Real McTube Hum

[ranchak]

I just recently finished building the Real McTube from the TonePad site. I anticipated having problems before I decided to build this project. My problem is I have a hum, what a surprise! I tried to mount the transformers and tube at one end of the enclosure with the circuitry at the other end. I twisted all of my wires together to try to minimize the hum. I have the AC grounded with the Input and Output jacks and the PCBs. I wired this with true bypass, but I have a squeal when I bypass the tube driver. Also while I'm at it, I wanted to use an LED as an indicator, can LEDs handle AC voltage? How much?

[ranchak]

Nobody has any ideas on how to reduce the noise generated from the AC voltage?

[BrianJ]

I usually try to keep high gain tube stages away from transformers, that could be part of your problem.  If the enclosure and power supply are "earth" grounded try lifting the grounds on the input and output from the chassis.  Try plastic jacks.  Usually if a pedal squeals when bypassed it's because the input of the circuit should be grounded when it is switched out.  Easy if you use a 3pdt.


Good luck

[Steve C]

Hum will also come from having the hot and neutral from the plug reversed.

[brett]

Hi
Hmmm....a common problem.
I found that using isolated jacks helped a lot.  And shielded wire.  Are you grounding via the box AND a wire to the input jack?  If so, that could be a significant problem.  Star-grounding is the way to go.  In low-current pedals you can get away with hell concerning grounds, but no in high-power high-gain stuff like this. 
The biggest source of emissions will be the high-current AC lines running (1) to the rectifier (then quietly as DC to the heater), and (2) to the step-up transformer.  As you know, twisting these wires can help, as can running them close to the box or in a shield.
good luck

[ranchak]

Would copper shielding tape help? Maybe soldering one end of the tape to ground?