JMT45 kit build crackle and hum

[jude]

Yes it worked , lesson learned. The reason I was asking for help is that its my first amp build and of course I still have a lot to learn about electronics. Of I appreciate the advice. I might ask about a better grounding scheme later. Cheers

[kuDo]

Hello jude,

Could please share what it was that solved your problem. I am quite curious.

Thanks

[pdf64]

It would be far better to isolate and diagnose the issue with your amp.
Just randomly applying fixes that fixed other amps is poor practice.
As evidenced in this thread, as jude wanted to replace the treble cap in the tone stack, because he’d read that worked for other people’s amps

[Blindog]

I think kuDo is just curious (as am I) as to what the fix ended up being mate...

[pdf64]

I took the implication that what worked was replacing the 100k anode load resistor of the bright channel’s input stage.
It seemed like the typical sizzling noise CC resistors make if they enter that fault mode, when used as an anode load resistor. And the (Chinese) kit came with CC resistors...

[jude]

Yes thanks, I get the point. I should have looked carefully at the signal path for Channel 1 in the layout and then used logic to exclude components that were not exclusive to that path. Experience also plays a part as I wasn't familiar with uVAC in failing resistors and just learning about how the circuits in guitar amps actually work. Anyway in good working order now thanks to your guidance. I need to try a guitar with humbuckers to see if that mitigates the grounding hum/EMI issue although this seems to be common to the JTM45 design based on what I have read from other builds.

[kuDo]

It would be far better to isolate and diagnose the issue with your amp.
Just randomly applying fixes that fixed other amps is poor practice.
As evidenced in this thread, as jude wanted to replace the treble cap in the tone stack, because he’d read that worked for other people’s amps

Hi pdf64,

I have no problems with my amp (jet), I still in a building process.

I though for the sake of this forum, it would be nice to have a conclusion at the end of this thread.

[jude]

Just to reiterate it was the 100K resistor in the Channel 1 (bright channel) signal input path. A would add that the possible cause was my soldering technique, the turrets are stainless steel and at times required several attempts to get a good solder joint. I think my flux is standard and possibly better to use a flux that etches the stainless steel for faster soldering and less heating of the components. For the wires on the underside of the turret I used diluted rust converter that contains orthophosphoric acid and was able to get very good solder joints quickly as it was very difficult with standard flux.

[angelodp]

A cold solder joint can really create invisible issues. Glad you found it.

[jude]

Not a cold solder joint, the soldering iron probably fried the 100K resistor during the turret build, and the issue was uVAC in that failing 100k resistor which was replaced with a new one.

[pdf64]

...the soldering iron probably fried the 100K resistor during the turret build...

It might not have been due to heat damage, rather they (ie CC resistors passing DC) just flip into becoming noisy over time, it can take anywhere from a few minutes or a few decades for it to happen.
Anyone old enough to remember the old landline phones that used carbon granule mics will be familiar with it. With them, a sharp knock to the handset would clear it up for a while, till the next time.