Some help with output transformers induced hum

[00940]

I've just finished wiring a small heapdhones amp. It's nothing fancy, basically a derivative of the bottlehead crack: ecc82 gain stage +6080 in cathode follower + parafeed output transformers.

But I'm getting some low hum. Not crazy loud but noticeable. If I remove the 6080, the hum is still there. If I move the output transformers as much as the leads allow (still with the ecc82 in circuit to load the power transformer), no hum audible. So I'm affraid they're too close to the toroidal power transformer...

Changing the layout or the case is a bit difficult... should I just move those transformers to an external box or does someone have another suggestion ?

 

[knockbill]

Can you put a metal shield around the OPTs... to isolate them from the rest of the amp?

 

[Alastair E]

Try changing the transformer's orientation....

Turn 'em sideways or upside down--or both...

try same with toroid too.

 

[00940]

Can you put a metal shield around the OPTs... to isolate them from the rest of the amp?

I can search for something suitable. It's not going to be easy...

Try changing the transformer's orientation....

Turn 'em sideways or upside down--or both...

try same with toroid too.

Changing the output transformers's orientation doesn't seem to change the hum much. Only distance does the trick. I'll try tomorrow with the toroid.

 

[Rundmaus]

I once solved a hum problem by twisting not only heater wiring, but also HV and signal wiring with its corresponding return/ground wire. Hum gone!

Regards,
Andreas

 

[knockbill]

With the mostly wood base theres' not much shielding, and its a small box,,, I've taken a piece of metal and moved it between txs or tubes etc, to find teh cause of hum,,, If it stops teh noise, you can probably figure a way to install it permanently...
Good luck...

 

[00940]

Well, I decided to remove the output transformers and give them their own external box. It's going to be less work than trying to work within the box.

With only caps from the cathode followers to the output, the amp is dead silent into senn hd650 and hd25.