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Author Topic: M49 lower output?  (Read 6074 times)

klaus

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Re: M49 lower output?
« Reply #15 on: November 19, 2016, 12:20:45 pm »

Replace the brown ceramic disk capacitor C1 (10.000pf/0.01mfd) viewable here:
https://groupdiy.com/index.php?topic=44667.40

If that does not work, your work might be done, and a real brain surgeon may need to take over.
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Klaus Heyne
German Masterworks®
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Koen

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Re: M49 lower output?
« Reply #16 on: November 19, 2016, 01:10:04 pm »

Will do.
Replace it with the same type ceramic disc or another type?
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klaus

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Re: M49 lower output?
« Reply #17 on: November 19, 2016, 01:31:57 pm »

Any non-polarized type that fits is fine. It's a low voltage application, so any type with a 50VDC rating will do.
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Klaus Heyne
German Masterworks®
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usattler

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Re: M49 lower output?
« Reply #18 on: November 19, 2016, 09:24:29 pm »

Aside from the NDWR prototype, to the best of my knowledge, there were only three original versions of the Neumann model M49:
the original M49 (without any suffix), the M49b - like the initial release this version had its bias derived by a simple voltage divider (R6/R7) from the filament voltage, and the M49c with the negative DC feedback via the cathode resistor (R7) and the AC feedback canceled by the bridging capacitor (C9).
The photos do apparently depict an unmodified M49b.

Uwe Sattler,
Technical Director (retired) - Neumann|USA
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Uwe Sattler
Technical Director - Neumann|USA (retired)

usattler

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Re: M49 lower output?
« Reply #19 on: November 19, 2016, 09:26:21 pm »

Schematic for the first generation M49 attached.
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Uwe Sattler
Technical Director - Neumann|USA (retired)

usattler

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Re: M49 lower output?
« Reply #20 on: November 19, 2016, 09:27:35 pm »

Schematic for the M49b and M49b3 attached.
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Uwe Sattler
Technical Director - Neumann|USA (retired)

usattler

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Re: M49 lower output?
« Reply #21 on: November 19, 2016, 09:28:35 pm »

Schematic for the M49c attached.
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Uwe Sattler
Technical Director - Neumann|USA (retired)

klaus

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Re: M49 lower output?
« Reply #22 on: November 20, 2016, 01:25:58 am »

Excellent resource.
Thanks, Uwe!
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Klaus Heyne
German Masterworks®
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Koen

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Re: M49 lower output?
« Reply #23 on: November 20, 2016, 07:31:10 am »

Wow, yes, many thanks!

Last point of confusion:
Klaus, the original schematics show that C1 calls for 1000pF (1nF) instead of the 10000pF (10nF) you mentioned earlier in the thread.
Is there a particular reason to alter this value to the one you suggested?
Kindest regards,

Koen.
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usattler

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Re: M49 lower output?
« Reply #24 on: November 20, 2016, 11:14:56 am »

 Capacitor C1 bridges both halves of the 80pF capsules, and the difference in value between 1000pF and 10,000pF (1nF and 10nF) in this circuit does not make any difference for the function. Since this is the most sensitive section of the circuit though, it is important for this capacitor to be of the highest quality available, and Styroflex types have been used in the originals.
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Uwe Sattler
Technical Director - Neumann|USA (retired)

klaus

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Re: M49 lower output?
« Reply #25 on: November 20, 2016, 01:56:11 pm »

Last point of confusion:
Klaus, the original schematics show that C1 calls for 1000pF (1nF) instead of the 10000pF (10nF) you mentioned earlier in the thread.
Is there a particular reason to alter this value to the one you suggested?
The confusion came from you mixing up the designation of "C1" in the photo I referenced, with "C1" in the Neumann schematic. They are not the same part! C1 in the photo is labeled as the ceramic brown disk cap (10.000pf). I mentioned this part as possibly being suspect, and to replace it.

 "C1" of the schematic Uwe referred to serves an entirely different function. For space reasons, I would retain the 1000pf styrene cap currently installed.
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Klaus Heyne
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Koen

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Re: M49 lower output?
« Reply #26 on: November 20, 2016, 01:58:00 pm »

Hi all,
After replacing the defective 300Kohm resistor and the 0,01 mfd ceramic disc, Measured from anode (at the valve pin) to ground I still only have 29V, but measured at the actual turret on the board, I see it climbing up to 35V (???). Is this at all possible?
Also: a few db's more output. The noisefloor however is the same (like a distant highway kind of noise).

Concerning the actual M49'B' schematic: I carefully followed the leads on the microphone's board and think the ceramic disc cap is referred to as C8 on this schematic - maybe Klaus or Uwe could confirm this?

Overall, compared to my other M49, it the output is still considerably lower and I'm experiencing some bass rolloff as well.
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klaus

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Re: M49 lower output?
« Reply #27 on: November 20, 2016, 02:32:51 pm »

C8 is correctly identified as being the ceramic disc capacitor.
I suggest to send the mic to Neumann or a qualified tube mic specialist for repair;  tele-diagnosis beyond this point seems fruitless.
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Klaus Heyne
German Masterworks®
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Koen

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Re: M49 lower output?
« Reply #28 on: November 20, 2016, 02:48:49 pm »

 :'(
Ok, thanks for the help.
I'll inquire with Andreas Grosser and Neumann Berlin on what their turnaround is.
Kindest regards,

Koen.
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