Carvin Nomad 112 Crackling and Hissing

[Perkinsman]

The noise goes up and down with volume and is in both the clean & soak channel. The tubes are new and tested good. Would the problem be a resistor at the preamp or the power amp stage? Would it most likely be a bad cathode or plate resistor?

[vintagekiki]

Is the earthing from the wall to the mains cable correct
Does exist noise when the guitar is plugged into the amplifier:
- when the volume on the guitar is at max (10)
- when the volume on the guitar is at min (0)

Check for cold solder joints on G1 (ferrite bead), R1, J1 (input jack) ¹⁾

[Perkinsman]

Is the earthing from the wall to the mains cable correct ......
Does exist noise when the guitar is plugged into the amplifier:........................................
- when the volume on the guitar is at max (10) ........................................................ ......
- when the volume on the guitar is at min (0)..................................................... .............

Check for cold solder joints on G1 (ferrite bead), R1, J1 (input jack) ¹⁾

.....
Mains ground is fine. Noise is ONLY present when jack is plugged in. Noise increases and decreases with either guitar or amp volume. When I pull the jack out, it's dead quiet. I resoldered J1, G1 and R1. Noise still present.

5 minutes later I turned it back on and no noise. I'm baffled, help!

[g1]

A fault like that would not turn up on a tester, and is not unheard of for new tubes. Was the problem already there before you put the new tubes in?

[Chuck H]

A fault like that would not turn up on a tester, and is not unheard of for new tubes. Was the problem already there before you put the new tubes in?

This^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I've had several new tubes right out of the box that caused problems. Including problems like your having. Another thing might be dirty contacts. Tube pin socket holes, jack contacts and any non solder connection. That amp isn't a spring chicken It might be time for some Cramolin.

[Enzo]

New is not the same thing as good. Quite a while ago I bought a box of 100 new 12AT7 GE tubes. EVERY SINGLE ONE of them, for the first minute or so of power up would crackle and make noise, and then they were quiet and fine, never to bother us again. I used them until they were gone, never had any issues other than their first moment of life. So tubes with problems can wind up good. Point being, never take tubes for granted.

[vintagekiki]

... for the first minute or so of power up would crackle and make noise, and then they were quiet and fine, never to bother us again...

A long time ago the tubes warm (6.3 VAC without +HV) for 10 days for reheat and getter activated.

[Perkinsman]

New is not the same thing as good. Quite a while ago I bought a box of 100 new 12AT7 GE tubes. EVERY SINGLE ONE of them, for the first minute or so of power up would crackle and make noise, and then they were quiet and fine, never to bother us again. I used them until they were gone, never had any issues other than their first moment of life. So tubes with problems can wind up good. Point being, never take tubes for granted.

This problem is a little different in that it’s intermittent. Yesterday I started it & it hissed, today it’s not. Is there a way to test the “barrel” type jack or the ferrite bead?

[Chuck H]

...

Another thing might be dirty contacts. Tube pin socket holes, jack contacts and any non solder connection. That amp isn't a spring chicken It might be time for some Cramolin.

[Perkinsman]

I’ll clean the contacts today. Is there a way to test the “barrel” type jack or the ferrite bead?

[g1]

I’ll clean the contacts today. Is there a way to test the “barrel” type jack or the ferrite bead?

Can you post the schematic? You said the noise goes up and down with volume? Does that mean you can make it go away by turning down the volume control?
Ideally you would test the jack & bead by grounding the signal right after it. You may need to ground with a cap if there is DC present at the point you are grounding. If it makes the noise disappear, then you have isolated the problem to the jack, bead, or their connections.

[vintagekiki]

Can you post the schematic?

http://schems.com/bmampscom/carvin/112%20Nomad%20212%20Bel%20Air%20REV-E1.pdf

http://i1282.photobucket.com/albums/a527/tamedragon66/Nomad_6_zps2d17ce5c.jpg
Carvin Nomad 112 chassis ¹⁾

[g1]

Great. You can directly ground the tube side of the ferrite bead. Does the problem remain or disappear?

[Perkinsman]

Great. You can directly ground the tube side of the ferrite bead. Does the problem remain or disappear?

Are u saying that I can attach one end of a wire from the tube side of the bead direct to chassis with power on? Do I need to pull V1 or leave it in?

[Chuck H]

The "barrel type jack" (Cliff jack) is as easy to test as it is to see what it's doing with it's contacts. Just look at it to determine when as where it should contact with and without a jack plugged in and use your meter to check continuity.

I'm not experienced with this, but what could go wrong with a ferrite bead? It's ferrite and it doesn't connect directly/conductively to anything. The way I figure it, it's either there or it's not. If it's there then it's doing what a ferrite bead does. Unless they can become somehow polarized or otherwise incorrectly "charged" or something.?.