Moog Music Forum

Hey there,

The vision of the super synth I've been assembling is to mix polyphony, polytimbral, semi-modular synthesis and the phat Moog tone all together. It consists of a Little Phatty Stage II (CV Out Mod) polychained (midi din) with two Slim Phattys (to create 3 voices), two CP-251's with an adjacent easily-accessible patchbay (for patching the CP-251's into the Phattys) and a line mixer. All units are rackmounted behind the Little Phatty in a 19" rack flight case. The phattys can be arranged in any combination - all polychained together, all stand alone units (e.g. Slim's effected by CP-251's or similar to create drones/textures etc, while LP is played by keyboard), all units stacked on one keypress (e.g. 6 osc. massive saw bass on same patch, or polytimbral layers of different patches) and everything inbetween (e.g. two unit polyphony with one unit stand alone).

I have all these units assembled in my rack and everything is working well, except for one major issue I've been trying to overcome for some time: Both the Slim Phattys' (but not the Little Phatty's) dials move around by themselves, changing the sound and changing preset mode to panel active (even with no cables inserted except power - i.e. no other devices are grounding through the phattys). I think this also effects the tuning range of oscillator 2 on one of the Slim Phattys which is out of whack when detuned with the other two phattys (perhaps the unit is not stable enough during calibration).

If you've read some of my other posts in the past, you might know I've been trying to tackle the problem - I first noticed the issue when moving apartment, and I assumed something was wrong with my apartment's grounding or something as every power lead I use is 3-prong (with ground). I tried swapping my power leads, multibox, extension leads and using different wall outlets in my apartment with no improvement. I have tried using surge protection, an isolation transformer, a power conditioning UPS, and a pro Furman Voltage Regulator/Power Conditioner (which would have cost me US$1800 if it worked anyway!). I also tried taking a Slim Phatty to my parents' house, which to my surprise, still changed to panel active by itself (a dial value changed), but who knows - is the wiring bad at both mine and my parents' seperate addresses?

Moog mentioned that there was a ground modification I could get done by their tech here in New Zealand to try and decrease the sensitivity to ground. I sent my phattys away but it turns out both the Slims already had the mod installed at the factory (Slims came out later than the Little Phatty), so there was no fix there - although the units were ground tested and passed perfectly apparently. Sending them away wasn't a complete waste as I got all of the Pitch CV In's scaled to 1v/oct., but it did take a while and it's hard sending them away for ages.

So to sum it up, my Little Phatty and CP-251's are solid, but the Slims are still having this dial problem (plus the osc. 2 tuning range problem on one of the Slims - possibly related), and they could still possibly be fine at other locations - if the two locations I tested it at have bad power somehow.

Does anyone have any ideas to try? Get an electrician around? Try a step-down transformer maybe (i.e. US Voltage)? What would you do in my situation? Would you just sell them? Who would buy my two potentially glitchy Slim's anyway?

Regards,
David Smyth
NZ

I feel for you.

Really sorry to hear about your problems David (particularly since I'm looking at a similar poly-chain myself).

Out of curiosity, you say the problem occurred at your parent house as well but did the problem occur for the Moog technician? I kind of wonder if the Phattys themselves might be creating some interference. Do they exhibit this behaviour if only one of them is switched on?

Thanks for the synth sympathy guys!

Mike wrote:Out of curiosity, you say the problem occurred at your parent house as well but did the problem occur for the Moog technician? I kind of wonder if the Phattys themselves might be creating some interference. Do they exhibit this behaviour if only one of them is switched on?

I can't say if the problem occured for the technician, I probably should have got him to check - but at the time I was convinced the ground modification was the answer. He did however test the grounding, so I feel that the unit shouldn't have grounding problems - But maybe it only does at certain locations (with bad wiring or bad power quality maybe)?

One Slim Phatty by itself, with only a 3-pronged power lead plugged in still shows the same behaviour. Although it seems many people have Slim Phattys without any problems, so I'm wondering what makes my situation different..

David.
NZ

Hey there,

Here's an update on my Slim Phatty "dancing dial syndrome" problem:

In my case (two Slim Phattys) the cause of the problem was electromagnetic radiation from the power supply (not a grounding problem as I originally thought). Other user's problems may be caused by this or something else - I'm not sure.

I've been testing out a mod to fix the spurious parameter glitches, working well so far. Whereas before it would usually glitch within 20 minutes, now it goes more than a week without any (no parameter shifts observed). The mod was done by an electronics engineer, it's fully reversable, doesn't involve changes to circuits, firmware or circuit boards, no change to outer appearance, and no possible changes to sounds or performance. It proves the original design is good. However the mod details are too complex to post here and should be done by a service technician who can also verify performance, electrical safety, etc. The mod is open-heart surgery and would probably void the warrantee if not done by an authorized service center. If you are really stuck on this, contact me.

So I am relieved to get a successful result for this very annoying problem!

Regards,
David Smyth
NZ

I had the dancing lights on my Little Phatty Stage II and when I contacted support per someones suggestion on this forum they asked me to send it in. I've had it back for a week now and have not had any problems.

That's awesome news, David! Glad everything worked out for you finally!

