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Gear / Technical Help => Battery Boxes, Preamps, Mixers, ADCs, and Processors => Topic started by: poorlyconditioned on January 24, 2007, 05:13:29 PM

Title: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on January 24, 2007, 05:13:29 PM
I was browsing Soundprofessionals.com.   They have "Nady" brand phantom adapters (NADY-CBM-40T) for $29 each.

Also, I saw NADY DMP-2 portable preamp for $70 at Musician's Friend.  This is a stereo preamp with phantom power that runs off a single 9V battery!  I'd be curious to see what is inside, but it is certainly cheap enough to buy and play around with.  I expect battery life would be poor (25mA current draw), but it looks interesting.

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on January 24, 2007, 06:10:18 PM
You can get that pre-amp cheaper than that: http://www.keenzo.com/showproduct.asp?ID=940621&ref=FRG1
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: bdasilva on January 24, 2007, 06:21:11 PM
I'd be intrested to see whats in here... almost worth it for the chassis, connectors and knobs. maybe a few caps and a couple of opamps could make it usable... Maybe it sounds great right out of the box. (not likely) . You da right  man for the job.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on January 24, 2007, 08:07:28 PM
I'd be intrested to see whats in here... almost worth it for the chassis, connectors and knobs. maybe a few caps and a couple of opamps could make it usable... Maybe it sounds great right out of the box. (not likely) . You da right  man for the job.

I'd probably order one, but I am in Canada and shipping hassles make it difficult.

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on January 24, 2007, 09:23:56 PM
After looking at the manual, this looks pretty cool.

-metal chassis
-48v phantom power
-9v DC powerable
-XLR inputs and outputs
-Optional limiter
-separate gain controls
-peak lights

Gee... If you can get one for around $50, it would almost be worth it just for the case and hardware.
If you get one, let us know how it sounds.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on January 24, 2007, 09:47:03 PM
After looking at the manual, this looks pretty cool.

-metal chassis
-48v phantom power
-9v DC powerable
-XLR inputs and outputs
-Optional limiter
-separate gain controls
-peak lights

Gee... If you can get one for around $50, it would almost be worth it just for the case and hardware.
If you get one, let us know how it sounds.

If anyone feels like ordering (and maybe chipping in some cost) let me know.  I'm willing to evaluate it and possibly do some mods.

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on January 24, 2007, 09:54:13 PM
PM sent
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Patrick on January 25, 2007, 02:15:35 AM
Posting a picture of this thing because it took literally 10 minutes to find one on the internet.  None of the retail stores had pics of it and Google image search turned up nothing.  Might as well make the time spent somewhat worth it  :P

(http://www.nady.com/product_images/DMP2_i.jpg)
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on January 25, 2007, 02:46:10 AM
After looking at the manual, this looks pretty cool.

-metal chassis
-48v phantom power
-9v DC powerable
-XLR inputs and outputs
-Optional limiter
-separate gain controls
-peak lights

Gee... If you can get one for around $50, it would almost be worth it just for the case and hardware.
If you get one, let us know how it sounds.

If anyone feels like ordering (and maybe chipping in some cost) let me know.  I'm willing to evaluate it and possibly do some mods.

  Richard


This preamp will be very hard to mod because of the surface mount components that it uses. I am going to purchase one as well just to check it out. I want to see how they are getting a single 9 volt to do all this. I think this preamp is way to big for stealth use but I think its worth checking out to see if it can be improved.

It all depends on the circuit layout. And how much of it needs to be changed in order to make it work. I am going to remove the limiter from the circuit all together because I don't think its necessary for live recording.

I will post pictures when I get one in my hands.


Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on January 25, 2007, 08:25:24 AM
Thanks, Chris! Let us know what you find.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Todd R on January 25, 2007, 10:26:31 AM
Looks interesting.  Here's the manual:

http://www.nady.com/pdf_files/manuals_pdf/audio/DMP2_manual.pdf
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: rowjimmy on January 26, 2007, 08:16:40 PM
 :hmmm:
Keep us posted. Maybe some pics of the guts along with a report?

