MF 108 in a patch bay

[Mr Shave]

So i have a nice rack made for my foogers and I am planning on mounting the 108 in it at some point, but i decided to do a little homework first. Plugging cables into the jacks on the back to see what jacks are switched revealed that all of the CV inputs act in a similar manner as the 104z, so surprise here.

To fix this on the 104, I keep a dummy plug on my patch bay which has the tip soldered to the sleeve which solves this issue when there is no CV plugged into that jack. However, this doesnt appear to work with the 108. It sounds the same with a dummy plug as it does with a normal cable plugged in but not connected on the other side.

Anyone have any ideas or messed around with this in more detail?

Thanks

[DeFrag]

rack photo?

[latigid on]

The other trick is to use a dummy load, a 100k resistor from tip to ground (note, you should use a TRS dummy plug, with the ring terminal not connected).

Others here have had more luck with different loads, e.g. titi, whom I corresponded with offline, found 1.5k to be suitable for his 104Z. I'd be more comfortable using a larger value resistor as the current draw, while still small, is lower for a larger resistance.

Hope that helps, and YMMV.

[Mr Shave]

Latgid,

I was hoping you would reply, i got a lot of the information for my patch bay from all your other posts.

I tried the 100k resistor on the 104z when i made it, but I didnt like how it attenuated the signals going through it, so I opted for the jumper on the dummy cable. I did however have a couple of my patchbay slots modified when i tried this before (i was too lazy to de-solder everything, and i had more slots than I need) and I tried it with the 108M. It seems to help a little bit, but not completely. Maybe I'll just have to mess with it.

And de frag, here is a photo... Not the best thing, but I didnt want to have to remove the side panels to mount them, so its all custom. Made it with room to expand also, which Im finding I am filling up quick! I modified a 2A power supply to have 8 outs to power all of them.

[Mr Shave]

In case anyone was interested, I have almost resolved this issue after several conversations with Moog...

Basically, Moog confirmed that the CV input jacks on the 108 are indeed different than their other foogers. In essence, they always have 2.5V at the TIP, however, when you insert a plug, it disconnects that 2.5V source. This 2.5V source keeps the knob working as you would expect.

Alright, simple solution... on the patchbay switched jack solder a resistor from RING to TIP to get 2.5V on the tip... Well, that proved easier said than done.. Turns out there is something else going on inside the unit. I tried several iterations (short of throwing a pot on it) and couldnt get it to work properly. So, here is my solution (which Moog says should cause no issues)...

On the patch bay, change your switched jack so that there is a voltage regulator in between the ring and tip. Wire it in such a way that when you plug in something to that jack, it disconnects the voltage regulator circuit . The voltage regulator requires a regulator IC (mine look like 3 pin transistors), a trip pot, a cap, and a resistor (look at the circuit diagram of the voltage regulator IC). Wire it up so that the 5V from the Ring goes into the Vin pin, and the Vout pin goes to the TIP. Plug it into the 108 and adjust the trim pot to get 2.5V. That knob should now sound exactly as it should. When you plug in a cable to the patchbay, it disconnects the voltage regulator, supplies 5V to the Ring and accepts the voltage at the Tip of the cable you plugged in...

I got this working on a breadboard, but im going to have to make a couple patchbay jacks due to no room on the existing patch bay board and the traces being incompatible (parts are on order now!).

So, if anyone else was thinking about the MF108 in a patchbay, this is how i did it.. It might be overkill, but it should be stable. You might be able to get it working with a simple pot between ring and tip, but I didnt try it. Didnt think about it until after I orderd all the parts actually...

Peace

[Rosser]

Please refer to the Moogerfooger FAQ page for more information regarding the use of the MF-105 and 108M within a patch bay, as well as the bipolar nature of the CV inputs of these effects.

http://www.moogmusic.com/support/faqs/# ... 2%25AE-faq

Thanks

[Mr Shave]

Thanks Rosser,

I tried two same resistance resistors from Ring to Tip and Tip to Ground (although my description above didnt explicitly say that), but i didnt get an exact 2.5 volts when plugged in (got 2.3 on mix and feedback, and 3.1 on the other 3 jacks).

This was audibly different then with no jack plugged in in terms of full knob range. Perhaps i didnt try high enough valued resistors (I think i only did 67k), but that shouldnt matter for a voltage divider...

Shrug. I hope i didnt over step any bounds in terms of technical information.

[N871]

would it be a solution to use custom connectors that aren't as wide as a jack conncector so that the 2.5v isn't disconnected...? Maybe even solder the pins to some wires and connect a jack to the patchbay side of these wires...?