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Blues Junior Crackle, Pop & Hiss

Posted: Thu Nov 25, 2021 3:36 am
by Lost In Autumn
I have a modded Fender Blues Jr iii that after a few minutes, begins to crackle, pop and hiss. It's not terribly loud, but it's intrusive enough that I can't use it to record. the tube socket pcbs were recently replaced, the tubes are firmly seated and relatively new. The mods include bias trim pots, Deluxe Reverb tone stack, the BillM/Frommel cap and resistor mods and a 90's vintage Celestion , along with a solid pine cabinet. This amp would sound better than my Deluxe reverb, if not for the noise it's been making.

Re: Blues Junior Crackle, Pop & Hiss

Posted: Thu Nov 25, 2021 7:03 am
by jthomas
If the noise problem started after any of the mods, then I'd wonder about some error there. (Yea I know: Obvious.)

If the noise just started "out of the blue" one day, then there are too many possibilities to identify without either having the amp on a bench or without more information. PCB board amps are hard to diagnose because they are hard to work on, and they are built for a low price point with design and manufacturing designs made by accountants. I am not dissin' the amp because I have an old one and like its sound.

It may be important to note also that I'd differentiate between noise described as "hiss" (i.e., like an old analog tv tuned off-channel) and a crackle (i.e., like crumpling a piece of cellophane in your hand). A sound clip might help a bit.

Anyway: do the controls alter the noise (e.g., increase or decrease it); has the amp been dropped or damaged in any way; is the noise always present or is it intermittent; if the noise only shows up when the amp is played loud, then have you tried playing it through a different cab to see if the noise is associated with vibration; have you tried different known-tubes; have you tried playing it in some other environment (some noises reflect environmental electrical noise; have you tried other guitar cables (I bought a couple of cheap patch cables that are crazily capacitive and crackle when they are moved)?

All of these things noted, the most likely problem (if its more of a crackle and shows up after the amp warms up and isn't due to stray environmental electrical noise) is a cold solder joint somewhere. As the amp warms up and things expand, the traces and solder joints are stressed slightly and there is a little arcing that produces the noise. If it is more of a crackle and started soon after the mods were done, I'd look there first for a bad solder joint and/or damage to a PCB trace caused by one of the mods. If the noise fits what I described earlier in this paragraph and it was my amp, I'd open it up and chopstick around the modded circuits. Pressing gently on components in an energized amp with a non-conductive probe is an easy way to discover a bad solder joint. I have built some amps and know how to be safe and I would not recommend doing so if your electrical safety knowledge is limited, cause amps can carry lethal voltages... depending on the design, even when off and unplugged, sometimes. (So- Danger Will Robinson.)

I guess that I should note that carbon comp resistors can pick up moisture and develop invisible micro cracks which can produce both hiss and crackle. I don't remember if my Jr had carbon comps so cannot advise you specifically on that. That seems much less likely to me.

Best wishes.

Re: Blues Junior Crackle, Pop & Hiss

Posted: Sun Nov 28, 2021 6:32 am
by Lost In Autumn
jthomas wrote:
Thu Nov 25, 2021 7:03 am
If the noise problem started after any of the mods, then I'd wonder about some error there. (Yea I know: Obvious.)

If the noise just started "out of the blue" one day, then there are too many possibilities to identify without either having the amp on a bench or without more information. PCB board amps are hard to diagnose because they are hard to work on, and they are built for a low price point with design and manufacturing designs made by accountants. I am not dissin' the amp because I have an old one and like its sound.

It may be important to note also that I'd differentiate between noise described as "hiss" (i.e., like an old analog tv tuned off-channel) and a crackle (i.e., like crumpling a piece of cellophane in your hand). A sound clip might help a bit.

Anyway: do the controls alter the noise (e.g., increase or decrease it); has the amp been dropped or damaged in any way; is the noise always present or is it intermittent; if the noise only shows up when the amp is played loud, then have you tried playing it through a different cab to see if the noise is associated with vibration; have you tried different known-tubes; have you tried playing it in some other environment (some noises reflect environmental electrical noise; have you tried other guitar cables (I bought a couple of cheap patch cables that are crazily capacitive and crackle when they are moved)?

All of these things noted, the most likely problem (if its more of a crackle and shows up after the amp warms up and isn't due to stray environmental electrical noise) is a cold solder joint somewhere. As the amp warms up and things expand, the traces and solder joints are stressed slightly and there is a little arcing that produces the noise. If it is more of a crackle and started soon after the mods were done, I'd look there first for a bad solder joint and/or damage to a PCB trace caused by one of the mods. If the noise fits what I described earlier in this paragraph and it was my amp, I'd open it up and chopstick around the modded circuits. Pressing gently on components in an energized amp with a non-conductive probe is an easy way to discover a bad solder joint. I have built some amps and know how to be safe and I would not recommend doing so if your electrical safety knowledge is limited, cause amps can carry lethal voltages... depending on the design, even when off and unplugged, sometimes. (So- Danger Will Robinson.)

I guess that I should note that carbon comp resistors can pick up moisture and develop invisible micro cracks which can produce both hiss and crackle. I don't remember if my Jr had carbon comps so cannot advise you specifically on that. That seems much less likely to me.

Best wishes.
The noise existed prior. I had Rootbeer Audio in Philly do the mods and install new tubes. It worked for a while. I then had Strange Audio in Phoenixville, PA install new tube sockets and a PCB, as well as the phase inverter tube. again, that helped for a while.

It seems worse when playing through a 16ohm 1/15 cab, noticeably, but not significantly worse; it's definitely happening after the amp warms up. it's perhaps less a discreet "hiss" than a raising of the noise floor, accompanied by a low crackle. I'll try to get a clip uploaded later today.

Re: Blues Junior Crackle, Pop & Hiss

Posted: Wed Dec 01, 2021 3:50 pm
by Lost In Autumn
Image
Here’s the noise it makes

Re: Blues Junior Crackle, Pop & Hiss

Posted: Wed Dec 01, 2021 4:34 pm
by jthomas
I can't download the clip.

I will do whatever I can to help, but...

...you know, it probably would be best if you posted the issue over at The Gear Page, in the Amp Tech subforum. I am an amateur hacker. There are 4 or 5 high-level techs over there who really are sharp and are very generous with their time.

Re: Blues Junior Crackle, Pop & Hiss

Posted: Sun Dec 05, 2021 12:34 pm
by øøøøøøø
Those solder joints are vulnerable to cracking when tubes are inserted or disturbed.

Very often reflowing tube socket solder joints will fix it (until it breaks again)

Re: Blues Junior Crackle, Pop & Hiss

Posted: Sun Dec 05, 2021 12:36 pm
by fuzzking
perfectly normal for a blues junior. have it re- pre- soldered.