Ground modulation issue between .com and Arturia Microfreak

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Sir Ruff
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Ground modulation issue between .com and Arturia Microfreak

Post by Sir Ruff » Sun Jun 09, 2019 1:13 pm

I am using the MF to control some MU modules, but when I plug in the MF CV output into my control input, I get what appears to be ground modulation in the signal.

both the modular and the MF were plugged into same power strip (where you'd think ground hum would be minimized), but I changed the MF to a different outlet to test and am getting same issue. Power supply is a QPS-1. Anyone have any other suggestions as to how to address?

here's a photo of the setup just for ref:
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diophantine
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Post by diophantine » Sun Jun 09, 2019 3:15 pm

What exactly do you mean by "ground modulation"?

And what specific inputs & outputs are you connecting between the MU and MicroFreak?

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Post by Sir Ruff » Sun Jun 09, 2019 3:22 pm

diophantine wrote:What exactly do you mean by "ground modulation"?

And what specific inputs & outputs are you connecting between the MU and MicroFreak?
It sounds like subtle FM on the audio output, i.e., what you would expect if you modulated an oscillator with a 60 Hz modulator. Basically adds some weird buzzy overtones to the signal. It goes away as soon as I disconnect the MF.

I'm just connecting the MF's CV out to either a Moon Utility voltage summer, or directly into the S-W 901A Control Input. Same result either way.

EDIT: just discovered that the ground modulation is significantly decreased if i also use the MF pressure output (to the filter module in this case). But it's still audible enough to be an issue so this isn't really a complete solution. Someone on the MF thread on GS suggested using a non-grounded PSU; will try that next.
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Post by diophantine » Sun Jun 09, 2019 4:16 pm

Ok, gotcha. Have you tried sending either the Pressure or Gate outputs into the same modules? If so, do you still get the same sort of problem? That might help confirm or eliminate some possibilities.

EDIT: haha, you just beat me with your edit. You could try a cable with the ground wire cut to connect the two systems.

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Post by Sir Ruff » Sun Jun 09, 2019 4:30 pm

diophantine wrote:Ok, gotcha. Have you tried sending either the Pressure or Gate outputs into the same modules? If so, do you still get the same sort of problem? That might help confirm or eliminate some possibilities.

EDIT: haha, you just beat me with your edit. You could try a cable with the ground wire cut to connect the two systems.
Using a non-grounded PSU seems to have fixed it! Not ideal but under the circumstances it will suffice.
You could try a cable with the ground wire cut to connect the two systems.
Interesting--this also seems like it would work and is maybe a better long term solution. [/quote]
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Post by josaka » Sun Jun 09, 2019 4:48 pm

are you left handed..?

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Post by Sir Ruff » Sun Jun 09, 2019 4:50 pm

josaka wrote:are you left handed..?
no, why?
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Post by Rex Coil 7 » Sun Jun 09, 2019 5:35 pm

Sir Ruff wrote:
josaka wrote:are you left handed..?
no, why?
I'll take a guess at why he asked ... most of the patch cables in the picture are on the left side of the modular.

And secondly, I reckon Graham Hinton may be along sooner or later ...


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Post by Sir Ruff » Sun Jun 09, 2019 6:39 pm

Rex Coil 7 wrote:
Sir Ruff wrote:
josaka wrote:are you left handed..?
no, why?
I'll take a guess at why he asked ... most of the patch cables in the picture are on the left side of the modular.

And secondly, I reckon Graham Hinton may be along sooner or later ...


Image
ha... well it's just where all the pitch/gate sources are (there are more cables on the right now :hihi: ) I thought long and hard about the layout--was following the trad Moog IIIP layout, but came up against some hurdles due to a) screw holes not being perfectly aligned, and b) wood back stops in the case preventing placement of S-W modules on the edges. In any case it's working out well so far.

I've also read GH's previous comments about dealing with ground issues. I'm running all the modules off of one supply so no issues there--it's only when trying to interconnect external gear that this seems to become an issue. Short of running the MF off of the QPS1 (which is definitely beyond my pay grade), my current non-grounded PSU solution will have to work.
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JohnLRice

Post by JohnLRice » Sun Jun 09, 2019 11:21 pm

FWIW, if you run into problems with the keyboard not being responsive or something, consider the following from the manual:
The MicroFreak has a touch capacitive keyboard. It can be used with a power bank, but for it to be fully functional the MicroFreak must be properly grounded. It's why we recommend that you use the three pin wall plug provided by Arturia.

