Advice for fixing a faulty Neumann M149a power supply

[jondo]

About 2 weeks ago I purchased a 2nd hand M149 mic, and was very happy with it until it stopped working yesterday. The symptoms were after leaving the mic on for several hours during a session, i noticed more background noise in the signal path when usually it was quiet as a mouse. I turned off the m149a power supply, but then it didn't turn back on.

So I changed the fuse in the plug, no joy, then opened it up to see if there was another fuse inside, nope. after testing with a voltmeter, it looks like the faulty part is a cheap looking PSU inside made by Globtek that is soldered at two points onto the circuit board and switch.

Now i'm not the king of electronics, but i think even i could fix this one, but the PSU model is Globtek Switching Adapter GT-21089-1512-T2, which I can't seem to find anywhere. Written on it is Output 12v 1.25A, 15w max, it takes a 2 pin power cable. Obviously don't want to get this wrong, does anyone know where I could source an equivalent PSU to carry out the repair myself of similar or superior quality?

Thanks

[Folderol]

Can you post a picture?
Should be do-able, but difficult to suggest without seeing it.

[jondo]

Thanks for your reply. Can't see any option to upload photos here so have placed them here

https://1drv.ms/f/s!ApBwcIMmBsgnijzS5rlnwBQVRqX3

This one might be a replacement candidate, but there's nothing mentioning switch mode on it.

https://www.amazon.co.uk/Pike-Co-Branded-PI315-12-DESOCKETOP-x/dp/B00LRWNVQ0/ref=sr_1_65?s=computers&ie=UTF8&qid=1498682569&sr=1-65&keywords=12v+power+supply+1.25a

[ef37a]

Pin 1: –70 V
Pin 2: +5 V
Pin 3: audio signal (+phase)
Pin 4: +70 V
Pin 5: sensor line
Pin 6: ground
Pin 7: +32 V
Pin 8: audio signal (–phase)

Those ^ are the voltages that should come from the supply. THAT supply does not look like anything mssrs Neumann would produce!

If I have the right model we are looking at a £3000 microphone? I suspect that getting the PSU or its connections wrong could damage the mic and I would urge you to find the correct supply from a Neumann agent. Expensive? Probably but it could get much worse IMHO.

Last but CERTAINLY not least. Are you qualified to safely poke about in mains powered devices and are you certain you can leave them in a safe state for other people? Anytime you have mains kit apart and work on the '230V' side said kit should then be PAT tested.

Dave. http://www.studiocare.com/neumann-n149- ... gLKDfD_BwE

[Folderol]

Hmmm, does look a bit sus. Initially I was wondering if it was a dual conversion - mains to stable DC then DC to actual wanted voltages.
However, you said it had worked, so that still may be true. Is there any indication that a different input supply might once have been fitted?
That supply in the picture is a bog-standard one of a type that is readily available all over the world. wioth the mains side pre-packaged and double insulated, so unlike Dave, if that's the correct voltage I wouldn't see a problem replacing it with the same type.
The one below would seem to be a (slightly improved) replacement - provided you get the output polarity right!
http://uk.farnell.com/xp-power/vet18us1 ... dp/2708280

[ef37a]

OK Will, maybe I am being a bit over cautious but you have to ask...Why did that PSU fail?

Does not look like heavy duty required nor restricted airflow? SMPSUs are generally UBER reliable.

But, FTF, I hope OP at least has a decent digital test meter!

Dave.

[Hugh Robjohns]

Personally, with such an expensive mic, I'd contact Sennheiser UK (assuming you're in the UK -- else your local Sennheiser/Neumann agent) and get them to repair it properly. That way ensures guaranteed performance and future resale value...

I may be wrong, but I gather that PSU (N149a) has evolved a bit over the years.

Current models have an IEC mains inlet, rather than the C7 fig-8 type which was employed on older units. But they do all appear to use a universal switched-mode PSU module to supply 12V to the PCB, and that board then uses DC-DC conversions to provide all the power rails required by the valve mic.

Using an OEM PSU module is a routine technique to get around all the different international safety legislation... but like Dave I'd be a bit horrified to discover the OEM PSU simply stuck to the inside of the case with double-sided tape. Not at all what I'd expect in a £3k mic with a Neumann badge on the front.

