Fender Hot Rod Deluxe snap , crackle , pop ...

[themusic]

Yes another HRD problem...
I have a Fender HRD that when I first turn it on has a constant hiss, pop, crackle noise. The noise is not effected by volume control.
I can control noise when in drive channel thru master vol. After 10-12 min noise will go away with an occasional loud pop or crackle.
All new tubes...no change. Probed for loose connections...no change. Pulled boards check solder...no change. Wiggle tubes...no change.
When the amp quiets down , with doing all above I can't get it to make noise.!!! Somebody has change R78 , R79 but seem to do a good job.
Voltages are correct both sides...In fact all voltages seem steady and correct from schematic... I'll shut it off for 10mins then here we go again.
I'm stuck...thanks

[nickb]

What you have told us narrows it to V1A or V2B with the tone stack between them. So, does the tone stack setting affect the 'Rice Krispies' noise?

hotrod_deluxe.pdf

[Jazz P Bass]

Well it seems that you 'checked' everything but the power supply.

Soooo.....

Anytime I see the Drive Channel making noise, I shoot stright to C36.
Check the Volts ac ripple.
This is the preamp decoupling capacitor.
When you strike a chord, the notes will be impressed on that node & the cap will decouple them from the supply.

A faulty or failing cap will let the notes continue to ride on the supply.
Not a good thing.

In a situation like this it really could be anything.
The idea is to narrow that down to the fault.

[themusic]

Well it seems that you 'checked' everything but the power supply.

Soooo.....

Anytime I see the Drive Channel making noise, I shoot stright to C36.
Check the Volts ac ripple.
This is the preamp decoupling capacitor.
When you strike a chord, the notes will be impressed on that node & the cap will decouple them from the supply.

A faulty or failing cap will let the notes continue to ride on the supply.
Not a good thing.

In a situation like this it really could be anything.
The idea is to narrow that down to the fault.

Seems to be all over the place 10-13-15 ACmv at idle. soon as you play its all over the place.
Tone stack doesn't seem to effect noise. Thanks

[Jazz P Bass]

Seems to be all over the place 10-13-15 ACmv at idle. soon as you play its all over the place.
Tone stack doesn't seem to effect noise. Thanks

O/k, when you play a chord, the ripple reading is 'all over the place'.

Without playing another chord, it should settle down.
Even with a volt meter, you should see a rise in the reading when the amp crackles, if you are on the problem circuit.
This is where a scope comes in handy.

Do you have another 500 volt cap that you can tag across the existing one?

[themusic]

yes I'll dig it out and give it a try...thanks

[themusic]

replaced with new cap...a little better but still here that pop and crackle in the back ground. the ac ripple does'n't seem as bad.
The amp plays great nice and clean, does'n't crap out when you lean on it.
I have my buddy's HRD here and C36 seems pretty steady what ever you do. thanks

[Jazz P Bass]

You can trace that pop & crackle with a meter.

Narrow down what control may or may not affect it.

It's before that.

Also, you should check the interstage coupling caps for Vdc leakage.
They are the caps that connect the preamp plates to the next stage.

The pop & crackle should show up on the meter.

[themusic]

thanks...I'll try that next.

[Enzo]

Do me a favor, use a bright light, and look CLOSELY at all the solder joints on the tube sockets, particularly the power tubes, but look at them ALL. Are any of them even remotely suspicious of cracked solder? I routinely resolder all the tube socket pins on the HR series amps, they are too often cracked.

I don't think of 11mv ripple as "bad". You can't measure ripple while you play, because these are not regulated supplies and the extra current draw while playing causes the B+ voltage to change constantly.

If it warms up and stops making the noise, that is what freeze spray is made for. CHilling circuits. And if chilling an area makes the noise start back up, we have found a sensitive area.

Isolate the problem.
Since the master volume controls the noise in dirt channel, we know the source is before that. And in clean, the volume makes no difference, so it is after that. But in dirt channel does the DRIVE control have any effect? Probably not but check.

Does the BRIGHT switch make the noise sound brighter? Do the tone controls, especially the treble, affect the TONE of the noise in anyway? If NO and NO, then V1b is safe. And we are left with the two triode in V2. So get a clip wire and ground it to chassis. Now CAREFULLy ground pin 2 of V2 with it. If it makes more hum, ignore that, we are only interested in what it does to the noise. Does grounding pin 2 kill the noise? If so, it is coming from before that grid, if not, move over to pin 7. Ground that, did it kill the noise or not? Again, ignore any resulting hum..Also it may make a POP when you touch it, don't be startled and it won't hurt it.

