Intermittent Popping/Crackling

[EddieDavis]

I've got a Fender Roc Pro 1000 combo amp - clean channel is solid state, and drive channel uses a single tube.

It's been crackling and popping intermittently while playing. Can't trust the amp to not do that at a gig so I've gotta fix it, until I can save up for a serious upgrade! 

I've tried replacing the tube and it seemed to not crackle for a while, but then it let out a real nasty pop.  Even though I was playing at super low volume, the pop was a single loud and sharp sound.

It has foil shielding inside so I'm thinking of replacing that with metal grill material, which I've heard is one thing that can help.

Is this something I can address myself?  Or should I take it to a shop?  I don't wanna put too much money into this amp anymore, as I've already paid a lot to have it repaired in the past.  (last time I took it to a tech a few summers ago it was almost a $100 dollar repair on an amp that cost me $175 used) so I've already spent $275 into an amp that I will be upgrading from in 6 months anyways. 

Ideas?  Anything else I should check or try that I can do myself?

 

[mayfly]

my money is on a coupling capacitor somewhere passing DC.  Look at either the input to the grid of the tube (which may or may not have one depending on the SS driving circuitry), or the signal cap on the plate.

 

[EddieDavis]

my money is on a coupling capacitor somewhere passing DC.  Look at either the input to the grid of the tube (which may or may not have one depending on the SS driving circuitry), or the signal cap on the plate.

Thanks!  Is that something I can do or is that Amp Tech territory?  I've heard capacitors can hold charge for up to a year even unplugged. 

 

[mayfly]

How about get some pics for us of the inside - above and below the board.  Got a DMM?  Got a soldering iron?  Got an electronics store nearby?  Got a schematic?

If the answer is yes to all of these, then I can walk you through it.

 

[mayfly]

It has foil shielding inside so I'm thinking of replacing that with metal grill material, which I've heard is one thing that can help.

oh yea - changing the foil to something else won't do squat.  Don't bother with that.

 

[mayfly]

Other stuff:  Does the crackling change/get worse/get better when you turn the channel volume up/down?  How about the master volume?  reverb? Any of the tone pots?  Try listening just through the effects send - any crackle there?  How about just plugged straight into the effects return?  Still crackle?

Oh - and I found a schematic for the amp.  I suspect that the tube is actually not doing much for you and you could just pull it out of there and the amp will work.

here's a link to the schematic:

http://schems.com/bmampscom/fender/Roc_Pro_1000_schematic.pdf

Update:

If you look at V1A, you'll see that it's acting as a cathode follower.  If you believe the voltage levels on the schematic, it's biased at a very very plate starved level. V1B is interesting.  It appears to be biased at a constant voltage (depending on which gain stage is turned on), but the signal path does not even go through the grid.  It appears to be either biased 'on' or 'off' depending on if it's the 'yellow' or 'red' channel.  Because of this I believe that it's just acting as a glorified clipping diode, likely only in the 'red' channel.  Anyhow, because of all this, you can just pull the entire tube out.  The cathode follower is just to provide a low impedance to drive the clipping thingy - the signal will pass through regardless.  Likely the red channel will get a LOT louder and cleaner, but other than that the amp will sound the same. 

Crackle might disappear as well 

 

[EddieDavis]

Other stuff:  Does the crackling change/get worse/get better when you turn the channel volume up/down?  How about the master volume?  reverb? Any of the tone pots?  Try listening just through the effects send - any crackle there?  How about just plugged straight into the effects return?  Still crackle?

Oh - and I found a schematic for the amp.  I suspect that the tube is actually not doing much for you and you could just pull it out of there and the amp will work.

Thanks for all the info!

I'm at a gig tonight but I will check all these things over the next few days and tell you what I observe on Thursday or Friday.

I can tell you that it seems more likely to crackle and pop when the channel volume is higher, and that I was using a lot of reverb for surf tunes. 

It crackled all over the place last time I tried to play out with it.  The most recent pop was just one big loud sound at pretty low volume, still using reverb though.

I'll check the other things out and check back with you later.

Thanks again!

 

[fdesalvo]

DO NOT TOUCH ANYTHING INSIDE THE AMP!  No - not without ensuring all electrical energy has been fully discharged!  Capacitors inside your amp can store lethal energy hours after unplugging, so do your troubleshooting on the unopened amp unless you know what you are doing.  Touching components on the [inside] chassis end opposite any filter capacitors can still discharge the capacitors' charge through your torso and across your heart, killing you HOURS AFTER UNPLUGGING. If you happen to touch the right something bad with one hand, you will get a nasty jolt that you won't forget.  PS, Nice Ibanez!)


