snap crackle pop (solved)

[mat]

I took my OD50 build to reherseals today and when cranking it and playing for few moments it started to give ugly distortion with some notes I played. After couple of minutes it started to give louder and louder hiss, pops and crackles that went madly loud and I had to turn the amp off quickly.

It has happened one time before (when not playing as loud as today).

I red the GEO article of the sound problems but did not find help for the problem of the amp.

What might cause this kind of phenomena ?

I have struggled with the build with the sound being too hard and harsh for long time and my plan has been to build new power filter board. The problem might be there..

[CaseyJones]

Possibilities include a cold solder joint, a failed tube, a cooked resistor or capacitor or a loose tube socket just about in that order.

Make sure your grounds really are grounded.

I'm an enormous proponent of NOS tubes and sockets, they save a lot of hassle in the long run.

Open it up and look for smoke trails or cooked parts. Sometimes it helps to turn off all the lights, if something is arcing (BIG pops) you'll see it right away in the dark.

[Bob-I]

The increased loudness make me think that you have a bad ground somewhere, possibly on a volume pot.

[mat]

Possibilities include a cold solder joint, a failed tube, a cooked resistor or capacitor or a loose tube socket just about in that order.

Make sure your grounds really are grounded.

I'm an enormous proponent of NOS tubes and sockets, they save a lot of hassle in the long run.

Open it up and look for smoke trails or cooked parts. Sometimes it helps to turn off all the lights, if something is arcing (BIG pops) you'll see it right away in the dark.

I have reflowed almost all solder joints + measured the ground points with dmm. The tube sockets has been changed to Belton ones. I've been chancing tubes (output tubes are brand new) when troubleshooting the harsh sound but not now when the big noise has came out.

If I rebember right, I saw once on the back of the amp the output tubes (that has blue glow on them) flashed bright blue when the amp made a pop sound.

Yesterday when not playing I started to hear the problem sound that was quite quiet. Then I picked notes and the harder I stroke to the strings the louder was the ugly distortion behind the note. And when cranking the amp the noise came by itself and went louder and louder.

I'll try to measure for the leaking coupling caps (with the GEO method). I presume that measuring a resistor on the live circuit is out of question ?

I also check carefully the volume pot grounds.

All in all the amp sounded surprisingly good with my strat (with Kinman PU's) before it went mad

[Bob-I]

I'd also check the bias supply.

[mat]

I checked the amp for burned components but no avail. I also chopsticked around the chassin but did not hear anything suspicious. Then I reflowed the volume and drive pot ground solderings + removed the two seperate bias trimmers + the grounding resistors and putted in a single 10k pot + 10k to ground. All voltages (including bias) are ok. While I was about to adjust the bias further the amp made again real loud noise (no guitar connected to the input). I jumped about half meter from the chair and quickly turned the amp off.

After a while I fired the amp again with guitar connected and the amp is silent. No sound with the guitar. I had only limited time to troubleshoot it but hope to nail the bug in a near future. I'll try the audioprobe to find where the sound stops.

When the loud noise occured first time I remember turning all volumes + drive to zero but the noise stayed still ? Would this suggest what might be the problem ?

Btw. the noise I'm talking about is really loud. Like the amp on full loud.

[Andy Le Blanc]

I had to clean insect mess out an old fender resently
it was shorting socket pins and the switched input jack

once a while back I had an amp where the phenolic tube
socket arc'd and left little carbon pathways that kept sparkin over
even though everything else looked good.... seen that on the phenolic
of a tube base as well

get a vacum and brush and make sure theres no forein material in and
around the tube sockets

[briane]

just guessin'

-arcing. Ive seen this do some strange things. clean socket undersides with a good electronics cleaner.
-originally sounded like blocking distortion was a possiblity. not so sure with the other problems.
-also beware the oscillation. its a possibility.

[jelle]

I had similar problems with an 50w ODS reverb that I build for a friend. Thanks to the help of the great people here at this forum, I found out that the preamp ground buss was not properly grounded to the chassis due to a cold solder joint. My ground buss was really noisy when I'd touch it with the chopstick. I'd try to look for a component that is susceptible to mechanic vibration with the chopstick in your case. Does the amp have the same problems when the amp is pysically away from the cab?

