FM3 humming in Gemini 2

F

Flobudi

Member
Hi folks,

I use the FM3 with a Mission Engineering Gemini 2. I great team but i have some humming.
I use the out 2 on the fm3 with a 2x 6,3 mono to 1x 6,3 stereo into the Gemini.

  • If i disconnect the cable there is silence
  • if i turn the volume on the gm2 down (3 o'clock) there is silence
  • if t turn the lights on in the room, the humming goes down :mad:
  • a di box take the humming a little bit down but it´s there

Have anyone a idea what´s the problem with the setup? I order a 2 XLR female to 1x XLR male to use the output 1 on the fractal. Or it´s better to use a Lehle P-ISO to delete the humming.
Or is a power conditioner the way to go?
 
If you unplug the guitar cable from the input of the FM3, what happens?

Flobudi said:
if t turn the lights on in the room, the humming goes down :mad:
Click to expand...
That's a bit odd... Unless the lights are on a dimmer? Are they?

Dimmer switches, florescent lights, LED lights, etc can all be sources for EMI and most likely that's coming in thru your guitar.
 
To confirm, your cable is TS on the two plugs from the FM3, and TRS on the end that plugs into the Gemini?

Is the hum present if you use a normal TS instrument cable from out2 (either left or right) into the Gemini input 1, with the Gemini’s switch set to ‘mono’? I understand that this isn’t how you want to run it, but this is a proposed troubleshooting step. Is the hum present if you connect the instrument cable to input 2 on the Gemini?

Are the FM3 and the Gemini plugged into the same A/C outlet/circuit? If not, try it with both on the same circuit.

A standard DI box likely won’t help, since they produce a balanced output circuit (not stereo XLR), and it doesn’t appear that the Gemini has balanced inputs. Transformer isolation may help, but for your setup you’d likely want a dual mono (or stereo) device that is designed for unbalanced instrument inputs and outputs OR one that takes balanced inputs from out1 on the FM3 and puts out dual mono (or stereo) unbalanced signals to feed the input of the Gemini.
 
Rumbletone said:
re the FM3 and the Gemini plugged into the same A/C outlet/circuit? If not, try it with both on the same circuit.
Click to expand...
Yes they are in the same A/C circuit with phase correct in.
Rumbletone said:
A standard DI box likely won’t help, since they produce a balanced output circuit
Click to expand...
A good point. It´s a normal passiv DI Box. Is a stereo DI Box the way to go? Yes I would like work with the stereo signal from the fm3.
Rumbletone said:
To confirm, your cable is TS on the two plugs from the FM3, and TRS on the end that plugs into the Gemini?
Click to expand...
Yes exactly. I ordered this one yesturday to use it on the output 1 on the FM3:

Cordial EY 0,3 MFF elements​


Rumbletone said:
Is the hum present if you use a normal TS instrument cable from out2
Click to expand...
The hum is done when i use a normal ts cable from out 2 to the input of the gemini.
 
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Flobudi said:
A good point. It´s a normal passiv DI Box. Is a stereo DI Box the way to go? Yes I would like work with the stereo signal from the fm3.
Click to expand...

Any typical DI box is not a great choice for going into a device that doesn't have balance inputs since it is designed to convert from an unbalanced instrument signal to a balanced signal. A better option I think would be an isolation device that has unbalanced input and unbalanced output options. I use an old BYOC stereo isolation box (I rarely need to use it, but always have it available, and it's been a saviour in a few situations ...), but something like the Radial SB-6 might be a better option (and it has additional useful features, and can also run balanced so would also work on out1 if you use those in the future).

If you don't get the hum using a single TS from out 2 to the Gemini, I wonder if it's the joining of the 2 ground connections of the FM3 outputs that is giving rise to a loop, and perhaps breaking that by disconnecting the ground on one side may solve the issue. Are you handy with a soldering iron? That said, I've done exactly what you are doing - running out2 from dual TS to a single stereo TRS input (on a Rolls unit for driving my IEMs) - and I didn't have any issues with hum or other noise, so I'm optimistic you should be able to make it work.
 
Flobudi said:
Yes exactly. I ordered this one yesturday to use it on the output 1 on the FM3:

Cordial EY 0,3 MFF elements​

Click to expand...

The link isn't working for me, but is it this Y connector: https://www.cordial-cables.com/en/products/ey-mff ? If so, it appears from the supplied wiring diagram that's it's in effect unbalancing the outputs and then putting one side on pin2 and the other side on pin3. The Gemini manual states "Use an XLR or TS cable to connect a mono signal to Input 1", which suggests to me that the XLR input on the Gemini is wired as a mono balanced signal, though it's not entirely clear. If it's mono balanced, plugging this cable in directly may work, but it would be mono and the polarity may not align well - i.e., if it's in effect summing L and R via the balanced input circuit but flipping the polarity of one side you may get unwanted cancellation, assuming the L and R of your signal is generally phase-aligned. In order to get stereo, you should be able to plug the XLR output of the Y cable into an XLR->TRS adaptor then plug the TRS into the Gemini stereo TRS input. It may or may not fix the noise issue, but you would have the option of trying the ground lift on the FM3 output1 to remedy it.
 