Anyway, +t to all for now.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 01, 2007, 11:41:08 AM
Did anyone get one yet? I have a bad feeling that the chips are all going to be blacked out or in house numbers.
So I cant figure things out. I had no luck what so ever getting a schematic from Nady, they consider it to be "proprietary" information LOL how the hell are you supposed to fix it??? Then Again I don't give out schematics ether so how mad can I be? I just want to take a look at the power supply section and see what they are using to get all that voltage from a little bitty 9 volt battery... I think it must be some sort of pump charge IC maybe even a few of them cascaded I found this little guy doing some research for my new upcoming product looks pretty promising... MAX1044 ic seems to be promising..

Chris Church
If anyone wants to buy it I would love to take a look but I am scared to be the first one :)
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: afri-cola-man on February 02, 2007, 05:39:29 AM
This seems to be the same make by a different distributor:
http://www.musik-produktiv.de/shop2/shop04.asp/artnr/100009940/sid/!18121995/quelle/listen (http://www.musik-produktiv.de/shop2/shop04.asp/artnr/100009940/sid/!18121995/quelle/listen)
I got one of them last year and taped one show [superlux > hitec preamp > jb3]. It didn't come out to bad IMO. The battery stood for the 4 hour show. I put it aside, because I managed to get an ua-5 meanwhile.
If anyone is interested, I could open it and post some pics of the 'inner secrets', if this is of any help.
Cheers from Germany
Ulrich
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on February 02, 2007, 09:03:38 AM
This seems to be the same make by a different distributor:
http://www.musik-produktiv.de/shop2/shop04.asp/artnr/100009940/sid/!18121995/quelle/listen (http://www.musik-produktiv.de/shop2/shop04.asp/artnr/100009940/sid/!18121995/quelle/listen)
I got one of them last year and taped one show [superlux > hitec preamp > jb3]. It didn't come out to bad IMO. The battery stood for the 4 hour show. I put it aside, because I managed to get an ua-5 meanwhile.
If anyone is interested, I could open it and post some pics of the 'inner secrets', if this is of any help.
Cheers from Germany
Ulrich

I would like to know if it puts out a true 48v DC for phantom power. Pictures would be nice too.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: afri-cola-man on February 02, 2007, 09:51:30 AM
I don't know if it's true 48 volts. But it did definitely power my mics. The instruction manual doesn't give any hints about the actual voltage supplied. I try to post some pics tomorrow or on Sunday.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 02, 2007, 10:05:38 AM
I don't know if it's true 48 volts. But it did definitely power my mics. The instruction manual doesn't give any hints about the actual voltage supplied. I try to post some pics tomorrow or on Sunday.

We need realy sharp pictures of the circuit board PLEASE :) thanks

Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Ryan Sims on February 02, 2007, 12:40:13 PM
FWIW, I own a Nady mixer for home use and the phantom power on this thing is a joke.  It will power my LDC but it is extremely noisy.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 02, 2007, 04:07:34 PM
FWIW, I own a Nady mixer for home use and the phantom power on this thing is a joke.  It will power my LDC but it is extremely noisy.

It might not be noisey for the little preamp so we have to take a look at it.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on February 02, 2007, 04:33:10 PM
FWIW, I own a Nady mixer for home use and the phantom power on this thing is a joke.  It will power my LDC but it is extremely noisy.

It might not be noisey for the little preamp so we have to take a look at it.


Yep.  The two questions I have are;
- what chip(s) generate phantom power from 9V
- do the opamps run on something better than 9V only (like +/- 12V or something)

If the power supply and build is reasonable it is easy to change opamps/caps/etc to get great sound.

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 02, 2007, 06:17:39 PM
FWIW, I own a Nady mixer for home use and the phantom power on this thing is a joke.  It will power my LDC but it is extremely noisy.

It might not be noisey for the little preamp so we have to take a look at it.


Yep.  The two questions I have are;
- what chip(s) generate phantom power from 9V
- do the opamps run on something better than 9V only (like +/- 12V or something)

If the power supply and build is reasonable it is easy to change opamps/caps/etc to get great sound.