Now, sorry I haven't read through the entire thing, but here's what usually goes on fender combos and in what order:

1. Tube
2. Cable (reverb send /return, your guitar cable)
3. Input jack
4. Poop inside the chassis (Phonetically, "shassy", if you are English and call trunks, "boots", and hoods, "bonnets") that can possibly kill you.
    A. I see the cat in your avatar.  If you fry yourself, that cat will eat your eyes.

Does this happen with no guitar cable plugged in?  Fender combos mount their inputs right onto the circuit board and strain is passed right onto the traces.  This is a common cause of this type of noise.

Does this happen wiht no preamp tube installed?  If it does, then your problem is after the preamp stage.  If not, then it is between the input and that tube.

Does it happen with no reverb cables plugged in?  Or is it digital reverb?  If there's a tank, these short out easily and reverb recovery stages are prone to noise.  Try gently wiggling the reverb cables/jacks and observe noise.

If these things happen with higher volume, welcome to combo hell!  The sound pressure and vibrations will make it into your chassis, exacerbating issues like cold solder joints, failing cables, shaky inputs, etc., any of which could have barely functioning connections that will open and close as vibrations propagate through the chassis.

I've got a Fender Roc Pro 1000 combo amp - clean channel is solid state, and drive channel uses a single tube.

It's been crackling and popping intermittently while playing. Can't trust the amp to not do that at a gig so I've gotta fix it, until I can save up for a serious upgrade! 

I've tried replacing the tube and it seemed to not crackle for a while, but then it let out a real nasty pop.  Even though I was playing at super low volume, the pop was a single loud and sharp sound.

It has foil shielding inside so I'm thinking of replacing that with metal grill material, which I've heard is one thing that can help.

Is this something I can address myself?  Or should I take it to a shop?  I don't wanna put too much money into this amp anymore, as I've already paid a lot to have it repaired in the past.  (last time I took it to a tech a few summers ago it was almost a $100 dollar repair on an amp that cost me $175 used) so I've already spent $275 into an amp that I will be upgrading from in 6 months anyways. 

Ideas?  Anything else I should check or try that I can do myself?

 

[mayfly]

psst... Frank....

.... it's a solid state amp.  The tube is just a clipping diode run at 16V DC.  Nothing higher than 48V in there.

 

[fdesalvo]

Par'don, my friend; I thought it was a "hy-bread" amp.  Other points applicable.

psst... Frank....

.... it's a solid state amp.  The tube is just a clipping diode run at 16V DC.  Nothing higher than 48V in there.

 

[Cagey]

 

[BigSteve22]

What's all this crap I hear about violins on television?.........  :laughing11: :laughing3: :laughing7:

 

[fdesalvo]

You guys are trolling for trouble!

 

[EddieDavis]

It could very well be the reverb tank.  I gave this amp a break because I was flustered with it but I'll keep trying to narrow it down. 

I'm starting to think maybe I'll just bite the bullet and take it in to a repair shop... 

If I can get this fixed for a small price, I won't be in such a hurry to buy a new amp... Then I can take more time to save up for something real creamy! 

:tard:

 

[fdesalvo]

Where do ya live? Maybe one of us is local to u.  Further esearch suggests cold solder joints are common on these.

 

[EddieDavis]

Where do ya live? Maybe one of us is local to u.  Further esearch suggests cold solder joints are common on these.

I live in Portland, OR.  ccasion14:

 

[fdesalvo]

If you could get the circuit board or chassis over to me I'd have a look at it, but I'm in the Los Angeles area.

 

[EddieDavis]

If you could get the circuit board or chassis over to me I'd have a look at it, but I'm in the Los Angeles area.

Thanks anyway!  I totally would if I were down there.  Some of the guys at Centaur Guitar up here said I should try using electronics contact cleaner on the pots.  So I'll try that.  If that doesn't work, I'll probably just bite the bullet and take it to a shop.  I can't quite bring myself to sell it.  Such a bad ass sounding amp when it's working!

 

[fdesalvo]

There's no finer excuse to get into this yourself.  If you need a walk-through, hit one of us up.  It's a very reqarding way to lose hair.

 

[EddieDavis]

There's no finer excuse to get into this yourself.  If you need a walk-through, hit one of us up.  It's a very rewarding way to lose hair.

It sounds like maybe just cleaning the pots with electronic contact cleaner could resolve the issue....  but I'm a bit of an ignoramus on this....  if it is dirty pots causing the crackling, would they still make that noise even if the pots aren't moving?  Because it makes the sound when I'm playing, and dials aren't being turned. 

I know it's not the reverb now because I disabled it and it still makes the noise. 

Going to try giving the pots a clean this weekend,

thanks for being willing to help a newbie!