"pop" when my tech21 trademark 60 is powering down

[Jimbilly]

This is my 2nd T60, the first one I had was dead quiet on/off from new, I think it was an early model, front loaded speaker.  I sold that one quite a while ago, and bought this one about 2 years ago, using it more now, it has always made a little annoying "pop" at the tail end of powering down, no difference if switched from the built in power switch or from a power strip.  I just installed the eyelet bolts to more easily zip tie the wall wart in, the 'pop' predates the eyelet bolts, no change there.  Coincidentally, very recently it was barely working with very low volume, and then blew a fuse on power up.  I sprayed all the pots with caig fader lube, and sprayed plastic safe electronic cleaner into all the 1/4" ins/outs, it seems to be working property now except for the power down "pop". 

Suggestions?

[JGale]

Hmmmm. My usual response to popping is a leaky capacitor, but that’s typically in the Audio path.

Could it be the rectifier? 
 

As an afterthought, check the long shielded cable that comes off the loop return and goes to a place at the other end of the board. It’s a tight fit and the plug in at the end can loosen with jostling. If it’s loose the M channel will cut out.

[HSB0531]

Replace the electrolytic caps in the power supply.  The power supply caps discharge voltage when the amp is turned off and when they start to go bad, they allow D.C. voltage to be present at the speaker(s).  This causes the popping sound. D.C. voltage is harmful to speakers.

If you have cleaned the volume and tone pots and you hear a scratchy noise when you turn the volume and tone pots, replace any electrolytic caps in the audio path.

Use Caps that are rated at a higher voltage than what's in there, and ones with a 105 degree rating if you can.  The typical ones are 85 degree rated and fail quicker in a high heat environment like a guitar amp.

[HSB0531]

AHA!!...I found your problem!

Disregard what I said previously.  It's the Eyebolt & Nylock nut on the end of the chassis.  They're causing reverse hysteresis of the Framus Modulator Tube and an inrush backflush of electrons to the speaker coil. Simply remove those, and fill the hole in with a wooden mahogany plug. That'll do it!

[JGale]

I was going to do that to mine before I cannibalised it. I may have those caps and a rectifier here. You are welcome to them. 
 

iffin I can find em

[velorush]

19 hours ago, HSB0531 said:

AHA!!...I found your problem!

Disregard what I said previously.  It's the Eyebolt & Nylock nut on the end of the chassis.  They're causing reverse hysteresis of the Framus Modulator Tube and an inrush backflush of electrons to the speaker coil. Simply remove those, and fill the hole in with a wooden mahogany plug. That'll do it!

Don't forget to replace the illudium Q-36 explosive space modulator!

[Jimbilly]

19 hours ago, HSB0531 said:

AHA!!...I found your problem!

Disregard what I said previously.  It's the Eyebolt & Nylock nut on the end of the chassis.  They're causing reverse hysteresis of the Framus Modulator Tube and an inrush backflush of electrons to the speaker coil. Simply remove those, and fill the hole in with a wooden mahogany plug. That'll do it!

African or Philipine?

 

This sounds like something I can actually do.  -thanks!

[HSB0531]

On 3/21/2024 at 10:56 AM, velorush said:

Don't forget to replace the illudium Q-36 explosive space modulator!

Was that a Marvin The Martian Quote?

[velorush]

14 hours ago, HSB0531 said:

Was that a Marvin The Martian Quote?

Absolutely:

ETA: used to jam in college with a guy that had a solid state Marshall that had a power-down pop.  I plugged it into a switched power strip and turning off the power strip first stopped the pop. Not a fix, but a workaround. 

[Jimbilly]

On 3/23/2024 at 7:44 AM, velorush said:

Absolutely:

ETA: used to jam in college with a guy that had a solid state Marshall that had a power-down pop.  I plugged it into a switched power strip and turning off the power strip first stopped the pop. Not a fix, but a workaround. 

No difference if leaving the switch 'on' and using the power strip for on/off. But:

it is much quieter without the footswitch plugged in. I need to take it apart and clean, look for cold solders on the footswitch plug I guess.  

[JGale]

What chu need to do is buy this and put it in the loop for use with the gain channel. That open back does okay with Fenderish, but lacks conviction for Marshallish. The cab sim gives a way to tweak the response. Easy peasy even I can do it, have done it. I sold it with the amp. 
Velcro a 9V to it and stick it inside the amp. 
https://reverb.com/item/70388847-pedal-pcb-uni-dsm-omni-cab-sim-cabinet-simulator-alchemy-audio-guitar-effects-pedal?utm_source=rev-ios-app&utm_medium=ios-share&utm_campaign=listing&utm_content=7038884

 

[JGale]

Here’s what the controls amount to in practice.

 

Annnnd it looks like they can be had on the used market. The clone was taken from a user group contributed by the designer who lives in Chile.

[Jimbilly]

4 hours ago, JGale said:

Here’s what the controls amount to in practice.

 

Annnnd it looks like they can be had on the used market. The clone was taken from a user group contributed by the designer who lives in Chile.

I'm mostly just using it as a monitor, with the di to the house, now with the di from the Flyrig to the house, so I don't actually need to use the footswitch anymore, but it would be nice to get it working correctly.   Those cab sims do look like fun, all by themselves, much more evolved that my old Redbox mkii !

 To clarify even further: a cable can be plugged into the footswitch plug in the amp without the footswitch connected and there is minimal "pop" (same as if the cable is not connected), the bigger pop occurs only when the footswitch is connected to the footswitch cable.