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Author Topic: Schoeps CMR (mshilarious please enter!)  (Read 23657 times)

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Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #60 on: April 09, 2008, 04:07:35 PM »
i def got the feeling this one is cheap. uses like 26 GA wire, connector literally fell apart when i opened it.

i'll check out the 8533 and see if i can get one and tear it apart

Quote
NADY CBM-40 phantom power supplies (the ones that come with AT943 mics)

The AT943 comes with a Audio-Technica phantom supply (AT8533), whereas the Nady is a common, cheaper alternative.  Many folks here use the Nady as they are carried by SoundPor's and are about half the price of the AT.  I would be willing to bet the AT has a much nicer transforer and parts....  Likely a better option for such expensive mics...

Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #61 on: April 09, 2008, 07:01:37 PM »
thanks much.

could you be a bit more specific on the specs on the diode and the caps - ie 'use tantalum caps of the same value', and 'you want a xxx value zener diode'





The resistor to ground drops voltage dependent upon the DC source resistance, as you have noted.  More than that, I can only guess, because I don't know what's inside the CMR.  I am kinda guessing it doesn't just use a single FET, or if it does, that it doesn't take signal off the FET drain.  So I don't think it does any harm, so long as the Nady transformer can tolerate the total DC current (one would hope).  It is probably current-limited by the circuit on the board.

The larger question is whether you want to use a Nady transformer with a Schoeps capsule  ???  Is there a need for a transformer at all?  I thought the Schoeps capsule was low-impedance output, unlike the AT capsules the Nady is designed for.  But I guess I don't really know that.  I also don't know if the Nady transformer is step-down . . .

Anyway, the Nady circuit looks like a simple voltage regulation with D1 and Q1, and a capacitor-coupled audio circuit.  This is actually pretty similar to my X-T circuit, except I didn't take the phantom through the transformer, because I wanted to save it for other things.

Rather than hanging resistors off the board, I would imagine that is a zener diode you are looking at for D1, so replace it with a more suitable value.  While you're at it, I would replace the capacitors with something nicer.  You shouldn't need another capacitor added, since one of those caps should be for filtration of the zener.

Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #62 on: April 10, 2008, 01:12:04 AM »
thanks!

Zeners are straightforward; if you want 9V to the capsule, use a 9V zener.  However first, measure the zener they are using, and compare that to the supply voltage, as they might drop the voltage a little on the way.  Something like 6-7.5V should do, I would think.

Replace caps with the same value in Panasonic FC or Nichicon PW range.

Offline Celac

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #63 on: April 12, 2008, 02:14:34 AM »


The larger question is whether you want to use a Nady transformer with a Schoeps capsule  ???  Is there a need for a transformer at all?  I thought the Schoeps capsule was low-impedance output, unlike the AT capsules the Nady is designed for.  But I guess I don't really know that.  I also don't know if the Nady transformer is step-down . . .

Anyway, the Nady circuit looks like a simple voltage regulation with D1 and Q1, and a capacitor-coupled audio circuit.  This is actually pretty similar to my X-T circuit, except I didn't take the phantom through the transformer, because I wanted to save it for other things.


Hi,
I think the transformer is unlikely to provide voltage stepping for the phantom supply as phantom is DC and transformers are AC devices. It could provide impedance matching (as you surmise).  A likely purpose however might be to balance the output of the unbalanced capsule attached to the supply.

It would seem to be a little bit of a quality mismatch for the Schoeps mic, but I certainly have no hard data to base that assumption on.



edit: for clarity, sorry for the inept use of the quote function
« Last Edit: April 13, 2008, 03:15:12 AM by Celac »
...can't get enough of nothing!

Did your friend consider that maybe he got a basically accurate recording of a bad P.A. system and/or a terrible-sounding performance venue? When you aim good microphones at ugly sound, the resulting recording will not be beautiful.
DSatz

Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #64 on: April 12, 2008, 05:02:06 PM »
correct me if im wrong, but it though tthat it was merely a decoupling circuit and should have a negligible affect on the audio signal. Would mshilarious's circuit be better in theory or practice?

thanks guys, i know a bit about electronics, but not the ins and outs of the effects of various components/circuits on audio.



The larger question is whether you want to use a Nady transformer with a Schoeps capsule  ???  Is there a need for a transformer at all?  I thought the Schoeps capsule was low-impedance output, unlike the AT capsules the Nady is designed for.  But I guess I don't really know that.  I also don't know if the Nady transformer is step-down . . .

Anyway, the Nady circuit looks like a simple voltage regulation with D1 and Q1, and a capacitor-coupled audio circuit.  This is actually pretty similar to my X-T circuit, except I didn't take the phantom through the transformer, because I wanted to save it for other things.


