Trouble w/VAC Standard 220's & Thiel CS 6's ?

Just moving into tube amplification with these 220's. I've been very pleased the Theils but found with solid state that they liked alot of juice. I hoped these VACs would do the trick but I'm having doubts. At higher listening levels things seem to be piling up a bit. The four KT88's must be working very hard. Also the gain on these amps is the highest I've ever encountered. I'm limited to the lowest quarter on my CAT SL-1 mk3 volume control. I also don't get the feedback control. Sounds pretty bad except in the first position. Would love to hear from someone with more knowledge about these VACs.
Hi Apcdan:

I ran a CAT Mk. III preamp with a VAC 70/70 and then VAC 140/140's for about a year, and had EXACTLY the same problem.

The problem is that CAT preamps have unusually high gain (I recall it being 28 db., while the norm with modern line stage preamps is about 15 db.), and VAC amps have unusually high sensitivity. The result is that you have very little variation in the volume control -- I only had seven "clicks" on the volume control from "no sound" to blowing the doors off. Like you, I could not turn up the volume beyond "9 O'Clock" without the system becoming extremely loud. When I upgraded to VAC 140's, which doubled the output power of my amplification, the problem got completely out of hand.

I spoke to Marty at CAT about it and they offered to built a device that would effectively lower the output. The device needs to be installed on each input on the CAT, however, so you would need one for each source you have. I was told by someone else (whom I recall was competent) that this is not a good solution, sonically.

I did additional research and discovered that, simply put, because of the CAT output / VAC sensitivity characteristics, these components simply don't pair well together as a practical matter. I sold my CAT and bought a Hovland, which cured the problem.

Perhaps someone out there has a better idea, or perhaps CAT now has a better solution (this occurred for me three years ago), but the simple answer is to replace your preamp with one that has a normal amount of gain (or get an amp with normal sensitivity).

Good luck.
Dear Apcdan:

My apologies -- I completely forgot to address your query about feedback.

All VAC amps have excellent power supplies and should have absolutely no trouble driving your Thiels with zero feedback (although the bigger Thiels, for their part, allegedly have complex crossovers that suck amps dry).

You should experiment, obviously, but feedback is generally a pernicious thing that should be avoided if possible. Feedback will help control woofers if there is a real mismatch between your amps and speakers (i.e., where the amps just can't control the woofers), but generally speaking, adding feedback flattens out the sound and can quickly make a tube amp sound like a bad, two-dimensional solid-state amp. In addition, and very importantly, an amp using feedback sounds worse the more you turn up the volume, as the sound hardens.

Make sure the amps have been warmed up for a good hour before you play music (15 minutes definitely is NOT enough).

I would set the amps for zero feedback, and very thoroughly run them through their paces with all kinds of music over a number of hours. They should sound better at all volume levels this way. You have a great preamp, amps and speakers, so the sound should be absolutely top-notch.

I'm confident that your only problem will be too much preamp gain (which really isn't a problem inasmuch as it is easily remedied).

Good luck.
Raquel, Thanks for your thoughtful response. It helps to have a little incouragement. The VACs are a whole new ball game for me and its taking some time to settle in. The CAT has been a fabulous pre-amp and I would hate to have to move it to solve the problem. Maybe the amps need to go? I do plan on calling Kevin. Your thoughts were very appreciated. apcdan
one thing i might add... i think that vac do a great deal of their testing with thiel speakers, in fact i was recommended to try out thiels by kevin. hence i would suggest that raquel is right and that the problem lays elsewhere...