I believe there is a problem with my Millett MOSFET-MAX after 2 years of excellent service.
Every now and again, when listening to music/movies, with music/movies paused, or very quiet passages in music/movies, I will hear a buzzing or "bzzzzzt" sound on the left. Today, I heard it again while watching a movie on my PC while the movie was paused. I shutdown the movie to investigate as follows:
Specs & Equipment:
- HifiMan HE-400s
- Power supply @ 27 V
- Tube Bias at 14.0 - 14.1 V
- Mosfet Bias at 275mV
- Tubes 12AE6 (matched from Beezar)
- CA2L/R Elna RFS Silmic II 1000uF, 35V (Handmade Electronics)
- CA7L/R Elna RFS Silmic II 1000uF, 35V (Handmade Electronics)
- CA8L/R VitQ 0.22uF 100V PIO Cap (Beezar)
Debug steps so far:
1. I turned up the volume from min to max - I hear a buzzing from the left earcup between 2 o'clock and 4 o'clock. Buzzing gets louder progressing from 2 to 4 o'clock then cuts out after 4 o'clock. No buzzing from right earcup.
Is it a bad driver in left earcup?
2. I swapped cable connections on the bottom of the HE-400 earcup terminals between left and right earcups. Now I heard buzzing on right earcup. No buzzing on left earcup.
Is it a bad headphone cable?
3. I plugged in a pair of Grado SR-60 and some Shure IEMs and I hear buzzing from both only on left side. No buzzing on right.
Is it a bad tube?
4. I swapped left and right tubes. Buzzing was still only in left earcup.
Is it a bad 1/4" Neutrik jack?
5. I plugged all headphones into the 1/8" jack and heard buzzing only in left earcup between 2 o'clock and 4 o'clock.
Is it a bad integrated grubDAC?
6. Buzzing still audible with grubDAC USB disconnected and only in left earcup..
7. Switched over to RCA inputs and buzzing still audible only in left earcup. Nothing plugged into RCA ports.
Can someone help with further recommendations for debug to root cause this problem? Or, better yet, does someone know what the problem is due to past experience? :-D