Modular Synthesis question...

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Modular Synthesis question...

Post by EricK » Fri Dec 14, 2007 3:45 pm

In March I will be ordering a 921B OSC, a 911 Envelope Generator and a 902 VCA to go along with my 921A Osc Driver.

I am going to control them with my MicroMoog.

Now Im trying to picture in my mind how to use the Driver with the 921B and if I don't intend on using the Driver, where Im supposed to put the input control signal for the OSC.

Heres what Im thinking....

1. MicroMoog S-Trig out to the S-Trig in on the Envelope Generator
2. Env Gen out to Control input on VCA
3. OSC out from MicroMoog to SYNC IN on 921B *
4. __Wave output to input on env gen.

here is a picture of the 921B Module

*Will I have to use the Osc Driver any time that I use the 921B? Like will I run my OSC out to the FREQ in on the Driver

I am pretty sure that since the Micro will be used as the controller then instead of using the ENV and the VCA, I can simply route the OSC back into the Micro for filter-env-vca processing all internally.

WHat im not quite sure about though is what exactly AC and DC modulation is.

Any help will be greatly appreciated. Anyone that can offer any insight into the function of the Driver will be praised.

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Post by Nick2012 » Fri Dec 14, 2007 4:41 pm

>>> WHat im not quite sure about though is what exactly AC and DC modulation is.

Here is my assumption based on my electronics background. The AC MOD input will block any DC component that the modulating wave is riding on. The DC MOD input will not. Say, for example, the modulation source generates a 2 volt peak-to-peak LFO sine wave that's centered on +3 volts. That means the sine wave swings from a maximum of +4 to a minimum of +2. If you connect such a wave to the AC MOD input, the DC (direct current)component (+3) will be blocked. Only the AC (alternating current) component is passed. Thus, what gets sent to the destination is a 2 volt peak-to-peak sine wave that is centered on 0 volts and swings from a maximum of +1 to a minimum of -1. The DC MOD input will not block the DC component. In the end, the choice of inputs determines whether the osc frequency swings above and below C4, or above and below C6.

Of course there's also the possibility that the AC and DC inputs are mixed (like a CV mixer). That means you could apply a fixed voltage to the DC input, and it would serve as an offset for the modulating signal applied to the AC input.

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Post by Kevin Lightner » Fri Dec 14, 2007 6:42 pm

Possibly I'm misinterpreting you, but in order to use a 921B, you need a 921A.
They must be paired together.
Any tracking CV must go to the 921A.
The 921B by itself won't work as a standalone tracking oscillator.

I don't understand the wave output thing mentioned.

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Post by EricK » Fri Dec 14, 2007 7:15 pm

Im going to really study that a few times.

I wasn't sure just by looking at the picture if there was a direct CV input. I figured that it coudl be used as a standalone until you wanted to control all 2 or three associated 921b's for that particular driver. I think that the modified version offered has a 921A disconnect switch. This woudl be the main difference between the 921 and the 921B aside from the other inputs and things? As far as what I was referring to on the Wave output was just whichever wave's output going to the input of the VCA.

I really appreciate your input on this. When i get the actual modules of corse Ill have a better understanding lololol Im trying to make the patches in my head. Sort of like learning to play an instrument without having one hehehe.

I havent gotten a copy of the owners manual yet.

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Post by Kevin Lightner » Sat Dec 15, 2007 1:29 pm

Well good luck with the project, though I'm more confused than ever... ;-)
Several questions come to mind.

Who's making the 921's? Mike Bucki?
Where do they put a 921A bypass switch?
How does one control a 921B without range switching? (does it respond to a wide CV range and then allow only an octave or so on the tuning knob?)
How would pulse width work with no PWM inputs or initial width control?
How are the modules to be powered?

Is your Micromoog modified for env out, osc out and vca in? (or would you use the pre-filter external in?)
If VCA in, wouldn't you get one env shaped signal then processed by another one?
If the 921B did indeed allow normal CV in and tracking, wouldn't there be only one input jack and no modulation from the micromoog?
That is, even if it tracked, it wouldn't seem to allow bending or modulation.

Sorry for my questions or comments. I'm thinking out loud really.
They're not criticisms at all.


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Post by EricK » Sat Dec 15, 2007 5:58 pm

I have a dream... its very close to the system 15A minus the CP panels.

