Beolab 9 - 3rd party preamp, proper way to wire DIN to Cinch?

2 replies
EP
Eric Peters
Bronze
40 posts
Posted January 7, 2019 at 10:07 GMT
#2116845

I'm a happy owner of a pair of Beolab 9 which I have connected to a 3rd party preamp using Steve's Cinch to Powerlink cables.  However there is a constant light hum in the speakers independant of the source used or volume level in the pre amp. The hum stays present if I disconnect the cinch cable from the pre-amp, but it disappears when only the cinch ground is connected to the pre amp's signal ground. This makes me think that the hum is caused by improper earthing of speaker and because an ICE amp is balanced by design and with all other balanced amps the signal minus should be separated from the actual ground. 

When using a B&O source the service manual of the B9 clearly states that MK3 powerlink must be used because of the extra data ground on pin 7. 

In cheaper pre-amps, data ground and chassis ground might be connected in better pre-amps this is not the case. In the service manual of the Beolab 9, B&O writes that the cable to be used with the Beolab 9 and 3rd party pre-amp should be "semi balanced” and as far as I know this means that there should be a “+" signal, a “-“ or “0” signal and a separate ground which should be connected to the chassis ground of the pre amplifier. (This is probably because all ICE power amplifiers are balanced by design) 
In the Beolink handbook the Powerlink MK3 shows clearly separated data gnd and signal ground (double shielded cable) but the adapter cables show a connected pin 7 and pin 2, but there is no where mention of connecting to a Balanced out pro amp.
Has anyone every tried this cable set-up. So the Cinch+ to the left or right signal+, the Cinch ground connected to the signal ground in the din plug and the Data ground (pin7) connected to a separate wire which is connected to the chassis ground on the pre amplifier?
Alternatively, because the ICE amplifier is a balanced design, has anyone ever connected the Beolab 9 to a pre-amplifier with a balance output? In this case I assume that: Pre + connects to signal +(pin 3 or 5) ,  Pre - connects to signal gnd 9 (pin 2)  and pre-amp "0" is connected to data gnd (pinm 7)?
Has anyone tried these options and do they solve the hum problem?

 

 

Steve at Sounds Heavenly
Steve at Sounds Heavenly
Gold
2501 posts
Posted January 7, 2019 at 14:43 GMT
#2116846

Hi Eriperi,

Thanks for your purchase from my store, I am sorry to hear that you are having problems.  There should not usually be any audible hum when using the Beolab 9 speakers with a good quality pre-amp, so this sounds as though the noise may have been induced into the wiring by nearby electrical equipment, or by an issue affecting the pre-amp.

Beolab 9 speakers have an unbalanced (single-ended) audio input, so they work best when used with the unbalanced output of a B&O system or pre-amp (in this case via RCA pre-out sockets).  My cables are correctly wired for this purpose, with the extra grounding pin added (pin 7) for the case of the ICE Power amplifier in the speaker.

I will email you directly to confirm the model number of your pre-amp and to help you to resolve this issue for you.

Please feel free to get in touch if you have any questions in the meantime.

Kind regards, Steve.

Location: The cable workshop, England

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