Midi Murf 200 freq resonant band anomaly

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scragg
Posts: 23
Joined: Tue Sep 30, 2008 5:55 pm

Midi Murf 200 freq resonant band anomaly

Post by scragg » Wed Nov 06, 2019 8:38 pm

Hello Everybody,

I just received a used Midimurf, yay! but am experiencing an audible ‘bump’ on the first bands when Mid toggle switch is selected.
Oddly enough it is more apparent when pattern 1 or 2 is selected.

I read an old post which seemed to be discussing similar symptoms but without hearing an example I cant be sure so wanted to check to see if this was normal?
Firmware was updated too I think unless
I made a user error.

Very much appreciate for a response when you have time.

scragg
Posts: 23
Joined: Tue Sep 30, 2008 5:55 pm

Re: Midi Murf 200 freq resonant band anomaly

Post by scragg » Sat Nov 09, 2019 2:56 pm

Hi All,

Just an update on this as I think I have found the problem -The Midi murf came with a Third party PSU.
I tested it with a genuine Mooger Fooger power supply and viola! problem solved, for now at least. So check and see if that helps.
Now onto my second question, does anyone know where to get an original PSU or suggest a compatible alternative?

Cheers

Markyboard
Posts: 323
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Midi Murf 200 freq resonant band anomaly

Post by Markyboard » Sun Nov 10, 2019 7:49 am

Hi-

From the user manual: +9V POWER INPUT jack – accepts +9VDC unregulated 300 mA power adapter with positive center.

I can't imagine why the power supply would cause the symptom you described. Assuming you're power supply meets or exceeds the spec above (more current capability) it shouldn't matter. However since Moog uses unregulated supplies there is potentially a good amount of variation in the voltage. 9V could really be 11V or more. In other words it's somewhat random and not tied to being a "Moog" supply. They don’t make these, just obtain them elsewhere. I try to use regulated supplies whenever I need to replace or buy one.

Still it doesn't explain why one supply "thumps" your lower bands and the other doesn't. I would guess you have a ground loop that may interfere with the audio at these lower frequencies causing cancellations of the signal in part. Ground loop paths change very easily as current always “seeks” the least resistive path. Changing supplies with the variation I described can be enough to alter that current path and maybe explains why the effect is no longer heard. But the ground loop is still there and may become evident again.

This is just a guess and there could be something in the design that better explains this. Can't tell without a schematic.

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