tube preamp w/ solid state amp

Krell power amps require a modification to run safely with a tube pre. I believe a resistor of some sort is put in the circuit to avoid some nasty situations, oscillation I believe, but don't quote me on that last detail!

Larryi makes a good point regarding the order of turning things on. If the main amp(s) are on already, or even switched on at the same time as the pre-amp, you could easily get a lot of nasty noise as the tube pre powers up. It is not something you want to hear from your nice speakers. The simple solution is to turn your amp on a few moments after turning the pre on.

Also, I am no expert on the matter, but Gill Audio did change some parts in my tube preamp (a Gill Audio Alana) specifically because I use SS amps - in my case Theta Enterprise monos. As Larryi also mentions, this may have to do with the impedance matching, I really don’t know. When I spoke to Gill about my preamp, they suggested these changes to what was already in there based upon my amp. The resulting improvement to what I thought was already a stellar preamp was very noticeable.

FWIW, they also added a time delayed 12v trigger. When I switch on my preamp, it will activate the 12v trigger about 20 seconds later so that the pre will be fully powered up by the time the main amps are triggered on. One switch does it all.

I regards to Pbb's comment, I believe the Krell “modification” is because it is direct coupled from the factory. This “modification” is user serviceable and is meant to protect the amp from DC leakage that can happen with a tube preamp…at least this is how I understood it when I had a Krell amp before my current amps. I never did this and never had a problem, but better safe than sorry – if you have a Krell, do some investigation first.

I've used tube preamps with solid state amps for several years now. I was carefull about turn-on and turn-off sequence at first, but found three of my preamps could be turned on and off while leaving the amp on with no ill effects. They were a BAT VK-31SE, Kora Eclipse, and Audio Research Reference TWO mk II. With the Audio Research preamp I do mute it before I turn it off. The Kora had a built in "warm-up while muted" turn-on sequence. I left the BAT in standby mode so when you turned it on it had a short warm-up delay and then was ready to go. I would think the amp you partner it with could make a diffence in the behavior, also.

I have done this for 15yrs now. The two things you need to be concerned with are; some tube preamps output impedance are high and or are high at the freq. extremes. If you match that with a SS amp with a low input imp. it will cause the amps freq. output to deviate. Second it is good practice to mute your tube pre, then turn off the amp, then the tube pre.

I ran a Conrad Johnson pv10a pre along with a Classe DR-9amp with very good effect with excellent sound while it all ran a pair of Sound dynamics300ti,MGIII,and numorous small british speakers.