Special Phantom Power

[chriss]

O.K. there have been very many words on Phantom-Power before. BUT:
I want something more!
I have a Neumann TLM-170 with U87-capsule (normally it has the U89-capsule). The Characteristic can be remote-controlled via Phantom-Power. One end is at +45V, the other at +51V. I don't know wich voltage leads to wich characteristic, but I'd like to find a reliable schematic for such use. Switch or Pot - I don't really care...
Is there any idea or does anyone have the original schematic for the N48R-2 power-supply?

best regards

Chris

 

[chriss]

back on top... :wink:

 

[Gus]

You have your answer in your question.

Make a var power supply set to the higher voltage, then switch resistors in parallel to drop the voltage.

I would guess the microphone uses a voltage comparator circuit in the microphone to sense a current draw change by measuring a voltage across a resistor(s).

Make a var supply, match two 6.8K resistors and change the voltage and check the pattern.

 

[bcarso]

You will do well to test to find out where the center of each detected voltage is. It would be bad if the mic detection circuit was switching back and forth at ~random during a session...

I could tell a war story or two on related matters but not now---you are spared.

 

[chriss]

@Gus: Well - ees you are right, but I'm so lazy, I want ready working things... O.K. I will try your idea. The last P48-supplys I have build were variable anyway, so what the f....

AND: regarding the electronics: here's more details:

http://www.neumann.com/infopool/mics/produkte.php?ProdID=tlm170r


@bcarso: I don't believe there are 'centers'. I think you could also do a pot and turn between all characteristics and their inbetween-characteristics.

Chris

 

[bcarso]

Oh...cool. It is a continuous pattern adjust then.

 

[Gus]

I think it is five patterns from the specs.

45 to 51 is 6 V

I would guess 45.6. 46.8

48.0

49.2 and 50.4

1.2 v a step


3 ma across 3.14K should be a 9.42 V drop, I don't think this will help much

the current must change a little and be measured across a resistor in the microphone

 

[chriss]

@bcarso:

I think all mics with a dual capsule could be continuous pattern adjusted if they had a pot instead of a switch. Just they usually use switches. Maybe because it always takes a short time, until the pattern is there, so you'd need to turn the pot, wait, check if the pattern is right, readjust and so on. So a switch is easier to 'recall'. But I'm almost sure that you could very easy do that to all remote-controllable mics like SM69, UM57, M49 and TLM170. Though I'm not sure about that.

@Gus:

I would guess 45.6. 46.8

I don't understand that, do you mean, the middle-position should be 48V? But the 1,2V-steps also sound right. Do you really think it is necessary to take care of the current? Couldn't I just adjust the voltages, with the mic plugged in?

Chris

 

[dukasound]

Hi
Pleese I have one question.
Because I made some circuit with phantom (adjustable) what excatly voltage I must adjust (before two 6,81K). I have dual preamps and do I check voltage with two mike in. I ask because I have different voltages when is one or two mikes connected.
Thanks
Duka

 

[chriss]

Duka,

you should adjust 48V. But the standard says that it works with 48V +4V or -4V, so everything between 44V and 52V should do. But anyway you should try to get as close as possible to 48V.
Or do you mean that your voltage is adjustable form the front-panel to vary the pattern?

Chris

 

[Rossi]

[quote author="chriss"] I'm almost sure that you could very easy do that to all remote-controllable mics like SM69, UM57, M49 and TLM170. Though I'm not sure about that.
Chris[/quote]

Hmm, I actually don't think so. I had a TLM127 plus phantom power/remote control last year. I can say for certain that there was a bad switching noise and it took a moment before the mic was up again with the new pattern. I may be wrong, but I don't think the remote control for TLM127 and TLM170R is comparable to the pattern controls for tube mics. To me it seemed like the mic sensed the voltage change and recalibrated itself once the voltage was above or below a certain value. But who knows? I'm curious as to the results of your experiments.

 

[dukasound]

[quote author="chriss"]Duka,

you should adjust 48V. But the standard says that it works with 48V +4V or -4V, so everything between 44V and 52V should do. But anyway you should try to get as close as possible to 48V.
Or do you mean that your voltage is adjustable form the front-panel to vary the pattern?

Chris[/quote]
Hi Chris
I mean I can adjust inside preamp +48V (not patern).
Is it mean 48V on-load when is both mike on Dual preamp connected?
Duka

 

[bcarso]

From the limited data on the Neumann site they have a patent on some aspect of this mic. If that is true it should be possible to get the number and see what they are doing.

If I knew Juergen Wahl better I would ask him. Unfortunately I already pissed him off when he did a presentation of Solution D at an AES meet and I challenged his pronouncements about noise :^) ---and he may remember that.

There's a pretty good explanation of one approach to the switchable direction charateristic in Ballou's chapter on mics in his 1st Ed. Handbook for Sound Engineers, pp. 376-378. The U87 is used as the example and the common backplate sits at 0 volts in the diagram. To the right of that figure are the corresponding patterns (not labelled despite what the text says).

 

[PRR]

> Oh...cool. It is a continuous pattern adjust then.