  Richard


I think there is only two ways to get that kind of voltage one is an inverter and switch the dc from the battery to ac. Then once its ac you can send it into a step up transformer with a center tap then use a pump charge IC to ram up the voltage or simply use a series of pump charge ic chips to get you there by cascading them does that make sense? its a dc to dc converter of some kind that for sure but as we increase voltage current must be reduced.. so I would say a supply like this might be good for 40mA max before it cacks out.. So if most mics need about 10mA to run properly that only leaves 20mA for the preamp that's not much... But most surface mount ic chips will work at 20mA...

Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: afri-cola-man on February 03, 2007, 08:56:42 AM
I don't know if it's true 48 volts. But it did definitely power my mics. The instruction manual doesn't give any hints about the actual voltage supplied. I try to post some pics tomorrow or on Sunday.

We need realy sharp pictures of the circuit board PLEASE :) thanks



You can find the pictures here.
http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html (http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html)
That's the best I could manage with my digital camera. I hope they're of any help.
Ulrich

I had to remove the pictures [2007-03-25] due to urgent need of the webspace they blocked. If anybody does still need them, please don't hesitate to pm me.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 03, 2007, 10:21:54 AM
I don't know if it's true 48 volts. But it did definitely power my mics. The instruction manual doesn't give any hints about the actual voltage supplied. I try to post some pics tomorrow or on Sunday.

We need realy sharp pictures of the circuit board PLEASE :) thanks



Dude HUGE +T thanks alot!!!


You can find the pictures here.
http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html (http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html)
That's the best I could manage with my digital camera. I hope they're of any help.
Ulrich
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 03, 2007, 10:49:46 AM
Well from what I have seen if the Nady is the same on the inside it could benefit from changing all the resistors to metal film and all 1% values because 5% does not cut it for me... This will help balance out the left and right sides and bring the noise floor down. The Tantalum coupling caps have to go... and get replaced with Mylar then I would take a good look at the electrolytics and see if they can be changed out for a better quality cap.. After that I would take a look at the opamps for a burr brown substitute that could be used current draw would obviously be a huge factor here. I would then take a huge look at the cheesy 1$ pots they are using and maybe replace them with a rotary 12 position pot with precision resistors on it. Then I would rip out that diode limiter peace of turd and use the switch for a high pass filter... that might be tricky you would probably have to put in a small sub board with the HPF caps on it. and swap them out for the coupling caps ether in the input ( preferred method ) or somewhere close the the first stage. But again in order to figure the cap out you need to figure out the source impedance of the circuit ( that's not something I can figure out ) or anyone with out a schematic.. So trial and error with a MLS analyzer could show what the cap is doing..

Then after that you might have a pretty good preamp or at least as good as it could be... They are using a SIX hex inverter hex chip to get the 48v or so voltage but I think max current is only going to be 12mA I suspected they were cascading inverters some how. So that's a pretty good chip they may be better ones that will drop in The chip is a TC4069UBP its a Toshiba chip here is the data sheet for it. I think that they must "split" of the supply and then use a virtual ground and create a + and - supply for the opamps.
http://www.datasheetcatalog.com/datasheets_pdf/T/C/4/0/TC4069UBP.shtml
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on February 03, 2007, 11:55:00 AM
Well from what I have seen if the Nady is the same on the inside it could benefit from changing all the resistors to metal film and all 1% values because 5% does not cut it for me... This will help balance out the left and right sides and bring the noise floor down. The Tantalum coupling caps have to go... and get replaced with Mylar then I would take a good look at the electrolytics and see if they can be changed out for a better quality cap.. After that I would take a look at the opamps for a burr brown substitute that could be used current draw would obviously be a huge factor here. I would then take a huge look at the cheesy 1$ pots they are using and maybe replace them with a rotary 12 position pot with precision resistors on it. Then I would rip out that diode limiter peace of turd and use the switch for a high pass filter... that might be tricky you would probably have to put in a small sub board with the HPF caps on it. and swap them out for the coupling caps ether in the input ( preferred method ) or somewhere close the the first stage. But again in order to figure the cap out you need to figure out the source impedance of the circuit ( that's not something I can figure out ) or anyone with out a schematic.. So trial and error with a MLS analyzer could show what the cap is doing..

