Mu metal shield around the jensen transformer.
If that doesn't fix it then it's likely a different kind of problem.
If that doesn't fix it then it's likely a different kind of problem.
That's helpful to know.
You could also try shielding the internal mains wiring, but I think it's likely the Jensen is picking up the hum field of the toroidal transformer.
It would be good to get a steel L bracket and have it mounted with the bracket facing the psu.
That's what I did...bracket or a metal panel facing the psu. And my F6 is dead quiet.
And make sure that it's not coming from the pre or the sources.
How is it different than the F6?
With say +- 34V rails and say 1A current (for roughly same dissipation):
It is still a Class A amplifier at up to ~ 15W into 8 ohm. The F6 works as an AB amp and so would be capable of going beyond that. It should output 50W into 8 ohm easily (or 100W into 4 ohm).
Since the F6 is a working AB amp you don't have to turn up the current. There is of course nothing preventing you from doing it 😉
2 picoDumbs,
In a few words would you describe the differences vs the standard F6 in voltage, output power, FE etc?
Nice PCB by JPS64.
Last edited:
Okay, here the update on my hunt for what’s caus8ng transformer hum through both speakers...
-Turning the transformer didn’t work.
-I unbolted the transformer and moved it away from the chassis and that didn’t work.
-I replaced the fine wire I twisted up for the inputs with shielded wire and that didn’t work.
-Waving my hand around various components doesn’t change the hum.
-Tapping components with a screw driver doesn’t change the hum.
-Holding a piece of steel between the input transformers and the toroidal power transformer didn’t get rid of the hum or do anything to change it.
-Grounding the purple wire on the transformer didn’t change anything.
If I put my ear to the toroidal I hear if humming and it vibrates a little. Is that normal.
What’s left to try?
-Turning the transformer didn’t work.
-I unbolted the transformer and moved it away from the chassis and that didn’t work.
-I replaced the fine wire I twisted up for the inputs with shielded wire and that didn’t work.
-Waving my hand around various components doesn’t change the hum.
-Tapping components with a screw driver doesn’t change the hum.
-Holding a piece of steel between the input transformers and the toroidal power transformer didn’t get rid of the hum or do anything to change it.
-Grounding the purple wire on the transformer didn’t change anything.
If I put my ear to the toroidal I hear if humming and it vibrates a little. Is that normal.
What’s left to try?
Attachments
Maybe you have dc on the mains. A possibility.
I think you already answered this, but does this hum still occur when no other equipment is connected to the amp.
I think you already answered this, but does this hum still occur when no other equipment is connected to the amp.
Your AC in is very close to your left channel. Try routing the AC right down the middle of the chassis, and locate your connection block between the PS board and transformer.
Also it is difficult to see whether you have a ground lift CL60 between PS ground and chassis ground.
Another thing that I just noticed - the power transformer purple shield wire is not connected to chassis ground.
Also it is difficult to see whether you have a ground lift CL60 between PS ground and chassis ground.
Another thing that I just noticed - the power transformer purple shield wire is not connected to chassis ground.
Last edited:
I would double-check your connections on the terminal strip. I’ve had a loose wire / bad connector post cause problems like you’re describing.
That may be it. Looking at the post 2498, the picture you've uploaded yesterday, it looks like you've connected the ground wire straight to the chassis. If so, you need to connect the ground wire to the chassis through a CL60.
6L6 illustrated that in the build guide in page 1 some where in the middle of the page.
- Well, the hum is even in both channels. Although the AC in does run down the left side, it’s really not close to the board. I did try moving the wires and that didn’t make a difference.
-The CL60 ground lift is there.
-I wasn’t sure if the purple shield needed to be grounded or not. However, I get the hum in both channels whether purple goes to ground or not.