Hi,
I think the transformer is unlikely to provide voltage stepping for the phantom supply as phantom is DC and transformers are AC devices. It could provide impedance matching (as you surmise).  A likely purpose however might be to balance the output of the unbalanced capsule attached to the supply.

It would seem to be a little bit of a quality mismatch for the Schoeps mic, but I certainly have no hard data to base that assumption on.



Rather than hanging resistors off the board, I would imagine that is a zener diode you are looking at for D1, so replace it with a more suitable value.  While you're at it, I would replace the capacitors with something nicer.  You shouldn't need another capacitor added, since one of those caps should be for filtration of the zener.
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Offline Church-Audio

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Re: Schoeps CMR
« Reply #65 on: April 16, 2008, 09:37:17 AM »
ok, so ive been playing with powering these from NADY CBM-40 phantom power supplies (the ones that come with AT943 mics)

out of the box, these are basically little transformers that provide an open-loop voltage of about 15.4V on the third pin of the mini-xlr out. when attached the the cmr bodies, they provide 10-10.5V to the mic (a little hot). with a little tweaking, they work, and they include a nice rugged casing and 90-110% of the circuitry we need, would be quicker than homebrewing a circuit

so i opened them up, and added a 3.7K resistor from the power pin to ground, which reduced the open-loop voltage to 9.5ish V. This was still a little close to the 10V spec so i also added a 1.5K resistor inline between the power lead and the mic, resulting in 4.9V to the mic (spec is 4-10V). i had these laying around,i would probably use a 500-700 ohm resistor in practice. Heres what they look like inside:





please excuse the hack soldering job, i tried a bunch of different things, and havent decided on the final version yet, your seeing the product of half a dozen hurry-up soldering jobs with a crappy 30w iron.

anyway, i wanted to post the pics, particularly for mshilarious, as im interested in the effect of what ive done here, esp in regard to just taking the resistor to ground, which creates an extra current flow. also any comments on the overall circuit design strategy and its implications/advantages/disadvantages for our use, both in terms of sonic quality and power consumption. i know the pics arent the best, but i think if we can figure out generally what the circuit is doing, i can measure resistances etc or read any cap values we need

ideally the transformer would be swapped for one that outputs 9V open loop, maybe swap a resistor or two without adding any components. although i dont know if transformers are a standard size and would fit that cutout int he board.

Also, berhnards simple powering circuit included a 1.5K resistor off a 9v (for two mics, and a 100 uF 'smoothing' capacitor as he described it between the power lead (on the mic side of the resistor and ground)



what is the purpose of this capacitor, and do i need to add this to this power supply.

i emailed bernhard last night and asked him about it, to which he replied "the CMR is not designed for being used with a phantom power. You may connect it that way at your own risk only. The high open loop voltage and the capability of high current peaks lead to a high risk for the CMR being damaged.". so i think its safe to say he's over it.

Here is the real problem that transformer is in the signal path so its changing the sound of your mics. Its probably a $2.00 transformer.. If it were me I would find a way to interface your mics that did not involve a $2.00 transformer.

Chris
for warranty returns email me at
EMAIL Sales@church-audio.com

Offline jerryfreak

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Re: Schoeps CMR
« Reply #66 on: April 28, 2008, 02:43:19 PM »

Here is the real problem that transformer is in the signal path so its changing the sound of your mics. Its probably a $2.00 transformer.. If it were me I would find a way to interface your mics that did not involve a $2.00 transformer.

Chris


so... better transformer, or no transformer? can you recommend a better option?

Offline Church-Audio

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Re: Schoeps CMR
« Reply #67 on: April 28, 2008, 03:03:26 PM »

Here is the real problem that transformer is in the signal path so its changing the sound of your mics. Its probably a $2.00 transformer.. If it were me I would find a way to interface your mics that did not involve a $2.00 transformer.

Chris


so... better transformer, or no transformer? can you recommend a better option?

The best option would be a 48-7volt converter with a voltage regulator and a pure signal path no transformer crap. I think I might know someone who can build such a think if there was enough demand for it. Also I am working on the battery operated CMR preamp.
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Offline jerryfreak

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Re: Schoeps CMR
« Reply #68 on: April 28, 2008, 03:34:18 PM »
cool, whats your timeline on getting mine back to me? im kinda veering in other directions for lack of the pre.


Here is the real problem that transformer is in the signal path so its changing the sound of your mics. Its probably a $2.00 transformer.. If it were me I would find a way to interface your mics that did not involve a $2.00 transformer.

Chris


so... better transformer, or no transformer? can you recommend a better option?

