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Author Topic: Neumann km74/mzn16t psu problem  (Read 11374 times)

Julien Asencio

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Neumann km74/mzn16t psu problem
« on: April 02, 2011, 01:16:53 PM »

Hi,
I am currently feeding a Neumann KM74 with a Sennheiser 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 is the schematic of the power supply:
http://i853.photobucket.com/albums/ab93/bernardduur/Schematics/Sennheiser-MZN16T.jpg

Please help!! Thanks! Regards.
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Julien Asencio

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Re: Neumann km74/mzn16t psu problem
« Reply #1 on: April 04, 2011, 07:35:52 AM »

Hi, somebody would have this psu?
It seems that two condensators are missing in mine...(C11/C12)
If someone could post a pic of the inside it would be really nice!!
Thanks!
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Oleh Malyy

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gpiccolini

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Re: Neumann km74/mzn16t psu problem
« Reply #3 on: April 09, 2011, 05:34:33 PM »

I had an MZN16T. Brand new. It never worked with any Neumann Fet70 mic. It worked perfectly with the Sennheiser brought by the guy that bought the PSU from me. Just for fun we tested the Sennheiser (don't remember the model) on my Neumann N91 PSU. It had hum...
It's weird because both are T-Power PSUs, but for some reason are not compatible. Down by the road I learned there is "regular" and "negative" T-Power. Don't know if this is the case...
Also, T-Power mics don't like certain preamps; don't know why, but I had that problem with  Telefunken V676a and V672. Then the guy that racked them came and did something on them and the noise dissapeared. Something about blocking voltage I think. Did not happen with Phantom power.
ATM I use V376a and all my Fet70s sound really nice.
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David Satz

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Re: Neumann km74/mzn16t psu problem
« Reply #4 on: April 11, 2011, 08:09:00 AM »

- "Tonaderspeisung" or parallel powering differs from phantom powering, in that the operating DC flows from the power supply through one modulation lead and back through the other. The shield and/or ground lead is not involved.

Sennheiser and Kudelski (Nagra) were using this powering method before it was standardized by the DIN. When the DIN standard came out, the opposite powering polarity was recommended from that which Sennheiser and Kudelski were already using; I don't know why or how that happened, but it caused a great deal of confusion.

Schoeps introduced parallel-powered microphones in several different models--the basic one (e.g. CMT 441 or CMC 441) complied with the DIN standard, but they also made microphones that worked directly with Nagra recorders (e.g. CMC 441 k, where the "k" stood for "Kudelski"). Most people who used Schoeps microphones for film and video sound either bought the "k" model or used adapters in their cables, although it inverted the signal polarity along with the powering.

There was no risk of harm if you connected a parallel-powered microphone to a parallel power supply having the opposite polarity; it simply wouldn't work. Since yours is working (but not well), I don't think this is the problem.

--The output of a parallel power supply must block the DC, or else it will flow across the inputs of a preamp or recorder in differential mode, and this can easily saturate an input transformer or cause a transformerless input circuit to block any audio signal at all. In addition, when multiple microphones are powered from the same parallel power supply, bypass capacitors are required in order to prevent audio crosstalk.

Parallel powering was never intended for use in studio microphones, and is a poor fit with studio practice in general. It can instantly destroy dynamic microphones, particularly ribbons, if left on when they are connected to a device. Its only advantage is that if you ever have to connect a condenser microphone to an unbalanced input, that can be arranged somewhat more easily with "T" power than with most phantom-powered microphones. But that hasn't been a frequent requirement for most professionals in the past forty years or so; it's pretty well obsolete by now.

--best regards
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Lukas

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Re: Neumann km74/mzn16t psu problem
« Reply #5 on: April 11, 2011, 03:35:05 PM »

As a Nagra user, I have to add up that the existence of the two different A-B or T-Power versions is a pretty confusing matter, as a lot of DIN-standard T-Powered microphones were modified by their users to work with Nagra recorders - and even though it was a common practice to mark such microphones (usually with red dots, Google "red dotting" for more information), there is still a lot of them with reversed leads but no markings to indicate such modification. These microphones will not work e.g. with P48 -> T-Power adapters etc.

But to stay on topic, here's the MZN-16T Manual/Schematic.

The blocking caps C11 and C12 should be installed, maybe the PSU was modified to work e.g. w/ MKH 110 etc.

Hope this helps!
Lukas
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Oleh Malyy

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Re: Neumann km74/mzn16t psu problem
« Reply #6 on: April 12, 2011, 01:03:19 AM »

from Kidbill’s photo
C11 and C12 already installed
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Oleh Malyy

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Re: Neumann km74/mzn16t psu problem
« Reply #7 on: April 15, 2011, 01:01:00 PM »

With Neumann U77 and Sennheiser MKH 405 I use Sennheiser BP-2 12 AB Power Supply, that was moded by local technical man.
It can be used with all 12v T-Power microphones which current consumption is 6mA.

With U77 result the same as with internal battery.

Schematics attached
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Julien Asencio

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Re: Neumann km74/mzn16t psu problem
« Reply #8 on: April 28, 2011, 03:01:04 PM »

Thanks guys for your answers! I didn't had notifications in my email so I just see this.
Problem solved!
 I think it could help many people because I already know 3/4 persons with km74/76 and the mzn16t never worked for them as well...
First, wiring was not correct and didn't match correctly with the + - g informations inside the psu, so it must be checked.
And the most important thing that I saw in the manual: FOR BALANCED OPERATION C9 AND C10 MUST BE BRIDGED!! This solve the problem immediatly.

Now my mics are very well working and are one of the most noise free mics I have
Good things as well is : mzn16t seems to be a better psu than n9i, less expensive and easily available.
Thanks for all and please share if it works now for you. ;)
Best, Kidbill.


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Oleh Malyy

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Re: Neumann km74/mzn16t psu problem
« Reply #9 on: May 02, 2011, 02:10:31 AM »

FOR BALANCED OPERATION C9 AND C10 MUST BE BRIDGED!! This solve the problem immediatly.
thanks
will try
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Oleh Malyy

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Re: Neumann km74/mzn16t psu problem
« Reply #10 on: June 28, 2011, 05:02:55 AM »

And the most important thing that I saw in the manual: FOR BALANCED OPERATION C9 AND C10 MUST BE BRIDGED!! This solve the problem immediatly.
must tell you
THANKS!!! for idea
has tried - works
maybe a little more noise, if compared with battery power supply, but very good solution
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