Then after that you might have a pretty good preamp or at least as good as it could be... They are using a SIX hex inverter hex chip to get the 48v or so voltage but I think max current is only going to be 12mA I suspected they were cascading inverters some how. So that's a pretty good chip they may be better ones that will drop in The chip is a TC4069UBP its a Toshiba chip here is the data sheet for it. I think that they must "split" of the supply and then use a virtual ground and create a + and - supply for the opamps.
http://www.datasheetcatalog.com/datasheets_pdf/T/C/4/0/TC4069UBP.shtml


Great diagnosis, Chris.

So what are those four transistors used for?  Is that part of the limiter circuit?

OK, it looks like they are using the TL074 chip for a preamp.  That is easily replaceable with any (FET input) opamp, right?

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on February 03, 2007, 11:55:38 AM
I don't know if it's true 48 volts. But it did definitely power my mics. The instruction manual doesn't give any hints about the actual voltage supplied. I try to post some pics tomorrow or on Sunday.

We need realy sharp pictures of the circuit board PLEASE :) thanks



You can find the pictures here.
http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html (http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html)
That's the best I could manage with my digital camera. I hope they're of any help.
Ulrich
++++thanks for the Photos!!!

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 03, 2007, 01:02:58 PM
Well from what I have seen if the Nady is the same on the inside it could benefit from changing all the resistors to metal film and all 1% values because 5% does not cut it for me... This will help balance out the left and right sides and bring the noise floor down. The Tantalum coupling caps have to go... and get replaced with Mylar then I would take a good look at the electrolytics and see if they can be changed out for a better quality cap.. After that I would take a look at the opamps for a burr brown substitute that could be used current draw would obviously be a huge factor here. I would then take a huge look at the cheesy 1$ pots they are using and maybe replace them with a rotary 12 position pot with precision resistors on it. Then I would rip out that diode limiter peace of turd and use the switch for a high pass filter... that might be tricky you would probably have to put in a small sub board with the HPF caps on it. and swap them out for the coupling caps ether in the input ( preferred method ) or somewhere close the the first stage. But again in order to figure the cap out you need to figure out the source impedance of the circuit ( that's not something I can figure out ) or anyone with out a schematic.. So trial and error with a MLS analyzer could show what the cap is doing..

Then after that you might have a pretty good preamp or at least as good as it could be... They are using a SIX hex inverter hex chip to get the 48v or so voltage but I think max current is only going to be 12mA I suspected they were cascading inverters some how. So that's a pretty good chip they may be better ones that will drop in The chip is a TC4069UBP its a Toshiba chip here is the data sheet for it. I think that they must "split" of the supply and then use a virtual ground and create a + and - supply for the opamps.
http://www.datasheetcatalog.com/datasheets_pdf/T/C/4/0/TC4069UBP.shtml


Great diagnosis, Chris.

So what are those four transistors used for?  Is that part of the limiter circuit?

OK, it looks like they are using the TL074 chip for a preamp.  That is easily replaceable with any (FET input) opamp, right?

  Richard

Yes the transistors are for the limiter. Its a way of ramping up the signal to drive the diodes hard enough to get them to clamp down lol its pretty lame. We are not talking state of the art here more state of the FART...
I would get rid of the tl074 that's a real dinosaur of an opamp anything by  burr brown would smoke it. I will check out substitutions based on chip size ect.. And see what we can come up with THAT corporation also makes really good opamps I am going to be designing a full sized stereo preamp based on the THAT chip the 1503 or something I forget the name but its a very good chip very easy to make a good preamp out of.

I wonder if the limiter is hard bypassed? I hope so.. This thing can be modified there is very little surface mount stuff going on, to be honest I really did think it was going to be all surface mount. I wondered how they could build it so cheap with out using surface mount. I really wonder if Nady did any changes to this unit? I think it would be a good thing to take a peek inside the Nady as well.. I have an email out the the company that makes this preamp to see if they will supply me with a schematic that will make it so much easier to see what they are doing in with this design..
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on February 03, 2007, 03:22:15 PM
The phantom power circuit looks like basically the same one in the Rolls 224. Oh well...
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 03, 2007, 05:47:24 PM
The phantom power circuit looks like basically the same one in the Rolls 224. Oh well...

