Acoustat servo amps ??

Well, yes, the servos can be great, but there are MANY different mods and levels of servos -- the best (and most lethal, literally) in my experience, are the AHT/Dan Fanny modified units that use the 6LB6 tubes and dual 7308 input drivers. Please note that high-voltage parts are sometimes hard to locate and these amps do require regular periodic maintenance to ensure top performance and to replace certain components BEFORE they disintegrate.

One advantage to the 6LB6 servos is that they can drive up to 8 panels per amp -- so if you own Acoustat Sixes or Eights, you don't need 2 amplifiers per speaker; one will do nicely.

Of the Acoustats I have owned the ones that I liked the best were 2+2s and IIIs. The Sixes are great with the AHT-modified servos if your listening room is VERY large (mine wans't big enough). They are capable of playing unbelieveably loud, with tremendous bass. A few of my friends own these systems/amps and are quite happy. :)

I have since moved on to the InnerSound Eros because it plays loudly and precisely, is smaller, and I no longer have to worry about dealing with the attention the servos require.

thanks for the posts everyone.

plato et al: i have found a pair of monitor 4s w/ the servo amps ($1600) and was wondering if anyone was able to compare what these might sound like (i'll drive to hear them next week if it seems promising) compared to my model 3s with the transformers or model 3s potentially 'upgraded' with separate servo amps i might find.

thanks

If the servos on the IVs are stock and the ESL panels are early generation vintage, then factor in the operational condition of the amps and tubes and I'd say you have a heck of a lot of variables and a wide performance span. Heck, the only way to sort that out is to go have a listen.

What vintage are your IIIs, anyway? --original coarse 3-wire, OFC-copper 3-wire with improved coating, or 5-wire version?

I will say that if the IVs are early vintage and the amps are stock then $1600 is probably top-dollar -- and that provided they are in good working order. You may be much better off picking up a good pair of updated/modified servos and using your present IIIs if they are at least the OFC-version panels.

BTW, Kubla, I'm not certain that you can use the servos correctly with Spectra-series panels, plus I'm not sure that Spectra panels are actually as good as the late 5-wire Acoustat panels.

Additionally, the servos come with different EQ curves depending on whether you are using stacked panels (e.g., 2+2s, 1+1s, or 6s) or non-stacked (1s, 2s, 3s). The bass EQ is increased to drive the taller models, I believe.

A passive preamp will drive stock servos OK, but then, the stock servos have adjustable input pots. Some modified servos have an input driver stage (and volume pot) removed and need a lot of input voltage -- these would not work well with passives but would sound better because the suboptimal active gain stage is deleted.

hey plato thanks again for all the great info.

i'm not sure the vintage of my model IIIs. they were bought new by my father in '81 or '82 i believe but they may have been store demos and older than that however. receipts are long gone unfortunately (i hooked up with a guy at rockford corp who could have replaced the panels for free if i had it. crap.) how can i check to find out which version i have? -these aren't the medallion btw and have the 'internally wired by monster cable' sticker on the back if that provides a clue to their year.

that same guy at rockford can do the medallion upgrades ($700 including shipping) and upgrade the caps and wire if i supply him with the parts (i figure about $3-400 including cardas posts, etc. that option is what im debating against the servos. he recommended infinicaps and solens (47uf) but i've been told by an acoustat freak NOT to go with the infinicaps for this application because they sound thin. someone once told me they personally only use black gate in their acoustats but i cant seem to find any w/ sufficient voltage.

thanks again.