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Post by Sir Ruff » Mon Jun 10, 2019 12:44 pm

JohnLRice wrote:FWIW, if you run into problems with the keyboard not being responsive or something, consider the following from the manual:
The MicroFreak has a touch capacitive keyboard. It can be used with a power bank, but for it to be fully functional the MicroFreak must be properly grounded. It's why we recommend that you use the three pin wall plug provided by Arturia.
yeah, neither that or the pitch bend have been acting up using an ungrounded supply. I suspect the issues mentioned might be related to the lower voltages involved in USB power (although the actual issue is supposed to be due to the need to earth the touch plates). Though other people seem to also have no issues when using some USB connections--it seems to just depend on the specific USB power source.
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JohnLRice

Post by JohnLRice » Mon Jun 10, 2019 1:33 pm

I hope it continues to work for you! :tu:

I don't have a MicroFreak so I'm hesitant to make any wild guess suggestions. Here's a picture of the back of the MF for everyone's reference:
Image

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Post by Scot Solida » Mon Jun 10, 2019 6:15 pm

I've just tried the Micro Freak with my own Dotcom system, and I'm getting no such issues. I have them plugged into the same line conditioner, both grounded. I've got the CV going out to my .com oscillators (via a normalization module) and the Gate out running to the Gate in on the Dotcom ADSR. I tried sending Pressure out to the filter cutoff- it worked as expected. :despair:

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Post by burdij » Mon Jun 10, 2019 6:18 pm

Sir, do you have something connected to the USB port?
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Post by Sir Ruff » Mon Jun 10, 2019 8:06 pm

Scot Solida wrote:I've just tried the Micro Freak with my own Dotcom system, and I'm getting no such issues. I have them plugged into the same line conditioner, both grounded. I've got the CV going out to my .com oscillators (via a normalization module) and the Gate out running to the Gate in on the Dotcom ADSR. I tried sending Pressure out to the filter cutoff- it worked as expected. :despair:
Thanks for confirming. I have had grounding issues with other pieces of gear before (although usually as audible hum, not CV modulation) so it's not surprising that it's manifesting itself here between these two units. It never seems to make difference whether or not they are connected to the same wall outlet or not.
burdij wrote:Sir, do you have something connected to the USB port?
Nothing, except when I was trying to power the unit via USB (12v supply was disconnected at that point)
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Post by Rex Coil 7 » Mon Jun 10, 2019 8:19 pm

Sir Ruff wrote:
diophantine wrote:What exactly do you mean by "ground modulation"?

And what specific inputs & outputs are you connecting between the MU and MicroFreak?
...Basically adds some weird buzzy overtones to the signal. It goes away as soon as I disconnect the MF.
Seems as though this may be "digital noise" rather than "ground hum" (as some folks call it).

The Micro Freak thread has a number of complaints about the firmware being rather under-done, it may be something that could be fixed with a firmware uprate. Soon, hopefully.

What does your 5U system's power draw look like? More specifically, how much current is drawn on the positive rails vs the negative rails? A large difference between positive and negative can be trouble makers.

Just spitballing here.

:despair:
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Post by Sir Ruff » Mon Jun 10, 2019 9:02 pm

Rex Coil 7 wrote:
Sir Ruff wrote:
diophantine wrote:What exactly do you mean by "ground modulation"?

And what specific inputs & outputs are you connecting between the MU and MicroFreak?
...Basically adds some weird buzzy overtones to the signal. It goes away as soon as I disconnect the MF.
Seems as though this may be "digital noise" rather than "ground hum" (as some folks call it).
I'm not sure I follow--the problem was solved when I removed the ground so that seems to strongly indicate that that's where the problem lay. Also, the ground hum/modulation actually sounded like something at the ground frequency (60 Hz). Patching in pressure at the same time also reduced it so that seems to also support it being a ground issue.
What does your 5U system's power draw look like? More specifically, how much current is drawn on the positive rails vs the negative rails? A large difference between positive and negative can be trouble makers.
This I can't answer offhand--a few of my modules don't really have good power specs (i.e., STG VCAs). But since the problem is now non-existent when using a non-grounded PSU, this doesn't seem to suggest anything on the power draw side.
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