Fizzy notes with treble and middle controls on zero

[bruzanhd]

I’ve got a dirty Shirley mini that’s been modded to the pink taco voicing. But when I turn the treble and middle controls to zero, it sounds dark as expected but then has this sort of fizz on top of the notes. It doesn’t happen when I’m using a cleaner sound. Even when I turn the middle and treble up, I can still slightly hear it until the fizz gets drowned out when those controls are turned high enough.

My guess right now are a bad cap somewhere in the tone stack but I don’t want to go changing things for fun if that’s unlikely. I tried with a full different tube set and speaker cab, and guitar as well.

Anyone run into something similar before? Or can anyone try those settings on any typical Marshall design for me and see if you get the same symptoms maybe it’s normal and I’m just not used to Marshall tone stack quirks? I’ve posted a link to a YouTube video where you can hear what I mean. Any jcm800 type amp owners please let me know if this is normal.

Thanks

 

[Snave]

Who did the mod? You should contact Dave Friedman since he knows the amp better than anyone: friedmanamps@gmail.com

That's not normal behavior on a vintage Marshall amp.

 

[bruzanhd]

Who did the mod? You should contact Dave Friedman since he knows the amp better than anyone: friedmanamps@gmail.com

That's not normal behavior on a vintage Marshall amp.

Previous owner. Not sure who did it.

 

[Chocol8]

Blocking distortion. Very normal for many tube amp designs.

 

[bruzanhd]

Blocking distortion. Very normal for many tube amp designs.

So this is normal behaviour when the TMB controls are all on zero? That fizz is expected? Like I said it becomes almost imperceptible when using “normal settings” on TMB controls.

 

[Chocol8]

So this is normal behaviour when the TMB controls are all on zero? That fizz is expected? Like I said it becomes almost imperceptible when using “normal settings” on TMB controls.

Hard to be certain listening on a phone and from your video, but I think it is blocking distortion occurring when a tube is going from distorted to clean. It depends on amp design, bias etc. but it can be heard in a lot of amps. If you play a note or chord in the edge of breakup and let it sustain, do you hear the fizz when it transitions from distorted to clean as the notes decay?

 

[bruzanhd]

Hard to be certain listening on a phone and from your video, but I think it is blocking distortion occurring when a tube is going from distorted to clean. It depends on amp design, bias etc. but it can be heard in a lot of amps. If you play a note or chord in the edge of breakup and let it sustain, do you hear the fizz when it transitions from distorted to clean as the notes decay?

No it goes away when the note cleans up.

 

[bruzanhd]

I’ve emailed Friedman and they said it’s most likely faulty filter caps. I’ve ordered replacements and we’ll see if that fixes it.

 

[dronerstone]

You might have a Dumble.