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using XLR balanced cables and plugs into and out of an unbalanced single v25 board  


Posts: 10
Customer
(@david-woodward)
Member
Joined: 5 months ago

Hi all

Keen to help get this new forum going 😉

As I await my delivery of a bare board and OLED, I am planning the project. I have a nice chassis (old refurbished Mission Cyrus 1 amp, they don’t make cases like this anymore!)

I am feeding the pre with a DAC that has balanced out, and a phono set from my turntable phono amp. The pre then outputs to a DBX Venu 360 to do digital crossover into two sets of power amps to drive a pair of hybrid ESLs. 

I like XLR plugs from an engineering standpoint and have all the necessary balanced quad core cables, so don’t really want to rip them apart to make a balanced to RCA cable. I have decided to not go for a dual v25 rig, as I don’t really see the added value nor fancy the complication of squeezing it all into the Cyrus. I am cheap too 😉

So my plan is to wire the XLR sockets and plugs in the amp to treat them as single ended. 

 

There are many views on how best to achieve a balanced out to unbalanced in and unbalanced out to balanced in. My research based on this site https://crookwood.com/blog/dealing-with-unbalanced-gear-in-the-studio/ leads me to the following plan, though I have to confess the more I think about, this more confused I get. Especially as what I am doing is a little different, in that I am trying to preserve standard XLR cables and get the right result by correctly wiring up internally. The DAC is a Chord Hugo TT, metal chassis with wallwart DC power (not sure if that makes it a floating or mains earth, I am guessing floating) The DBX is a pro unit with earthed mains in, so I am assuming this is a mains earthed unit. It also has a pin lift that can help with earth loops)

Please let me know if you agree or have a better suggestion.

For the input from the balance cables from the DAC

Internally within the amp, wire the hot pin 2 to the board, connect pin 1 and 3 together and earth on the chassis, or should the earth be taken from pin 1 and 3?  

For the output from the pre to my DBX, wire the signal +ve out to pin 2 again, and again connect pin 1 and 3, wire this to the -ve output signal.

Any help would be gratefully received

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Posts: 24
Admin
(@morten)
Member
Joined: 9 years ago
Posted by: @david-woodward

Internally within the amp, wire the hot pin 2 to the board, connect pin 1 and 3 together and earth on the chassis, or should the earth be taken from pin 1 and 3?  

For the output from the pre to my DBX, wire the signal +ve out to pin 2 again, and again connect pin 1 and 3, wire this to the -ve output signal.

 

Treat pin 1 as the ground and pin 2 as the signal. You could tie pin 3 to ground (pin 1) but in my view you could simply leave it as is – an unused wire in the cable. You should check how your cable handles the XLR shell/plug. Some are tied to pin 1 internally and some are not. Some XLR sockets tie the socket shell to pin 1 and some do not. Best to be aware of that to avoid surprises. 

The worthwhile resource on XLR cabling is the website pin1problem.com    Yes, that’s right, a website dedicated to the “pin 1 problem” with balanced XLR cables. It pulls together various resources on this topic. Some of the links may be broken but most work. 

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