I recently found some affordable stepped attenuators on that auction site and thought I'd give one a try in my Quickie. Mine is like this:
http://www.ebay.com/itm/DACT-Type-SMD-Stepped-Attenuator-21-step-/190844814249?hash=item2c6f3cc3a9. It uses SMD resistors, which has benefits, but they're not audiophile-approve resistors. Note that this pot won't fit into the stock holes, so I had to modify my plate slightly. This appears to be a series type attenuator so at low listening levels there are LOTS of resistors in the sound path. Better would be a ladder-type attenuator, but for experimental purposes, this seemed like a good start.
I installed it a few days ago and at higher listening levels it is a big improvement over the stock pot (no, I didn't do a double-blind test
). I noticed a bit of a veiled presentation at lower listening levels, possibly no better than or even worse than the stock pot, but I didn't give it much of a careful listen at low volume. I'm now thinking that I may try out a true ladder-type version that puts only 2 resistors in the sound path at any time. This was an experiment and I think for a modest increase in price there are better options out there. But this was a good mod nonetheless.
So part one in this post is that a better attenuator is well worth trying. The PEC pots that have been mentioned in this forum are also quite good, though they are somewhat pricey and I haven't compared them (I only have a 10k PEC in a SE amp).
Part 2 is that quite soon after installing the new pot, I found that one channel seemed to be quite a lot lower in volume than the other. I was worried I'd damaged something when re-wiring or that the pot suddenly failed. Next listening session, though, the other channel was out and the first was back. I was puzzled until I thought to look at battery voltage.
My filament batteries are OK at just over 1v each, but the 9v batteries were at about 3v each (though one was 6v or so)! Total B+ must have been about 15v!!! These were Radio Shack cheap batteries that had seemed to last forever, so I'd forgotten to check them. I was surprised it would even play at 15v much less sound decent until the channel dropout. In the past I've heard distortion when the batteries were dying somewhere between 5 and 6v, but not this time. Perhaps the drop from 5-6v down to 3v was precipitous?
I put in a new set of batteries and now it's singing again, sounds much better, and the stepped attenuator seems to be really shining. Now, only the lowest volume listening seems to be veiled and missing detail.
Hope these experiences are helpful to someone.