22 space ATA mixer case

921A OSC Driver
921B x2 OSC
921 VCO
911 x2 ENV GEN
902x2 VCA
904a VCLPF
923 Noise/LPF/HPF
1503 4 channel mixer
1528 Modified S&H

Dotcom 960 Seq Compliment

Moog Voyager
MF 102
MF (to be determined)

Roland Fantom XR (for layering pianos via Voyager)

Yes Mike Bucki is doing the building, this project is in its infancy. All that i have is the 921A (I bought it to commit myself lol) I haven't seen the 921B with the switch, i can only guess where it is. I don't know enough about the function of said modules to know if Ill NEED any others (attenuators reverseable attenuators, CV panels, etc.) or how the 921B will funstion with the switch. I probably wasn't going to get one. Having that switch, I assumed that a 921B coudl be controlled without the driver.
THe modules will be powered with just a regular power supply/harness we will talk about that when I place the order in march.

My MicroMoog does not have any modifications but it is a model with the Keyboard Output Attenuator on the back, so theres no ENV in's and outs. Mike told me that I really woudn't need the filter immediately because Id just run the OSC back into it and its filter would process it.

Eventually this system will be independant of the Micro or the Voyager, ill probably get a 952 Duophonic Board to play Atop my Rhodes and retire the Micro altogether.

Id like to get my Etherwave modded to send Pitch/Volume CVs but I don't know what that woudl entail.

Im also going to ask Mike about the 3/16th cables for the Modulation jack so that I woudl be able to send it to an external Module.

THis is my Dream baby, its going to take a long time to build and Ill shoot videos of it probably after I get the modules after March for youtube.

If you have any suggestions on any modules that you think that ill end up needing please shoot them to me because im just diving in.

I don't know a whole lot about synthesis, I just stare at the pictures and try to see how they woudl be patched based on my limited experience and based on what the manuals say. I know alot about what they do but I also know that there is alot of advanced Modular techniques that I don't have any concept about at this point.

THanks for your input!


Oh, and I don't know a darn thing about circuits! lololololololololol
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Post by jrlaudio » Sat Jan 19, 2008 9:39 am

Hi Erik,


I think you might need to brush-up on the details of these modules. Are you aware there are "edge connectors" on the rear of these modules that slid into place in the Moog modular cabinets, like what Kevin alluded to about the 921a & 921b Frequency Control and Rect Width nodes, as well as control nodes and parralels for the 904a?

I'm drawing a blank on the AC/DC modulation thing as well. DC Modulation? I don't even understand what that would do?

How do you intend to power these modules with the required +12V and -6V DC?

If you are dealing with Bucki, you should inquire about these specifics with him and ask if there is a case, like the Model 15 had, that has the edge connectors and power supply already assembled. Otherwise, unless you are very capable and savy electronically, this may be outside your scope to assemble.

Just to give you an idea of what I mean, here's a back view of just such a cabinet and the wiring involved ...


Keep talking ... sounds like a nice idea, and there are many of us here who can and are willing to help & advise you.

John LeVasseur

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Post by EricK » Sun Jan 20, 2008 4:39 pm

I appreciate the input. Ill raise that issue with him when i make the order probably in march or so.

He did say that the rack case that I mentioned would suffice depending on where i put the modules. He said that the power connection would be connected already and it woudl be ready to go just as soon as its installed and plugged in.

Now as far as one of those cabinets goes....its about 2500 dollars for a wired cabinet, which id much rather use for the voyager.

My only thing is that Ill have to connect the power housing to the side of the wall somehow and ill discuss that with him, but other than that I think that those cabinets just had a harness similar to the dotcom modules. Depending on the size, maybe just about 20 wires or so that are tied together, with a drop for which ever module. In essence, I don't believe that it is hard wired to the cabinet (meaning that they don't plug in like a sound card would into the motherboard) but its just a power connection that just hangs down to the stationary module.

Like my first order will be the Osc ENV and the VCA. He said that there would have to be power drops associated with the OSC Driver that would just hang freely for each subsequent oscilator that i plan to buy, that woudl just hang there until I was ready to buy my second oscilator. (I only want 2)

Now i may be wrong, and someone like Kevin might can correct me, but I think that adding modules woudl be pretty easy with that particular wiring harness. Just screw the module into the rails and snap on the power and get to patching away!

WHats going to happen is that I plan to have 17 modules taking up 19 rack spaces. 2 Moogerfoogers, the 2 expansion boxes, a Roland synth module and a dotcom sequencer c/ associated modules. I see this outgrowing the ata style cabinet but not for a long long time. At which point Ill probably figure something else out.

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Post by ColorForm2113 » Mon Jan 21, 2008 2:34 am

let us know how this project turns out. i too have a micromoog that i have been thinking of making into a micro-modular. just dont have the funds at the moment.

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