Hoping to get some help from the tube experts here, let me preface this with I am a very new to electrical engineering and DIY audio (as in built a bottlehead crack and that's about it) so apologies for likely some incorrect terminology use. I purchased a unique tube headphone amplifier off Facebook Marketplace and I'm having an issue with it I was hoping to get some help in diagnosing.
The headphone amplifier sounds great, but I get a fairly loud buzzing sound when using it that has an interesting behavior:
Does anyone know what could be causing this or how to fix it?
Things I've tried so far:
Some information on the build:
This is built on a TubeCAD 9 pin PCB. The PSU is a VR tube and MOSFET combo. Here's the link I was given:
https://www.tubecad.com/2004/blog00...u8wgPO2ZcM6vOlPV-NQ2fQYt7SuRA4jdCYCnbFCbnPeDZ
PSU Circuit, it's powered by a 0D3 VR tube:
https://wtfamps.com/2017/10/19/simp...FYeK7JORvnn-nHKWg0iEk86TQh4dtnkgPZc528sRnypMh
The headphone amplifier sounds great, but I get a fairly loud buzzing sound when using it that has an interesting behavior:
- At no-low volume on the potentiometer: the buzz is only audible in the right channel and decreases (as far as I can hear linearly) as the potentiometer increases, until the potentiometer rotates 90 degrees and the buzzing is minimized.
- After a 90 degree rotation: the buzzing increases with the potentiometer linearly but only in the left channel for another 90 degrees
- After 180 degrees of rotation: the buzzing appears in both channels again for the rest of the range.
Does anyone know what could be causing this or how to fix it?
Things I've tried so far:
- Reflowing solder joints, doesn't appear to have any cold joints
- Used multiple different sets of input/power chords and other sources, tried multiple locations in the house and the behavior is consistent
- Deoxit D5 on the potentiometer
Some information on the build:
This is built on a TubeCAD 9 pin PCB. The PSU is a VR tube and MOSFET combo. Here's the link I was given:
https://www.tubecad.com/2004/blog00...u8wgPO2ZcM6vOlPV-NQ2fQYt7SuRA4jdCYCnbFCbnPeDZ
PSU Circuit, it's powered by a 0D3 VR tube:
https://wtfamps.com/2017/10/19/simp...FYeK7JORvnn-nHKWg0iEk86TQh4dtnkgPZc528sRnypMh
Little bit baffled over here: What is the actual schematic diagram of the amplifier you are using?
Well that is not much of a help but, what is the headphone impedance?
When for instance 300 Ohm then unplug the headphone and connect the equivalent resistance to the input.
After that and increasing the volume, is the buzz is still audible and depending of the volume when adjusting the volume up and down?
If so the buzz is induced somewhere at the very input. Can be coming from the supply line to the input stage (insufficient decoupling?).
This still a simple starter to detect where that buzz is coming from.
There can be a dozen reasons as a cause so.....
When for instance 300 Ohm then unplug the headphone and connect the equivalent resistance to the input.
After that and increasing the volume, is the buzz is still audible and depending of the volume when adjusting the volume up and down?
If so the buzz is induced somewhere at the very input. Can be coming from the supply line to the input stage (insufficient decoupling?).
This still a simple starter to detect where that buzz is coming from.
There can be a dozen reasons as a cause so.....
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