Good luck,

Jelle

[Tonegeek]

Since you now have no sound, you should be able to figure out where it quits using your scope (seems I remember you got one recently...). This may seem obvious, but I would check that you did not blow your speaker from the last event. Also, check your speaker cable for a short. Might be a good idea at this point to also use a dummy load if you have one and monitor the output with your scope or like I do with a voltage divider & HV cap off my dummy load to a powered speaker that I scrounged. It will save your ears and expensive speaker. Check your power supply and bias supply for good voltages then do the signal path. Heres why I like the little powered speaker: If the problem is intermittent, then you can put a sine wave to the input and leave your speaker on loud enough to hear it while you do other stuff (like surf ampgarage ). Then when it starts popping, you can be ready with the scope to see what section it is coming from. Don't forget to look for DC getting past a coupler. I like the idea of turning out the lights during the pops to look for arcing - just don't get your nose in some high voltage! good luck!

[mat]

Thanks for Your answers,

So heres what I did. First took all tubes away and vacuumed the whole chassis. Then I sprayed cleaning spray to every socket and jacks. Let it dry and then fired the amp and chopsticked trough it. Did find the loose 8k2 nfb resistor. Soldered a 6k2 in there and fired it again. Sound After few hours playing the amp the crackling came again The crackling on the file: http://media.putfile.com/nhrmcrackle occurs also when all volumes at zero I can see the leds of the effect that is connected to the integrated d-lator to jump every time the crackling occurs. Can I presume that the problem might be upstream from the d-lator ? Between input and d-lator ?
The power transformed is quite close to the power tubes and gets hot. 'Cannot leave your fingers on it' - hot.

I have to measure the coupling caps too.

Before the crackling and thundering sounds the amp sounded fabulous with my 335-style and strat(with Kinmans). First time I'm really pleased how it sounds, very dumblyish fat sound. If I could just nail this crackling bug

btw. the amp was connected to not grounded wall socket when I recorded the crackling noise.

-edit- Ok, tried with the amp again(all volumes at zero). There is something terribly wrong of it. Tried first with nongrounded socket and then to grounded socket. Same results but almost immediatly very loud crackling noise appears: http://media.putfile.com/nhrmnoise

[tonelab2]

btw. the amp was connected to not grounded wall socket when I recorded the crackling noise.
I Don't like the sound of an ungrounded wall socket and would use a grounded one . Just too much danger IMHO.

What's the primary voltage on the PT? Sure your using the right tap? Seems abit to hot.

Have you taken secondary voltage readings?

[mat]

What's the primary voltage on the PT? Sure your using the right tap? Seems abit to hot.

Here are the specs for the PT:
VA185,8 230//3,15-0-3,15V(7A) / 5V 3.5A / 345-0-60-345V(0,18A)

Have you taken secondary voltage readings?

No I haven't. I might put a dummyload on the speaker jack and measure the voltages. I just hesitating to fire the amp again

The amp has 'worked' for about one year now so no wrong connections of the PT.

I edited my post with link to soundfile that I just recorded of firing the amp on nongrounded and then on grounded sockets. Normally I always use grounded sockets.

[tonelab2]

After listening to your sound clip, horrible BTW, I would say the problem is in the output stage for sure with that volume. You may have a faulty OT (I've had 1 similar with a Jap amp a few years ago) or it may be cooking. I would check resistance of OT. I would look for surges in voltage supply ( use alligator clips ).

[mat]

After listening to your sound clip, horrible BTW, I would say the problem is in the output stage for sure with that volume. You may have a faulty OT (I've had 1 similar with a Jap amp a few years ago) or it may be cooking. I would check resistance of OT. I would look for surges in voltage supply ( use alligator clips ).

I'll measure the ot resistances... I swapped known good tube for each spot of the pre amp one by one + swapped the 6L6's for KT77's but still every time I fire the amp after few seconds the noise starts first with few low level pops and then gets louder and louder