Neumann KH120A noise issue ...ANYONE?
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moamps
Well-known member
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.
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.
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moamps
Well-known member
pvision said:
Do you have any information what the fault was and what they replaced?
moamps said:
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
Well-known member
moamps said:
No and no
Nick Froome
moamps
Well-known member
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.btyreman said:
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
Well-known member
Thanks.pvision said:
moamps said:
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.
btyreman said:
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.
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.
here's a higher detailed photo of it, there are 4 small caps you missed out moamps as well as a huge brown one, was wondering if it's worth replacing them as well? were these deliberately left out? I have marked out the ones you mentioned with red and blue marker pen, thought I'd post before going ahead and removing them.
regards,
Ben.
regards,
Ben.
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I managed to take all the caps out, blue and red that was mentioned, just waiting on the replacement parts to arrive, the silicone was tricky to remove,
I cleaned away as much old solder as possible using copper wick,
the caps for both speakers cost me almost exactly £40, which isn't much considering,
will update with more progress pics soon.
I cleaned away as much old solder as possible using copper wick,
the caps for both speakers cost me almost exactly £40, which isn't much considering,
will update with more progress pics soon.
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scott2000
Well-known member
If you know anyone with an LCR meter you could check those removed caps just to see if they've gone off. I suppose an ESR meter would be great to check them in this scenario as well...
the right speaker is re-capped all the red and blue ones, and it's working perfectly again, no noise whatsoever! even when you put your ear right up to the speaker, silent, exactly as it was brand new, I have the second speaker board to re-cap, thanks in particular to moamps., will report back to let you know if that works as well, this has saved me a lot of money, I'm very happy.
That's great news!
Out of sheer curiosity, any chance you could post a photo with the removed stock caps, from either speaker? I'm mildly curious what brands and series they used (in these eyewateringly-priced monitors)...
Out of sheer curiosity, any chance you could post a photo with the removed stock caps, from either speaker? I'm mildly curious what brands and series they used (in these eyewateringly-priced monitors)...
btyreman said:
