Adding CV to 808 accent circuit

tommi · Posted: Tue Apr 21, 2009 7:50 am Post subject:

You want to put a vactrol in place of the tune pot?

creatorlars · Posted: Tue Apr 21, 2009 8:45 am Post subject:

Sort of -- One of these...
http://www.bridechamber.com/bridechamber.com/VC%20Res%20PCB.html

tommi · Posted: Tue Apr 21, 2009 9:25 am Post subject:

Please post some sample when you 're done with that!
I am sure it will be fun especially on bd tune control.

funkyfarm · Posted: Tue Apr 21, 2009 6:36 pm Post subject:

what is "accent" ?
just more voltage into vca cv input ? just more volume ?

a boost for velocity ?

creatorlars · Posted: Tue Apr 21, 2009 7:44 pm Post subject:

It's meant to simulate velocity -- I'm not sure whether it's just a simple volume boost or if it adjusts the dynamics or presence of the drum voice as well -- I haven't wired mine up yet and never used a real 808. I'd guess it might also depend on which drum voice we're talking about.

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

there is an accent in on my xoxbox IO mod kit

it is simply a signal hitting a 100k resistor going into the base of a 547 which hits the accent transistor. emitter to ground and collector to the accent transistor of the env in the xox

hope that helps

creatorlars · Posted: Wed Apr 22, 2009 6:56 am Post subject:

Perfect, thanks Luka!

tommi · Posted: Wed Apr 22, 2009 9:10 am Post subject:

Now I 've built Snare Drum and Clap. They are working, I just had to invert the wiring to some potentiometer. So I added noise input jack for both. I am feeding them with noises from Noise Cornucopia and I noticed some weird graininess on the decay. It's unique and beautiful, but now I found the schematics for noise on the 808 and it's specified that its noise output is +/-130mV rms. I think that Noise Cornucopia is outputting something like +/-5VPP. So I believe this weird graininess is caused by distortion. I thought I could add an attenuator on the noise input and see what happens. Or maybe a new pot on the panel...

Link to the noise circuit: http://xlargex.xl.funpic.de/projects/808/schema/808_NOISE300dpi.jpg

creatorlars · Posted: Wed Apr 22, 2009 9:18 am Post subject:

Awesome! Yeah, I'm excited about experimenting some with running the noise sources through an effects loop with Send/Receive!

Just FYI, I am almost finished with a PCB layout for Noise+Accent+Schmitt Trigger, using the same power header as the microLARGE PCBs and with enough output headers for all the 808 modules/mods -- these are the missing PCBs from that site. I'll post it when I'm done with it (sometime this week.)

I also have a PCB layout finished for Thomas Henry's Trigger Conditioner/LED Driver, but I can't post that -- let me know if you own the book and I'll send it to you, though. (It is available from Magic Smoke.) It has provisions for three different trigger inputs and one trigger output. In my case, the inputs will be 1) trigger input jack, 2) a MIDIbox-based Midi-to-Trigger, and in some cases 3) a panel-mounted pushbutton trigger. The conditioning circuit will make sure that the output trigger from all of these sources going into the 808 board is identical no matter what the source. And the built in LED driver is handy, because the 808 doesn't have LEDs for each module.

tommi · Posted: Wed Apr 22, 2009 9:39 am Post subject:

Wich book? I got 'The VCO Chip Cookbook' but I am sure you 're not talking about it! Nice solution the trigger merger, maybe I could add it to my system in the future. For now I am ok with the SEQ01 wich have 12 trigger outs. Also I got no more space on my racks... I filled 3 floors of eurorack!
By the other side, I would be pretty happy to add trigger leds to this modules!

creatorlars · Posted: Wed Apr 22, 2009 10:24 am Post subject:

Cool! The book is "The Electronic Drum Cookbook".

KrIVIUM2323 · Joined: Jan 01, 2009 Posts: 42 Location: Besancon/France/EU

Hi everybody.

CreatorLars/Tommi i wish to thank you opening this thread as it answer on a lot of question i was asking about the BD of the 808.

I've trying to breadboard the circuit some weeks ago but it wasn't working.

Beside many fault on the layout even if it was ok it won't have work 'ok' anyway as my seq can't reach +15v on the cv output (Doepfer Regelwerk) and the gate signal maybe a bit weak to.

So i decided to use the trigger conditionner from Mr. T.HENRY for the gate input (nice and simple cost effective circuit! BUY THIS BOOK you who are interested in drum synth... you can't regret it!).

Now i've to deal with the accent circuit. My thought about it is to use two part of circuits which fly around the net:

The first part of the circuit would be an inverting opamp dc coupled with a gain of 2 to get the cv in the range 0/10v (precision should'nt matter tomuch i think it's only accent anyway...).

Then i would use a part of the circuit from the Tellun TLN-861 Dunsel, more precisely the 'A+5' :wich offset +5v the signal at input to reach a usable range of 5/15V for the cv input.

