Tracking down a ground issue - ACG01 preamp

[kesslari]

Zon bass, ACG-EQ01 preamp, with an external power supply built by our own @Jeff Scott. This system has worked flawlessly for many years - 8 or 10 or so.
I have an email in to Alan and John East, but meanwhile, this is a head-scratcher. And of course, there were multiple issues to be debugged... I didn't get to the ground issue until last, and now I'm stuck.

I got back from vacation, fired up my bass, and had a definite high pitched buzz.
Different amp - same.
Different (passive) bass - same.
Different cables - same.
I checked the quality of the outlet - good.
Swapped out the power cable - problem solved with both basses.

But... with the Zon/ACG, now I have what I believe to be a ground problem.
Untouched, the bass is quiet.
If I touch the strings, I get a low buzz.
If I also touch the (metal) jack, the buzz goes away. Same thing happens with a different cable. It does not happen with the passive bass.

The wiring looks OK. What am I missing or what should I look for?

 

[eniac]

If I were troubleshooting the problem, I'd begin with the following:

1) Take end-to-end resistance readings on both power cables' three conductors

2) Take resistance readings across all the BG's ground points and expect to see zero ohms or not much higher. Bridge, output jack nut, strings, cavity shielding

3) Check closely for metal corrosion/pitting if you live in a humid/foggy area and/or if the air is salty from proximity to the coast

4) Any non-soldered connections in the preamp, loosen the clamping screws and re-tighten them. Any removable cables, re-seat them.

5) Check whether or not running without the cavity cover produces more noise.

6) Walk around the room while you have the noise, turn from side to side, etc., check whether the noise gets better or worse.

7) Make a recording of the noise so we can hear it. There may be a "signature frequency" in there somewhere.

 

[Aloe]

well, jack is ground. can you verify, you have a working connection between strings and the jack sleeve? use a multimeter, not your eyes.

 

[Bob_Ross]

Zon bass, ACG-EQ01 preamp

I can't help with you're buzzing/grounding issue, I'm just here to opine that a Zon bass with an ACG EQ01 preamp must be a killer sounding instrument!

 

[kesslari]

I can't help with you're buzzing/grounding issue, I'm just here to opine that a Zon bass with an ACG EQ01 preamp must be a killer sounding instrument!

You can hear it in any of the links in my sig

 

[sunbeast]

Zon bass, ACG-EQ01 preamp, with an external power supply built by our own @Jeff Scott. This system has worked flawlessly for many years - 8 or 10 or so.
I have an email in to Alan and John East, but meanwhile, this is a head-scratcher. And of course, there were multiple issues to be debugged... I didn't get to the ground issue until last, and now I'm stuck.

I got back from vacation, fired up my bass, and had a definite high pitched buzz.
Different amp - same.
Different (passive) bass - same.
Different cables - same.
I checked the quality of the outlet - good.
Swapped out the power cable - problem solved with both basses.

But... with the Zon/ACG, now I have what I believe to be a ground problem.
Untouched, the bass is quiet.
If I touch the strings, I get a low buzz.
If I also touch the (metal) jack, the buzz goes away. Same thing happens with a different cable. It does not happen with the passive bass.

The wiring looks OK. What am I missing or what should I look for?

I don't see any bridge ground wire in your cavity picture. What pickups are you using in the Zon? Also, what is the switch in your bass?

 

[kesslari]

@sunbeast , @eniac , @Bob_Ross and @Aloe - I'm back to working on this.
I found it wasn't bothering me... and then realized that I was playing with the bridge pup almost solo'd. With it fully solo'd there's virtually no noise. The problem starts when I start to blend in the neck pup, and gets worse the more of it I pan to.

So - I'd say the issue seems to be a neck pickup ground issue. Tomorrow (or this weekend - whenever I have time) I'll look inside.

@sunbeast There are some solder spots in the shielding, and I suspect one of them is the bridge ground.
And the switch is a "producer switch" lol - an unwired switch that's simply there to fill a hole in the top.

 

[sunbeast]

@sunbeast , @eniac , @Bob_Ross and @Aloe - I'm back to working on this.
I found it wasn't bothering me... and then realized that I was playing with the bridge pup almost solo'd. With it fully solo'd there's virtually no noise. The problem starts when I start to blend in the neck pup, and gets worse the more of it I pan to.

So - I'd say the issue seems to be a neck pickup ground issue. Tomorrow (or this weekend - whenever I have time) I'll look inside.

@sunbeast There are some solder spots in the shielding, and I suspect one of them is the bridge ground.
And the switch is a "producer switch" lol - an unwired switch that's simply there to fill a hole in the top.

The bridge ground should be a wire coming into the control cavity that is touching the bottom of the bridge on the other end. The only wires I see entering the cavity are the wire bundles from the two pickups (but quite possible I am just missing something). The noise you describe (increased buzz when touching the strings) is usually indicative of an ungrounded bridge and inducing some noise from your body (which until grounded is basically a big meat antenna for noise) into the circuit via the strings, as you can expect the opposite when the bridge is grounded (when touching ground, environmental noise from your body is now sent to ground via the strings). The fact that touching the jack kills this noise confirms this, as the strings/bridge and jack should be attached to the same ground plane to begin with. That the bridge pickup is not affected likely just means that it is better shielded than the neck pickup from outside noise. Are your pickup cavities shielded? And if so, ensure that there is a ground connection running from that shielding that eventually gets connected to the ground at the jack. I see the solder points in the shielding in your control cavity, but don’t see any wires attached to them or a connection to the ground point on the preamp or output jack- without connection to ground, shielding acts as a noise antenna rather than shielding!

Get a multimeter and check for continuity between the bridge and ground and also any shielding and ground. And based on my experience with East/ACG preamps, its also worth going in and rescrewing all the preamp connections as these attachments can be a bit fiddly and there could be a loose or intermittent one. Even the ribbon cables connecting all the boards together might be due for a check as well

 

[kesslari]

Problem solved thanks to your inputs here and help from Alan at ACG and Martin at Zon (confirming that the Zon bridge is indeed grounded to the shielding, as I thought.

Alan pointed out that the second green wire (was going from the preamp to the jack) should be connected to the bridge. That turned the tide.
The bridge was indeed connected to the shielding. But the shielding was not actually connected to the rest of the ground circuit.
Soldering that second green ground wire to the shielding fixed the problem.

I suspect that years ago when I originally installed it I figured "to ground" for that second wire might as well mean "to the jack". I mean, what could possibly go wrong?