Fizzle Noise

[passfan]

Twice now when I'm playing at low volume, I got this fizzle sound on my notes. It sounds like scratching, and only when I play a note. The first time I shut it off and changed out my 12ax's and it was fine all night. It just did it again and I shut it down and brought it right back up and it's been fine since. Anyone ever experience this?

[Structo]

Sounds like you may have a heat related issue.
Many times that can be a bad solder joint or ground.

Double check all your solder joints and grounding.

[passfan]

Sounds like you may have a heat related issue.
Many times that can be a bad solder joint or ground.

Double check all your solder joints and grounding.

Usually when it does it, it's within 5 minutes of turn on , then it's fine. I'll be swapping out a multicap soon so I'll touch everything with the iron to be safe.

[passfan]

Messed around a bit today and found my volume pot went off when I touched the ground so I changed it out to a new one and things got a bit better but started again. It seems when I try the bright switch or add any presence it starts up again and then I realized I used 1/2 watt pots throughout . Could these be overheating and causing this? Does this amp really need 2 watt pots or are they overkill ?

[Structo]

No those pots should be fine.
That's pretty much the standard wattage for amps.

Have you tried poking around with a chopstick while powered up?
Be careful but a lot of times you can pin point the problem this way and find something you can't see.

[passfan]

No those pots should be fine.
That's pretty much the standard wattage for amps.

Have you tried poking around with a chopstick while powered up?
Be careful but a lot of times you can pin point the problem this way and find something you can't see.

Well I chopsticked that first bad volume pot and found it crackled everytime I choped the ground and changed it. Nothing else gives any indication at all. All my voltages are spot on and quite frankly the tone of this thing sounds wonderful with my guitar it's just every note I hit is like a carrier for this ever so faint fizzle type crackle. I can barely hear it, but I can hear it. I resweated my solder joints on the card and everything went to crap until I found the volume pot. Then it seemed fine until I engaged the bright switch and off it went so I took out the bright switch. Now if I turn up the presence it sets it off. Anything that brightens up the amp causes this and my best pre tube a GE JAN 6072 that sounds sweet but sets it off constantly. I've checked back through the forums and can't find anything like this so I appreciate your help. Would my OT being in the 20 watt range be causing this? Could it be a winding heating up?
I honestly have to find it. I have to have this amp.

[passfan]

I'm going to try a different direction before I tear into this thing. First the two 12" speakers in my combo cabinet are close to 30 years old and haven't been hit this hard in years so I have a new 10" 75 watter that I'm going to plug it into tommorrow and see if perhaps one of my drivers is to blame. Failing that I am going to dust off the scope and signal generator and see if I can pinpoint where this crap is coming from. I will post what I find in case this can be of use in the future.

[Cliff Schecht]

Yeah, the scope is your friend when it comes to debugging circuits. Start at the input and work your way forward until you find the offending stage.

[passfan]

played it for an hour this afternoon and couldn't get it to do it anymore. I'm screwed.

[rfgordon]

Intermittent problems like this can make you crazy!

I had an amp that was making odd static like noises on the attack of the notes. Like it says in the Grinch, I puzzed and I puzzed until my puzzler was sore. Somehow I ended up happening to look into the back of the cab while playing with some of the lights in the room off. That's when I saw tiny blue sparks on one of the speaker terminals. The spade clip was loose enough to vibrate on the note, and the movement caused sparks, which got translated into static on the speaker. Gave the clips a squeeze and the static was gone.

The point of that story is to say that sometimes the answers some when/how you least expect them.

[Cliff Schecht]

Gordon, I've had similar problems before. It's great when you figure them out but very frustrating until then. A tremolo I recently built worked in the box only when the circuit board was oriented a certain way. Turned out that one of the pots I was using wasn't making a good connection between the terminal, the terminal crimp and the body.. How frustrating is that!?!

Also, anybody ever notice that a tremolo is completely useless in front of an Express?

