Hello,
I have a SqueezeBox that has unbalanced RCA/phono/cinch sockets on it and have bought some KRK VXT4 active speakers with balanced XLR Combo (accepts 1/4" TRS/Jack plug).
I need to make two cables. From what I've read screened interconnects are a good thing in noisy environments so I'd like to build two screened interconnects.
KRK's advice is two connect pins 1+3 (ring and sleeve) at the ^source end^ (at the SqueezeBox.) This suggests, to me, using 3 cores + a screen. Two cores going to the ground on the RCA and the third to the live pin.
1st question: Is this overkill? Should I just join pins 1+3 at the XLR/TRS or is the 'wasted' core useful?
I've attached a 'diagram' of what I mean. Are the two options equivalent in term of audio quality?
From:
http://wiki.slimdevices.com/index.php/Balanced_Power_Amps
Slim Devices advice on wiring includes:
connect the screen of the interconnect to the ground at the source end. This will shunt the Squeezebox's ground to earth via the power amp's ground.
and:
But there is an added subtlety. Some balanced power amps don't have the screen of their XLR inputs connected directly to ground. (For example, the power amps in my ATC speakers have a 47 Ohm resistor between pin 1 of their XLR inputs and ground. I don't know why this is so - I'm not an amplifier designer, but I'm sure ATC have good reasons for including it). So connecting up the screen at the Squeezebox end only establishes a partial shunt to earth. The hum is reduced, but not eliminated. The solution here is to connect the ground plane of the Squeezebox to the mains earth - preferably the same one used by the power amp. I used the screen of the Squeezebox's COAX SPDIF output, which was not in use in my system, for this purpose.
2nd question: How dumb is connecting the screen/ground of the SPDIF to the earth of a 3 pin plug AND plugging it into the wall? Sounds dangerous to me.
Thanks for any advice,
Owen.
I have a SqueezeBox that has unbalanced RCA/phono/cinch sockets on it and have bought some KRK VXT4 active speakers with balanced XLR Combo (accepts 1/4" TRS/Jack plug).
I need to make two cables. From what I've read screened interconnects are a good thing in noisy environments so I'd like to build two screened interconnects.
KRK's advice is two connect pins 1+3 (ring and sleeve) at the ^source end^ (at the SqueezeBox.) This suggests, to me, using 3 cores + a screen. Two cores going to the ground on the RCA and the third to the live pin.
1st question: Is this overkill? Should I just join pins 1+3 at the XLR/TRS or is the 'wasted' core useful?
I've attached a 'diagram' of what I mean. Are the two options equivalent in term of audio quality?
From:
http://wiki.slimdevices.com/index.php/Balanced_Power_Amps
Slim Devices advice on wiring includes:
connect the screen of the interconnect to the ground at the source end. This will shunt the Squeezebox's ground to earth via the power amp's ground.
and:
But there is an added subtlety. Some balanced power amps don't have the screen of their XLR inputs connected directly to ground. (For example, the power amps in my ATC speakers have a 47 Ohm resistor between pin 1 of their XLR inputs and ground. I don't know why this is so - I'm not an amplifier designer, but I'm sure ATC have good reasons for including it). So connecting up the screen at the Squeezebox end only establishes a partial shunt to earth. The hum is reduced, but not eliminated. The solution here is to connect the ground plane of the Squeezebox to the mains earth - preferably the same one used by the power amp. I used the screen of the Squeezebox's COAX SPDIF output, which was not in use in my system, for this purpose.
2nd question: How dumb is connecting the screen/ground of the SPDIF to the earth of a 3 pin plug AND plugging it into the wall? Sounds dangerous to me.
Thanks for any advice,
Owen.
Attachments
Gosh, a namesake, and in the midlands... 😀
Now to your question.
I'd build the recipe as follows. Screened dual core cable (standard balanced cable) - One core to the ground (and the screen to ground), and the other to the center pin on the RCA.
If you want to get the most 'noise rejection', then the main length of interconnect will need to be balanced in operation - this can be achieved using some 600:600 transformers.
High Performance PCB Mounting AF Transformers
http://www.maplin.co.uk/Module.aspx?ModuleNo=46782.
Wire up one side with an RCA pigtail to plug into the SB, connect positive, ground and negative to the output from the transformer +, center-tap and - respectively.
Presto, one unbalanced to balanced link. This could be build in a project box, sweet tin, etc etc.
Any questions, then drop me a line.
Hope this helps
Owen
Now to your question.
I'd build the recipe as follows. Screened dual core cable (standard balanced cable) - One core to the ground (and the screen to ground), and the other to the center pin on the RCA.
If you want to get the most 'noise rejection', then the main length of interconnect will need to be balanced in operation - this can be achieved using some 600:600 transformers.
High Performance PCB Mounting AF Transformers
http://www.maplin.co.uk/Module.aspx?ModuleNo=46782.
Wire up one side with an RCA pigtail to plug into the SB, connect positive, ground and negative to the output from the transformer +, center-tap and - respectively.
Presto, one unbalanced to balanced link. This could be build in a project box, sweet tin, etc etc.
Any questions, then drop me a line.
Hope this helps
Owen
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