Remote control panels - best practices

[xtian]

I'm going to break this out of my earlier thread. I'm having a tough time moving my Volume, Tone and Reverb Mix controls off the chassis and 24 inches away to a control panel without introducing hum, even with all shielded (RG-174) wire.

What are best practices for remote control panels?

[JazzGuitarGimp]

I'm going to break this out of my earlier thread. I'm having a tough time moving my Volume, Tone and Reverb Mix controls off the chassis and 24 inches away to a control panel without introducing hum, even with all shielded (RG-174) wire.

What are best practices for remote control panels?

When I saw the photos in your other thread, I wondered about this. My gut feeling is, unless you can substantially lower the impedance of the connections between the control panel and the amp chassis, you're going to have some hum. I think all the pots want to be much lower in value, but how do you do this when you're interfacing with high-impedance tube circuits? If you used a cathode follower before the control panel run, that would be a good start, perhaps. Just thinking out loud here....

[Leo_Gnardo]

I'm going to break this out of my earlier thread. I'm having a tough time moving my Volume, Tone and Reverb Mix controls off the chassis and 24 inches away to a control panel without introducing hum, even with all shielded (RG-174) wire.

What are best practices for remote control panels?

If your shields are grounded at both ends, could be you're setting up ground loop(s). Run a separate wire to carry ground and attach the RG174 shields at only one end - I'd pick the amp end. Also make sure your panel is grounded too. OR if that's impractical, run the shielded cables only to the controls and a separate ground wire to the panel. Goes w/out saying to keep all the wiring away from the PT. You knew that...

[JazzGuitarGimp]

Another thing I would look at, is the potential of ground loops caused by the multiple runs of coax to the control panel. I would ground both ends of only one of the coax runs. All the others should be grounded at one end only.

[DonMoose]

You could also use a cover on the back of that ctl chassis (if you don't already).

The amps I'm familiar with that have controls remote from the power amp, all have the preamp in the control chassis (old ampegs, current fender excelsior, and so forth).

One braided gnd connection (coax shield would count) between the two chassis. Other shields grounded at one end only - as almost everyone else here has suggested.

[xtian]

If your shields are grounded at both ends, could be you're setting up ground loop(s). Run a separate wire to carry ground and attach the RG174 shields at only one end - I'd pick the amp end. Also make sure your panel is grounded too.

Already done, as detailed.

Panel is grounded to pots, pot backs grounded to wire, wire now runs to shield on Mogami guitar cable, then to chassis main star ground point (which is the only ground point on the chassis, other than the Earth safety ground).

In this config, as I mentioned, hum is acceptably low. I'll proceed one step at a time when I add more controls.

So, thanks, guys, for trying to solve the problems with my Stout, but I was actually just asking about best practices, like driving the panel controls with a cathode follower.

[JazzGuitarGimp]

I just looked at your photos again, and I notice you've bundled the wires of the on-off switch with the audio-carrying coax cables. Are those two wires to the switch carrying 120VAC, or a low-voltage DC for a relay coil? If they are carrying AC, I would keep them away from the coax cables by at least 6". Shielding isn't absolute. Some shielded cables are better than others but even with the best, I would not advise bundling with AC wiring.

[xtian]

I just looked at your photos again, and I notice you've bundled the wires of the on-off switch with the audio-carrying coax cables. Are those two wires to the switch carrying 120VAC, or a low-voltage DC for a relay coil? If they are carrying AC, I would keep them away from the coax cables by at least 6". Shielding isn't absolute. Some shielded cables are better than others but even with the best, I would not advise bundling with AC wiring.

Thanks, Lou. Mentioned that in my last post with the photos. You're right; those 120vac lines caused a lot of hum. Right now the power switch is disconnected.

[Tillydog]

I was actually just asking about best practices...

As has been said, make one, and only one connection between the metalwork of the remote box and the main chassis. Make this where the connections leave the chassis - not at an internal ground point. This also acts as your safety ground, so use something substantial.

Signal wires should be sceened, but with the screen connected at one end only, to the same place where the cables leave the chassis as the interconnecting gound is connected. Don't use screens for ground returns.

Don't run the "ground" wires of any controls to the metalwork in the remote panel, or the interconnecting ground wire. Treat the "ground" connections from the pots as signal wires and run them individually back to the correct place on the turret board in the main chassis - you may be able to use 2 or 3 core screened cable to keep all 2 or 3 wires from any single control together and make things a bit neater. By extension, there shouldn't be any common ground connections in the remote panel.

Watch out for the capacitance of the screened cables - you will lose high frequencies if you use enough of it / mediocre quality.

You may be able to get away with breaking some of these rules, but you won't know until you try!

Aside: I once got the job of developing a 'production' version of a strain gauge amplifier, DAC, etc. for a company who'd employed an Indian PhD to construct the prototype. Sounded fine on paper, but the prototype was a mess and didn't actually work properly. I was lectured by the PhD on what parts I needed to specify to improve the pretty mediocre performance he'd managed to wring out of some high quality kit. I re-wired it using correct grounding practice, as outlined above and it worked just fine (you could barely tell it was switched on, noise wise). He point-blank refused to believe that it was the same kit, accused me of tricking him and demanded I tell him exactly what I'd changed (much of it was removing the "extra" grounding connections he'd added between random places to try and get rid of the noise). He took it as a personal insult that I'd made it work better than he could and became quite unpleasant. As the project would nean working with him for a few months, I got my money for the work done to date & told the company to **** off! /aside