The best option would be a 48-7volt converter with a voltage regulator and a pure signal path no transformer crap. I think I might know someone who can build such a think if there was enough demand for it. Also I am working on the battery operated CMR preamp.

Offline jerryfreak

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Re: Schoeps CMR
« Reply #69 on: April 28, 2008, 03:38:54 PM »
is that even possible when decoupling power from a signal line aka phantom power?

I'm thinking about givining up on using the phantom in the V3 at all, and just building a b-box with schoeps uber-simple power circuit, which would be totally isolated from the audio (sans ground)


Here is the real problem that transformer is in the signal path so its changing the sound of your mics. Its probably a $2.00 transformer.. If it were me I would find a way to interface your mics that did not involve a $2.00 transformer.

Chris


so... better transformer, or no transformer? can you recommend a better option?

The best option would be a 48-7volt converter with a voltage regulator and a pure signal path no transformer crap. I think I might know someone who can build such a think if there was enough demand for it. Also I am working on the battery operated CMR preamp.

Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #70 on: April 28, 2008, 07:43:15 PM »
what is Q1/PF5102 in that schematic? im not familiar with that symbol.

would you want to build me a test board with this setup to try? according to schoeps, each mic will draw 1mA, 4-10V is acceptable


The schematic I posted is pretty much a linear voltage regulator followed by filtration.  The currents involved are small, phantom supplies plenty, so a DC converter circuit is overkill for this situation, and a potential noise source if not well designed.

Mics don't generally use step-down DC converters unless for some odd reason they need gobs of current (the tube in the AT3060, for example).  Step-up DC converters are used where polarization voltage needs to be higher than 48V.  But if you have enough voltage and current from the phantom supply, a DC converter is not indicated.

Assuming the mic needs 2mA, we're talking around 0.08W of wasted power.  If you are concerned with power consumption, you can select supply resistor values to drop the exact voltage you want to hit that figure, but you'd need to know the CMR's current consumption, and it would limit flexibility with less than full P48 power supplies.  There is a way around that, as I mentioned earlier; I'll post it below--this is probably similar to the Nady, without the transformer (paste it into my earlier schemo).

But I don't think there is an off-the-shelf DC converter that is going to improve on that efficiency.

Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #71 on: April 29, 2008, 03:18:22 PM »
I'll take two, please! ;)

seriously, id love to test it

Test board?  Heck, I have a PCB to do this that fits in an XLR!


Offline Jhurlbs81

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #72 on: May 08, 2008, 06:20:40 PM »
interesting read.  Any updates, guys?

Offline jerryfreak

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #73 on: May 10, 2008, 02:17:35 AM »
just an addition, as i didnt know there was outside interest in this topic. (I think im the sole cmr owner on this site?)

we had moved it to email, and i asked mr. hilarious the following question:

does it require any change to run from 12V
phantom? i just picked up a pre that has 12V phantom only, and i can easily jumper my v3
to either 12 or 48V.

i think we discussed that using 12V power would be a bit more efficient somewhere in
that thread.


his reply:

The power supply voltage doesn't matter, anything from 9V to 48V is good as long as it
can supply the necessary current--1mA if specs can be believed!

12V may be more efficient, depending on how the recorder/preamp works.  The power
regulation circuit of the adaptor will force the excess voltage (above 7.5V) to drop
across the supply resistance, which basically means the power loss is current * excess
voltage.  All things being equal, the closer the supply voltage is to the regulated
voltage, the less wasted power (this is why I always cringe when I read about people
using 7805 regulators on 9V batteries).  But all things aren't always equal; if in
switching from 48V to 12V, the preamp does the same thing the regulation circuit does,
it's going to be wasted anyway.  But I would expect a portable device would use a DC
converter to generate 48V; in that case 12V will easily be more efficient.

Either way, the adaptor doesn't care, it will work with any voltage up to 50V (over that,
its component ratings will be exceeded).


i was thinking about this later, and was wondering if the V3 would run longer powering a pair of CMC6s on 12V phantom vs 48V phantom? the mics use double the current at 12V, but thats still half the wattage compared to 48V. i think the V2 can be jumpered to 12V as well

when i get these adapters im gonna try to do some runtime tests with the following setups:

v3+cmc6@48V
v3+cmc6@12V
v3+cmr@48V
v3+cmr@12V
v3+cmr externally powered

and maybe the same with V2 if i have the time.

always nice to squeeze some more battery life out of your gear. there should be no sonic consequences to run cmc6s at 12V vs. 48V



Offline Jhurlbs81

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Re: Schoeps CMR (mshilarious please enter!)
« Reply #74 on: May 10, 2008, 08:13:57 AM »
So, Jamie can you dumb this down for me and explain what would need to go between these CMR cables and say a V3?

Very interesting option,
Jesse

 

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