Topic: Edirol R-44 - 4 Channel Recorder (Part Tres)

[Ozpeter]

OK, here are some actual measurements. Open-circuit voltage with no mikes connected, 46.8 Volts. Connect one CMC 541 mike and the voltage at the unused input drops to 46.0 Volts. Connect a second CMC 541 mike and this drops another 0.8 Volts to 45.2 Volts, which is still just fine.

Add a CMC 58 (for double M/S, perhaps) and now the voltage on the unused input is 44.5, which as I've been saying is quite OK although it implies some small (ca. 200 Ohm) non-standard series resistance between the regulated supply and the phantom resistor pairs--though that low a value wouldn't give them much extra filtering of the DC or protection from inrush current, so it's hard to imagine the motive for it.

Anyway with another CMC 58 connected to the fourth input there are no more unused inputs, so if I unscrew the connector shell and measure across the terminals I get 31.2 Volts. Now 2 mA through a 6.8 kOhm resistor gives a 13.6-Volt drop while 2.5 mA gives 17 Volts. Since even the lower of the two figures doesn't quite add up to the 43.8-ish voltage I would expect, I have to suspect that the phantom resistors are lower in value than the nominal 6.8 kOhms. And potentially (no pun unintended) that could also be quite OK--the absolute tolerance is 20% as I recall, as long as the resistors are matched within each pair to within 0.4%.

So to me it still seems that as far as the microphones are concerned, this recorder's powering is a little below its own specifications. It's probably just barely OK for running four Schoeps CMC 5--s even though the supply by that point has fallen slightly below the official standard--but can the circuit put out nearly its maximum current for an indefinite length of time without risk of failure? Unless I can find out more, I'd have qualms about running this class of equipment that way on a steady basis.

I bought the $65 extra insurance policy and I suppose I could plug in four testers and leave the unit running for a week to see whether its power supply burns out or not, but if it does burn out and the insurance won't pay for a new one ... Main thing is, though, people with even higher-current microphones such as Shure KSMs, CAD Equiteks or Earthworks should continue to use outboard phantom supplies with this recorder.

--best regards

Seemed to be based on measurements??  Or are you saying he made it up?

[Roving Sign]

Your test says one thing, his another - I don't see where 'speculation' comes into it.  Presumably you were using the same model of mic as in his test?  Otherwise your test as a check on his would appear to be invalid.

The "speculation" is his "calculations" indicating that currents drawn in one XLR connector will affect the phantom supply voltage in other XLR connectors, because of the 6.8 K ohm. This is simply not true, a conclusion obviously not based on measurements. 

Just so you realize - you're being a total ass to one the most respected members here...

Cool to question or clarify...but no need to be such a douche

[MaxJames]

Just so you realize - you're being a total ass to one the most respected members here...


Cool to question or clarify...but no need to be such a douche

I respect facts, not misleading info/statements. Regarding being as ass, yes you can lick my ass!

[kirk97132]

{edited to reflect things as they are not as they were}

[DSatz]

Hello, MaxJames. What you posted is very interesting. You've misinterpreted some of what I wrote and you're using language that I think is uncalled for, but the main thing is that you measured the voltages and posted your results--so now we all have more information than we had before, and I appreciate the contribution.

I don't assume that either one of us is necessarily mistaken, but it is a bit of a surprise that two samples of the same model would differ this much unless there's been a circuit revision. For reference, the serial number on mine is ZX527 followed by two further digits. If my R-44 behaved more like yours, I'd be happier--but for me the net result is just that I will bring along a phantom power supply for two of the mikes if I ever want to connect four transformerless Schoeps mikes directly to this recorder. Sometimes I use older microphones with output transformers; those microphones draw less than 1 mA apiece so there'd be no problem using a pair of them with a pair of newer ones. All in all it's no tragedy.

Just to clarify, when the load on one socket causes the voltage on a different socket to sag, that is not because of the 6.8 kOhm resistors on either socket. I never said or implied that in any way! But if you thought that I'd said it, you'd be right to call it mistaken. The voltage sag could have a number of possible causes, but the fact that it was so regular--0.8 Volts for each additional 4.5 mA microphone I connected--made me think that there might be some extra series resistance going from the regulated 48 VDC supply to the four pairs of (what should be) 6.8 kOhm phantom resistors.

