btyreman

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #20 on: May 21, 2020, 09:14:23 PM »
photo one


btyreman

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #21 on: May 21, 2020, 09:14:54 PM »
photo two

btyreman

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #22 on: May 21, 2020, 09:16:35 PM »
I can post far more detailed photos if needed,  hope that helps,

regards,

Ben.

moamps

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #23 on: May 22, 2020, 07:08:15 AM »
I forgot to ask you did you hear the noise from both drivers, LF and HF?
You can try to replace all capacitors which belong to the power supply, marked with red line. It might help.
Caps lot will cost you about 20-30 Euros, just try to find "low ESR" types, Panasonic, Nichicon, Vishay are good manufacturers.
Capacitors marked with blue lines belong to analog power amplifier ICs, you can replace them also but I don't think that there is a problem. That's all you can do without a scope.


 

moamps

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #24 on: May 22, 2020, 07:11:22 AM »
£240 per speaker

Do you have any information what the fault was and what they replaced?

btyreman

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #25 on: May 22, 2020, 10:14:27 AM »
I forgot to ask you did you hear the noise from both drivers, LF and HF?



 

the noise appears to only be coming from the tweeters, and I'm having a different issue with the left one, that one the noise doesn't go away, but the right one it does go away after about 6 minutes as I posted in the recordings., hope that helps.

Ben

pvision

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #26 on: May 22, 2020, 11:30:39 AM »
Do you have any information what the fault was and what they replaced?

No and no

Nick Froome

moamps

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #27 on: May 23, 2020, 07:34:28 AM »
the noise appears to only be coming from the tweeters, and I'm having a different issue with the left one, that one the noise doesn't go away, but the right one it does go away after about 6 minutes as I posted in the recordings., hope that helps.
Then there is a small chance that the problem is in the HF power IC, but the fact that no noise is heard from the LF driver may be caused by the LF driver not being able to reproduce that high pitch sound.

Visually all parts look ok, and as I said,  if you are good in soldering, you can try to replace capacitors and see will it cure the problem. Without a scope, you can't do a further analysis.

moamps

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #28 on: May 23, 2020, 07:35:06 AM »

beatnik

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #29 on: May 23, 2020, 08:12:25 AM »
Do you have any information what the fault was and what they replaced?

I had a unit with a power supply failure that I couldn't repair, I ended up sending it to Sennheiser UK, they said their procedure is just fitting in a new circuit board assembly and calibrate... I guess it's not worth for them to invest time in component level troubleshooting.


beatnik

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #30 on: May 23, 2020, 08:21:54 AM »
the noise appears to only be coming from the tweeters, and I'm having a different issue with the left one, that one the noise doesn't go away, but the right one it does go away after about 6 minutes as I posted in the recordings., hope that helps.

Ben

You definitely need an oscilloscope and probe around to find where the noise is being generated. If it's in the amplifier stage then it might be easier to repair. There are two LM regulators that come after the switch mode transformer, worth to check these. I would worry this sort of high frequency noise might be generated in the switch mode power supply itself though.

btyreman

Re: Neumann KH120A noise issue ...ANYONE?
« Reply #31 on: May 23, 2020, 07:35:40 PM »
ok I currently do not have an oscillope but may be able to get hold of one from a guitar tech friend, I do have a decent fluke multimeter though, I'd be willing to try changing out the caps, I noticed though that they all look fine physically, can they be gone and still look ok as in no signs of them bursting e.t.c? p.s thank for the help so far.


 

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