MF-105 MuRF - Wrong polarity / Noise

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aztecbride
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MF-105 MuRF - Wrong polarity / Noise

Post by aztecbride » Tue Nov 08, 2022 9:13 pm

I bought a used MF-105 MuRF yesterday,

I've seen this question be asked once before here, but the thread had way too much jargon and colloquialisms for me to understand the actual consequences...

Anyway, the pedal came with a polarity adaptor and a pretty standard 9V power supply. I plugged it in and everything worked fine. But, me being dumb and curious, I noticed that the size of the plugs were the same and so I wondered why do I need the extra adaptor? (I didn't know at the time about the center-positive polarity requirement of the pedal). I plugged it in, tapped the footswitch, but nothing, so I quickly unplugged it again.

The pedal still works when I plug it the correct way, and the adaptor and power supply are also fine. However, there is an ever so slight high pitched noise when the pedal is plugged in, even when it's not engaged. I can't remember if the noise was there when I first plugged it in correctly, or if it came after my little experiment with the power supply.

In any case, could I have damaged the pedal? I read somewhere on the forum that I can send the pedal to Moog for them to fix in any case. How can I do that, where do I reach out?

Any help is much appreciated! The pedal is quite expensive and I'd hate to know I broke it in literally 5 minutes haha..

FeelinDank
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by FeelinDank » Thu Nov 24, 2022 9:07 pm

It very well could have damaged one or two components in the pedal instead of a different one or two things in the pedal. Since it seems to still basically work I would suggest trying a few different tests with it: a few different instruments, nothing plugged in and resonances up variously, maybe try on a different outlet or different house/apartment outlet if you can test at a friend or family’s.

Easy to send it in: make an account on moogmusic.com, click the “talk to us” button near the top right of the main page, and start describing your situation. Probably provide your email, name, address, and the number on your pedal so that they can get the process started. They’ll get the process going and what it’ll probably cost. They may also just have you send it to a local shop (they did that for a previous owner’s Moog MF-107, it was just easier for another shop to look at it).

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stiiiiiiive
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by stiiiiiiive » Fri Nov 25, 2022 7:03 am

Not sure it helps, but I throw this anyway.

First of all, just so that you know (or you've just learned it): even if the plug dimensions are similar, you can get several different kinds of power from a PSU : alternative vs direct/continuous (AC vs DC), the voltage (usually from 3 to 15 Volts for effects usage), the intensity (usually some hundreds of mA or milli-amperes) and the polarity (i.e. what part of the plug is carrying the negative part of the current and what part is carrying the positive part).
Plugging by mistake a PSU with the correct current type, voltage and intensity BUT the wrong polarity may or may not damage the unit. It depends on the implementation of a protection in it.

Now, about the MoogerFoogers, I used them many times with anything else than the original PSU and sometimes, I get that high pitch sound too. Hence this question: are you sure this sound was not present before you use the wrong PSU?
I would recommend further test with different PSUs, in particular with a higher intensity (you won't hurt the pedal using an 800 mA PSU when the pedal requires 500 mA).

Hope this helps!

aztecbride
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by aztecbride » Fri Nov 25, 2022 8:15 am

Hey guys,

So I've been playing with the pedal. It seems to be fine.

So far the noise seems to have gone away, but I sometimes experience some kind of noise when the pedal is disengaged.

I'm gonna try the stereo output on disengaged mod, since it's pretty ridiculous the pedal isn't stereo when not in use. I'll post here if there are any developments.


Thank you for your answers!

JimF
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by JimF » Fri Nov 25, 2022 8:11 pm

Hi aztecbride,

quick addition to Stiiiiiive's comments.

Not sure if there is a protection diode in the MFs, but it would surprise me if there weren't. Nevertheless:

High-pitch sound: my MFs (101, 102, 103, 107) suffer from this _if_ I try to power more than one unit from a single power supply (even though the current ratings are ok). So if you're not already doing so, just power one unit (ie the MuRF) from one supply and check whether that helps.

PSU types: In my experience, the MFs prefer galvanic PSUs (ie with a transformer, rectifier and voltage regulator) rather than switch-mode PSUs. In particular, cheap switch-mode PSUs can introduce all sorts of garbage (including high pitch noise) into an audio device. Unfortunately, switch-mode PSUs have more or less taken over the PSU market, so you may to have to search around a bit for a transformer-based unit. And as Stiiiiiive says, make sure your PSU type (DC), plug size, voltage and polarity are correct.

Also in my experience, MIDI can introduce junk into an audio device, even though it's not supposed to. If you haven't done so already, try the MuRF without any MIDI cables attached.

Good luck!

Jim F.

aztecbride
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by aztecbride » Sat Nov 26, 2022 12:10 am

Hey Jim F.

Thank you for the suggestion on the PSU. I am currently using a run of the mill ZOOM AC adaptor 9v / 300mA which is the one that the guy I bought it from included, with the polarity adapter, but I will check out galvanic power supplies. Any recommendations? I guess it's not urgent but interested in looking into it.

PS. My MuRF is not the MIDI version just the regular one so in that respect there's no other noise.

Thank you!

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stiiiiiiive
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by stiiiiiiive » Sat Nov 26, 2022 12:40 pm

Thanks for those details Jim F., in particular about the different kinds of PSUs. By "switch PSUs" do you mean those with a voltage/polarity selector?

About powering multiple MF together, I undewent the same symptomes several times.

JimF
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Re: MF-105 MuRF - Wrong polarity / Noise

Post by JimF » Mon Nov 28, 2022 8:21 pm

Hi People,

- PSU recommendations - nothing special really, with my MFs I use fairly basic models bought in Germany (where I was living at the time) with the brand name 'Voltcraft'. But these were basically generic transformer/rectifier/regulator PSUs, and cost about €10. So simply see what you can find, and buy a couple and try them out - making sure, of course, that current rating, polarity and voltage are ok.

- switch-mode PSUs: these are PSUs that function basically by using switching elements (transistor etc) switching on and off in turn as input voltage reaches a certain point, with charge being stored and drawn from there for the output . The switching process (usually at an audio frequency, thus the high-pitch noise) can generate a _lot_ of noise/interference, which will find its way into the audio path if the PSU doesn't filter it out properly. Cheaper ones cost also around €10. Some companies make better quality ones (eg current-day PSUs from Boss/Roland for the guitar pedals etc), but they're a lot more expensive.

Another example of switch-mode PSU problems: with my Etherwave and Etherwave Pro theremins, having a cheap switch-mode PSU anywhere in the area, and especially on the same power board, adds all sorts of rubbish to the signal. (The Boss ones on the attached pedals that I use are fine.)

More info here: https://en.wikipedia.org/wiki/Switched- ... wer_supply

Cheers,

Jim F.

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