What microphones did you use that draw 5 mA? Just curious. Mine were Schoeps CMC 5-series mikes which actually draw something more like 4 mA when used without active accessories.

By the way, all the quoting back of entire messages is kind of unnecessary on a board like this, isn't it?

--best regards

[mblindsey]

By the way, all the quoting back of entire messages is kind of unnecessary on a board like this, isn't it?

--best regards

I would love to know how to measure these types of things.  I have an R-44, various mics, and a multimeter.  Is that enough?  If so, can someone post an idiot proof, step by step method for doing so?

Always learning,

--Michael

[Ozpeter]

By the way, all the quoting back of entire messages is kind of unnecessary on a board like this, isn't it?

Should be, but I got the distinct impression that your earlier post which I quoted hadn't been read by MaxJames.  But indeed it seems to have been subsequently re-quoted a few more times!

[DSatz]

Michael, you can easily make this measurement with the equipment you mentioned. Just turn on the phantom powering and push one of your multimeter's probes into the hole for pin 1 of any XLR microphone socket--that will be the ground pin--and push the other probe into either of the other two holes. With no microphones connected you should see 44-52 VDC.

Then connect one (or more) of your microphones and again make this measurement at an unoccupied socket. Strangely the ISO standard for phantom powering doesn't address this topic directly, but from a common-sense engineering standpoint, the voltage at the unused socket should be the same as whatever it was before. I found that it dropped distinctly farther than MaxJames found that it dropped for him, and it would be great to know what you find.

One important variable is the number and type of the microphone(s) you plug in, since different ones draw different amounts of current, anywhere from < 1 mA apiece to 10 mA apiece (or even more in some unorthodox cases). If you're going to do this, I'd appreciate your telling us that information as well.

For making other types of measurements, such as measuring frequency response or finding the input overload point of a preamp or recorder's microphone inputs, it really helps to have an audio tone generator with adjustable levels; I'm excessively fond of the NTI (=Neutrik) "Minirator" series and wish they were still inexpensive, which unfortunately they're not any more. But there are alternatives, including the crafty use of recording software or pre-recorded samples.

--best regards

[kirk97132]

fixed

[kirk97132]

So following the method described by Dsatz, I tested the phantom on my R-44, S/N ZX0099xx.  Ground on pin1 test lead on pin2.  Phantom on set for 4chx1 Voltage reads 47.5 with multi meter set in 200 range.  Connect one Busman modded ADK A51s(main bias resistor changes and capacitors) Voltage drops to 47.2v.  Connect two mics voltage drops to 47.1v
I repeated the test in various setting , stereox2 and monox4 and got the same results. 

[mblindsey]

One important variable is the number and type of the microphone(s) you plug in, since different ones draw different amounts of current, anywhere from < 1 mA apiece to 10 mA apiece (or even more in some unorthodox cases). If you're going to do this, I'd appreciate your telling us that information as well.


--best regards

Thanks for the instructions!

Test #1
- With no mics attached, the first channel reads 47.6
- Add one Beyer MC930 on the second channel and the reading is 47.5
- Add a second Beyer MC930 on channel number three and the reading is 47.4
- Add a Naiant XT on the fourth channel and the reading is 47.3

Test #2
- With no mics attached, the first channel reads 47.6
- Add one Naiant XT on the second channel and the reading is 47.6
- Add a second Naiant XT on channel number three and the reading is 47.5
- Add a Beyer MC930  on the fourth channel and the reading is 47.4

Test #3
- With no mics attached, the first channel reads 47.6
- Add one Beyer MPC66 VJ on the second channel and the reading is 47.5
- Add a second Beyer MPC66 VJ on channel number three and the reading is 47.3
- Add a Beyer MC930  on the fourth channel and the reading is 47.2


I ran this with the R-44 on the wall-wart and off of a wally-world 9V Lion with the same results.  The mics specs should be easily accessible on the web. I'm not sure exactly what to report.  The Beyer MPC 66 specs might not be easy to find, but I've been told it is a Panasonic capsule:

http://taperssection.com/index.php/topic,109937.msg1471569.html#msg1471569

Serial no = ZW802##

Does this help?

--Michael

[DSatz]

Michael, many thanks for your report. Beyer specifies your microphones to draw 4.6 mA apiece, which is directly comparable to the current which my Schoeps CMC-series microphones draw. I don't know the current drawn by the microphones that kirkd used in his test, nor do I know which microphones MaxJames used so I can't confirm his statement that they draw 5 mA. But by now there have been two or possibly three tests in which other people's phantom supplies in their R-44s have held up better under load than mine did for me.

