Acoustat Question?

[Gary Hubbard]

I am trying to sort out a claim by my local audio medic - that my beloved Spectra 22s some how blew the rail fuses in my B&K ST202 power amp. Should I be reading 1.6-1.8 ohms at the R & L. transformer inputs with Acoustats plugged in but not amp connected. Thanks for the time. GH

[E-Stat]

I am trying to sort out a claim by my local audio medic - that my beloved Spectra 22s some how blew the rail fuses in my B&K ST202 power amp.
I'll respond to the first claim. First of all, I've been using electrostatic speakers for over thirty years and would have it no other way. The challenge, however, is they present an exceptionally challenging load to an amplifier. Stats are highly reactive and like a bratty child, throw a part of the signal right back at the amplifier. They drop to very low impedance at different frequency ranges. Acoustats do this at both frequency extremes. Many amplifiers are simply not able to drive full power into these loads without overloading their output stages. Rail fuses open to protect the amp.

I lived with Acoustats for over twenty-five years. I purchased a Threshold Stasis because Nelson Pass specifically designed it to handle an electrostatic load - the infamous Dayton-Wright at that. Such requires a far more stalwart output stage. While everything I've read suggests that the 202 is a fine sounding amplifier, it appears from this photo that it uses only a couple of output devices per channel and has very modestly sized heat sinks.

ST-202 (http://vancouver.en.craigslist.ca/van/ele/1426241380.html)

By contrast, my similarly powered Stasis Three uses thirty-two large T0-3 case output devices using huge heat sinks and weighs nearly fifty pounds. I never had problems opening rail fuses.

http://home.cablelynx.com/~rhw/audio/stasis.jpg

While this is not the 202, I found a review of the 140 in Stereophile that noted while it is a fine sounding amplifier, it gets very unhappy with low impedance loads. ST-140 (http://www.stereophile.com/historical/675/index9.html)

You likely need a different amp to properly drive electrostats.

rw

[JoeE SP9]

As can be seen from my sig, I use a pair of Spectra 22's. Although I currently use a pair of radically modified Dyna MK-III's to drive them. I have used both Adcom GFA-545/555's and Hafler DH200/220's with very good results. The B&K ST140 and 202 have a reputation of being uncomfortable with low impedance loads