Topic: Schoeps problem - very low signal - T-powered mics????

[KLowe]

Hey TS'rs.

quick question for ya.  I recently bought a CMC 6 u w/ MK 4 cap off of ebay.  The add and seller said that the mic was working perfectly.... (I know, I know... it could be a scam  )

Here is the symptoms.  I hook the mic upto the R-4 and barely get any levels with the gain maxed out.  ( I tested with my Neumanns and the R-4 and cable are working normally).  After a quick google search I found that the sympoms Could be due to it being a T-powered mic.  It does have a lower Serial N umber and is not an XT body.

Question for yall is. 
How can I tell if this mic is a T-powered mic or not.  Is there a way to check the SN against a Schoeps Database?
Are there any known problems with older CMC 6 u's and R-4's?  Current draw issues?
any help from yall would be greatly appreciated.

If not... then it is off to reddingaudio for a look over.

===== a little read up on T-power and Schoeps============

T-power is also known as A-B power. Unlike traditional phantom power, which puts equal voltage on pins 2 and 3 with respect to ground, T-power systems put a 12-volt potential difference between pins 2 and 3. In some systems, pin 2 is 12 volts above pin 3, and in other systems, pin 3 is 12 volts above pin 2. What's more, the DC voltage on these pins is called a floating voltage, because it's not referenced to ground. Some equipment, such as Nagra recorders and the Shure mixer mentioned earlier, have switches that select T- power or phantom power, which lets you determine the configuration of the pins.

T-power was invented primarily for use by location film recordists, who frequently need to run long microphone cables. Not too long ago, both T-power configurations were common in the United States and Europe; they were associated primarily with Sennheiser and early Schoeps microphones. However, T- power isn't used much anymore.

It's important to know that only T-powered microphones should be used with T-power supplies. Connecting a T-powered mic to a more conventional phantom power supply is likely to damage the mic, the power supply, or both. Conversely, connecting a microphone intended for use with 48-volt phantom power to a T-power supply will result in similar consequences.

Thanks yall.

KLowe

[rokpunk]

Well, yeah, if it's a T-powered mic, the R4 won't power it.
Try finding a T-power supply (I have one if you want to send it to me for testing).

[Shawn]

if it's a cmc6 body then it should not be a t-powered body. the current cmc6u bodies can be 12v - 48v phantom powered so basically the r-4 should be able to poweer them if everything is working correctly.

I was afraid of current draw issues too because the schoeps cmc4uk bodies that I have are listed as drawing more power than the r-4 can supply, but momule (i believe) confirmed with edirol that the r-4 can push more power than it's specs state. Also the cmc6 bodies draw much less current than the cmc4 bodies so that should not be a problem at all.

The model number should be listed at the base of the body. what does the numer on your body read?

I suggesst calling the guys at redding. The schoeps cmc4uk bodies that I have require one of the rarest forms of mic power on the planet, and after much research and fear that I had destroyed my mics a quick call to redding set me straight on my power issues. FWIW the cmc4uk bodies I am using are 20 years old and they do work properly with th r-4 using 48V to 12T adapters.

[DSatz]

KLowe, a CMC 6-- microphone is definitely not T-powered. You can dispense with that particular concern completely. A microphone with a CMC 6-- amplifier can be powered by either of the two main forms of phantom powering defined in the DIN EN standard:

(1) standard +12 Volt phantom powering at ca. 8 mA, or else
(2) standard +48 Volt phantom powering at 4 to 5 mA.

One implementation or the other must be followed; the circuitry looks at the incoming voltage and switches its DC/DC converter into one of two possible modes. In other words, these microphones are not "12 through 48 Volt" microphones, since there is no such definition in DIN EN 61938.

Unfortunately, some phantom power supplies, especially in lightweight/portable equipment, don't follow either standard implementation consistently. The two most common problems that I've found are (a) greater than the standard 6.8 kOhm series resistance (which causes the output voltage to sag farther than normal when current is drawn), and/or (b) a simple inability to sustain 4 - 5 mA of current output per microphone.

