Converting Gefell MV692 to 48V (from 12V t-power)

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dynomike
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Converting Gefell MV692 to 48V (from 12V t-power)

Post by dynomike » Sat Nov 08, 2008 1:33 pm

The N691 power supply (or the connectors, actually) keeps crapping out, and I'd really like to get these mics running on normal phantom power. I could easily make 7-pin tuschel to XLR cables, but I'd still have to change some stuff in the mic body to drop the voltage down to 12V, right?

Ideas, schematics would be helpful. I already have a power supply schematic and a wiring diagram for the 7-pin to XLR.

-Mike
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dynomike
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Post by dynomike » Sat Nov 08, 2008 2:11 pm

I found this: http://www.uneeda-audio.com/phantom/p48t122.jpg on converting 48V phantom to 12V T...

and this: http://www.leosloetlabor.de/pdf/Solderi ... le-XLR.pdf for wiring from the mv692.

Should any tech be able to build me a special cable to run the mics on 48v with this info? I already have cables that I could modify... I'll try to get in touch with a tech and send him this stuff.

-Mike
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Marik
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Post by Marik » Sun Nov 09, 2008 8:48 pm

Here is the 12V schemo:
Image

and here is 48V:

Image

Instead of D1/2 and C12 install a multiturn trimpot R8 and then adjust until you get 12V on C9/R6 junction (no capsule on). Or even better, 60V on VD2/VD3/Tr2 junction.

Be careful, you need to take off a bolt, which is very close to a hair thin wire of Tr2. It is very easy for the screwdriver to slip and break it.
If you need any additional help you can contact me privately.

Best, M

skinsincyn
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Post by skinsincyn » Sun Nov 09, 2008 10:14 pm

I bought a second set of mv691s that came with phantom-ready cables. The guy sent me a schematic of how he made the cables. I don't know anything about electronics, but I know the cables work!

http://picasaweb.google.com/lh/photo/Dw ... 6H4TLMl0JA

dynomike
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Post by dynomike » Mon Nov 10, 2008 3:12 pm

skinsincyn wrote:I bought a second set of mv691s that came with phantom-ready cables. The guy sent me a schematic of how he made the cables. I don't know anything about electronics, but I know the cables work!

http://picasaweb.google.com/lh/photo/Dw ... 6H4TLMl0JA
If this works, this is *exactly* what I'm looking for. I'm a little concerned about 48V getting into the mic though. Are those two resistors really going to change the voltage to 12V? I think what I'll do is take a readout of the voltage from the power supply (the channel that works), then build these cables, then take a readout of the voltage from the cable (plugged into 48v phantom) If its similar, I'll go ahead and try the mics.

Of course, Marik, your post was incredibly helpful also. The cables idea seems to suit me well as I'm not too comfortable poking around inside vintage mics (though I am comfortable poking around in shitty Apex mics etc). If this cables thing doesn't turn out, perhaps I can send the mics to you for conversion to 48V? Email me with a quote, if you like: mikekuehn@gmail.com I've already been in contact with Gefell, and a local guy, but the local guy isn't familiar with the mics, and Gefell is in Germany... so... :)

Thanks very much to both of you!

-Mike
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skinsincyn
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Post by skinsincyn » Mon Nov 10, 2008 4:20 pm

That's cool that you can test it. Would you let me know the results? Like I said, they've worked for me so far. But, if they're carrying 24V or something, I'd like to know!

Good luck.
Eric

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Post by dynomike » Mon Nov 10, 2008 4:25 pm

skinsincyn wrote:That's cool that you can test it. Would you let me know the results? Like I said, they've worked for me so far. But, if they're carrying 24V or something, I'd like to know!

Good luck.
Eric
I just wonder if the 692 and 691 might be electrically different. I know they used a few different parts, besides the 692 having pad and rolloff switches.
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Post by skinsincyn » Mon Nov 10, 2008 4:40 pm

i have both models, and the cables work for both. As far as I know the pad and rolloff are the only diferences. Both of which are passive, right? So, shouldn't affect how much power they need.

But I'm just speculating. By the way, i love these mics.

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Post by JohnDavisNYC » Mon Nov 10, 2008 6:26 pm

sshhhhh...

can people please stop posting about how great these mics are until i have at least 6 of them?

THESE MICS SUCK, BUY RODE, MXL, WAY BETTER, LESS MONEYZ!!!!

by the way, thanks for posting the schematic... one of our pairs is converted, the other is not... much easier than reverse engineering....

john
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dynomike
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Post by dynomike » Mon Nov 10, 2008 7:34 pm

toaster3000 wrote:sshhhhh...

can people please stop posting about how great these mics are until i have at least 6 of them?

THESE MICS SUCK, BUY RODE, MXL, WAY BETTER, LESS MONEYZ!!!!

by the way, thanks for posting the schematic... one of our pairs is converted, the other is not... much easier than reverse engineering....

john
hahaha... i wouldn't worry about it. most people don't really care enough to get old foreign mics that run on 12V to work properly, and they WILL buy rode and mxl. but man, great mics. i'd love to try a pair of 582's.
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Post by dynomike » Mon Nov 10, 2008 7:38 pm

skinsincyn wrote:i have both models, and the cables work for both. As far as I know the pad and rolloff are the only diferences. Both of which are passive, right? So, shouldn't affect how much power they need.

But I'm just speculating. By the way, i love these mics.
amazing. i'm gonna build em tomorrow.
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Post by ubertar » Tue Nov 11, 2008 9:18 am

http://www.canford.co.uk/Products/49-224.aspx

phantom to t-power converter. I'm sure there are others out there... this is the first that comes up in a google search. I know I've seen ones in the US for about $60 or so a while back. Could be a lot easier than trying to make something.

edit:

here's one from Sennheiser for $54.

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Post by Marik » Tue Nov 11, 2008 9:49 am

skinsincyn wrote:I bought a second set of mv691s that came with phantom-ready cables. The guy sent me a schematic of how he made the cables. I don't know anything about electronics, but I know the cables work!

http://picasaweb.google.com/lh/photo/Dw ... 6H4TLMl0JA
Sorry, but this cable is not ideal solution. The problem is the 2.2K resistors are in parallel with input impedance of the pre. Say it is 2K, then what we have is the microphone loaded already by 1.1K, which can be quite low for this mic.
dynomike wrote:
I just wonder if the 692 and 691 might be electrically different. I know they used a few different parts, besides the 692 having pad and rolloff switches.
They are somewhat different. THe 691 has a discreet circuit FET+BJT, and 692 uses in-house chip instead of BJT. They use the same BV130 transformer.

Best, M

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Post by vanakaru » Sun Jan 04, 2009 12:15 pm

Hi.
I wonder if anybody has the schematics for the Gefell N691 power supply. I got parts from the original unit, but have no idea how they wire together.

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Post by vanakaru » Sun Jan 04, 2009 12:20 pm

Marik wrote: Instead of D1/2 and C12 install a multiturn trimpot R8 and then adjust until you get 12V on C9/R6 junction (no capsule on). Or even better, 60V on VD2/VD3/Tr2 junction.

Be careful, you need to take off a bolt, which is very close to a hair thin wire of Tr2. It is very easy for the screwdriver to slip and break it.
If you need any additional help you can contact me privately.

Best, M
Do you install just the trimpot or you replace other different parts as well (like T2-3 and T4)?
BTW does this http://www.uneeda-audio.com/phantom/p48t122.jpg did the trick?

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