Amp buzz radio interference

[Ampzone]

Yes the wire/lead coming from the input Cliff jack is shielded/with a ground wire and terminates into pin 7 V1. All the noises have stopped save the radio interference which comes and goes depending on the guitar cord location. The ticking/scratchy low noise sound seems to affect the other amps so I think it not an issue for this amp specifically.

If I could minimize the radio noise this one is fixed.

[Helmholtz]

Yes the wire/lead coming from the input Cliff jack is shielded/with a ground wire and terminates into pin 7 V1. All the noises have stopped save the radio interference which comes and goes depending on the guitar cord location. The ticking/scratchy low noise sound seems to affect the other amps so I think it not an issue for this amp specifically.

If I could minimize the radio noise this one is fixed.

The question was if the input jack has a (close-by) chassis ground connection.

[Ampzone]

https://drtube.com/schematics/hiwatt/hwpre1.gif

https://drtube.com/schematics/hiwatt/hwpwr100w.gif

https://drtube.com/schematics/hiwatt/hwpsu1.gif

[nickb]

Ampzone

To answer HH's question, a picture of the jack in your amp from the inside would be worth a thousand words.

[Ampzone]

I added a 100pf Silver Mica cap ..all I had on hand. From the Cliff jack ground tab to chassis. Radio interference went away. Quiet and normal.

I wonder if it needs to be closer to a 47pf?

[pdf64]

Another win for raiken

I guess that the actual value is immaterial, won’t affect the sound.
100pF is pretty low though, I wouldn’t go lower.

[Helmholtz]

It's actually an established RFI rejection measure for equipment where the shield of the input cable is not directly connected to the chassis.
IIRC, I first learned about this in an EMC seminar in the late 80s.

[Ampzone]

It's actually an established RFI rejection measure for equipment where the shield of the input cable is not directly connected to the chassis.
IIRC, I first learned about this in an EMC seminar in the late 80s.

Very cool! You think 47pf is better is 100pf okay in your opinion? Obviously its not part of the original circuit, but it seems to work very well. I can try and locate a 47pf if its preferred.

[Helmholtz]

Very cool! You think 47pf is better is 100pf okay in your opinion? Obviously its not part of the original circuit, but it seems to work very well. I can try and locate a 47pf if its preferred.

Why change the value if it works well?
The cap shorts radio frequencies to chassis ground. Higher value has lower impedance and also shorts lower RFI frequencies. There's no optimum capacitance. Just needs to be large enough for the RF involved.

Cap has absolutely no effect on amp sound.

Great amp, btw.