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Using coax cable for interconnects

jlc280z

jlc280z

New Member
Repaired a Phase Linear 1000 II last week. Yesterday the customer complained about "noise" when the autocorrelator is on. Sure enough I went over to his house and it is making the weirdest noises I ever heard. changes pitch and volume when adjusting the correlator knob. Get it on the bench and there isn't a bit of noise hooked up to my equipment! what goes?
Found out he is using coax cables with RCA plugs on the ends. It seems that might put excessive loading on the output op-amps. I am going to try to replicate the problem with some coax cables and see what happens.
I think it is not a good idea to use low impedance coax with audio signals, but maybe that is not the problem.

any thoughts on this ?

thanks..
 
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Uhm, maybe you have a different definition of coax cable that I do, but the majority of RCA termininated audio interconnects uses regular coax cables (at least as I'd define coaxial), so I wonder what you might mean?

Greetings from Munich!

Manfred / lini
 
I have used flexible RG-58 in the past for interconnects, but once I started using dedicated cables designed for the job I realized the RG-58 was not doing the job. Now I use Blue Jeans Cables exclusively.
 
RG-62, though hard to bend, makes a very good low capacitance interconnect. Not sure about RG-58, but it's hard to believe any normal coax would be much different than most audio coax in terms of loading or stability. I'm betting either there's something really strange with the particular cables, or there's some other RF pickup or grounding problem.
 
I use Belden 1505A which is a RG59 with a 20 gauge center versus the 22 gauge in the 9259. It is available in a variety of colors, works for digital with 75ohm connectors and as others have noted, has low capacitance. I use basic nickel plated Steren crimp on connectors.
 
Splat has been using component video cable for audio for a few years now. Works great - just peel off one of the three and enjoy.
 
AvFan said:
I use Belden 1505A which is a RG59 with a 20 gauge center versus the 22 gauge in the 9259. It is available in a variety of colors, works for digital with 75ohm connectors and as others have noted, has low capacitance. I use basic nickel plated Steren crimp on connectors.
Click to expand...

Belden 1505F is the high flexibility version. Blue Jeans has it.
 
was just going to say that BJC uses straight up coax for their interconnects, save for LC-1 which is built to their specs for audio but is, essentially, coax. So I'm not sure what the problem is with your customer's system but either his homemade interconnects are just bad or there's something else going on.
 
In common usage, "coax" means cable that is designed for radio frequency work. Intertwined braid shield and copper or silver plated inner conductor, and dielectric insulation between the two selected for low loss at radio frequencies.
 
In the case of the RG-58 I was using it was the high grade stuff I use with my hamradio gear. The problem I was having with the version I was using is it had a double shield, copper braid outer and a 100% aluminum shield on the inner foam insulator. It was a royal pain to strip the inner foil off the center foam, and the foam it's self in the tight confines of an RCA plug was a nightmare, it would melt and contaminate the center pin soldering job. With BJC I stopped wasting the coax for my radio station on stuff it was not designed for. For those interested my source for coax such as RG-58 is The Wireman and has been for most of 20 years. For this group perhaps the product they carry that would have the most use is braided copper in a number of width for grounding straps. they also have everything you need to build wire antennas should you need one. Great place!

For those of you with Dish Network, or Direct TV if you want to get ambitious make up a set of cables for it using good quality copper conductor coax. The stuff the installation tech's use is the cheapest aluminum cable, and crimp on connectors, they can get their hands on. It does make a difference.

https://www.thewireman.com/
 
There is definitely a difference in cables. The "best" expensive cables cause it to oscillate, while the cheap type don't seem to cause it. I have one of the cables that caused the problem for the owner, but they work fine plugged into my Carver 900 receiver. He was using a Pioneer receiver and some other equipment. Will have to try some Pioneer amps and receivers I have and see what happens.
 
The impedance of the cables only matters at RF frequencies. If he is using RG-59 which is the elcheapo cable for RF, it does not matter up to about maybe 8 MHz. nobody's eaars are golden enough to hear that.

However, lot of the varieties of this cable are aluminum shielded to which you cannot solder. Most have a stranded braid around them as well but that could be aluminum. If so, he cannot get a good ground.

You might have a situation where he has a whole bunch of shitty grounds and the thing is forming an ersatz antenna.

Why is he using those cables, does he think them better ? Or is a cheapness thing ? I mean like he is running 100 feet and those audio cable would break the banks ? If it is a cheapness thing or not, look at the fittings. For RF coax like RG this or that, you get connectors that squeeze the outer shield. there should be standard, crimped for real (not screwon) connectors then adapted to RCA or whatever he needs. If he needs XLR he should just buy XLR cables. I know RCA has its limitations.

Hell you might have to get ahold of a sheetmetal brake and make a little box with F connectors and RCA jacks on it to make this right. but the problem there is you need this on the other side as well. so adapters are the way to go I say.

Who knows. Bring in more info when you screw with this more. Everything is figuroutable. Might take a minute though. I would definitely go to the venue and try some other type of cable. That might solve it right there.
 
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