Minimoog Model D [Mod Src Input] and external mod control

[The Inflatable T-Rex]

Just received a beautiful Re-issue Minimoog Model D and had a question about the intended use for the the [Mod Src Input] jack and how one might go about controlling modulation externally.

On the re-issue there are 4 total modulation mix inputs, and you can blend between 2 of the rocker-switch groups as shown below.

[OSC3 / EG] <---- MOD MIX ----> [NOISE / LFO]

So with a 50% MOD MIX you can for example make a modulation source that blends together [OSC3] and [NOISE] as your modulation input source. At 0% it will only use [OSC3] and at 100% it will only use [NOISE] as the modulation input source. You can then set the modulation output destination to [PITCH] and/or [FILTER] as needed. The mod wheel then applies the amount of desired modulation from the mod source to destination.

What I would like to be able to do is control the modulation amount externally somehow (to recreate performance modulation and vibrato effects). I was thinking I could use a midi-cv convertor and playback captured mod wheel changes, as cv mod wheel amounts during playback. Since I don't have a midi-cv converter, I experimented both by attaching a Moog [EP-3] expression pedal and using the [pitch,velocity, after pressure] CV outs directly into the [MOD SRC] input to see what was possible. What I found is that I can only control the amount of [NOISE] modulation that is blended into the overall modulation mix, but none of the other 3 modulation sources of [OSC3], [LFO], [EG] could be controlled in any way externally.

I consulted the manual.

MOD. SRC. INPUT
A varying control voltage signal connected to this input jack can be used as a modulation source.
Inserting a standard 1/4” cable into this jack breaks the normalled connection of the Noise modulation
source, and any external control voltage applied will take its place. With no cable connected, this jack
remains normalled, connecting the Noise send to the
MOD. SRC
. input, and
NOISE
can be selected as
a modulation source.
TIP:
This jack is equipped with a TRS (Tip/Ring/Sleeve) connector, which allows it to also function as a
send for the Noise Generator. With
WHITE
NOISE
selected, the modulation source becomes Pink Noise.
With
PINK NOISE
selected, the modulation source becomes Red Noise.

From the manual snippet "A varying control voltage signal connected to this input jack can be used as a modulation source." it seems to elude that I can control more than just the [NOISE] amount blended into the final modulation mix signal. It sounds like I should even be able to provide my own external modulation mix/signal somehow, but it eludes me how I would go about doing such a thing.

As of right now I can only seem to externally control the amount of modulation source [NOISE] blended into the overall modulation mix signal, which seems extremely limiting and not very useful as being able to control: how much of [OSC3] or [LFO] or [EG] get blended into the modulation signal or being able to control the overall modulation wheel amount itself.

Minimally what I'm after is a way to capture and playback vibrato effects. I thought the very worst case I'd be able to take the [AFTER TOUCH] CV out into the [MOD SRC] input and be able to capture and playback the modulation effects, but [MOD SRC] doesn't appear to work this way.

Questions Are:
Is there a way one can control the modulation amount or modulation signal externally (that isn't just noise modulation amount)?
Is the only purpose of [MOD SRC] input, to control the [NOISE] mod source amount, but nothing else?
Is there a way to capture and playback modulated vibrato effects from an external MIDI sequencer?

[The Inflatable T-Rex]

So I did work out that my issue and wanted to share with others how the [MOD SRC] input functions in practice.

This does get me into the possibility of being able to control the modulation effects externally. Although this is not the same as controlling the mod wheel amount (to get control of the blend of all the different mod sources together), you can indeed feed in a CV source to create a (smooth) changing modulation effect. The key in doing so is to use an unbalanced 1/4" TS mono cable, and not a 1/4" TRS balanced cable. Each reacts differently as described in the manual.

With the balanced TRS (EP-3 footpedal) it allows you to keep and fade in/out the [noise] modulation source amount.
With the unbalanced TS (mono cable) it will bypass the [noise] source modulation and act like a completely independent modulation source.

So if you take [aftertouch] CV out and put it into the [mod source] input (using unbalanced TS) on the back panel and routing the mod destination to osc pitch, hitting the aftertouch will control the pitch like you plugged the (unbalanced TS) CV out directly into the [OSC pitch] input on the backpanel. Pressing aftertouch raises the pitch, and no aftertouch results in no change. For this to work your mod source must be blended to use [NOISE], and the mod wheel should be turned up.

This is more on par with what I would expect from the [MOD SRC] input. In theory one could provide an externally (MIDI-to-CV controllable) CV signal to output an LFO shape. Increasing the LFO amplitude would be like increasing the vibrato effect, and turning the LFO amplitude down to nothing (flat signal), would be like removing the vibrato effect.

I did notice that the tests I did were all additive, so I'm not sure how this would work in practice using one of the midi-CV solutions for external control. For example using the [LFO]/[OSC3] as a mod source allows one to get both positive and negative changes in pitch and filter from the LFO rise and fall. Using the provided [velocity/aftertouch/pitch] CV outs is only able to produce rises.

I don't have much experience using CV inputs for modulation sources, so I'm hoping one can provide a negative CV value to get decreases in the modulation amounts as well. This would make the most sense to me and would be very limiting if not the case. At this time however, I don't have anything on hand that can produce negative CV to test this with and the manual doesn't specify if the the [mod src] input can accept negative CV values or what the CV range is. For example the [FILTER] input clearly states that it accepts voltages of 0 to +5. I may need reach out to moog to find out what is safe to input into the [MOD SRC] input, since it doesn't seem to specify.

[Hooch]

Very very interesting indeed. I was just tackling this myself as I would
really like vibrato under pressure and am not finding a way to do it.

The other big one is setting the pitch bend to a more usefull interval
I haven't figured that one out either.
I think it's 9 semi tones now? Which isn't great at all harmonically.
A harmonic 2nd or 5th might be more useful.

Hooch

[MichaelLudwigsburg]

hello,
i play the model d reissue and control the external mod src with a source audio reflex pedal, it contains a lfo as source.
i use it in the same way as the modulation wheel but controlled via the pedal.

How to configure the model d for this:
A mono cable is needed at the mod src input to get the external source instead of noise activated.
Then you have to choose noise as modulation source on the minimoog panel.
Oscilator modulation needs to be switched on. And with the modulation wheel position you choose the maximal depth of the modulation. This has a side effect. The position of the modulation wheels detunes the moog. you have to compensate this with the master tuning. Done.

does anybody know a method without retuning ?

regards
michael