Hey Chuck do they use the same chip? to get the voltage up? and I can assume from your reaction that the Rolls does not work very well??
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on February 03, 2007, 06:03:20 PM
Well from what I have seen if the Nady is the same on the inside it could benefit from changing all the resistors to metal film and all 1% values because 5% does not cut it for me... This will help balance out the left and right sides and bring the noise floor down. The Tantalum coupling caps have to go... and get replaced with Mylar then I would take a good look at the electrolytics and see if they can be changed out for a better quality cap.. After that I would take a look at the opamps for a burr brown substitute that could be used current draw would obviously be a huge factor here. I would then take a huge look at the cheesy 1$ pots they are using and maybe replace them with a rotary 12 position pot with precision resistors on it. Then I would rip out that diode limiter peace of turd and use the switch for a high pass filter... that might be tricky you would probably have to put in a small sub board with the HPF caps on it. and swap them out for the coupling caps ether in the input ( preferred method ) or somewhere close the the first stage. But again in order to figure the cap out you need to figure out the source impedance of the circuit ( that's not something I can figure out ) or anyone with out a schematic.. So trial and error with a MLS analyzer could show what the cap is doing..

Then after that you might have a pretty good preamp or at least as good as it could be... They are using a SIX hex inverter hex chip to get the 48v or so voltage but I think max current is only going to be 12mA I suspected they were cascading inverters some how. So that's a pretty good chip they may be better ones that will drop in The chip is a TC4069UBP its a Toshiba chip here is the data sheet for it. I think that they must "split" of the supply and then use a virtual ground and create a + and - supply for the opamps.
http://www.datasheetcatalog.com/datasheets_pdf/T/C/4/0/TC4069UBP.shtml


Great diagnosis, Chris.

So what are those four transistors used for?  Is that part of the limiter circuit?

OK, it looks like they are using the TL074 chip for a preamp.  That is easily replaceable with any (FET input) opamp, right?

  Richard

Yes the transistors are for the limiter. Its a way of ramping up the signal to drive the diodes hard enough to get them to clamp down lol its pretty lame. We are not talking state of the art here more state of the FART...
I would get rid of the tl074 that's a real dinosaur of an opamp anything by  burr brown would smoke it. I will check out substitutions based on chip size ect.. And see what we can come up with THAT corporation also makes really good opamps I am going to be designing a full sized stereo preamp based on the THAT chip the 1503 or something I forget the name but its a very good chip very easy to make a good preamp out of.


Nice plan.  You're talking about the THAT 1510/1512.  Those are replacement for TI INA217, which are replacements for AD SSM2017/19.  All nice chips, that's for sure.  They are what is inside the DMIC-20.  They use a boost circuit to get from +6V to +/-12V.  Theirs is an inductor-based one (Maxim 743), but you can also use "charge pumps" (LT1054) to do it too.  I actually started breadboarding this before I started buying (and hacking) so much gear.  And now I've just bought an Edirol R09  :P.  When will it end.  Someone save me from myself!

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Chuck on February 03, 2007, 09:50:33 PM
The phantom power circuit looks like basically the same one in the Rolls 224. Oh well...

Hey Chuck do they use the same chip? to get the voltage up? and I can assume from your reaction that the Rolls does not work very well??


Yeah, the 4069 is used in the Rolls too. The Rolls box I had provided ~45v when un-loaded. But, under load, that dropped to anywhere from 15v to 24v depending on the current draw of the microphones. It powers most microphones that way, but I wasn't happy with it. I tried replacing that hex inverter with a higher speed inverter, but it introduced too much noise. I also experimented with different capacitors, but it never improved that much.

If I remember right, the Denecke PS-2 uses A medium speed hex inverter too, but with a different circuit design. That box provides consistant 48v even with high current microphones.
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: rowjimmy on February 03, 2007, 10:06:24 PM
These threads fascinate me. And to think I don't even own a soldering iron...
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: poorlyconditioned on February 03, 2007, 10:08:19 PM
The phantom power circuit looks like basically the same one in the Rolls 224. Oh well...

Hey Chuck do they use the same chip? to get the voltage up? and I can assume from your reaction that the Rolls does not work very well??


