Adding CV to 808 accent circuit

creatorlars · Last edited by creatorlars on Fri May 01, 2009 8:51 am; edited 1 time in total

I am trying to add CV modulation to the 808 accent circuit. Basically I just need to sum the CV input voltage with the output of the "accent level" pot, which produces a reference voltage between 5V & 15V. The schematic is attached.

Now, I know I could do this by replicating a dual inverting op-amp DC mixer circuit such as on Ken Stone's site, but I am trying to beef up my electronics skills/knowledge a little bit and know there's probably a much easier way. I can follow simple op-amp circuits okay, but this one is beyond me.

Maybe just putting another 4.7K resistor at the junction and connecting the other end to the external CV?

Any helpful information both in a solution to this problem and/or the reasoning behind it would be great.

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tommi · Posted: Tue Mar 31, 2009 9:29 am Post subject:

Hi,
Sorry to answer you wiyh a question, but I 've seen on another thread that you 've built 808 drum modules using http://xlargex.xl.funpic.de/ schematics.
I am preparing to build the bd, sd and clap modules, but I 've noticed that on the 'modifications' page the values for the potentiometers added are different from the same ones indicated on the PCB/Layouts page. For example, on the mod page, for 'Snappy filter' (Snare Drum) I got a 22K Log potentiometer, but on the PCB/Layouts page I got a 4.7KLog one.
The same problem on Tune osc1 where I got 2.2MLog and also 1MLog.
Can you remember wich value have you choosed for this controls?
thanks,
tommi

creatorlars · Posted: Tue Mar 31, 2009 9:45 am Post subject:

I'm pretty sure I went with the values listed on the "modifications" page. I don't think the original schematics illustrate any of the modifications, so it would be my guess that those part values are from the original circuit, and the ones on the "modifications" page are alternate values.

tommi · Posted: Tue Mar 31, 2009 11:21 am Post subject:

Here is the page I was referring to: http://xlargex.xl.funpic.de/projects/808/docs/808sdV1.0.pdf
on the top page the connectors writings refers to pots with different values than on the mod page, for example the snappy filter is said to be 4.7K instead of 22K.
But if you're sure you built it with the modifications page values and it works, I 'll go with them.
cheers,
t

creatorlars · Posted: Tue Mar 31, 2009 12:10 pm Post subject:

I can double check which pot I used when I get home. I couldn't say positively at this point.

Probably a much more reliable reference is the Midibox 808 bill-of-materials available at http://www.eight-oh-eight.org. It won't have info on the microLARGE mods, but it will have all the correct parts values.

Also, be sure to check the build threads on that site -- There is some essential information on the noise source and clap circuits. I've made the changes suggested in these threads and my clap and noise source sound way better.

Another note: on the 808 SD PCB, a power trace is missing for one of the dual op-amps. Make sure both op-amps are getting +V and -V power to the right pins. There will be problems with output level if you don't do this.

tommi · Posted: Tue Mar 31, 2009 2:46 pm Post subject:

Ok, thanks for the precious information about the missing trace. There will be a trouble less at the building time.
I 've seen that link about the 808's construction and now I 'll check it for sure.
thanks,
tommi

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

creatorlars · Posted: Tue Mar 31, 2009 7:31 pm Post subject:

The information is all in the Assembly Instructions threads:
http://eight-oh-eight.org/phpbb2/viewforum.php?f=3&sid=ed7b237c9e5faa8074f1f312c373c4dd

Read through Noise Pt 1 & 2, and CP Pt 1 & 2.

creatorlars · Posted: Tue Mar 31, 2009 7:36 pm Post subject:

tommi · Posted: Wed Apr 01, 2009 3:51 pm Post subject:

I am planning to add a noise input jack on SD and Clap panels, so that I con use my noise module (MFOS cornucopia, wich is the module I am building at the moment), or any other source to experiment.
At the present time I 've just ordered the PCBs and I have not yet made the order of components, big order since is for six modules and a new wooden rack. I'll post any news.
cheers,
t

creatorlars · Posted: Wed Apr 01, 2009 4:29 pm Post subject:

Cool! I did the same thing with the noise input, except at the moment it's just implemented as send/receive jacks for the White Noise and Pink Noise outputs. So I could use alternative noise sources or easily send the noise through a filter or FX chain. I have the Noise Cornucopia and a CGS Digital noise as well. We'll have to compare notes about various experiments.