No. The TLM-170 has 5(?) discrete patterns. You can hand-switch them, or set to a sixth position and buy the special power supply. It puts out 45V to 52V (all perfectly legal "48V" Phantom). The voltages are very exact. The mike has a very exact voltage reference. It can measure the Phantom supply voltage (making a clever adjustment for current in the Phantom resistors). Basically an A/D converter with 5 output states from 45V to 52V. This is logic-ed into various capsule bias combinations as in any electrical-variable mike.

My guess of the mid-point voltages for each state would be 45.5 47 48.5 50 51.5. +/-0.5V slop in the power supply means it would still always be legal P48 for non-TLM-170 mikes. But it could be real annoying if these are not the right steps, if say 48V (not 48.5V) was really the threshold between omni and hypercard, and the mike kept wandering from wide to narrow as the reference drifted. I doubt the steady-state current consumption changes as the supply crosses thresholds. If, as Rossi says, the pattern-switching is very obvious, some experimentation will find the thresholds and then just shoot for the mid-points.

Somewhere on Neumann's site I found 1.5V steps. One cute trick would be to build a 50V-52V supply. Fiddle it to find the top threshold, then turn 0.7V higher. Stick four 1.5V AA alkaline batteries in series with the output (before the Phantom resistors) and wire a switch to tap at 0, 1, 2, 3 or 4 batteries lower than the top voltage. The batteries would give full shelf life or more, because mike current actually charges them.

 

[chriss]

hi,

yes after a closer look at the schematics i have to agree: the electronics inside of the tlm170 seems to put out four voltages for the back-capsule: +60, +23, -23, -60 and for cardoide it is connected to ground. these voltages are switched manually or via remote-control-electronics.

it should be no fun if anything gets damaged inside of this mic. finding a new vf14 for an u47 would probably be much easier than to replace any of the special-parts inside of the tlm170... it has five custom-made ic's inside! maybe i should better have bought an u87?!...

prr: 1,5V sounds like the only right solution to select five pattern: 45 - 46,5 - 48 - 49,5 - 51 Volts. everything else would make no sense, would it?

rossi: you are right, that the switching in the tlm170 is not comparable to most other remote-switchables, but the sm69 is continous switchable even in the transistor-version. (besides the problem to find a mic-cable with 11 leads....) so tube or transistor is not the question for this feature. just to teach a bit. :roll: how do you like the tlm127 by the way?

chris

 

[gyraf]

[quote author="chriss"] ..yes after a closer look at the schematics i have to agree.. [/quote]

..is there any chance that we can have a look at those schematics? ..please..?

Jakob E.

 

[chriss]

Jakob!

..is there any chance that we can have a look at those schematics? ..please..?

Jakob E.

Well I'd love to share but I always spend my money on mics and 19"-thingies rather than on a scanner... Actually it is on the back of my TLM-manual, but on the .pdf that you can download it is not! Well, in german there is a nice word that I can't translate - it's 'Herrschaftswissen' wich means knowledge that you best keep for yourself to have the profit of knowing more than others.... But if I find the time, I will do a redraw with target and post it.

Chris

 

[chriss]

Maybe one chance: Does anyone know of a 19"-scanner? No Behringer, please!

 

[rickc]

I believe there was an AES paper on this. yes!
----------------------------------
A method is presented of remote-controlling the polar pattern of a condenser microphone which has standard phantom powering and the usual 3-pin XLR connector found in all studios. Remote control is affected with a stepping switch in P 48 power unit, which imposes the control information on the modulation leads. An interpretation circuit in the microphone senses the information in the remote position and selects the required polar pattern.
Preprint Number: 3592 Convention: 94 (February 1993)
Authors: Peus, Stephan; Kern, Otmar

The paper confirms that the step values are 1.5v
----------------------------------------------
The german patent number for the TLM170 is: DE 39 33 870C2
Sorry, it's in German.
You can access patents of all countries from the german patent office:
http://depatisnet.dpma.de

you can also reach this site from the AES HQ webpage: http://www.aes.org
then click on the historical committee, then click on "access patents of all countries"
When you get to the first screen, click on the union jack (brit flag) to access the English user interface.

Remember that the TLM170 is really a P24 microphone, so changing the P48 +/- 3V is no big deal as far as the microphone is concerned.

--rick chinn

 

[PRR]

> I believe there was an AES paper on this. yes!

Yes. I think I found it through Neumann's site.

> the TLM170 is really a P24 microphone, so changing the P48 +/- 3V is no big deal as far as the microphone is concerned.

Correct; but what if some fool uses the TLM170 power supply with another microphone? You order your idiot assistant to "try the AKG414s instead of the TLM170s" and he forgets to take the TLM170 power supply out of the line. The "other" mike still gets fully legal P48. The AKG414 doesn't really care (it will eat 10V to 60V and live), but there are a few mikes that MUST have ~48V to be happy, would not like a power supply that used, say, 25V 35V 45V 55V 65V steps to control the pattern of the mike it was supposed to be used with. Neumann's cleverness (or Herrschaftswissen) is in making a mike voltage-detector that is so selective that it can sense "insignificant" variations from 48V and find meaning in them, yet the supply still works with (and will not hurt) other mikes.