Yeah, the 4069 is used in the Rolls too. The Rolls box I had provided ~45v when un-loaded. But, under load, that dropped to anywhere from 15v to 24v depending on the current draw of the microphones. It powers most microphones that way, but I wasn't happy with it. I tried replacing that hex inverter with a higher speed inverter, but it introduced too much noise. I also experimented with different capacitors, but it never improved that much.

If I remember right, the Denecke PS-2 uses A medium speed hex inverter too, but with a different circuit design. That box provides consistant 48v even with high current microphones.

You realize that the phantom power goes down in voltage under use, right?  The spec is a perfect 48V in series with a 6.8K resistor.  So, the maximum current is something like 7mA, and at that, the voltage would be zero (all dropped on the 6.8K resistor, internal to the phantom power supply).

An easy test is to put a sample load resistor, say 10K, on the output.  See how many volts you get on that resistor.  According to my quick calculation, you should get about 28V on that resistor.  Any more than that and you're fine.

I tend to trust the Denecke circuit, though.  Those guys build tough gear!

  Richard
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: DSatz on February 07, 2007, 06:06:04 AM
Richard, actually it's 7 mA per 6.8 kOhm resistor for a total of about 14 mA as the "short circuit" current. A preamp or supply should be able tolerate that for a few seconds or minutes on one channel at least; accidental short circuits do occasionally happen. However, that requires a more robust construction than is found in many pieces of portable equipment that I've tested.

For P48 microphones, the DIN EN standard gives 10 mA as the maximum. Above 7 mA, more energy is spent heating up the phantom resistors than actually reaches the microphone, and many lightweight preamps or phantom supplies fall out of regulation. So most manufacturers don't go into that zone of diminishing returns. Nonetheless there are the inevitable wacky exceptions: many Earthworks models draw the full 10 mA, and many CAD Equitek models draw 8 mA.

Most modern P48 condenser microphones draw less than 6 mA apiece. Shure KSM-series microphones are typically specified at 5.5 mA or thereabouts. Schoeps CMC 5-- and 6-- preamps normally draw about 4.5 mA apiece from a 48 Volt supply, but the CMC 6-- amplifier, if it senses too low a supply voltage, may switch over to its 12-Volt mode and try to draw 10 mA. (It isn't a "12 through 48 Volt" amplifier; it's a dual-mode amplifier which requires either standard 12 Volt phantom powering with adequate current or standard 48 Volt phantom powering with adequate current.) Neumann TLM and fet 100 mikes typically draw 2 - 3 mA.

Neumann's older fet 80 designs (KM 84, U 87, etc.) draw less than 1 mA, as did Schoeps' pre-Colette-series CMT 5-series microphones. But the age of a design isn't a reliable guide. To many people's surprise, the original AKG C 451 from the 1970s--not the electret "reissue" (cough, cough)--tries to draw 6 mA from a standard 48 Volt supply. It really was a P12 microphone with a tolerance for 48 Volts, not a 48-Volt microphone as such.

A hint: If you're revamping a cheap phantom power supply, check its 6.8 kOhm supply resistors; make sure that the pair on each input is matched as closely as possible, since any imbalance there reduces the preamp's common mode rejection. Also, the closer the match, the better your protection against any hum or hash from the DC supply getting into the audio.

The specification says that the two resistors in any one pair (i.e. on any one input) should not differ from one another by more than 0.4%. Even expensive "audiophile grade" 1% resistors may thus be out of spec by as much as a factor of 5--a real case of misplaced priorities, which is unfortunately fairly common. The absolute 6.8 kOhm value has a 20% tolerance on it; having equal value resistors within each pair is far more important.

--best regards
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: rowjimmy on February 07, 2007, 08:37:51 AM
Nice post. Even I got something from it. +t
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on February 07, 2007, 11:19:10 AM
Richard, actually it's 7 mA per 6.8 kOhm resistor for a total of about 14 mA as the "short circuit" current. A preamp or supply should be able tolerate that for a few seconds or minutes on one channel at least; accidental short circuits do occasionally happen. However, that requires a more robust construction than is found in many pieces of portable equipment that I've tested.