Just a thought. I use my LP stage II live exclusively (only plugged into a DI in various club/theater situations in various environments) and have noticed the dancing dial LED issue I believe you expressed only in certain conditions. The instrument will behave fine until I plug the audio out into a Radial brand DI. If I use a cheaper DI like a Whirlwind Imp, I have no issues. It was explained to me as a ground loop issue and I don't know why another DI solves the issue but it always works so without further information on the root cause, that remains my practical solution.

I just got my Little Phatty in last Thursdsay. That night I plugged it in and got the "dancing dials" problem. It was a real bummer obviously because when the dials/leds are moving, so is the sound. I moved the phatty and equipment into a different room of my house and haven't had a single issue yet! I'm not sure if it was the wiring in that particular room that made the dials dance (I've had suspicions in the past in regards to the rooms wiring,) or mabey if it was the synth being right beside my computer (just a hunch,) but I've had no issues since moving the synth into a different room of my house.

hi everyone - new to the forum. my SP has just developed the dancing dials issue

knob-wise, it's pretty mild - just the occasional momentary movement of a the filter/envelope dials by one LED light and back again. the main issue is that the SP now won't stay in 'preset active' mode for more than a few seconds anymore. and most of the time it jumps back immediately, making A/B comparisons of panel/preset impossible.

the issue happens when plugged into power only, and i have tried other power circuits in my house, with no change. pretty sure that the unit is out of warranty (and i'm the 2nd owner). my serial is 00250, so i'm thinking that the unit would probably benefit from the ground mod. does anyone know what it is/cost for authorised service place to fix? i'm reasonably skilled with a soldering iron, so if it's a basic 'wire from here to there' type mod, i'd be pretty confident to do it myself...

any info appreciated.

*update on previous post*

after opening the unit up (mine is out of warranty), i found that the connector from the power board to the front panel board (red connector, multi-coloured wires) wasn't sat properly. after pushing it fully down, it seems the problem is fixed! simple and easy... the best feeling fixing your own gear ;P

a word of warning if you try this - be careful opening the case after the screws are removed - the i/o board is connected directly to the front panel board (multi-pin connector) rather than by ribbon cable, so you have to pull the front panel downwards (i.e. at a 90 degree angle from the i/o board) to disconnect them. reverse this (or remove i/o board and then reconnect to front panel board) before re-fitting into case. doing this would would any warranty you have left, of course.

bauer wrote:hi everyone - new to the forum. my SP has just developed the dancing dials issue

knob-wise, it's pretty mild - just the occasional momentary movement of a the filter/envelope dials by one LED light and back again. the main issue is that the SP now won't stay in 'preset active' mode for more than a few seconds anymore. and most of the time it jumps back immediately, making A/B comparisons of panel/preset impossible.

the issue happens when plugged into power only, and i have tried other power circuits in my house, with no change. pretty sure that the unit is out of warranty (and i'm the 2nd owner). my serial is 00250, so i'm thinking that the unit would probably benefit from the ground mod. does anyone know what it is/cost for authorised service place to fix? i'm reasonably skilled with a soldering iron, so if it's a basic 'wire from here to there' type mod, i'd be pretty confident to do it myself...

any info appreciated.

Hi and welcome to the forum!

The first step I would recommend is contacting Moog tech support (you can do this here: http://moogmusic.com/contact ) and explain your problem to them.

I would also ask them whether all Slim Phattys have the ground mod installed from the factory, or perhaps from a certain serial number. The reason I say this is because when I had my dancing dial problem with my two SP's, I sent both units to have the ground mod installed but the technician found that they had already been installed from the factory during the manufacturing process. If it turns out your unit doesn't have the mod, then perhaps it will correct your situation (tech support should be able to give you details regarding getting it installed).

In my case, since I already had the ground mod installed (with the problem still occurring), I contacted an Electrical Engineer who helped me with another mod (which ultimately solved it), but since these problems can have multiple causes, our problems may have different fixes.

Just out of interest, what country/power grid (voltage, hertz) are you running the unit on? I was having the problem with SP 01109 & SP _____ here in New Zealand with 230/240v, 50/60hz power. I am unsure if power grid specs and unit serial number have anything to do with it, but it's worth seeing if there's a pattern.

Let us know how you get on.

Regards,
David Smyth
NZ

thanks dave. i had posted an update, but it seems to have disappeared.

i did contact tech support, but in my impatience (and on realising my SP was out of warranty), i opened the unit up and found that the connector on the cable from the PSU board to the UI boards wasn't seated fully. after pushing it home, problem seems solved!

an easy win. i'll post again if the problem recurs.

ps: i'm in the UK, so 240v and SP serial is 00250.

bauer wrote:thanks dave. i had posted an update, but it seems to have disappeared.

i did contact tech support, but in my impatience (and on realising my SP was out of warranty), i opened the unit up and found that the connector on the cable from the PSU board to the UI boards wasn't seated fully. after pushing it home, problem seems solved!

an easy win. i'll post again if the problem recurs.

ps: i'm in the UK, so 240v and SP serial is 00250.

That's a great result! I know how annoying that problem can be, so it's fortunate that the fix was something simple like that.

David.
NZ