I'm intrigued... Anyone else got an M149/M147 mic with the N149a PSU that can open the box and see what's inside for us?

H

[jondo]

Thanks for all your replies, I had already sent in a request for repair quote to Neumann thats come in at £300 fixed fee. I also sent photos of the unit to them and they have been really helpful and confirmed it genuine and that globtek psu is used.

Ive establshed no volts are coming out of the globtek, it also has bulging leaky caps inside, Sennheiser spares are charging £200 for its replacement, so I will try and source it direct from the manufacturer.

I'm certain i can undertake this repair safely, it involves one replacement psu soldered in two places that are well away from anything else (on the switch and pcb). Dave totally understand the need for safety/caution, believe me if it was anything more complicated I wouldn't be doing this, and I do know someone who can PAT test it afterwards.

[jondo]

Hugh, there is a metal support cage that held the psu, I took that out before it was photographed, so the trickiest part willbe finding a psu that will also fit that cage. I did own an M147 before buying this that had an IEC power connector, never went wrong in 15 years, so never opened it up, the only difference i noticed was that this newer N 149a is lighter than the other before I sold it.

Just bad luck that it's gone wrong in 2 weeks, and I don't think the mic is anymore than 5 years old if that, it's immaculate.

[Hugh Robjohns]

Sennheiser spares are charging £200 for its replacement, so I will try and source it direct from the manufacturer.

Hmmm... I wish you luck with the one. Appreciate £200 is a bit steep, but a least it will have the correct output wiring and maintain the integrity of the whole thing.

Pleased to hear aot the cage -- that restores my faith!

H

[Folderol]

That's one hell of a mark-up for a PSU that costs about 10 quid trade Even a 'medical' grade PSU is less than £50.

Are the connections on the board marked + and - ? if so, there's no doubt what I'd go for. Yes, yes, I know that's easy from me to say but...

P.S.
If it was me I wouldn't need them marked - many years experience replacing anonymous dead PSUs

[Sahib]

At the end of the day the decision is yours but I would not hesitate to use an off the shelf power supply. I do not think there is anything special about that Globetek.

[jondo]

I've found what i hope is an almost identical Globtek replacement it's the same manufacturer, same model number, 12v 1.25A 15watt, appears to be the same size. The only differences is max input current says 0.5A instead of 1A on the label of the current one, can anyone tell me if that lower input current is going to cause a problem, I have no idea what the tube in the mic might actually use whilst on, but because the psu can still provide max output 1.25A, that should be OK right?

Also it doesn't say switching on it, just ITE power supply, but I'd hope that with it being the same model, that's it's the same.

[Folderol]

I've found what i hope is an almost identical Globtek replacement it's the same manufacturer, same model number, 12v 1.25A 15watt, appears to be the same size. The only differences is max input current says 0.5A instead of 1A on the label of the current one, can anyone tell me if that lower input current is going to cause a problem, I have no idea what the tube in the mic might actually use whilst on, but because the psu can still provide max output 1.25A, that should be OK right?

Also it doesn't say switching on it, just ITE power supply, but I'd hope that with it being the same model, that's it's the same.

I'm wondering if they are playing games with the rating. Like you can draw 15W but only briefly It's highly suspicious if it has exactly the same model number. The numbers don't make sense, but if it is rated at only 0,5A it will almost certainly be inferior, and likely to fail early. If anything you should go the other way and fit one with a slightly higher current rating. I'd be very surprised if you couldn't get one in the same size package. These things have shrunk dramatically over the last few years.

Hardly any PSUs have the word switching these days, it's more-or-less assumed that it will be.

[Sam Spoons]

If it's a 'world wide' power supply, it may be rated at 1A for 115VAC which would mean it would be rated at 0.5A for 230VAC....... I suppose it depends on the target market.....

[jondo]

Just an update on this, the replacement power pack arrived from the US, I've soldered it in, and fortunately there's no sparks, smoke and tears, just a green power light that is now on

Left it on for an hour to make sure it didn't subsequently explode, then turned off and sheepishly connected the M149 mic to it and........... happy days fully working again, been on for 10 hours now and no problems.

The cost, £4 + postage, but i did also buy an extra 2 spares, just in case.

