Carvin Nomad 112 Crackling and Hissing

[vintagekiki]

Not a problem with ferrite bead, but whether the wire passing through the ferrite maybe have a cold solder on the PCB.

[g1]

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?

Yes you can do it here because there is no DC to worry about. Leave V1 in circuit. Try with various volume control settings and see if the problem remains or disappears.

[Perkinsman]

Ok, I still have hissing (similar to rf white noise) when I grounded a lead from the tube side of the bead to chassis ground. The hissing increases/decreases with amp volume. Noise present whether guitar jack in or out. Btw, I've resoldered the bead, the cliff jack and R1 & cleaned both preamp & power tube sockets with deox.

[Randall]

Pull V1, is the noise still there?

[Perkinsman]

Pull V1, is the noise still there?

Pulled V1, noise still present. Noise is with jack in or out and goes up/down with amp volume. (Earlier statement I made said that noise was only when the jack was in, but that has changed)

[Chuck H]

Pulled V1, noise still present. Noise is with jack in or out and goes up/down with amp volume. (Earlier statement I made said that noise was only when the jack was in, but that has changed)

Noise in BOTH channels with V1 pulled?

[Perkinsman]

With V1 pulled, there's hissing noise only on the clean channel which increases/decreases with amp volume, the soak channel is quiet.

[Perkinsman]

Not a problem with ferrite bead, but whether the wire passing through the ferrite maybe have a cold solder on the PCB.

I had already resoldered G1, R1 & J1

[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.

Is it very common for a new tube to be intermittently noisy, and if so, it more likely to be a power or preamp tube?

[vintagekiki]

Is it very common for a new tube to be intermittently noisy

If you don't have noise if remove from socket V1, or if the drive and volume 1 potentiometers (P1, P5) at min (0), then probably the new tube V1 is noisy.
Try replace with some other tube from the amplifier, Carvin has a few.
Are the voltages at V1 (pin1 and pin6) as written by schematics (190 VDC)

[Perkinsman]

If you don't have noise if remove from socket V1, or if the drive and volume 1 potentiometers (P1, P5) at min (0), then probably the new tube V1 is noisy.
Try replace with some other tube from the amplifier, Carvin has a few.
Are the voltages at V1 (pin1 and pin6) as written by schematics (190 VDC)

As I said above, after removing V1, noise was still present so it's not V1. I haven't checked voltages yet.

[Enzo]

OK, so the noise comes from after V1 and before the volume control.

[Chuck H]

As stated:

With V1 pulled, there's hissing noise only on the clean channel which increases/decreases with amp volume, the soak channel is quiet.

As correctly assesed:

OK, so the noise comes from after V1 and before the volume control.

And the circuit:



Shown with V1 removed. There's no amplifier prior to the volume control in this scenario so I expect there must be an error in the testing and/or reporting. Unless the hiss is entering through the power supply or 0V. Which seems unlikely unless either is compromised such that the amp should be exhibiting other symptoms.

[vintagekiki]

Unless the hiss is entering through the power supply ¹⁾ or 0V.

¹⁾ This is easily checked by removing R3 (220k) or C2 (.01)
If hiss disappears when the treble (P4) on min (cut), the duty culprit could be C6 ceramics (120 pF)

[Perkinsman]

¹⁾ This is easily checked by removing R3 (220k) or C2 (.01)
If hiss disappears when the treble (P4) on min (cut), the duty culprit could be C6 ceramics (120 pF)

Are you saying that I can lift a leg of R3 and C2 to check for hiss? Is that with V1 in or out? Btw, with V1 in, I had 175 at pin 1, 189 at pin 6 & 191vdc at R3. I also resoldered pin 6 because it looked like a possible cold solder and the noise has diminished quite a bit but I'm going to let it warm up awhile to see whether that may have been the problem. Would a cold solder at pin 6 make the hissing sound?