Mogami shielded wire, anyone else using it? Suggestions for in-chassis shielded wire?

[jmaf]

During some experiments here I've noticed that Mogami shielded wire still lets a lot of noise through. I've tested extensively getting the lead to a regular ~ 60x gain stage using a 12ax7 close to sources of noise, like diode bridges and the region near the power supply and it would still pick up a lot of noise.

I tried outdoor antenna cables which have the solid aluminum shield along with a braided shield and it is much much quieter, but these antenna cables are hard to work with, the lead breaks easily and they're clumsy...and not quite as classy as alternatives.

So I know there is an overkill solution which completely shields and I know there's another one in between which is quieter than non shielded cable but still picks up noise. Is there a better alternative?

I've used the Mogami cables for 3 years now, but I'm wondering if the community could suggest a better alternative for shielded cables that is not hard to work with, one where the leads don't break easily and it's still quiet. Thanks very much in advance for your feedback.

[Enzo]

The only time I personally use braided shield is when I want flexibility, as in a stage cord. Inside an amp or behind a rack - permanent wiring - I generally reach for foil shield with a drain wire. I grew up on Benden 8451, but generally use cheaper brands. Every wire maker makes the stuff. I have plenty now, but when I was buying a lot of wire and heat shrink, I used mainly Weico Wire & Cable.

Coax and jacketed wire tends to be just too fat and bulky inside a chassis, at least in my view. The foil stuff is a lot smaller.

I once got a roll of lavalier mic wire - the kind they use on wireless headset mics down to the belt pack. Very tiny and easy to work with. I used it inside things from time to time. I still have a hank of that in the wire pile.

And one of my cathartic exercises, when I need an uplift for my mood, is to tear down an old VCR or tape deck. I mean take out every single screw or fastener, and leave a pile of parts/junk sitting there. I wind up with a slew of metric screws, some tiny E-rings, a power cord, maybe a low voltage transformer, and on many of them, some small diameter shielded wire. The kind that run from the heads back to the boards. This stuff is easy to work with, and does not fight me when I put it in an amp chassis. Stripping down VCRs may not provide production quantities, but for those occasional uses, just the thing.

[clyde1]

I use Belden 9396, 25awg, slightly less than 1/8" diameter, nice and flexible.

[diagrammatiks]

shielded wire is hardly going to help in the situations you are describing no matter how thick or covered it is.

diode and power supply noise is inductive coupling.

[jmaf]

Enzo, thanks so much for the valuable tips. Curiously, I've quite a few pieces of VCR shielded cable from taking some old ones apart(it is a nice passtime isn't it ). I've tried them and they let a lot of noise through. I'm going for the foil ones now. I assume when you said Benden it's the same clyde1 suggested? Belden?

clyde1, thanks for the tip. searching I already found it at Mouser....will buy a few meters and test it.

[jmaf]

shielded wire is hardly going to help in the situations you are describing no matter how thick or covered it is.

diode and power supply noise is inductive coupling.

I wish I knew precisely what electrical phenomenon is happening when the cable is picking up noise. It's been 20 years since I saw Maxwell's equations.

When I flick the Mogami cable with my fingernail or beat it with a chopstick or something hard, it makes a loud noise on even a medium gain stage. I assume that's capacitive pickup? Can you ellaborate further on inductive coupling, is it due to the shield being wound around the lead? Thanks.

Correction: It's been 15 years since my days in Physics, not 20. I can use the extra 5.

[exclamationmark]

I once had to run an input lead all the way past a couple of gain stages, to the other side of the amplifier due to some *ahem* design choices. As you can imagine, it squeeled even with the gain on 0. Having no shielded cable handy, for a temporary solution I wrapped the lead in aluminium foil and grounded it. It actually worked! The funny part was when I decided to remove it and replace it with proper shielded cable, I found the al-foil wrap actually worked better... Shielded cable is black magic I tell ya!

I've had better luck with the coax stuff, but since it's relatively thick I only use it for the input and the foil stuff for tube connections.

[diagrammatiks]

shielded wire only decreases noise from high frequency rf sources.

It's good for decreasing noise from the input to the gain stages.

Noise induced from rectification, ac power lines, and heaters is low frequency and or voltage fluctuation induced.

you need twisted pairs. It's the same reason why shielding heater wires isn't that effective.

[Enzo]

Belden, not Benden, sorry, fat fingers.

I have not noticed much difference between brands of foil shield, so I used the Belden as a reference. You can find equivalent a lot cheaper.

[jmaf]

I once had to run an input lead all the way past a couple of gain stages, to the other side of the amplifier due to some *ahem* design choices. As you can imagine, it squeeled even with the gain on 0. Having no shielded cable handy, for a temporary solution I wrapped the lead in aluminium foil and grounded it. It actually worked! The funny part was when I decided to remove it and replace it with proper shielded cable, I found the al-foil wrap actually worked better... Shielded cable is black magic I tell ya!

I've had better luck with the coax stuff, but since it's relatively thick I only use it for the input and the foil stuff for tube connections.

The other day I was having a look at my older experiments(trying to clean up the place, actually). When I opened one I was surprised to find I had wound a tiny strip of aluminum foil around a lead from one gain stage, across the chassis. Sounds like exactly what you describe there! Looks like I had some leftover think aluminum foil from the chassis shielding and I took that strip and wound it around a lead... As I had a look at why I had done that, I thought exactly what you said "*design choices*".

[Enzo]

And the poor man's shield - even to be seen in some Fender amps - is a simple piece of wire wound around the shieldee. Wound like you were wrapping a pencil with wire to form a coil, then grounding one free end.