For P48 microphones, the DIN EN standard gives 10 mA as the maximum. Above 7 mA, more energy is spent heating up the phantom resistors than actually reaches the microphone, and many lightweight preamps or phantom supplies fall out of regulation. So most manufacturers don't go into that zone of diminishing returns. Nonetheless there are the inevitable wacky exceptions: many Earthworks models draw the full 10 mA, and many CAD Equitek models draw 8 mA.

Most modern P48 condenser microphones draw less than 6 mA apiece. Shure KSM-series microphones are typically specified at 5.5 mA or thereabouts. Schoeps CMC 5-- and 6-- preamps normally draw about 4.5 mA apiece from a 48 Volt supply, but the CMC 6-- amplifier, if it senses too low a supply voltage, may switch over to its 12-Volt mode and try to draw 10 mA. (It isn't a "12 through 48 Volt" amplifier; it's a dual-mode amplifier which requires either standard 12 Volt phantom powering with adequate current or standard 48 Volt phantom powering with adequate current.) Neumann TLM and fet 100 mikes typically draw 2 - 3 mA.

Neumann's older fet 80 designs (KM 84, U 87, etc.) draw less than 1 mA, as did Schoeps' pre-Colette-series CMT 5-series microphones. But the age of a design isn't a reliable guide. To many people's surprise, the original AKG C 451 from the 1970s--not the electret "reissue" (cough, cough)--tries to draw 6 mA from a standard 48 Volt supply. It really was a P12 microphone with a tolerance for 48 Volts, not a 48-Volt microphone as such.

A hint: If you're revamping a cheap phantom power supply, check its 6.8 kOhm supply resistors; make sure that the pair on each input is matched as closely as possible, since any imbalance there reduces the preamp's common mode rejection. Also, the closer the match, the better your protection against any hum or hash from the DC supply getting into the audio.

The specification says that the two resistors in any one pair (i.e. on any one input) should not differ from one another by more than 0.4%. Even expensive "audiophile grade" 1% resistors may thus be out of spec by as much as a factor of 5--a real case of misplaced priorities, which is unfortunately fairly common. The absolute 6.8 kOhm value has a 20% tolerance on it; having equal value resistors within each pair is far more important.

--best regards

Great info I learned a few things too! T+
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: nem on February 28, 2007, 12:44:07 AM
would anyone be so kind as to point me in the direction of an inexpensive pre that has both xlr ins and outs? or is the Nady the only one?
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: Church-Audio on March 03, 2007, 02:04:37 AM
would anyone be so kind as to point me in the direction of an inexpensive pre that has both xlr ins and outs? or is the Nady the only one?

This is right now as far as I know the only one at this price point. But you have to remember its not going to be pretty.... :) I think the term you get what you pay for will apply to this product. I think if your looking for 40+db of gain I would stay away if you only need maybe 20 or so db of gain I am pretty sure this will have a half decent noise floor at that range. But the other issue is sound quality and that's one I can't answer because I have never used it.. This thing is cheap you will have to baby it if you drop it on a knob say bye bye. I still think its pretty cool though I must admit.. I think for the $60 its worth a try.. I would love to get one to mod it. But as it turns out its too much of a pain in the ass to get in Canada..
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: sunjan on May 23, 2009, 05:52:26 AM
You can find the pictures here.
http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html (http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html)
That's the best I could manage with my digital camera. I hope they're of any help.
Ulrich

I had to remove the pictures [2007-03-25] due to urgent need of the webspace they blocked. If anybody does still need them, please don't hesitate to pm me.
For the archive, I just noted that afri-cola put the pictures up again at the same address:
http://www.mp-acm.de/hitec_audio/hitec_audio_pre_mobile_2.html

Meanwhile, the Nady DMP-2 has dropped to $31.98!
http://yhst-38616620066226.stores.yahoo.net/dbdmp-2.html
Title: Re: Inexpensive "NADY" Preamp and Phantom adapters
Post by: heyitsmejess on May 23, 2009, 05:59:54 AM
ive never used it with the gain cranked all the way up, but halfway, it dosent sound TOO bad....for the price, im happy with what it does.