Posted by Lew on September 08, 2004 at 07:47:24:
In Reply to: Re: Variac posted by Roy on September 07, 2004 at 14:58:35:
Roy, I may have misunderstood your previous post, but I could have sworn you said that at one
time you used a Variac to cut back on the bias supply voltage when your speakers were not going
to be used for a while. This was when there was lot of fretting on SLOG about the longterm
negative effects of letting the speakers sit with full bias applied. (In the final iteration of your
backplate, I believe you now have installed a circuit that cuts the bias voltage automatically when
your speakers are out of use for a specified time.) Anyway, you guys got me worrying about
exhausting the mylar coating on the diaphragm, and since I had a Variac lying around my
workshop, I decided to try it myself in order to preserve my speakers (in theory).
In attempting to explain my observation, you state above, "Perhaps the effect you hear is because
the microblock is not being supplied with mains potential 100% of the time." What I did was to
turn up the Variac to 120V about one to two hours before I wanted to listen to music. I did not
use the Variac per se to set the bias voltage level; this was done using the potentiometer on each
speaker as per normal practise. In between listening sessions, e.g., when I was away on
vacation, I set the Variac to about 50V. So at all times when listening to music, the Microblock
was receiving 120V. (By the way, I checked the Variac with my VOM to be certain that it was
indeed putting out 120V when set to 120V, etc.)
Placing the Variac between the Microblock and the speakers would to some degree defeat the
optimal function of the Microblock, in my opinion.
I have completely dispensed with the Variac in any case.