Does it make sense for you?

Don't be to hard if it doesn't make sense it's my first approach to design something to solve a problem... Wink

I think this way i'll have acces to the 'normal' behavior of the kick regarding accent and CV from the Doepfer seq. I don't need a push button to trigger by hand on the face of the module like you but it shouldn't be difficult to implement a switch to do that anyway if i need it (tying +15v to accent and input to trigger conditionner)...

Could you give me your opinion about that? Smile

creatorlars · Posted: Thu Apr 23, 2009 7:21 am Post subject:

Hi! I'm glad the information was useful!

creatorlars · Posted: Thu Apr 23, 2009 7:25 am Post subject:

I thought I'd share my 19" rack, Serge-grid-style 808 drum panel layout. I'm sure I've forgotten lots of awesome stuff I could add, but it should be pretty crazy when done. It connects to my "Master Drum Control" module which distributes MIDI triggers to all the voices, behind the panels.

The V8 Sim is CGS and I just threw it on there because I had an extra slot. In hindsight maybe some sort of an effect is better. 909 BD is also there for extra space (and because I want two, and after building my 9090, I'll have 'em!)

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tommi · Posted: Thu Apr 23, 2009 8:05 am Post subject:

Hi KrIVIUM2323 !
This Forum helped me too! When I saw that Creatorlars had successfully builded the 808 modules using xlargex's PCB I 've gone directly with PCBs and they worked! I only had a bug with bd but it was only a broken pwr bypass cap.
I think your plans for trigger and accent are ok. Since I 'll trigger the drums with a variable trigger I simply tied trig and accent together and I can confirm that this setting is velocity sensitive, cause yesterday I put an attenuator between trigger out and bd's trigger in and the amplitude changed.
Nice panel creatorlars! Also crowded! I 've seen you 've added nice features, like noise gain, boost for 808 bd, noise/ osc for 'brass drums', mix out... REALLY NICE!
P.S. I added attenuation trims for noise inputs on sd and clap and it's better now.

KrIVIUM2323 · Joined: Jan 01, 2009 Posts: 42 Location: Besancon/France/EU

CreatorLars,Tommi, Thank you answering so fast! Wink

creatorlars · Posted: Thu Apr 23, 2009 9:12 am Post subject:

KrIVIUM2323 · Joined: Jan 01, 2009 Posts: 42 Location: Besancon/France/EU

creatorlars · Posted: Thu Apr 23, 2009 5:18 pm Post subject:

The BD Boost and other mods have PCB layouts here...
http://xlargex.xl.funpic.de/

I haven't built the 909 kick yet, but it's based on a PCB I found -- I'll dig up the link. I am pretty sure it has an onboard noise generator, but if it doesn't I will send it the 808 white noise.

creatorlars · Posted: Fri May 01, 2009 8:50 am Post subject:

I wired up my Noise/Schmitt/Accent circuit board layout last night but am having trouble getting the accent to behave properly. Rather than try to debug the circuit (which is a little over my head), I decided to come up with my own using a CD4053 as a logic-controlled switch.

Here's the schematic -- can anyone tell me if this looks right? The diode at the External CV input is what I'm most worried about -- the intended purpose of this is to remove any negative voltage from the external input. Will it work that way? CD4053 can only accept a 15V p-p input signal range, so I tied negative power pin to GND (and that's also the point of the diode on the Ext CV input.)

The circuit should produce a constant +5V when not triggered, but +5V to +15V when triggered.

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creatorlars · Posted: Mon May 04, 2009 8:00 am Post subject:

After a very long weekend of work, I'm happy to report that this new accent circuit works great (with a couple resistor changes). Please let me know if you'd like an updated schematic.

My PCB layout for Noise+Schmitt Trigger works fine too, but I need to revise it for easier etching before posting (if there's interest.)

Also, the vactrol VC mod for BD tuning works as well! It doesn't respond well to audio rates, but LFO/Envelope inputs work fine.

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Hi Creatorlars:
This week I will be re-taking the work on my 808, I want to make individual
accents for every drum sound, all controlled by a single accent knob. I was
thinking in use CD4053s so if you could share your circuit, will be great.
Thank you.

creatorlars · Posted: Mon May 04, 2009 10:28 pm Post subject:

Sebo -- no problem, I'll post it tomorrow. The circuit is pretty clean as-is and works great. If you have no need for a CV summer and are using all three channels of the CD4053 you can avoid the op-amp and associated resistors entirely I think.

creatorlars · Posted: Tue May 05, 2009 9:03 am Post subject:

Okay, here are two versions of the circuit. The full CV/Buffered version is working and tested.

The minimal version shouldn't have any problems at all (I doubt the output buffer is really necessary). Furthermore, you could easily access the remaining B and C pins on the 4053 to get three accent circuits out of a single 4053, making this an extremely lightweight solution.

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Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

I was thinking in something like the first circuit (the simpler one).
Thanks a lot!!!