[passfan]

Well , not only have I not been able to find it, I've managed to make matters worse. My 40/20/20/20 multicap came in as well as my EL34m's so I swapped it all out and to add good measure I changed all my Russian coupling caps out to orange drops and I've lost my tone. What was a beautifully warm sounding amplifier is trebley as all getup. So much to the point that I can't stick anything but a 12AU7 is the first socket or she squeals uncontrollably. I still have my underlying fizzle problem and now my tone stack does nothing. My only saving grace is a recently finished Rocket, which keeps me playing.
When you turn down all the tone nobs on the Express does the sound cut off completely. Mine did before, and now that my tone stack does nothing I still get sound through it with all the pots turned down.

[marcoloco961]

Well , not only have I not been able to find it, I've managed to make matters worse. My 40/20/20/20 multicap came in as well as my EL34m's so I swapped it all out and to add good measure I changed all my Russian coupling caps out to orange drops and I've lost my tone. What was a beautifully warm sounding amplifier is trebley as all getup. So much to the point that I can't stick anything but a 12AU7 is the first socket or she squeals uncontrollably. I still have my underlying fizzle problem and now my tone stack does nothing. My only saving grace is a recently finished Rocket, which keeps me playing.
When you turn down all the tone nobs on the Express does the sound cut off completely. Mine did before, and now that my tone stack does nothing I still get sound through it with all the pots turned down.

Whenever making several changes to an amp, I always try to do them one at a time, then check for expected results before doing the next change. That way if something goes badly you can pinpoint the problem easier. It might be as simple as the tube change that changed your tone.

Sounds like a definite problem with a pot or wiring in the tone stack. When all tone knobs are fully CCW or off, you should get little or no real sound from the amp. I would start there.

I have had a lot of trouble with pots going bad. I think I might be overheating them during soldering and "letting the smoke out" so to speak. Try turning the lights down like someone suggested earlier and watch while you play. I have found several tough to troubleshoot problems this way. Sparking is a dead giveaway, and usually present with the fizzling sounds.

[passfan]

Well , not only have I not been able to find it, I've managed to make matters worse. My 40/20/20/20 multicap came in as well as my EL34m's so I swapped it all out and to add good measure I changed all my Russian coupling caps out to orange drops and I've lost my tone. What was a beautifully warm sounding amplifier is trebley as all getup. So much to the point that I can't stick anything but a 12AU7 is the first socket or she squeals uncontrollably. I still have my underlying fizzle problem and now my tone stack does nothing. My only saving grace is a recently finished Rocket, which keeps me playing.
When you turn down all the tone nobs on the Express does the sound cut off completely. Mine did before, and now that my tone stack does nothing I still get sound through it with all the pots turned down.

Whenever making several changes to an amp, I always try to do them one at a time, then check for expected results before doing the next change. That way if something goes badly you can pinpoint the problem easier. It might be as simple as the tube change that changed your tone.

Sounds like a definite problem with a pot or wiring in the tone stack. When all tone knobs are fully CCW or off, you should get little or no real sound from the amp. I would start there.

I have had a lot of trouble with pots going bad. I think I might be overheating them during soldering and "letting the smoke out" so to speak. Try turning the lights down like someone suggested earlier and watch while you play. I have found several tough to troubleshoot problems this way. Sparking is a dead giveaway, and usually present with the fizzling sounds.

Well to my credit most all the changes were made andf then listened to. The orange drops are what ruined it and in the proces I screwed up my tone stack. Thanks for verifying the little to no sound. It was correct before now it's not. I will find it.

[rooster]

Rawnster had this exact problem and it turned out to be a loose leg on his (inexpensive) Bourns volume pot. He changed it to a PEC pot and the problem went away. It seems the rivet that secures the lug onto the carbon trace can sometimes either be loose or get loose. I think you have danced all around this. Change the pot and let us know. ...Are you using the Bourns version?