cyrus 1 or two ribbon cable

keland

Member
2019-09-25 12:16 am
cambridge
Hi, I'm fixing the hum on a 2nd hand Cyrus one and not liking the ribbon cable that connects the phono sockets (5) to the input/output switches at the front via a "dodgy" ribbon socket(1). I'm not asking about hum problems here, just what is good practice for internal amplifier wiring.....



Its a twelve way ribbon connecting to 5 pairs of phono sockets(2) only two go to the earth planes around the phono connectors (marked as 3 on 2nd photo, which I also believe is a photo of the Cyrus 2 Signature edition where they removed the ribbon cable and put links on the underside.
Mission Cyrus 2 Signature edition info request


Photo 3 is a mod where some has used "Sommer Cable SC-Albedo MKII" to connect to just 3 phono sockets (looks like same cyrus 1 board, but different box (Inca Tech Claymore)) Cyrus One Power Caps - Bypassing Advice | Rock Grotto


1) Hard to tell from the photo 3 but I suspect that he has used the twisted pair in the cable to connect to earth on the back chassis (ie one connect one end of shielding, and the other twisted pair to the respective left and right channels. Is it good practice to only connect one end of the shielding to earth?


2) I was going to use Cat 5 twisted pair, but after discussing it RJM audio (Richard Murdy) he thinks that each channel should have a separate earth around it which considering there are only two earth points would be a bit of a mess as he says "is the ribbon cable such a bad idea after all?" So got me thinking why not use some shielded Cat 6 cable, connect one end of shield to convenient earth and use a twisted pair for each set of inputs. Or is that just plain silly:)



3) Or should I just hardwire on the back as per 2nd photo of signature edition?

 

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I can't give you "Best Practices", but "Better Practices" is certainly doable.

You will need:
* Wire of a decent cross-section that still isn't a total pain to work with
* Thin, preferably flexible audio coax (scavenge some from old run of the mill RCA cables if need be)
* A cutter, scalpel or similar scraping utensil, next to the implied soldering iron, flux etc.

1. Run wires (blue) from star ground to convenient central attachment points at (a) shared ground for 4 stereo inputs (which is being used as a sub-star) and (b) tape out ground.
2. Run coax (yellow) from each jack (both signal and ground), leave open at other end. Not all shown.

Ideally, blue ground wires should be run among yellow coax to minimize inductance, much like the original cable. Twisting L and R channel coax and bunching up the 4 pairs may not be a bad idea, assuming this doesn't result in a major mess that won't fit.

Optional: Connecting open shield ends to ground via a few nF each... but I guess it'll be messy enough as-is.

Twisted pair is kinda "eh" for unbalanced audio wiring. You can use a shielded twisted pair as makeshift coax with the two inner conductors connected, but it'll probably have higher capacitance. Still worth a shot if you have network cable that's built like that, but Al shields may be virtually impossible to solder.
 

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