Any point in the signal path you ground that kills a noise is after its source. And if grounding has no effect on the noise, then the noise is coming from further along.

There are ways to "ground" the signal path at points with DC voltages, like the tube plates, but I will leave that for later, for now, do those things to isolate the stage that is noisy.

[themusic]

Do me a favor, use a bright light, and look CLOSELY at all the solder joints on the tube sockets, particularly the power tubes, but look at them ALL. Are any of them even remotely suspicious of cracked solder? I routinely resolder all the tube socket pins on the HR series amps, they are too often cracked.

I don't think of 11mv ripple as "bad". You can't measure ripple while you play, because these are not regulated supplies and the extra current draw while playing causes the B+ voltage to change constantly.

If it warms up and stops making the noise, that is what freeze spray is made for. CHilling circuits. And if chilling an area makes the noise start back up, we have found a sensitive area.

Isolate the problem.
Since the master volume controls the noise in dirt channel, we know the source is before that. And in clean, the volume makes no difference, so it is after that. But in dirt channel does the DRIVE control have any effect? Probably not but check.

Does the BRIGHT switch make the noise sound brighter? Do the tone controls, especially the treble, affect the TONE of the noise in anyway? If NO and NO, then V1b is safe. And we are left with the two triode in V2. So get a clip wire and ground it to chassis. Now CAREFULLy ground pin 2 of V2 with it. If it makes more hum, ignore that, we are only interested in what it does to the noise. Does grounding pin 2 kill the noise? If so, it is coming from before that grid, if not, move over to pin 7. Ground that, did it kill the noise or not? Again, ignore any resulting hum..Also it may make a POP when you touch it, don't be startled and it won't hurt it.

Any point in the signal path you ground that kills a noise is after its source. And if grounding has no effect on the noise, then the noise is coming from further along.

There are ways to "ground" the signal path at points with DC voltages, like the tube plates, but I will leave that for later, for now, do those things to isolate the stage that is noisy.

Thanks Enzo you've help me freeze spray before...lots to do tonight...thanks everybody

[themusic]

Do me a favor, use a bright light, and look CLOSELY at all the solder joints on the tube sockets, particularly the power tubes, but look at them ALL. Are any of them even remotely suspicious of cracked solder? I routinely resolder all the tube socket pins on the HR series amps, they are too often cracked.

I don't think of 11mv ripple as "bad". You can't measure ripple while you play, because these are not regulated supplies and the extra current draw while playing causes the B+ voltage to change constantly.

If it warms up and stops making the noise, that is what freeze spray is made for. CHilling circuits. And if chilling an area makes the noise start back up, we have found a sensitive area.

Isolate the problem.
Since the master volume controls the noise in dirt channel, we know the source is before that. And in clean, the volume makes no difference, so it is after that. But in dirt channel does the DRIVE control have any effect? Probably not but check.

Does the BRIGHT switch make the noise sound brighter? Do the tone controls, especially the treble, affect the TONE of the noise in anyway? If NO and NO, then V1b is safe. And we are left with the two triode in V2. So get a clip wire and ground it to chassis. Now CAREFULLy ground pin 2 of V2 with it. If it makes more hum, ignore that, we are only interested in what it does to the noise. Does grounding pin 2 kill the noise? If so, it is coming from before that grid, if not, move over to pin 7. Ground that, did it kill the noise or not? Again, ignore any resulting hum..Also it may make a POP when you touch it, don't be startled and it won't hurt it.

Any point in the signal path you ground that kills a noise is after its source. And if grounding has no effect on the noise, then the noise is coming from further along.

There are ways to "ground" the signal path at points with DC voltages, like the tube plates, but I will leave that for later, for now, do those things to isolate the stage that is noisy.

ok finally back at this , checked solder joints ok , treble does't effect noise, when I grounded pin 2 everything went quiet, pin 7 no change.
After about 45min everything quiets down but you can always hear a faint hiss in background even with volume all the way off.
Work my way around with freeze and got no change. Always seems the worst when I leave off over night and turn on next day gets quieter
as day goes on even if I turn it off or go to standby... Just to make sure I used power amp in with signal and have no issues...thnaks

[themusic]

Problem Solved...When Enzo gave me the clue to check out V2's path I traced it back to pin 2... when amp got quiet I sprayed C5 & C6 area with freeze spray
and instant snap, crackle, pop ! Replaced C5 & C6 cleaned up area and VICTORY !!! Thanks for everybody's help...and of course ENZO