Rumbletone said:
The link isn't working for me, but is it this Y connector: https://www.cordial-cables.com/en/products/ey-mff ? If so, it appears from the supplied wiring diagram that's it's in effect unbalancing the outputs and then putting one side on pin2 and the other side on pin3. The Gemini manual states "Use an XLR or TS cable to connect a mono signal to Input 1", which suggests to me that the XLR input on the Gemini is wired as a mono balanced signal, though it's not entirely clear. If it's mono balanced, plugging this cable in directly may work, but it would be mono and the polarity may not align well - i.e., if it's in effect summing L and R via the balanced input circuit but flipping the polarity of one side you may get unwanted cancellation, assuming the L and R of your signal is generally phase-aligned. In order to get stereo, you should be able to plug the XLR output of the Y cable into an XLR->TRS adaptor then plug the TRS into the Gemini stereo TRS input. It may or may not fix the noise issue, but you would have the option of trying the ground lift on the FM3 output1 to remedy it.
Click to expand...
From my reading of the Gemini 2 I/O summary:

Input 1 – Combo XLR-1/4″ TRS jack line input (mono or stereo)
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It seems like the XLR is mono and the TRS is the usual stereo in.

I think it'd be useful for the owner to contact Mission Engineering for a clarification.
 
Yesterday, I spoke to Knut from G66/Fractal on the phone. After several attempts, he came to the conclusion that the Gemini can only have a mono-symmetrical input.
He says you can probably get it to work with a modified Humbuster cable. However, the smartest solution is to use an isolation box. He then recommended two of these:
https://www.thomann.de/de/lehle_p_iso.htm?gad_source=1&gad_campaignid=1576042978& gclid=Cj0KCQjw9JLHBhC-ARIsAK4Phcp75nS3l4zPTEPhvy6yyPkirBVU8Drun0K91tcyYKsgEtbpwh5-v7QaAiwKEALw_wcB

The Radial SB-6 is just as good, if not better. This allows me to use output 1 of the FM3 as well.
 
FractalAudio said:
I don't know. It seems that product only has a single XLR input. If you want stereo you'll need an ISO box. If you can live with mono then just run a single XLR cable from Output 1 Left.
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It has a TRS input for stereo as far as I remember.

It's supposed to work with a Y cable.
 
FractalAudio said:
Curious design choice. This invites ground loops. Two XLR inputs would've been better.
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Yes, it always seemed like a poor choice to me.

From their manual:

ConnE􏰃ions
There are three inputs and one output on the rear panel of the GM-2 as follows:
Input 1 – The combo connector supports XLR, 1⁄4” TS or 1⁄4” TRS jacks. Use a 1⁄4” TRS cable to connect the output from a line level device such as a modeling amp, preamp, or multi effects device to Input 1. The right channel is on the tip and the left channel is on the ring. If your input device outputs left and right signals on separate jacks, you will need a TRS insert cable to connect the two output jacks to the single TRS input jack on the GM-2.
Use an XLR or TS cable to connect a mono signal to Input 1. When using a mono input, use the stereo/mono toggle switch to control how the signal is routed to the drivers. In stereo mode, the signal will use one of the internal drivers. In mono mode, the mono signal will be bridged to the two sets of speaker drivers.
Stereo Out – This connector supports 1⁄4” TS cables. If using two GM-2 systems in a stereo configuration, use a 1⁄4” TRS (stereo) cable to connect a line level stereo output to Input 1 and a TS (mono) cable to connect the stereo out to the second GM-2. Switch both systems to mono mode via the toggle switch. The right stereo channel will be routed to the second GM-2 system.
When using mono mode, high level input signals may cause clipping. If this occurs, either reduce the input signal level, or switch to stereo mode.
Input 2 - This connector supports 1⁄4” TS cables. When using
the USB audio interface on the GM-2, connect your guitar or other instrument to Input 2. This will allow you to use your instrument with an audio workstation application such as Avid® Pro Tools or Apple® Logic ProX, or a software based modeler such as Scuffham S-Gear. The Gemini audio interface supports multiple simultaneous streams, so you can, for example, play along with recorded music on your computer, or practice with online tutorial
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„If your input device outputs left and right signals on separate jacks, you will need a TRS insert cable to connect the two output jacks to the single TRS input jack on the GM-2.“

So i think for stereo the y cable 2x xlr female to one trs is the way.
 
Flobudi said:
„If your input device outputs left and right signals on separate jacks, you will need a TRS insert cable to connect the two output jacks to the single TRS input jack on the GM-2.“

So i think for stereo the y cable 2x xlr female to one trs is the way.
Click to expand...
An "insert" cable is TRS to dual TS with one side wired to Tip and one side wired to Sleeve.
 
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