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I have a 1/2" 4-track tape machine that I am trying to hook up to a conventional stereo system. The machine has 4 xlr inputs and 4 xlr outputs. My stereo is mostly vintage tube stuff, the preamp is a Scott 130. I made a pair of cables to connect two of the xlr outputs to one set of stereo inputs on the preamp to listen to two of the tracks, but I am getting a significant buzz. I used some Radio shack 20-ft. cables, cut them in half and attached the xlr connectors. The negative wire is a braid wrapped around the positive wire, I guess making a pseudo shield. I attached it to pins 1 and 3 on the xlr connecter (they are shorted), positive to pin 2.
The sound comes through fine and sounds great, but there is a very clear buzz in the system regardless of which input is selected as long as the wires are connected and the tape machine is on. I am assuming this has something to do with joining pins 1 and 3, and I am wondering how I can make this connection without the buzz. Any help appreciated.
Dave
Follow Ups:
Dave,
If you picked up an aftermarket cable, Pins 1 and 3 are likely shorted together.
You may want to do the following:
1. remove the shorting jumper between 1 and 3.
2. use pin 2 for RCA ground and pin 3 for RCA hot or center pin. I do not know for sure, but I am going to guess that Sony (like the other Japanese pro manufacturers) used the traditional Pin coding for their XLR pins that was originated by Ampex in the US. Pin 3 = hot, Pin 2 = cold, and Pin 1 = ground.
Once you find out for sure which way your MCI is wired, I'd suggest your change it to Pin 2 being hot and Pin 3 being cold, since that is the method used now by almost all modern day pro gear.
Also if you want to make up your own cables, you can source all the materials you need from markertek dot com. They carry the Canare Star Quad and Mogami cables, and Neutrik XLRs with gold or tin plated pins.
Best
John
Thanks again for the further info, John. I made the cables myself, pins 1 and 3 shorted to negative, 2 to RCA positive (based on info I found on the net - I did see about the discrepancy between the pin systems but assumed the machine would fall within the mainstream).
I guess you are saying that on most older gear pin 3 was hot, on newer gear it's pin 2. The scheme would likely come from MCI rather than Sony, they weren't bought up by Sony I don't think until some time in the '80's, likely after my machine was built. Anyway, I'll see what the manual says when I get it.
In the mean time I'll try reversing 2 and 3 and see what that does (do you recommend still shorting 1 and 2 or leaving 1 disconnected?), someone else also showed me a schematic that involved some dividing resistors for the negative signal and a switch from the ground pin to take that in and out. The pin reversal is a little quicker so I'll try that first.
If the MCI is pin 3 hot, you're suggesting rewiring the xlr input and output jacks reversing pins 2 and 3, correct? Thanks again.
Dave
Dave,
you did not mention what brand of tape deck you have. Keep in mind some manufacturers used pin 3 as the hot and not pin 2. If you are connecting pin 2 to the hot center pin on the RCA, you could be sending an out of phase signal to your tube pre amp. That may also explain why you are getting the ground hum.
best of luck
J
Hi John,
It's an MCI JH-110B. I don't have a manual yet to know definitively about the XLR wiring I should have one in the next couple of weeks.
Dave
typical XLR type
> signals are +4 typical unbalanced signals are -10, once again, you
> need some type of active device to adjust this signal level difference
> there is also an impendence> difference in
> the signals, Balanced signals are typically 600 ohms, and unbalanced
> signals are typically 10-50K ohm.
Thanks for the replies, I'll try disconnecting the short.
The preamp has an input level pot so I can adjust the gain, and it isn't a problem.
Dave
Try using pins 2 and 3 and leave 1 open
Or try using pins 1 and 2 and leave 3 open
What have you to lose
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