Does anyone have integrated tube amp that encounters with hum or bug sound? At 1/3 volume, it's great but when I turn the volume to 1/2, I can hear hum on both speakers. So my best way is to hook up with another preamp to use the volume while setting the tube volume at 1/3. What other options to fix it?
If the hum is max when vol pot is in the middle position and the pot is high value above 100k a quick and dirty solution is to fit a 47k resistor across the pot
or one 47k from wiper to one end and onother 47k from wiper to the other end (this will change the characteristic of volume control)
quick because it can be tested easily
dirty because it does not tackle the root cause ...
Do you have a schematic of the amplifier?
Does this amp have an input selector switch?
Is the same hum on all signal sources (phono, tuner, CD player)?
Did you change something (add one more signal source at the input jacks, change out one CD player for another, etc.)?
What changed? . . .
Did this amplifier always have hum, or did it just start recently?
Did you make a modification, or even move some wires inside the amp?
With so little information, I am only troubleshooting in the dark.
Does this amp have an input selector switch?
Is the same hum on all signal sources (phono, tuner, CD player)?
Did you change something (add one more signal source at the input jacks, change out one CD player for another, etc.)?
What changed? . . .
Did this amplifier always have hum, or did it just start recently?
Did you make a modification, or even move some wires inside the amp?
With so little information, I am only troubleshooting in the dark.
If the hum suddenly starts at a certain point in the volume control, there could be
a physical problem in the control, perhaps related to the loudness tap.
Are you sure the hum is totally gone at lower settings, or just not as loud?
Be honest, there was a thump when turned on before upgraded the coupling caps and pot. I didn't pay attention to the hum but I remember exactly there was none either but I was using 1/3. Didn't go 1/2 or max yet. I should have tested all before upgrade, that was a mistake.
If setting with at 1/3 and use an external preamp, it's all good.
Replaced Pot and Coupling Caps
So far only thump in left channel when turn on from cold but no thumb after the amp is warm
No hum from 0 - 1/3 volume
1/2 : hum on tweeter and woofer on both speakers
I haven't tried other input: there are 2 separate inputs (0.25v for phono, cd, etc) (0.6v is a single input) I have been using 0.6v input so haven't tested with 0.25v yet
If setting with at 1/3 and use an external preamp, it's all good.
Replaced Pot and Coupling Caps
So far only thump in left channel when turn on from cold but no thumb after the amp is warm
No hum from 0 - 1/3 volume
1/2 : hum on tweeter and woofer on both speakers
I haven't tried other input: there are 2 separate inputs (0.25v for phono, cd, etc) (0.6v is a single input) I have been using 0.6v input so haven't tested with 0.25v yet
Yaqin_MC-100b
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Shorting the inputs will eliminate problems 'from outside' the amp like ground loops, and picking up noise via the cables somehow..
But, as you say, perhaps not necessary to try...it's just one of the things I do when hunting down hum and noise problems.
I can't see a volume control on the Yaquin schematic you posted...am I missing something or did you add a volume control?
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How much hum, ______ mV?
What frequency? Hum, 1x and 2x the power line frequency? Oscillation? Motor boating? Noise? What kind of "Hum"? It is interesting that the hum is in both the woofer and the tweeter.
Did you disturb the wiring position when you replaced parts? Did you change where the ground of the pot connected to? Did you change any other parts, transformers, feedback parts, or tubes?
There are 3 DC coupled gain stages. There is lots of gain in the amp, and it has global negative feedback. It might be on the margin of unstable.
Did you change what speakers you are using? Did you change what output tap you are using? Is there a problem with both Ultra Linear mode, and with Triode mode? Is there a problem with both positions of the Negative Feedback Switch?
What frequency? Hum, 1x and 2x the power line frequency? Oscillation? Motor boating? Noise? What kind of "Hum"? It is interesting that the hum is in both the woofer and the tweeter.
Did you disturb the wiring position when you replaced parts? Did you change where the ground of the pot connected to? Did you change any other parts, transformers, feedback parts, or tubes?
There are 3 DC coupled gain stages. There is lots of gain in the amp, and it has global negative feedback. It might be on the margin of unstable.
