Microphonic wire?

[johnnyreece]

Hey, all! I ran into something interesting on a build I'd done a while back. The guy who bought it said he was running into some intermittent noise issues, which I have not been able to duplicate. However, I found something interesting: All of my preamp grid wires seemed to be microphonic. Specifically, when I ran a chopstick up and down it, I got a static-like crackling sound. It's the Weber Teflon wire. I've never had issues before, but I've not really paid this much attention to that specific kind of thing. I went ahead and put some weather stripping in certain places to keep the wire from bouncing around. Anyone else ever have this kind of issue?

[Stevem]

Yup, 100% normal for the first gain stage!
Hook up a big 1" diameter flat Ciramic cap across it instead of a input Jack and you can talk right into it like a old time crystal Mic!

[rp]

There's some talk that PVC is less microphonic, in as much as the thicker softer jacket dampens a bit vs hard thin teflon when right against the chassis. A bit like using silicon tube rings. Maybe this was why KF preferred PVC? I buy it, I've noticed chopsticking teflon makes more noise at least at the input. I would use PVC happily but it's no good for imperfect builders/tweakers. Looks like hell after a few goofs/mods melts it all up.

[johnnyreece]

I somewhat expected it on the first gain stage, but all three grid wires were microphonic on the first two tubes...Maybe I'll try a different brand. It'll give me an excuse to see what goodies I can pick up from Steve at Apex Jr.

Any thoughts on whether stranded would be better/worse? I like using solid core, because it stays where I put it.

[Leo_Gnardo]

Hook up a big 1" diameter flat Ciramic cap across it instead of a input Jack and you can talk right into it like a old time crystal Mic!

but it's true...

Yes I've found on rare occasion a length of wire that's either microphonic itself, or acts as a spring and sets off midrange ringing effects in a tube it's attached to. I can pluck the wire and hear "doink doink doink" noises like Tweetybird picking hairs off of Sylvester's nose. (A sound effect that was probably done by Fender's Freddy Tavares.) Swapping in a floppier piece of wire, stranded with plastic not Teflon insulation fixes the problem.

[martin manning]

This may be where the "different wire sounds different" hoodoo comes from.

[Bob S]

Get the best of both worlds. Stranded, pre- tinned Belden.
I think it's Belden J TEW. Stays put & has a 105 Celsius rated coating.

[jjman]

I had a short microphonic wire in the reverb circuit of my SFDR. It would cause feedback and noise.

[johnnyreece]

I can pluck the wire and hear "doink doink doink" noises like Tweetybird picking hairs off of Sylvester's nose. (A sound effect that was probably done by Fender's Freddy Tavares.) Swapping in a floppier piece of wire, stranded with plastic not Teflon insulation fixes the problem.

Yes, this is one of the noises I could get it to make! I think I may give this a shot.

[Structo]

In the past I have used silicone, zip ties and other anchor points to minimize microphonics in the preamp.

When I got back into tube amps a few years back, the first thing I heard was using a chopstick or other similar item to troubleshoot an amp.
I would tap, poke and move things around in the preamp.

Well I thought it was all screwed up because just about anywhere I tapped made a noise through the speaker!

So yeah, it's pretty normal for the preamp to do that.

[rp]

Well I thought it was all screwed up because just about anywhere I tapped made a noise through the speaker!

Tubes suck, no wonder they were abandoned.

I'll tap the chassis an inch from the wire then the wire to see if there's a difference, and teflon is definitely worse than pvc. Cloth might be good, I never tapped around the wires in old Fenders. The modern stuff is cloth around pvc so it might be very good here.

I've done goofy things like running the wire through tiny rubber grommets as standoffs, touch of silicon to hold the grommet to the chassis. I've even put large grommets around coupling caps as damping, with ptp a cap floating across a long distance is pretty boingy (though I never heard it through the speaker). In the end I always pulled the kluges, looked too desperate. This stuff never bothered Fender or Marshall, much less Silvertone, Valco, Thomas Vox, so I'm not going to bother much either.

[johnnyreece]

Thanks again for all the feedback. I've previously been aware of tapping certain areas/wires that would make sounds in the speaker, but this was the first time I was able to pick anything up by just rubbing the wire with a chopstick (which induced a weird static-like noise). I resoldered the joints and everything, to no avail. I'm not saying I'll never use this stuff again, but I'm definitely open to experimenting with other sources/types to see if I can minimize the noise.

[vibratoking]

...this was the first time I was able to pick anything up by just rubbing the wire with a chopstick (which induced a weird static-like noise).

This sounds something like the pick guard static problem that is pretty well known. Could be that Teflon jacket is storing charge on it.