I've just completed a built of the NuHybrid amp from Pete Millett. Nice little amp, very interesting sound so far. Had some serious issues at first which were solved by grounding the pot. But there's a subtle-yet-noticeable hiss in the right channel, and I'm not entirely sure how to fix it. My EE knowledge is pretty limited, so I don't even know where to begin when it comes to diagnosing and fixing the issue. If anyone is willing to help me figure this out, I'd surely appreciate it.
EDIT: OK, here's an update: I've just verified that it's NOT just on the right channel. It's equally hissing in both channels, even when the volume pot is turned all the way down.
Maybe that knowledge will help us figure this out?
I'll put a link to Pete's page about this project here, which contains lots of information including the schematic. I'll also post a picture of my build.
Thanks!
NuHybrid Headphone Amp
EDIT: OK, here's an update: I've just verified that it's NOT just on the right channel. It's equally hissing in both channels, even when the volume pot is turned all the way down.
Maybe that knowledge will help us figure this out?
I'll put a link to Pete's page about this project here, which contains lots of information including the schematic. I'll also post a picture of my build.
Thanks!
NuHybrid Headphone Amp
An externally hosted image should be here but it was not working when we last tested it.
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Lift one end of both C13 and C14. Is the noise gone now?
If so, then the noise is in the first buffer stage. Not too likely, though.
The values of R19, R20, R22, R23 do seem to be unnecessarily very high.
If the noise is still there, then it is in the tubes or the bias regulator.
Have you tried swapping the tubes?
If so, then the noise is in the first buffer stage. Not too likely, though.
The values of R19, R20, R22, R23 do seem to be unnecessarily very high.
If the noise is still there, then it is in the tubes or the bias regulator.
Have you tried swapping the tubes?
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Whichever is convenient, but the input side would be a little safer for the circuit.
Don't let the bare leads touch anything else.
Don't let the bare leads touch anything else.
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Pardon my ignorance, but which side is the input side?
I don't suspect the NuTube, as I have another amp with that same tube and it's quiet as the grave.
I'll report back when I've tested that capacitor leg lift maneuver.
OK, here's an update:
Before I tried lifting those capacitor legs, I did another listening test with some sensitive IEMS. I wanted to be sure what the hiss was all about.
Well, I've just verified that it's NOT just on the right channel. It's equally hissing in both channels, even when the volume pot is turned all the way down.
Maybe that knowledge will help us figure this out?
Before I tried lifting those capacitor legs, I did another listening test with some sensitive IEMS. I wanted to be sure what the hiss was all about.
Well, I've just verified that it's NOT just on the right channel. It's equally hissing in both channels, even when the volume pot is turned all the way down.
Maybe that knowledge will help us figure this out?
Depends, is the noise exactly the same in both channels, like mono would be?
Or is there rather, about equal, but different, noise in the two channels? If you used headphones,
would the noise be in the middle of your head, or in each ear? Listen right between the speakers.
Does the noise center at your head, or do you hear two noise sources, at the left and right?
Or is there rather, about equal, but different, noise in the two channels? If you used headphones,
would the noise be in the middle of your head, or in each ear? Listen right between the speakers.
Does the noise center at your head, or do you hear two noise sources, at the left and right?
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Ok, lift the capacitor legs, but let the power bleed down first.
Verify with a meter that it is 0VDC before lifting.
Verify with a meter that it is 0VDC before lifting.
In order to have a chance of eliminating the noise, first you have to know the source.
This test will determine whether the noise is from the first stage or the second stage.
Generally one would expect the noise to be from the tubes. However, this circuit
has several possible noise sources, and this test will localize the noise and eliminate
some of the possibilities.
This test will determine whether the noise is from the first stage or the second stage.
Generally one would expect the noise to be from the tubes. However, this circuit
has several possible noise sources, and this test will localize the noise and eliminate
some of the possibilities.
Can't really get one leg out without potentially snapping the other off. Can I just take those caps out completely to do the test? That'd be the easiest thing for me, and allow me to put them back if needed.
OK, Test complete. If anything, that made the hiss louder. Also, perhaps obviously, no audio signal was heard.
Ok, the noise is in the power supply, the tubes, or the regulator. My guess is the tubes.
What kind of power supply are you using, is it a linear type or a switching type?
Some cheap SWPS could be noisy.
What kind of power supply are you using, is it a linear type or a switching type?
Some cheap SWPS could be noisy.
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I've tried two different power supplies, one smaller Mean Well 24v, and one larger (not sure if switching or linear) brick-type supply borrowed from a Nobsound speaker amp. Same hiss from both. Also tried plugging into a power conditioner, no dice.
I'm still reticent to suspect the tubes, since my Korg NuTekt which uses the exact same NuTube is completely silent.
Is there a way we can test the regulator?
I'll put the caps back.
I'm still reticent to suspect the tubes, since my Korg NuTekt which uses the exact same NuTube is completely silent.
Is there a way we can test the regulator?
I'll put the caps back.
This circuit uses very high resistance values, and very low plate current.
Did you use metal film resistors?
There's no easy way to check the regulator except by replacing it,
but it is not very likely to be the problem. And there is already some filtering on it.
Can you install different tubes to see if the noise changes?
Did you use metal film resistors?
There's no easy way to check the regulator except by replacing it,
but it is not very likely to be the problem. And there is already some filtering on it.
Can you install different tubes to see if the noise changes?