Did you change what speakers you are using? Did you change what output tap you are using? Is there a problem with both Ultra Linear mode, and with Triode mode? Is there a problem with both positions of the Negative Feedback Switch?
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I won't be home until next Monday so I will take a look again later.
I don't have equipment to answer those questions.
Did you disturb the wiring position when you replaced parts?
Nothing change except the pot and caps.
All hookup wires are the same, except swap between the tube and SS amp.
Did you change where the ground of the pot connected to?
No, I removed the pot then put back to the same location
Did you change any other parts, transformers, feedback parts, or tubes?
I did change all the upgrade tubes but swapped back to test again and got the same problem. All the original tubes have label from V1 to V5 so I put in all the same location. Even I tried the swap the upgrade tubes around still not help.
Both UL and TM are the same problem when turn the volume to 1/2, otherwise no hum between 0-1/3. When turn between 1/3 to 1.2, the hum keeps louder, can be heard at 6 feet away.
Is there a problem with both positions of the Negative Feedback Switch?
-I am not sure, there is not switch
-There are two switches: I always turn off before change the mode.
----1. UL and TM
--- 2. Input switch .6v (like pure mode) and .25v (CD, Aux1, Aux2, etc)
Between 1/3 - 1/2, the hum sound very small when stand next to speaker until reach to 1/2 then can hear from 6 ft away
The sound is pretty awesome with SACD except I can't turn its louder but at 1/3 is good enough. If I want more volume, I can hook up an external preamp to pump up more but I really don't need that loud.
I don't have equipment to answer those questions.
Did you disturb the wiring position when you replaced parts?
Nothing change except the pot and caps.
All hookup wires are the same, except swap between the tube and SS amp.
Did you change where the ground of the pot connected to?
No, I removed the pot then put back to the same location
Did you change any other parts, transformers, feedback parts, or tubes?
I did change all the upgrade tubes but swapped back to test again and got the same problem. All the original tubes have label from V1 to V5 so I put in all the same location. Even I tried the swap the upgrade tubes around still not help.
Both UL and TM are the same problem when turn the volume to 1/2, otherwise no hum between 0-1/3. When turn between 1/3 to 1.2, the hum keeps louder, can be heard at 6 feet away.
Is there a problem with both positions of the Negative Feedback Switch?
-I am not sure, there is not switch
-There are two switches: I always turn off before change the mode.
----1. UL and TM
--- 2. Input switch .6v (like pure mode) and .25v (CD, Aux1, Aux2, etc)
Between 1/3 - 1/2, the hum sound very small when stand next to speaker until reach to 1/2 then can hear from 6 ft away
The sound is pretty awesome with SACD except I can't turn its louder but at 1/3 is good enough. If I want more volume, I can hook up an external preamp to pump up more but I really don't need that loud.
Hums and noises are some of the trickiest things to troubleshoot in a discussion group. Folks with a lot of experience distinguish between hums at the power line frequency or at twice that - these have different causes. Then they try to distinguish other noises by characteristic sounds that are often difficult for folks with less experience to describe in words. But everybody muddles on doing our group best.
One important first step is to isolate the amplifier as much as possible, to eliminate confounding factors. In this first step the amplifier is connected to *only* the speakers and AC power - no other wires touch it or the speakers, no powered subs or anything else. It's usual to insert shorting plugs in the tested input. Do that first and let us know.
All good fortune,
Chris
One important first step is to isolate the amplifier as much as possible, to eliminate confounding factors. In this first step the amplifier is connected to *only* the speakers and AC power - no other wires touch it or the speakers, no powered subs or anything else. It's usual to insert shorting plugs in the tested input. Do that first and let us know.
All good fortune,
Chris
'Upgrading' coupling caps sometimes means swapping physically small caps for physically large caps (e.g. polypropylene). In some cases this can cause direct hum pickup, or instability via capacitive feedback. Try putting the old caps back and see if that solves the problem. Another thing to try is adding a grid stopper resistor to the first triode. The symptoms you describe could be caused by parasitic oscillation, or just old-fashioned lack of shielding on wires.
The 'Input switch' actually selects between two 'amounts' of Negative Feedback by changing the resistance to ground for the NFB.
Perhaps these quick sketches will help...
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