Preamp Ground Bus Hum

[Lowerleftcoast]

PROBLEM SOLVED!!! This is what I did:

Good to hear!

I had a look at the the picture on the build journal. To continue with the tutorial with ground scheme practices...
I noticed the orange wire from the PT is connected with the other grounds (ground bus) on the terminal strip. I presume the orange wire is the shield wire for the PT. If it is indeed a shield wire, it should be connected to the chassis. The orange wire does not have return current for the B+ so it should not be associated with the ground bus or any of the nodes. It is only a shield. No current.

 

[King Fan]

^^^. If I'm right (?!?) the 'shield' is one wire that can ground with the household, safety, green.

 

[gabasa]

Yes, you're both correct. I must be getting old, I can't believe I didn't think of that! Thanks.

 

[Lowerleftcoast]

If I'm right (?!?) the 'shield' is one wire that can ground with the household, safety, green.

That is my understanding as well.

Hammond says when the secondary is grounded there is little benefit using the shield.

What is an “Electrostatic Shield”?

Electrostatically shielded (Faraday Shield) transformers provides a copper electrostatic shield between the primary and secondary windings. The shield is grounded and thus shunts some noise and transients to the ground path rather than passing them through to the secondary. Transformers having a...

americas.hammondpowersolutions.com

 

[gabasa]

I use isolated loudspeaker jacks because they are isolated and cheaper than Switchcraft.

Hi @2L man, which jacks do you use? I just purchased a handful of Cliff jacks and they require me to enlarge the holes on my chassis, so I'm wondering if the ones you use might be able to fit without any modifications. Thanks.

 

[2L man]

Hi @2L man, which jacks do you use? I just purchased a handful of Cliff jacks and they require me to enlarge the holes on my chassis, so I'm wondering if the ones you use might be able to fit without any modifications. Thanks.

The plastic jacks I have used are Neutrik, Cliff or their copies and they have fit to the Tube Town chassis which I have used on few builds. I have made most of my chassis so I have not even think whay the hole size standard is. Someone wrote that when Switchcraft is installed using insulated washers the hole needs to be enlarged which sound logical.

 

[King Fan]

I haven't used plastic jacks, but the Neutrik jacks I see at at Mouser or Hoffman go in 11.4 mm holes, so roughly .45". Switchcraft go in 3/8" holes, so roughly .38". The shoulder washers I use (like Doug Hoffman sells) go comfortably in ½" holes.

Are there plastic/Cliff/Neutrik jacks made for 3/8" holes?

In any case, if you want to isolate jacks, it's easy enough to widen a 3/8" hole to ½ -- *if* you have a good step drill bit.