Moog rack kit for cp251

[CountingToes]

So I finally got round to racking up my 251 and 351, followed the instructions to the letter. And now when I try to use the Lfo on the 251 to modulate say my 303s filter cut off, I get a high pitched note over the top of my acid line, the note seems to be generated by the 251 as it comes up in both the 303s mixer channel and the moogs channel, any ideas what might have happened here? Most frustrating

[CountingToes]

Has anyone had a similar problem? The tone appears on other outputs of the 251 aswell

[schmuck]

Originally Posted by CountingToes

Has anyone had a similar problem? The tone appears on other outputs of the 251 aswell

Don't understand what you meant with "other outputs of th 251"? Maybe you are modulating the cutoff with such a high lfo frequency that it starts whining? It can get pretty fast...

[CountingToes]

Na it's not that. Basically, if I connect the 251 to anything external of the moog, I get a very high pitched continuous tone on the moog channel and the channel of the device I'm trying to modulate, sounds rubbish

[TitusRaindrops]

Yes!

This is a known issue and Moog has never bothered to update their instructions, which totally sucks! Moog?

The problem is caused by the power jumper that allows the CP-251 to share the power of the VX-351. The problem is resolved if the CP-251 uses its own PSU, just like it did before you installed the rack kit.

Crack the rack open again, get rid of the power jumper. The power connector for the CP-251 is on the top and it will protrude enough to cause problems if you intend to mount another rack device above it.

I suggest that you move the barrel-type power connector on the CP-251 from the top to one of the holes conveniently provided in the back of the rack housing. It's a little tricky to do this as the wires are short, but they are just long enough to make it. If you accomplish this you don't have to worry about installing another rack device on top of the VX/CP.

Anyway, this completely eliminates the whine. Moog should have told us about this...

[CountingToes]

Fantastic, thank you mate, I have got my rme above it and my sequencer below, taking up all available rack space do I'm gonna have to move the connector. Is it basic enough for a complete novice to do? No soldering or anything, I was most apprehensive opening the 2 units in the 1st place. Spose I could rack up the 351 and 352 next to each other and have the 251 standalone again, might make more sense

[TitusRaindrops]

Originally Posted by CountingToes

Fantastic, thank you mate, I have got my rme above it and my sequencer below, taking up all available rack space do I'm gonna have to move the connector. Is it basic enough for a complete novice to do? No soldering or anything, I was most apprehensive opening the 2 units in the 1st place. Spose I could rack up the 351 and 352 next to each other and have the 251 standalone again, might make more sense

There is no soldering involved.

Open the rack back up. unplug the power jumper from the VX-351 and discard/set aside. You won't need it anymore.

Find the nut that holds the barrel connector in place on the CP-251. Remove the nut and remove the connector from the board by detaching it from the headers on the PCB (same type of connector as the power jumper, they only go together one way so you can't mix things up).

Thread the connector into the upper left-hand hole on the back of the rack housing and secure it with the nut. When you fit the housing back on to the pedals, you'll have to plug the barrel connector back into the PCB. It's a tight fit because of the length of wire. You may need forceps, tweezers, or a pair of needle-nose pliers. It's not that difficult. Just requires some patience and concentration.

Once you've got it plugged back in, just reassemble and you're done.

With regard to racking both VXs, think about where the 25-pin connectors will be. When the VX and CP are racked together, the VX goes on the left so the huge 25-pin connector/wire isn't in the way of the controls. If you have two VXs, will one of their 25-pin connectors be in the middle? Might not be ideal...

PM me if you run into trouble.

[CountingToes]

Mate you're a star, thanks do much, I'm back at my studio in about 10 days so will give it a go then. Much obliged sir
CT

[TitusRaindrops]

Originally Posted by CountingToes

Mate you're a star, thanks do much, I'm back at my studio in about 10 days so will give it a go then. Much obliged sir
CT

It's no problem. Moog needs to change their instructions to:

a) Warn users that sharing power with the VX may cause a horrible constant whine. Using 2 PSUs produces no whine.

b) Demonstrate how to change the location of the CP-251 barrel plug so its PSU can be used without losing a rack space above the assembly.