If your phantom power supply has either or both of these problems, then the mike will switch into its 12 Volt mode, and will attempt to draw about 8 mA from the supply. If your supply was unable to put out 4 - 5 mA, it will certainly be unable to supply 8 mA! Its output voltage will drop even further, and this may be why your microphone isn't giving you much if any signal.

I'm sorry that I don't know the R-4; that's one of those four-channel Edirol hard disk recorders, right? I've tested the phantom powering circuits of a lot of preamps, mixers and recorders, but unfortunately never that one, and I hesitate to guess about it. Do you have a voltmeter handy, and can you test:

(1) the voltage between either pin 2 or pin 3 and pin 1, with no microphones connected to any inputs, and
(2) the voltage that on the socket once you plug in your CMC 64? To measure that, use an extension cable where you've opened one connector or the other up, so that you can put your voltmeter probes right onto its contacts. It has to be the same socket where the microphone is connected.

Voltage (1) must be between 44 and 52 Volts DC, while (2) should be around 15 Volts lower than (1), since you're drawing around 2.25 mA through each 6.8 kOhm feed resistor. So voltage (2) should be +30 or above, with a little wiggle room, but definitely not lower than about 27 Volts. Please let us know what you find.

--best regards

[KLowe]

Thank you for that in depth answer.  I'll be running that test when I get home tonight. 
I'll post all results.

The guy I bought it from is emphatic that it worked before he shipped it.  So.... Im wondering if the R-4 is the suspect.  I also have a SD mp2 unit that is coming home soon so I'll try it on that one also.

I called reddingaudio and described the symptoms.... the said "oh yeah, send that bad boy in".

I'll still check the R-4 out tonight but I'll probably let the Schoeps folks give it a clean bill of health anyway since it was an ebay purchase.

Thanks yall.

Kevin

[Shawn]

FWIW I know of a couple of people running schoeps directly into an R4 so my guess is that unless your unit is somehow defective the mic is probably the problem.

I'm assuming you've done most of this, but you can try to eliminate some of the other variables...
have you tried using different mic cables?
Have you tried plugging the R4 in or are you strictly using battery power?
Have you tried using a different power cable?
have you tried some other mics?
Are you sure the R-4 is configured correctly (phantom is on, analog input is selecte, etc...)?
Have you tried using different inputs on the R-4 (if you are using channels 1&2 try 3&4 or the other way around)?

[KLowe]

Shawn,

have done most all of that except the battery option.  I'll try that one also tonight.

but if a battery wont push it then I have no use for it anyway.

Thanks for the ideas.  I'll post the tech results tonight.

Kevin

[Shawn]

yeah I really doubt battery power would be the root of the problem, but it's just about eliminating variables in the chain.

[Stagger]

The T-Power model is the CMC-4 it is pretty rare these days and only really used in some film applications. There is No way that any CMC6 (or 5 for that matter) body would be T-Power. Sounds like there is something else going on.

[shaggy]

Damn kevin, were u the one that scored that single CMC64 set up on ebay with BIN for $200?

[dennisrtyler]

Damn kevin, were u the one that scored that single CMC64 set up on ebay with BIN for $200?

yes he was

[Shawn]

Damn kevin, were u the one that scored that single CMC64 set up on ebay with BIN for $200?

yes he was

I've been monitoring schoeps auctions on ebay for months. how did I miss that? that's even crazier than the pair of AKG 391s that sold here for $100 last year.

[Brian]

i've got this problem too with one of my schoeps (i run CMC64 as well) but it only happens when i'm outside   i've been meaning to send them back to germany for the longest time, but haven't bothered yet.  they work fine inside, but after being outside for about 30 minutes the one loses all kinds of signal.

[kennedy]

Damn kevin, were u the one that scored that single CMC64 set up on ebay with BIN for $200?

yes he was