Carvin Nomad 112 Crackling and Hissing

[vintagekiki]

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.

Free lift a leg of R3 and C2 to identify the source of hiss
For this check status V1 does not matter

1)
Any cold solder or semi-corrected component (due to aging) can produce audible sensations (hiss, crackling ...)
What is the result when you lift a leg of R3 or C2 to check for hiss?

Voltages 189 VDC at pin 6 is incorrect.
Check (replace) R3 (220k) most likely changed the value more

[Perkinsman]

Free lift a leg of R3 and C2 to identify the source of hiss
For this check status V1 does not matter

1)
Any cold solder or semi-corrected component (due to aging) can produce audible sensations (hiss, crackling ...)
What is the result when you lift a leg of R3 or C2 to check for hiss?
..
Voltages 189 VDC at pin 6 is incorrect.
Check (replace) R3 (220k) most likely changed the value more

Ok, I lifted both R3 & C2, hiss noise still present. Changed V1 tube, noise still present, replaced R3, noise still present. Per schematic, pin 6 is 190vdc.

[Perkinsman]

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?

No, problem was not present before i put in new tubes.

[g1]

Then I would suspect them above all. Or possibly a socket solder connection due to the pressure and wiggling of replacing tubes.
I've had plenty of noise issues from brand new tubes, constant and intermittent noises/hiss etc.

If the amp was working with the old tubes and you still have them, I would just put them back in and test.

[Perkinsman]

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

I thought we narrowed it down to Enzo's theory. I've tried multiple tubes in V1 with the same hiss so I'm very confident that the tubes fine...but I'm leaning toward a bad solder joint. I've reflowed each of the 9 pins on V1. Is there any reason to suck up the old solder and use new solder? I'm open to any suggestions or solutions!

[Chuck H]

I thought we narrowed it down to Enzo's theory. I've tried multiple tubes in V1 with the same hiss so I'm very confident that the tubes fine...but I'm leaning toward a bad solder joint. I've reflowed each of the 9 pins on V1. Is there any reason to suck up the old solder and use new solder? I'm open to any suggestions or solutions!

I just want to confirm that the hiss is there WITHOUT the tube (V1) in place. If this is the case then that tube position is absolutely ruled out. BECAUSE THERE'S NO DAMN TUBE IN THERE TO MAKE NOISE!!!! And I also want to confirm that with this tube removed and using the clean channel the hiss can still be mitigated by the volume control. If this is the case then it rules out any tubes ahead of the volume control. Which is all the rest of them. So tubes would be ruled out entirely. I also want to confirm that with V1 removed the soak channel is quiet (as reported). I also want to confirm that with all the above having been established that disconnecting R3 and C2 did not change the hiss. This would eliminate the power supply as a possible cause.

And I also want to confirm that under these conditions, as they have been reported, there cannot be a problem. So either there is no problem or there is an error in the testing or reporting. As long as this thread has gone I find this unacceptable to be honest. People that only wish to help have invested time into this issue with no benefit to themselves. Cavalier testing and evaluation wastes the time of well meaning and knowledgeable people here.

YOU need to find where the error is in your testing and reporting. Because we cannot do this part of the process for you. You are the only one that has the amp in your possession and can put your hands (and test instruments) to it. It's my position that by asking for assistance here you are accountable for accuracy to every one who has attempted to help. You have not provided that and we cannot move forward before you do.

[vintagekiki]

Ok, I lifted both R3 & C2, hiss noise still present. Changed V1 tube, noise still present, replaced R3, noise still present. Per schematic, pin 6 is 190vdc.

Per schematic, voltage on pin 6 is not 190vdc.
On the one side R3 voltage is 190 VDC (point D) and on the other side R3 is anode V1b (pin 6), voltage on pin 6 must be less than 190 VDC.

If you are not wrong in the measurement, and if the voltage at pin 6 is still 190 VDC, the fault may be: faulty V1b, faulty tube socket, faulty R3 (220 k), R2 (1.5 k)

Question: what are the voltages on pin 6 and pin 8 tube V1b

[Helmholtz]

If hiss disappears when the treble (P4) on min (cut), the duty culprit could be C6 ceramics (120 pF)

Have we ruled out a cracked C6?

Especially with noisy components freeze spray can be a big help (don't use on tubes, though).

[Chuck H]

Ok, I lifted both R3 & C2, hiss noise still present. Changed V1 tube, noise still present, replaced R3, noise still present. Per schematic, pin 6 is 190vdc.

If I read this in order it seems to indicate that with R3 lifted that there is still 190V on pin 6 of V1. Is this correct? Because it sure shouldn't be!!! It should be 0V. And there should be NO TUBE IN THERE. With no tube in there the voltage on that pin should be over 400V if R3 is still connected. Which it shouldn't be.

Have we ruled out a cracked C6?

How is C6 going to make noise with no voltage applied to it?

How many things can possibly be wrong with the same tests in the same place at one time!?!

I'm starting to wonder if we're not being F'd with here.

[vintagekiki]

Perkinsman my apology.

Now I have noticed that the voltage at the point is D + 385 VDC and the voltages near the tubes represent the anode voltages.
The voltages you measured (175 at pin 1, 189 at pin 6) on the V1 tube are correct.

After noticing my mistake I have a question.
Do you have hiss when lift C2 (.01)?
If you have hiss is it on
- P4 (Treble) at boost (max)
- P4 (Treble) at cut (min)

[Helmholtz]

How is C6 going to make noise with no voltage applied to it?

You're right, there shouldn't be any DCV across C6 (especially when V1 is pulled) .
Should have checked with the schem more carefully.

The whole story doesn't seem to make sense. Either there is more than one fault or V3B is noisy - or the noise is actually interference picked up from outside.

An audio file would be interesting. A periodic interference could be displayed with a scope.

[vintagekiki]

If hiss disappears when the treble (P4) on min (cut), the duty culprit could be C6 ceramics (120 pF)

Some capacitors exhibit acoustic noise when operated at frequencies in the audio range.
The acoustic noise phenomenon occurs due to the piezoelectric properties of ceramic.

https://www.edn.com/design/components-and-packaging/4364020/Reduce-acoustic-noise-from-capacitors
https://www.murata.com/en-global/support/faqs/products/capacitor/mlcc/char/0020
https://www.murata.com/en-global/products/capacitor/mlcc/solution/naki

[Helmholtz]

Some capacitors exhibit acoustic noise when operated at frequencies in the audio range.
The acoustic noise phenomenon occurs due to the piezoelectric properties of ceramic.

Yes, but we are looking for a source of electrical not acoustic noise.

[vintagekiki]

Yes, but we are looking for a source of electrical not acoustic noise.

Electrical noise through the speaker manifests as acoustic noise.
The acoustic noise occurs due to the piezoelectric properties of ceramic.

[Helmholtz]

The reversible piezo effect of high dielectric ceramics either converts mechanical vibration into an electrical signal (e.g. piezoelectric microphone) or an electrical signal into a mechanical vibration (e.g. piezo tweeter). It does not change signal frequency.
Especially it does not generate random noise on its own. At least, that's what my books on Solid State Physics (R.P. Feynman, C. Kittel) tell me.

The acoustic noise produced by some ceramic caps mainly consists of harmonics contained in the applied AC voltage. Typically it requires a large AC signal containing a lot of higher frequencies (e.g. pulsed rectifier voltage) to produce an audible effect. Surface mounted cercaps may excite vibrations of the whole board thus increasing sound radiation efficiency and lower frequency content.

https://en.wikipedia.org/wiki/Piezoelectricity