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Author Topic: SX-M2 phantom problems  (Read 4481 times)

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Offline weroflu

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SX-M2 phantom problems
« on: April 13, 2015, 05:18:25 AM »
I was having some low level output problems with a SX-M2, sent it in for repair, clean bill of health reported, and then still experienced the same problems.

Tracked it down to insufficent phantom voltage. Phantom is about 3V below whichever supply voltage is fed, which made me think regulation is working but not the dc-dc converter.

However phantom was working fine during the checkup at repair, so it's a mystery.

The only thing I can think of now is that they used a higher voltage to test it at the shop and this is somehow responsible for it working there and not here. The only external power I have here is 12V. I have tried two sets of batteries as well.

Anyone have a clue to what the problem is?

Sonosax says that this is an older dc-dc converter and not replaceable, they are still working on finding a solution.

It may turn into my dedicated dynamic microphone amplifier.


stevetoney

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Re: SX-M2 phantom problems
« Reply #1 on: April 13, 2015, 09:19:50 AM »
I'm not sure I understand what you mean "phantom is 3v below whichever the supply voltage is fed".  I haven't run a Sonosax extensively, but with an input voltage range from 12vto 24v, doesn't it supply 48V phantom regardless of the input voltage?  Regardless, I didn't use mine with batteries, but whenever I used it I supplied it with more than 12V external from a Tekkeon.  Could it be that since your external is at the low end of the range, that's your issue (though you said you'd tried batteries, which of course should give you at least 18V).  Stating the obvious other question...the batteries were good and the battery contacts are clean?

Offline weroflu

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Re: SX-M2 phantom problems
« Reply #2 on: April 13, 2015, 09:48:16 AM »
'm not sure I understand what you mean "phantom is 3v below whichever the supply voltage is fed".

It means if I feed it 12v external phantom measures at about 9.xV, if i feed 18v from new batteries phantom measures at 15.xV, and slightly used batteries result in phantom voltage of about 13.xV.


 I haven't run a Sonosax extensively, but with an input voltage range from 12vto 24v, doesn't it supply 48V phantom regardless of the input voltage? 

That's what's SUPPOSED to be happening but it isn't

Regardless, I didn't use mine with batteries, but whenever I used it I supplied it with more than 12V external from a Tekkeon.  Could it be that since your external is at the low end of the range, that's your issue (though you said you'd tried batteries, which of course should give you at least 18V). 

see above

Stating the obvious other question...the batteries were good and the battery contacts are clean?

Yes everything is good, i tried swapping cables a bunch of times too. Running a 1k tone through it worked fine with all the power sources, the problem looks like it's only related to phantom, but I have no idea why it would only appear here and not at the factory. I'm testing phantom right at the inout jack, no load, no microphones, no cables.

Compounding the problem is that it got a clean bill of health from the factory.

From my little knowledge of things electronic I remember that regulators drop voltage about 3v so that was my guess, but it doesn't solve anything.


Offline hi and lo

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Re: SX-M2 phantom problems
« Reply #3 on: April 13, 2015, 11:04:45 AM »
The Sonosax should measure ~47.5v at the input jack with no load (or at least, both of mine measure exactly the same). Certainly if you're measuring ~9-15v, something is definitely not right. I have no idea what might actually be wrong with the unit.

One thing to mention is that if you're using an external power supply, it must be at least 14v. The normal operating range is 14-24v. Between 12v and 14v, the unit will operate with the low battery warning light and significantly reduced headroom.

Online JD

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Re: SX-M2 phantom problems
« Reply #4 on: April 13, 2015, 02:01:54 PM »
Not sure if it would help you out or not, but somewhere I have some basic electrical schematics for the SX-M2. LMK if you have any interest in them, I'll see if I can find them and post a copy.
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Offline weroflu

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Re: SX-M2 phantom problems
« Reply #5 on: April 13, 2015, 02:15:38 PM »
Thanks,  I have the schematics as well.

There is a sub-board power supply section on the bottom assembly. I think I will need the whole thing since it's potted/spray painted.

I'm waiting on sonosax to get back to me with a solution but I'm pessimistic since they sort of left me in the cold after the service was complete. They basically just told me that it tested fine and that was that. I told the guy that I would try to find the problem myself, which I did with very rudimentary electronic skills.

So I think I'm prepared to just take a loss on it now or maybe look for a cheap parts machine to harvest the power supply board, unless they come through with a workable solution. Shipping to and from was like $200, plus VAT on the shipping, plus the repair time.

It's karma for me since I didn't need it to begin with and I had in the back of my mind selling it at a premium.


