R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: Schoeps BZ 41 Unk  (Read 471 times)

onekid

  • Newbie
  • *
  • Offline Offline
  • Posts: 39
Schoeps BZ 41 Unk
« on: April 09, 2017, 09:17:56 pm »

I just purchased a BZ 41 Unk to go with my CMC4. I'm looking for a schematic as I would like to re-cap and get a good understanding of this unit. To my knowledge the k stands of Nagra reverse polarity. I assume this means I should be using a phase reverse cable with this setup for recording to modern recorders. Any night into this unit for be appreciated.
Logged
Jeffrey Lonigro

David Satz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 89
Re: Schoeps BZ 41 Unk
« Reply #1 on: April 12, 2017, 12:13:02 am »

In parallel powering the + side of the supply is fed to the microphone via one modulation (signal) lead, and the current returns via the other modulation lead; the shield isn't involved. This contrasts with phantom powering, in which the two modulation leads carry the DC voltage in common mode, while the shield is the "ground" for powering purposes.

The "k" in the model designation stands for "Kudelski" (= Nagra). Sennheiser and Nagra had introduced parallel (or "T") powering for condenser microphones, but the DIN committee then standardized the opposite signal polarity from what those two companies were using. When Schoeps introduced the CMC ("Colette") series in 1973/74, they offered a standard-compliant CMC 4-- amplifier model (without the "k"), and later added the "k" model which was powered, and had its audio signal polarity arranged, the same as the Sennheiser shotguns of the time.

Parallel powering was never prevalent in recording studios, so for the most part, people didn't have to worry about polarity conflicts among multiple microphones. Powering multiple T-powered microphones from a central supply is problematic in terms of crosstalk as well; few people mourn its passing.

Filtering of the DC supply is critical for parallel powering, since any residue of hum or other noise will be directly overlaid onto the audio signal (= differential mode). Also, the DC must be blocked on the output side of the power supply, or else it will flow across the inputs of the preamp, recorder or mixer to which the microphone is connected--but I'm fairly certain that it is blocked by electrolytic capacitors in the BZ 41; it's easy enough to verify that.

If your supply is unmodified, the "n" in its name would indicate a 10 dB resistive pad at the output, which you could presumably bypass today. When the CMC 4-- was new, it was still considered a very high-output microphone, and preamp overload in general was more often a problem then than it is today.

--best regards
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1346
Re: Schoeps BZ 41 Unk
« Reply #2 on: April 12, 2017, 12:33:00 pm »

Thanks, David, for your concise reply. Excellent as always!

For the unwashed, could you please decipher, in simpler terms than Wikipedia, what "common mode" refers to?
Logged
Klaus Heyne
German Masterworks
www.GermanMasterworks.com

David Satz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 89
Re: Schoeps BZ 41 Unk
« Reply #3 on: April 12, 2017, 09:59:28 pm »

Thanks for the kind words. Balanced inputs suppress common-mode signals--where the voltage is "in phase" between the two modulation leads. No voltage difference = no signal that a balanced input should respond to.

Differential-mode signals are what balanced inputs accept; they're represented by the voltage difference at a given moment between the two modulation leads. As that voltage difference fluctuates over time, it represents the desired signal.

It's the main reason balanced connections are so effective at suppressing most kinds of interference. Interfering signals generally affect both modulation leads more or less equally and in phase--so the resulting noise voltage reaches the two terminals of the input in phase and at similar amplitude. Thus the noise is hardly "sensed" at all by that input, because there is so little voltage difference at any given moment for the input to respond to. This is called "common-mode rejection."

--best regards
Logged

Jim Williams

  • Hero Member
  • *****
  • Online Online
  • Posts: 524
Re: Schoeps BZ 41 Unk
« Reply #4 on: April 13, 2017, 11:20:23 am »

Adding the spec to measure/determine it's effectiveness is called CMRR, or common mode rejection ratio, usually stated in db's.

Those specs are sometimes thrown around without any frequency specified so they usually pick the frequency that shows the best rejection. Usually in audio gear it's in the low end or midrange. CMRR specs shown to 10k hz are complete and show the true depth of rejection. A frequency vs CMRR sweep on a graphical analyzer like the Audio Precision will show everything.
Logged
Pages: [1]   Go Up