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

Thanks creatorlars!!!
I found the thread!
I have my 808 clone half finished for a while, now I'm finishing the first batch
of modules of my modular, once done I will continue with it.
I etched the 3 big microLARGE PCBs (not the individual ones), and populated
almost all components. I'm missing some capacitors, all pots, the wiring, and the case.

creatorlars · Posted: Thu Apr 02, 2009 7:58 am Post subject:

tommi · Posted: Sun Apr 05, 2009 2:35 pm Post subject:

Do you have a picture of it? I am so curious!

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

tommi · Posted: Fri Apr 17, 2009 2:38 am Post subject:

Now I begin to understand the reason of your first question on this thread Creatorlars. I 've noticed that the 808 voices needs two pulses to be triggered, the trigger AND the accent. As explained here http://eight-oh-eight.org/phpbb2/topic-106.html&sid=b46557bf49725dccdb53e8a4a5ef8f0e
there is an and gate who needs two simultaneous pulses to fire the envelope.
I am thinking to simply bypass the and gate in order to have just one trigger input. What do you think?
Cheers
tommi

creatorlars · Posted: Fri Apr 17, 2009 7:45 am Post subject:

tommi · Posted: Fri Apr 17, 2009 8:11 am Post subject:

Right, thanks. I think I 'll go with the first option because the sequencer I planned to use with the modules have the accent on trigger outs. Also, the trigger level is adjustable from 0..1V to 0..10V. I hope this last trigger voltage is enough for 808 clones.

creatorlars · Posted: Fri Apr 17, 2009 8:48 am Post subject:

The 808 voices respond to 5-15V. You could add +5V to your 0-10V triggers at the module inputs, somehow maybe?

Or send the trigger to the trigger input, but add it to +5V when it goes into the Accent input...

Out of curiosity, which sequencer are you using?

tommi · Posted: Fri Apr 17, 2009 4:11 pm Post subject:

I am awaiting for MFB Seq01. I bought it from www.schneidersladen.com.
This is the link to the manual if you wanna know something about it:
http://www.mfberlin.de/Manual/Manual_e/SEQ-01_be.pdf
I could not figure out how to sum +5V to the max. trigger level of this sequencer (10V - I believe this is when the accent is set to high on the seq01).
Also, I have planned a +/-12V supply for the drum modules and I hope it will work properly... otherwise I must add +/-15V regulators.

creatorlars · Posted: Mon Apr 20, 2009 6:44 am Post subject:

tommi · Posted: Mon Apr 20, 2009 8:03 am Post subject:

Well, I built the 808BD last saturday and when I first tested it the 'sonic' part of the signal was missing, There was only the 'impact' portion. A sound like 'tick' or 'toc'. And the controls like decay, xtra decay, tune and envelope were ther with no effect on the sound, of course.
But, after some manipulation of the board I realized that one of the bypass caps were faulty... I changed it and... BOOOOM! Very Happy

I tried feeding this module on both +/-12 and +/-15V and I don't see any difference, so I'll go with +/-12 wich is ok.
Weird things: xtra decay does something like resonating from 3 o' clock.
Is it the same for you?
Next step: 808 SD
Cheers,
tommi

About the trigger/accent: For the moment I tied them toghether and I 'll see what will be the effect with a variable trigger like the one of the seq01...

creatorlars · Posted: Mon Apr 20, 2009 9:05 am Post subject:

Glad to hear you got it working!!! I'm jealous, I am in the process of repaneling mine, still - and haven't had it in the system for several months. I miss it. Sad

Yes, Xtra decay behaves in a rather bizarre manner. You can get the bass drum to self oscillate indefinitely. I did a drone track with self-resonating 808 BD as the only sound source once.

tommi · Posted: Mon Apr 20, 2009 9:30 am Post subject:

creatorlars · Posted: Mon Apr 20, 2009 9:51 am Post subject:

I can definitely confirm similar behavior with the envelope as well. Wild, huh?! I'm adding some Vactrol-based CV to the tuning on mine -- CV over the XTra Decay would be crazy too, I bet.