Neumann Km74/sennheiser mzn16t psu problem

thekid777 · Apr 3, 2011

Hi,
I am currently feeding a Neumann KM74 with an MZN16T power supply, and I have a buzz/hum problem.
Mics and psu are perfectly working, cables are good, wiring is done correctly according to the KM74 schematic. I don't know what to do.
Here the mzn16t schematic:
http://i853.photobucket.com/albums/ab93/bernardduur/Schematics/Sennheiser-MZN16T.jpg
Please help!! Thanks! Regards.

bobschwenkler · Apr 3, 2011

An obvious first is what shape are the caps in?

Have you loaded the PS with a dummy load and check it with a scope or meter to see if it's actually the PS?

thekid777 · Apr 3, 2011

Hi Bob,
psu is freshly recapped, I tested the voltages going out and they are around 11,5 so it's ok I think.
Unfortunately I don't have a dummy load, what could I do instead?
Thanks!!

bobschwenkler · Apr 3, 2011

Just use a resistor to simulate the load the mic presents. You could use anything somewhat close to this value if you're just testing to see if there's ripple/noise.

thekid777 · Apr 3, 2011

Just made the test and seems ok.
Maybe mzn16t design is too much different from the neumann n9i?
I would have to mod the mzn16t to make it work with km74?...
Help!

bobschwenkler · Apr 3, 2011

Oh, I didn't realize it was not the original. Basically if it provides the same voltage and can meet or exceed the mic's current needs you should be fine. The Neumann board would be a good place to ask about this.

thekid777 · Apr 4, 2011

Just found the mzn16t manual:
http://www.sennheiser.com/sennheiser/old_manual.nsf/resources/MZN_16T_MZN_16T-U_oNr_1284_Sp3.pdf/$File/MZN_16T_MZN_16T-U_oNr_1284_Sp3.pdf

Current is enough for the mics= 10ma for each mic provided by the psu.
Something weird, C11 and C12 are missing inside mine and seems to have never been here.
Any other MZN16T owners here??
Just see that C9 and C10 would need to be bridged for balanced operation, that could be the source of the problem,
will check that!

bobschwenkler · Apr 4, 2011

C9, 10 are pretty small values to be too effective at filtering, I don't see that they'd be the source of a problem like you're describing.

How much have you looked at the mic? If you're getting no noise at the PS with a dummy load it would seem that it is working properly.

USattler · Jul 13, 2011

By now you must have found out that C11 and C12 (100uV/16V) are essential in the Sennheiser MZN 16-T(U) for their proper operation. C9 and C10 are not, and may actually be bridged with short circuits.

Neumann Km74/sennheiser mzn16t psu problem

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