@gdnrbob - In 2012 I had Lithium batteries installed. Date in Sharpie for replacement is 2022. Batteries have expiration date of 2020, so I was hoping they would last past 2018.
@mr_m - I am sure of nothing. This would be the first time I replace batteries since I bought the M5-HPs.
@tomic601 - (Atomic! I get it!) I tend to agree with you. Here is a sequence of changes in my system:
I was really digging the sound of my system, including the 2Wqs, when I upgraded cables connecting my DAC to my pre. This was in June of 2017, IIRC. The cables were a definite improvement, although I did notice a slight reduction in overal bass output. I chalked it up to cable differences and resolved to increase the output of 2Wqs as soon as I had some time (the controls are not that accessible, and I mass load the 2Wqs, so it is a bit of a project to move everything around). Before I had gotten to adjusting the levels of the 2Wqs, my amp croaked on me. After speaking with the designer/builder of the amp, I decided to send it in for repairs and upgrades. The upgrades included almost all new interior parts (circuit board, transformer, wiring, etc.). This took three months (don't ask), so for three months, the 2Wqs and M5-HPs sat unpowered and disconnected.
When the amp finally came back last week, I connected everything, and adjusted the M5-HPs to 20k (single ended) to reflect the change in input impedance of the upgraded amp from 10k to 22k (Johnny's concerns notwithstanding, I doubt my amp builder would get the input impedance wrong; he is a bit of a wiz at these things). While the upgraded amp has much to offer over the amp as it was before, the bass is just MIA. I know some additional burn-in time might be needed, but this is extreme absence of bass below ~150Hz. If I max out the bass control on my preamp, I get an acceptable level of bass, but it lacks punch and extension. Doing that did, at least, allow me to determine that the 2Wqs are functioning, as I could feel very slight cab vibrations.
OTOH, since the old in-line filters and my speakers run full range have marginally better bass (but still nowhere near acceptable), I do suspect the M5-HPs as well.
I am scheduled for a call with the amp builder tonight, who suggests that the amp may not be properly biased for my system. Not sure how this could affect the bass output. Once I have the amp squeared away, I will focus on the M5-HP battery replacements.
