Tube preamp for SS amp

If you want a tube preamp to drive a solid state amplifier, the thing to look at is the output impedance at 20Hz. What it is at 1000Hz is really not that important- most any tube preamp will have an acceptable output impedance at that frequency. Its how the preamp behaves in the bass that is important.

This is because most tube preamps have an output coupling capacitor that is part of the equation of output impedance. At 1KHz, its no big deal but at 20Hz that coupling cap becomes a major influence on the numbers and can cause a loss of bass impact.

To counter this issue, some tube preamps have a large coupling cap so they can drive solid state. The problem is, the bigger you make that capacitor, the more it can color the sound, even if its Teflon. The reason has to do with the inductance that the cap has which is something independent of the insulator in the cap. The bigger the cap, the more inductance (due to the fact that the cap is wound). This creates a tension in the design where the cap is chosen to color the sound the least, while at the same time not affecting the bass. It is at best a compromise.

A very small number of tube preamps have a direct-coupled output, which sidesteps the issue.

Interesting. Thanks, Ralph.

Chad2635,

I've had a CJ pre/Pass amp combo for several years now. It is one of the best combos I've ever put together. They seem to be made for each other. Hope you get a chance to try it yourself.

I wouldn't worry about the volume control, it's a very good one and they are important. It's not push, push, push. You just hold the remote or preamp button down and a motor moves it until you get where you want. There is the "clicking" but I got used to it immediately. As far as longevity, it should last a long time.

I've also found that the 3 CJ preamps I use, two ARTs (6922 based) and one ACT 2.2 (6h30 based), have been very compatible with other amps I have used...SET's, PP tubes and a couple Tripath based chip amps. !5' rca interconnects were no problem with my CJ's 500 ohm "average" output impedance.

Good luck with your choice.

Onemug, how quiet is the cj gear? Thanks for the feedback by the way!

Chad2635, My pleasure.

The ART and ACT 2.2 are very quiet. They are line stage only so I can't speak for CJ's phono stages. I do run an outboard phono stage thru the ART and it sounds great (and quiet).

In my previous post I meant to type that I use "15" foot rca interconnects. Somehow a "1" became an exclamation mark. Hate when that happens. :-)