Offline jbell

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Re: SX-M2 phantom problems
« Reply #6 on: April 13, 2015, 02:40:10 PM »
One of the problems with the older preamps like the SX-M2, Aeta PSP3, EAA PSP2 is that they are no longer being serviced.  You might want to contact Vark Audio they fixed a friends VMS02ib.  Schoeps only services the VMS 5U these days. 
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Offline tgakidis

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Re: SX-M2 phantom problems
« Reply #7 on: April 13, 2015, 03:57:26 PM »
I had a sx-m2 saga about a year+ ago.  One of the channels was 20dbs lower.  Sent it to Trew Audio and they "patched" it up.  It failed a couple weeks later and off to them again for further "patching".  Couldn't fix the problem and said it was the xlr input and the part was no longer available.  Found the part myself and changed out the xlr input, didn't fix the problem.  Sent it to Sonosax and they said they would have to rebuild the whole board.  Didn't want to invest anymore $$$ so It is now a paper weight  :(
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Offline weroflu

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Re: SX-M2 phantom problems
« Reply #8 on: April 13, 2015, 04:16:13 PM »
I would almost rather they had said  it's unfixable instead of it tested perfectly on their bench.

Send me your dch148 dc converter  :)

Actually why not just part out the whole thing and recoup your loss.

It gives me some pause in buying older equipment now, though my pr6 mixer is much older but in perfect working order.
 
The one I have here is in absolutely mint condition, it looks brand new but I guess that counts for nothing if a discontinued part fails (intermittently)

Offline weroflu

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Re: SX-M2 phantom problems
« Reply #9 on: April 16, 2015, 12:14:13 PM »
Does anyone have  suggestion where I might be able to find a Neumann  DCH148 phantom supply board?

Offline yug du nord

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Re: SX-M2 phantom problems
« Reply #10 on: April 16, 2015, 12:27:06 PM »
Before you go to all sorts of crazy trouble, you should try using an external P48 supply > SX-M2 and see if that solves your problem.
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Offline ero3030

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Re: SX-M2 phantom problems
« Reply #11 on: April 16, 2015, 03:20:08 PM »
Sounds like the cheap solution.  Alittle rolls 9v phantom added to the sonosax would keep the box useable.  Ed
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Offline H₂O

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Re: SX-M2 phantom problems
« Reply #12 on: April 16, 2015, 03:23:53 PM »
Do you have the schematic and/or specs for the dch148?
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Offline weroflu

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Re: SX-M2 phantom problems
« Reply #13 on: April 17, 2015, 01:41:09 AM »
I have the design note for the dch148, but it's not going to help much. It's a very small board, spray painted, and I would not even attempt to fix it.
I have the pinouts so I could test phantom right at its output but what's the point.



Offline weroflu

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Re: SX-M2 phantom problems
« Reply #14 on: April 17, 2015, 06:27:32 AM »
Neumann got back to me:  dch248, the newer version of the dch148 is available through distributors. 

Looks like there is a good chance to fix it.

Offline weroflu

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Re: SX-M2 phantom problems
« Reply #15 on: May 06, 2015, 09:59:00 AM »
I wound up doubling down on the problem being the dc converter and purchased a replacement.

It arrived monday and I got around to removing the old one - not so easy to do and risked pulling up the pads but it worked.

New converter is installed and phantom is measuring 48.3V.


Offline H₂O

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Re: SX-M2 phantom problems
« Reply #16 on: May 06, 2015, 10:04:34 AM »
how much was the dc-dc converter?
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Offline weroflu

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Re: SX-M2 phantom problems
« Reply #17 on: May 06, 2015, 10:14:39 AM »
125 Euros from the distributor.

These things are very cool -  tiny, laser trimmed resistor pair for 2 channels of phantom and a 48V pin for more channels.

I mght buy another for use in my next preamp project.

Offline H₂O

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Re: SX-M2 phantom problems
« Reply #18 on: May 07, 2015, 01:37:24 PM »
any pics?
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Offline Bob S

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Re: SX-M2 phantom problems
« Reply #19 on: October 23, 2018, 11:23:56 PM »
A few people here mentioned having schematics for the Sonosax. Could I get a copy and if it's for the SX-M2/LS that would be even better. Mine was sitting at Vark for a while before they told me the capsule (MK) bias voltage is only 36V. Both they and I asked for some help from Sonosax but neither of us has heard back from them. Mine was assembled in the mid 90s and I know its dated, but I've always loved it and considering the cables with it, its not an easy thing to turn the page on.

Any advice or suggestions would be greatly appreciated.

Offline weroflu

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Re: SX-M2 phantom problems
« Reply #20 on: October 24, 2018, 10:12:47 AM »
schems

Offline Bob S

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Re: SX-M2 phantom problems
« Reply #21 on: October 26, 2018, 02:10:52 AM »
Very nice of you. Thanks!

 

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