Again, for many situations and purposes, mine is quite OK, too. So now I wonder whether I have an individual sample that is a little below par, or whether perhaps there are different circuit versions out there. Both seem plausible enough to me.

--best regards

[kirk97132]

Is there a way to test what the modded ADK mics draw?  My DVOM  has settings for 10A; 200m; 20m; 2000u; 200u.  You guys got my geek side showing and I love learning about this kind of stuff. 

[DSatz]

kirkd, the manufacturer really ought to specify this. It can be measured directly by wiring up a barrel adapter that has an XLR-3 plug on one end and an XLR-3 socket on the other; Switchcraft makes these (called the "S3FM," or at least they used to be). Wire it from pin 1 on one end to pin 1 on the other and pin 2, likewise. Finally, attach an insulated wire to pin 3 of either connector, and assemble the barrel connector only halfway--leaving the other connector sitting out of the barrel adapter. That way you have a wire leading to pin 3 of one connector while the other connector has its pin 3 directly exposed.

Plug the barrel adapter into one socket of the recorder, and connect one of your microphones to the barrel adapter's socket via an ordinary mike cable. Then wrap the wire from pin 3 of one connector around one probe of your meter, while holding the other probe to the exposed pin 3 of the open connector. Now turn on the phantom powering for that channel and you can measure the current. Multiply that by 2 and you'll know how much your microphone draws--most likely somewhere between 0.5 mA and 10 mA.

If we knew that the R-44's DC supply remained steady at 48 Volts and that it used standard 6.8 kOhm phantom feed resistors, we could infer the current from the voltage drop (by opening the plug end of a mike cable and measuring the voltage with and without the microphone connected to the other end of that cable). But those are things we don't know, so we can't do that in this case.

--best regards

[MaxJames]

Just to clarify, when the load on one socket causes the voltage on a different socket to sag, that is not because of the 6.8 kOhm resistors on either socket. I never said or implied that in any way!

This was indeed the way I (mis)interpreted your original post - it was late in the evening and I did not read it carefully (and did not understand phantom power supply in the first place), before making a hasty measurement and post. My bad and I am sorry.

I am relatively new with recording and recorders, and the R-44 is my first and only recorder I have so far - bought mine in the first week it started general shipping in the US (s/n ZW80244) based on the specs only (without reading any reviews).  Never made any measurement until the other day on the phantom power supply, and more measurements today – Here is a summary:

-   The phantom supply indeed has a 6.8K for the pin #2 and a 6.8K for the pin #3 – pretty conventional and nothing unusual

-   Have a pair of AKG 414, a Rode NT-4 (stereo mic with two XLR connectors), a Rode NT1A, a number of pots, and a half dozen of the Switchcraft XLR barrels (left over from a dozen I bought for making various attenuation pads) – they come in really handy.

-   I used the mics with the pots in parallel to draw the exactly 5mA in each connector in the previous measurement

-   In today’s measurements I shorted pins #1, #2, and #3 – measured current 14 mA. I did this to both input 1 and input 2, drawing 28 mA in total. The phantom voltage in this case dropped to 47.3V. This is pretty good compared to the spec (20 mA max current, 48 +/- 4 volts). Did not go further because I did not want to risk damaging the circuitry.
 
-      Also measured the output noise floor today as below:
      o   Used a RF spectrum analyzer to measure the output in 20Hz – 20KHz only
      o   R-44: level setting centered, 16 bits/48 KHz (what I always use in recording), no filtering
      o   The EIN is calculated by assuming the gain is -20 dB - the “sensitivity” setting (i.e. for sens = -44 dB, the gain = -20 – (-44) = 24 dB). Not sure if assumption and/or measurements are correct.

Sensitivity Output noise, EIN dB
Setting   
 4   -123   -99
-2   -122   -104
-8   -121   -109
-14   -122   -116
-20   -122   -122
-26   -118   -124
-32   -112   -124
-38   -106   -124
-44   -100   -124
-50   -93   -123
-56   -87   -123

If the measurements are correct, then the actual noise performance is pretty good compared to the specs and the results by some others (will repeat the measurements using a proper audio analyzer at work next week). Not sure about variations from unit to unit though, in terms of both the phantom supply and the noise floor.