difference between an active and a passive preamp?

King Rex preamp under $400. As transparent as a passive with tube like mids and deep bass of the solid state pre it is. I believe it has 15 db of gain. A real fine sounding unit the sounds well above its price.

There are a lot of caveats when using a passive preamp. As Elizabeth said, you have to make sure your source component has a very robust analogue output section with low output impedance. In addition, your interconnect lengths from source to preamp to amp (short as possible) and capacitance of the interconnects (lower the better) and the input impedance of the amplifier (higher the better) are critical as well. There are passive preamps made of pots, stepped resistors, LDRs, transformers, and autoformers. I prefer the latter three. If all of these are taken into consideration and executed correctly, a passive preamp is better sounding than any active preamp I have ever heard. But I have not heard the mega expensive $15k+ preamps like darTZeel, Atma-Sphere MP-1 with upgrades, etc.

Very nice clear responses...the way they build upon one another...nice to see someone get a direct answer(s) to their questions. Educational too....One for the archives!

The input impedance of your amp is 20k ohms. IMO this is not a great match for a passive preamp. There could be exceptions, but I am not aware of any.

On the other hand you could use a buffered preamp. This uses active circuitry with no gain. The active circuitry greatly minimizes the risk of impedance mismatches. There are tube buffers and solid state buffers. A few solid state options that come to mind are the Pass B-1, Burson Audio, and Horn Shoppe Truth. The latter of which I own and can state that it is extremely fast, detailed, and transparent. It gets out of the way which is what I believe a preamp should do. However, I would not classify it, as well as other solid state buffers, as having a tube like sound.

Also note, not all buffers have a volume control. If you desire something "tubey" you should probably stick to an active tube preamp or a tube buffer with volume control.