Thanks for everyone for their advice who helped me get it working again.

[Hugh Robjohns]

Excellent... and a lot more pleasant than the £200 plus option....

H

[yannlu]

I had the same problem with mine. A pad of the mains connector in the Ault SPSU has broken and started to burn. Probably due to the mechanical traction. After fix it I got 12VDC again on its output. I checked all the voltages but probably something else failed in the main board. Is someone has the schematics of it ? Thanx

Pin 1: –70 V
Pin 2: +5 V
Pin 3: audio signal (+phase)
Pin 4: +70 V
Pin 5: sensor line
Pin 6: ground
Pin 7: +32 V
Pin 8: audio signal (–phase)

Those ^ are the voltages that should come from the supply. THAT supply does not look like anything mssrs Neumann would produce!

If I have the right model we are looking at a £3000 microphone? I suspect that getting the PSU or its connections wrong could damage the mic and I would urge you to find the correct supply from a Neumann agent. Expensive? Probably but it could get much worse IMHO.

Last but CERTAINLY not least. Are you qualified to safely poke about in mains powered devices and are you certain you can leave them in a safe state for other people? Anytime you have mains kit apart and work on the '230V' side said kit should then be PAT tested.

Dave. http://www.studiocare.com/neumann-n149- ... gLKDfD_BwE

[gdowling]

Just wanted to say thanks for the info here.

My 2 box style power supply failed last night before a session today, after reading the advice here I was able to use a spare 12V switched mode power supply to get it working again.

Will do a proper job at some point - but would never have attempted it without the thoughts here.

Thanks guys!

[crescentmoon66]

Here is a link to the actual model and part..... https://en.globtek.com/search/?q=TR9KE1 ... &x=11&y=13

[yannlu]

I fixed the 12V power supply but there is a problem on the main board (not the correct voltages). I need to replace/fix this board but it is not possible to get a new board or the schematics from a Neumann distributor or retailer....

[avalonvt]

Just an update on this, the replacement power pack arrived from the US, I've soldered it in, and fortunately there's no sparks, smoke and tears, just a green power light that is now on

Left it on for an hour to make sure it didn't subsequently explode, then turned off and sheepishly connected the M149 mic to it and........... happy days fully working again, been on for 10 hours now and no problems.

The cost, £4 + postage, but i did also buy an extra 2 spares, just in case.

Thanks for everyone for their advice who helped me get it working again.

HI!
My n149 stopped working, the led wont turn on. this mic should be at least 15 years old, probably even more! the n149 looks very different than the one i have seen on sale now, it has two boxes one with the plug and one with the xlrs. Sennheiser is asking for those £300 which it is quite a lot... did you say you have a couple of spares ? would i be able to buy one from you ? are you in london by any chance ? thanks!!!

[gdowling]

With luck what has failed is the 12V switched mode power supply (the bit that plugs into the mains).

If so you can easily replace it with another. I had a couple of 1A ones floating around (my Neumann supplied one was 12V 640ma), I tried both and they both worked and sounded identical. I think the serious work is done by the second power supply box with the XLR connector.

My new supply is a fraction of the weight of the old one!

So check if you’re getting 12V from the initial supply, and if not replace it. I think the cable between the supplies is colour coded red / black, so it’s easy to get the polarity right.

I added a trailing 12V power socket to the Neuman cable - so can now use any supply with the standard laptop style plug.

[avalonvt]

With luck what has failed is the 12V switched mode power supply (the bit that plugs into the mains).

If so you can easily replace it with another. I had a couple of 1A ones floating around (my Neumann supplied one was 12V 640ma), I tried both and they both worked and sounded identical. I think the serious work is done by the second power supply box with the XLR connector.

My new supply is a fraction of the weight of the old one!

So check if you’re getting 12V from the initial supply, and if not replace it. I think the cable between the supplies is colour coded red / black, so it’s easy to get the polarity right.

I added a trailing 12V power socket to the Neuman cable - so can now use any supply with the standard laptop style plug.

Mine looks exactly like this one, any idea on where i could find the parts?
Thx

[gdowling]

This one worked fine.

https://uk.farnell.com/xp-power/vet18us ... dp/2708280