Ground hum on Prophet-10 rev4

[backdoorranky]

Last night and this morning I noticed a pretty bad clicking/noisy floor. It is faint but still audible at normal gain of the Prophet-10 output.

It sounds like this when the gain from my mixer is pushed further: https://soundcloud.com/tombrews/noisy-prophet-output/s-Eg4HhSnVBdj?utm_source=clipboard&utm_medium=text&utm_campaign=social_sharing

It sounds like this even when turned off and only plugged in.

I tried using different TS cables, different power outlets, different channels on the mixer, etc. No dice.

This morning I tried using a balanced cable and it seems to have completely fixed the issue. Sounds nice and silent now.

I was confused by this since the Prophet-5/10 has an unbalanced output. Why would a balanced cable fix the issue if the output is unbalanced?

Then I started thinking, well, why shouldn't I just use balanced cables for everything, even if some gear only has unbalanced outputs?

Found an old thread on a forum where someone with the same issue with their P5/10 says:
The sleeve is grounded.
The tip is audio out with 600 ohm impedance.
The ring is a 600 ohm resistor to ground.

Is this true? I imagine so since the issue has simply been fixed with a balanced cable, though this was (pleasantly) surprising to learn.

[mbenz]

Thank you for this helpful observation!  I have observed similar hum issues with my Prophet-10 rev 4 when connecting it to an RME Fireface UFX+ input with a TS cable.  The Sequential Owner's Manual states that the audio output on the Prophet-10 is 1/4" unbalanced.   Somewhere I recall reading that the output is actually TRS, but since it is a mono output I always wondered why it was designed this way.   After running across your post, I found an article that explains why it works.  See page 5 starting at the last paragraph in the article (link below).  Essentially, the output circuit is designed to operate both in an unbalanced and balanced manner, by using a clever and inexpensive method.  Why the audio output specification is not listed as such in the manual (e.g. balanced/unbalanced), I do not know.

I tried a TRS cable instead, as you did, plugged into a balanced line level input on my RME interface.  No more hum!! Magical.  I am so pleased. 

Regarding your thought about using balanced cables for everything.  My sense is that will only work if the output circuitry is designed to operate in this fashion, but would not if the output is unbalanced only. So I guess you could test each device to find out with no potential for harm.  Thanks again!

https://mikeriversaudio.files.wordpress.com/2010/12/balanced-unbalanced_revised.pdf

[Analog Prophet]

Do you use the USB connection? USB is a well known source of hum issues in studios.

[mbenz]

Yes, but for MIDI only. My thought is that since no audio is transmitted via USB on the P10 (just MIDI), hum would not transmit, unless it created a ground loop of some sort. Perhaps I'll try disconnecting it just to be sure.  Nevertheless, the balanced cable fully solved the issue, but thanks for the suggestion, as it is good to keep in mind in general.

[Analog Prophet]

P5/10 only transmit MIDI through USB, no audio. USB (MIDI or any signal, the signal is not the source of issue) is still a well known hum issue in many studios. Not necessary the case with P5/10 but worth trying if hum related or other disturbing audio problems.

[backdoorranky]

P5/10 only transmit MIDI through USB, no audio. USB (MIDI or any signal, the signal is not the source of issue) is still a well known hum issue in many studios. Not necessary the case with P5/10 but worth trying if hum related or other disturbing audio problems.

I had tested mine just alone with nothing else but a mixer turned on in the room and was getting this noise. Tried different power strips too. I'm just glad a balanced TRS fixes it, though I can't get around this noise if I want to plug it into something like my Arion SCH-1 stereo chorus as it has unbalanced I/O. It's not a huge deal really.

[backdoorranky]

Thank you for this helpful observation!  I have observed similar hum issues with my Prophet-10 rev 4 when connecting it to an RME Fireface UFX+ input with a TS cable.  The Sequential Owner's Manual states that the audio output on the Prophet-10 is 1/4" unbalanced.   Somewhere I recall reading that the output is actually TRS, but since it is a mono output I always wondered why it was designed this way.   After running across your post, I found an article that explains why it works.  See page 5 starting at the last paragraph in the article (link below).  Essentially, the output circuit is designed to operate both in an unbalanced and balanced manner, by using a clever and inexpensive method.  Why the audio output specification is not listed as such in the manual (e.g. balanced/unbalanced), I do not know.

I tried a TRS cable instead, as you did, plugged into a balanced line level input on my RME interface.  No more hum!! Magical.  I am so pleased. 

Regarding your thought about using balanced cables for everything.  My sense is that will only work if the output circuitry is designed to operate in this fashion, but would not if the output is unbalanced only. So I guess you could test each device to find out with no potential for harm.  Thanks again!

https://mikeriversaudio.files.wordpress.com/2010/12/balanced-unbalanced_revised.pdf

Thank you for this info!

[IslandGhost]

I experienced ground loop noise when I moved from using a laptop to a much higher spec desktop PC.  The noise was noticeable for both my Prophet-10 and my Rev 2 when connected to my PC.  The noise increased when I moved my mouse or opened other apps which I understand is a classic symptom.
I ended up buying an idefender plus which connects to the USB cable and this cleaned the sound up nicely.  An expensive piece of kit for what you get in the box but did the job.
I did find TRS cables also worked but the noise came back when I added effect pedals, even with multiple TRS cables.

[backdoorranky]

I experienced ground loop noise when I moved from using a laptop to a much higher spec desktop PC.  The noise was noticeable for both my Prophet-10 and my Rev 2 when connected to my PC.  The noise increased when I moved my mouse or opened other apps which I understand is a classic symptom.
I ended up buying an idefender plus which connects to the USB cable and this cleaned the sound up nicely.  An expensive piece of kit for what you get in the box but did the job.
I did find TRS cables also worked but the noise came back when I added effect pedals, even with multiple TRS cables.

Yeah, same issue here. If I want to use an effect pedal that uses a TS input, then I have to deal with that clicking noise. It's definitely not a nice or passable noise either.  Only way around this is to set up the effect as a send through a mixer instead. I'm just using DIN MIDI here, no USB. The noise is there with no midi connected.