C-lator hum

[ynor]

I’m having some trouble with AC hum. I’m in Norway, 230 V 50 Hz. I recently got a new C-lator which injects power line hum (50 Hz, with harmonics of dominantly 150 Hz hum) into the FX loop of the OTS. To exclude other factors I’ve have disconnected every cable from the amp and C-lator, and only running the C-lator into the amp FX loop using high quality cables. Nothing in the C-lator loop. Only speaker cable from amp to the cabinet. Mains AC cords from amp and C-lator plugged into the same wall socket.

Problem is that when the C-lator is powered on, there is a bothersome hum, mainly 150 Hz. When I turn the power of the C-lator off, the hum disappears. Standby on or off on the C-lator doesn’t change a thing; hum is there. Neither does adjusting any of the levels on the C-lator. So I conclude that it is probably coming from a grounding issue, or could the PTs close proximity to the AC filtering circuit be the problem? This new C-lator has an internal PT, while the ones I’ve seen from earlier builds have them on the outside rear chassis. I also see that the filtering circuit is much closer now on the same board than on previous builds when it was separated on two different boards. This has a new layout, with radial vs axial filter caps.

Attached a picture. Any thoughts?

New C-lator.jpg

[bepone]

power transformer is inserting it in the chain.. or bad filtering.. maybe remount transformer totally to the end in right direction, but in fist place measure with ocilloscope residual humm in each Ub+ node

[sluckey]

Disconnect the mains earth ground wire from the chassis. If the hum disappears you have a ground loop. There is a simple ground isolator circuit that works well and allows the earth ground to be connected to chassis.

[ynor]

Disconnect the mains earth ground wire from the chassis. If the hum disappears you have a ground loop. There is a simple ground isolator circuit that works well and allows the earth ground to be connected to chassis.

Thanks! As in unsoldering the arrowed ground wire from the AC socket shown in the picture..?

Screenshot_20240314_165005_Gallery.jpg

[sluckey]

You could do that. May be quicker/easier to just unscrew the nut and lift that lug with the single green wire from chassis. Fasten the other lug back to chassis.

[ynor]

You could do that. May be quicker/easier to just unscrew the nut and lift that lug with the single green wire from chassis. Fasten the other lug back to chassis.

Yes of course! Thanks!

And if that helps, I can remove the standby/operate wiring and use that switch as a chassis ground in/out instead of a standby switch. Don't know if the standby mode is needed. I know this has been debated for years, but don't know whats the consensus these days...

[ayan]

Disconnect the mains earth ground wire from the chassis. If the hum disappears you have a ground loop. There is a simple ground isolator circuit that works well and allows the earth ground to be connected to chassis.

Thanks! As in unsoldering the arrowed ground wire from the AC socket shown in the picture..?

Screenshot_20240314_165005_Gallery.jpg

Do you have a ground lift like the one in the picture?
G.

[Richard1001]

The groundwire of the two 33uF caps need to go to signalground.

[ynor]

I unscrewed the AC ground only from the chassis. Hum is still there. No change. Yes, I left the other two from the big caps still connected to ground.

So lifting the AC ground did not help. Any other ideas?

[award70]

Does your heater circuit have a path to ground?

[ynor]

Does your heater circuit have a path to ground?

According to the schematics and the layout provided by C-tone it should, through 2x 100R resistors if I understand the schematics correctly..(?). I can measure that on this build tomorrow.

[Richard1001]

I unscrewed the AC ground only from the chassis. Hum is still there. No change. Yes, I left the other two from the big caps still connected to ground.

So lifting the AC ground did not help. Any other ideas?

1. Did you take the paint off the chassis for all connections to the chassis? (Solder lugs, pots etc ) If not, you should do so.
2. Your powersupply grounds are not wired correct. Take a look at the layouts on this forum.

[ynor]

1. Did you take the paint off the chassis for all connections to the chassis? (Solder lugs, pots etc ) If not, you should do so.
2. Your powersupply grounds are not wired correct. Take a look at the layouts on this forum.

1. This is built and assembled by Ceriatone. I did see that the paint was removed for the one lug I did loosen. Can check the others.

2. I can not see what's wrong with the PS ground wiring. I think they match Ceriatones layout, also in accordance to other layouts I've seen, but I can't see where I'm wrong. Could you be more specific? Thanks

[dbharris]

1. Did you take the paint off the chassis for all connections to the chassis? (Solder lugs, pots etc ) If not, you should do so.
2. Your powersupply grounds are not wired correct. Take a look at the layouts on this forum.

1. This is built and assembled by Ceriatone. I did see that the paint was removed for the one lug I did loosen. Can check the others.

2. I can not see what's wrong with the PS ground wiring. I think they match Ceriatones layout, also in accordance to other layouts I've seen, but I can't see where I'm wrong. Could you be more specific? Thanks

The mains ground should be by itself. The first power cap ground goes to its own location and the second power cap ground goes to the star between the pots and the PCB. Check the layout in the files section.

-Dan

[ynor]

1. Did you take the paint off the chassis for all connections to the chassis? (Solder lugs, pots etc ) If not, you should do so.
2. Your powersupply grounds are not wired correct. Take a look at the layouts on this forum.

1. This is built and assembled by Ceriatone. I did see that the paint was removed for the one lug I did loosen. Can check the others.

2. I can not see what's wrong with the PS ground wiring. I think they match Ceriatones layout, also in accordance to other layouts I've seen, but I can't see where I'm wrong. Could you be more specific? Thanks

The mains ground should be by itself. The first power cap ground goes to its own location and the second power cap ground goes to the star between the pots and the PCB. Check the layout in the files section.

-Dan

Move the ground wire of the 33 uF to the star between PCB and pots, while keeping the 47 uF at its current location together with the AC inlet ground point? Can try that tomorrow.