Neumann KH 750 - BNC connector repair

[chaptervaudio]

Hello everyone!

Although I’ve been lurking around this forum for years, this is my first post here. I'm really sad that this has to be my first thread, but I need some help in case anyone knows.

I have a Neumann system consisting of a pair of KH120 and a KH750 subwoofer. The connection between my RME interface and the Neumann KH 750 is digital, using the BNC input connector of the subwoofer.

A couple of days ago, I disconnected the BNC cable from the subwoofer, and the hot pin of the BNC connector on the speaker panel was removed. Attaching 2 photos below.

I contacted Neumann for technical assistance on how to properly desolder and remove the damaged connector, but they informed me that they cannot provide details about it. Instead, they asked me to send the subwoofer for a full board replacement and a speaker recalibration in their labs. I’m quite impressed that a single BNC connector requires all this.

I’m curious to know if anyone has experience repairing a Neumann KH 750 speaker. Have you ever disassembled it? If so, do you have any tips or advice on the process?
I’m particularly interested in knowing if the BNC connector can be easily desoldered or if it’s somehow attached in a specific way on the board or the panel and requires the removal of the entire board.

I’d like to weigh all the options before sending it for a repair that will likely cost at least half of the speaker’s value.

Thank you in advance!

 

[somebodyelse]

I contacted Neumann for technical assistance on how to properly desolder and remove the damaged connector, but they informed me that they cannot provide details about it. Instead, they asked me to send the subwoofer for a full board replacement and a speaker recalibration in their labs. I’m quite impressed that a single BNC connector requires all this.

There's a difference between necessary and cost effective. The technician time to strip, replace the connector, perform a battery of tests to ensure it's working to spec then reassemble may cost more than simply swapping out for a known-working replacement.

 

[staticV3]

OTOH, for an experienced board repair technician, swapping the connector out is likely a trivial job of a few minutes at most, if the connector is publicly available as replacement part that is.

 

[LTig]

One could try to reinsert the pin, maybe it works. At least it costs nothing.

 

[wwenze]

One could try to reinsert the pin, maybe it works. At least it costs nothing.

This.

You can just stuff the pin back in.

 

[chaptervaudio]

This.

You can just stuff the pin back in.

View attachment 509026

I owe you a beer! Thanks so much for this. Fixed it yesterday night.

 

[chaptervaudio]

OTOH, for an experienced board repair technician, swapping the connector out is likely a trivial job of a few minutes at most, if the connector is publicly available as replacement part that is.

The connector is a simple vertical BNC connector and PCB-compatible. What concerned me most was how they have attached the PCB to the back panel. There’s a (glued?) foam-like material between the board and the panel. I might be mistaken since I didn’t have much time to inspect it, but unsoldering and removing the connector felt more complicated than usual because the connector looks tucked in this material.

However, I managed to fix it by following the graph that wwenze posted!

Thanks for your input anyway!

 

[dfuller]

I contacted Neumann for technical assistance on how to properly desolder and remove the damaged connector, but they informed me that they cannot provide details about it. Instead, they asked me to send the subwoofer for a full board replacement and a speaker recalibration in their labs. I’m quite impressed that a single BNC connector requires all this.

I've spoken to Neumann directly in person about this, it's a liability thing more than anything else - the boards also have power supplies with dangerous voltages present, so they don't want someone to hurt themselves and then get litigious.

 

[Taker]

Can I ask you what cable do you use to connect the Rme to the 750kh ?
I have a similar system but use the analogs instead .
Thanks in advance

 

[LTig]

I use a DIY cable (RG59) with RCA plugs and an RCA-BNC Adapter on the KH750 side. For short distances any RCA cable should work.

 

[chaptervaudio]

Can I ask you what cable do you use to connect the Rme to the 750kh ?
I have a similar system but use the analogs instead .
Thanks in advance

I made the XLR cable using a Mogami 110 Ohm cable with Neutrik connectors.
The XLR cable connects to a Neutrik NADITBNC (recommended in the Neumann user manual) for impedance conversion.
Then a Sommer BNC 75 Ohm cable is used to connect to the subwoofer.

RME AES XLR OUT ---> XLR 110 Ohm ---> Neutrik NADITBNC ---> Sommer BNC 75 Ohm ---> Neumann KH 750 BNC IN

 

[Taker]

Thanks for the reply’s and sorry to hijack this thread .
Was reading the manual and if I connect the Adi 2 pro AES out it bypasses the optical in/out. The system will no longer be in sync so i can only use the analog outs .

 

[markstein]

Thanks for the reply’s and sorry to hijack this thread .
Was reading the manual and if I connect the Adi 2 pro AES out it bypasses the optical in/out. The system will no longer be in sync so i can only use the analog outs .

Hi, all digital outputs should be connected in parallel if I read the manual correctly.

 

[Taker]

Hi, all digital outputs should be connected in parallel if I read the manual correctly.

View attachment 509801

Does this means I can have both “Optical” and the “AES” working ?

Adi 2 pro is my Ad/Da to monitors and I confess if 750kh connected digital would sound any better than by Analog because one less conversion step .

 

[chaptervaudio]

Does this means I can have both “Optical” and the “AES” working ?

Adi 2 pro is my Ad/Da to monitors and I confess if 750kh connected digital would sound any better than by Analog because one less conversion step .

Normally yes, but since I don't have any experience with ADI2 ( my interface is RME 802), can you share a link so I can check the manual, too?

Btw, not sure how audible is the extra conversion step, never did an actual comparison, but it's really convenient to run the signal only through one cable.

 

[Taker]

Yeah , sure :

https://rme-audio.de/downloads/adi2profsr_e.pdf

Yes, never saw anyone commenting about it

 

[LTig]

Btw, not sure how audible is the extra conversion step, never did an actual comparison, but it's really convenient to run the signal only through one cable.

I couldn't detect any difference in sound quality between analog output and SPDIF out.

 

[Taker]

I couldn't detect any difference in sound quality between analog output and SPDIF out.

Probably there isn’t , manny thanks for sharing your experience