardc64 wrote:
Q2 would do a better job of shortening the Open decay if it took its base voltage from C5&R12 and C7&R19, as shown in the earlier, hand-drawn schematic.


Do you mean remove the diodes D2 and D4 entirely as well? Wouldn't the 2 CH voices interact in that case?


No, you could keep them, or replace both AND R9 with two resistors larger than 10k, say 100k minimum.

Quote:
Quote:
I don't see what C3 is supposed to do. It's so much smaller than C2 I doubt it has much effect.


I assumed it elongates the trigger pulse a little, which means Q2 is activated for longer, but now I'm confused about whether I put it in the right place. I think maybe it really was intended to go at the cathode of D2/D4.


Yeah, it would have a greater effect there, but not much because it's so small. Maybe you just drew it wrong?

Here's the relevant portion of the DR-110 HiHat. Although the complexity of the 808 and 606 schematics obscures what's going on, the same mechanism is used in those two designs as well.


oh_ch_110.gif
 Description:
Equals Q25 in the 606 or Q23 in the 808.
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oh_ch_110.gif



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stewpye



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PostPosted: Mon Nov 07, 2011 2:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

C3 should be at the cathode of D2 and D4. Even 47n into 10k should stretch the pulse enough to discharge C2. So you'll only need a single pole switch. You should have a resistor between base and emitter of Q2 so that the base voltage doesn't float up. 100k would be fine.

If you want to you could move the switch across base-emitter of Q2 so that if the switch is on it will not allow you to turn Q2 on so will not be in hi hat mode.

Your summing circuit is incorrect.
The summing op amp should be a normal summer: input resistors to - input. Feedback resistor from output to - input. + input to gnd. Output from the glide buffer will be inverted output. Feed this via 100k into the op amp with R25 in the feedback path. This is non inverting out. Get rid of the op amp with R26.

Cheers,
Stew.
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jumunius



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PostPosted: Wed Nov 09, 2011 12:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, lots of things to check out.... I was certainly hoping this was closer than it appears to be. After all it basically does what I expect it to do. (Maybe it could be doing it better though!)

Anyways, I hope to give this a good going-over at some point but as my wife is due to have a baby any day now, I may disappear for a while. So don't take any lack of response or investigation as a sign of disinterest. Smile

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Paradigm X



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PostPosted: Thu Nov 10, 2011 6:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool man, ill have a look through. Im quite new so no guarantees of course, but it will be a fun challenge.

Good luck with the birth and everything - we had our first 18 months ago and its the best thing that ever happened. Enjoy! You will be puched for time for a while i imagine but it does get easier !

Best wishes.

Ben
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jumunius



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PostPosted: Thu Nov 10, 2011 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Paradigm X wrote:
Cool man, ill have a look through. Im quite new so no guarantees of course, but it will be a fun challenge.


Yeah, better wait til I figure out some of these issues people have been bringing up. Or help sort them out in your build!

Quote:
Good luck with the birth and everything - we had our first 18 months ago and its the best thing that ever happened. Enjoy! You will be puched for time for a while i imagine but it does get easier !


Thanks Ben! This is #2 so I have a bit of an idea of how it will go, but then, who knows how #1 will take it.

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Paradigm X



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PostPosted: Fri Nov 11, 2011 4:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool, sorry man, youll know exactly what to expect then !

more coffee!!

Good luck. Im going to try to build a simple 2 input version. Why are you using three for the LHH anyway out of interest?

Cheers
Ben
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jumunius



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PostPosted: Fri Nov 11, 2011 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Paradigm X wrote:
Cool, sorry man, youll know exactly what to expect then !


Well, they say every one is different. We'll see. No matter what:

more coffee!!

Quote:
Good luck. Im going to try to build a simple 2 input version. Why are you using three for the LHH anyway out of interest?


Generally speaking, I consider this a multi-purpose module, and with a little tweaking it fits a 2u MOTM panel this way. So you can use it as a general purpose Percussive EG (say to trigger VCFs or VCAs for multiple drums). Or you can use it as a digital mixer with no EG functionality. In either case, having 3 is better than having 2, so why not?

In the case of hi hats, many sampled hi hats include 3 samples, Closed, Open, and Open-Close (what happens when you go from open to close with a foot pedal). So you could imagine this working that way. OR you could imagine it like you have 2 closed hi hats, and one is accented for slightly more interesting rhythmic effect. (You can also imagine that 3 EGs running into a filter CV input might create a nice patterned effect on a synth sound.)

Of course, in the MOTM world, these could be two separate 1u modules, one a mixer and one an EG. Personally, after building various units I'm now gravitating towards all 2u and 4u modules for visual reasons. Also, when I built a module that will often benefit from direct connection to another module, I find it handy to hardwire them, so long as they are also usable individually. Everyone has a different philosophy about this it seems.

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jumunius



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PostPosted: Wed Nov 23, 2011 3:25 am    Post subject: Reply with quote  Mark this post and the followings unread

stewpye wrote:
C3 should be at the cathode of D2 and D4. Even 47n into 10k should stretch the pulse enough to discharge C2. So you'll only need a single pole switch. You should have a resistor between base and emitter of Q2 so that the base voltage doesn't float up. 100k would be fine.

If you want to you could move the switch across base-emitter of Q2 so that if the switch is on it will not allow you to turn Q2 on so will not be in hi hat mode.


So, indeed, my schematics were incorrect. I finally have come up for air enough to look at the hi hat switch (gonna save the digital mixer/glide for another night). Here's a revised P1 of the schematics -- I'm pretty sure this is more accurate to my build. So if I read you right, what I have now fixes everything except it would require an additional 100k between base and emitter of Q2 (which is 100k to ground from the base, yes?). Or does the fact that I've placed the switch at the base make this unnecessary?


3xPercussionEG_p1.pdf
 Description:
11-23-11 revised P1 schematic, Percussion EG; edited to revise

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jumunius



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PostPosted: Wed Nov 23, 2011 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

jumunius wrote:
So, indeed, my schematics were incorrect.


And yet again.... I just adjusted the switch once more to make it clearer what it's doing. (Updated the attachment in previous post.)

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stewpye



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PostPosted: Wed Nov 23, 2011 7:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

The section around the switch looks overly complicated and doesn't make sense.

Here's what I'd do...
Bugger off the switch.
Put C3 between cathode of D2 and ground. Also connect anode of D2 directly to R9.

Have a 100k resistor in parallel with C3 to drain C3 completely and prevent it from floating up. You'll have to adjust this resistor and R9 to get a suitable pulse width.

Put a switch between base of Q2 and ground to select the mode.
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