Hi Dan,
The .5 was and still is a very good pre-amp, although as they are older, not too sure what age would have on the components.
If you are looking at a used BP20, try to get a later model with the better connectors, I believe the earlier models had the same RCA jacks as the .5/.4/11/12 which could become loose over time, my .5 jacks where all replaced under warranty.
The more recent BP20/25’s have the newer jacks, which can be easily identified because they are longer and protrude about ¾”s from the chassis.
When I upgraded to my current BP25P the first thing I noticed was that there was less gain than the .5, so you’ll have to turn the volume up to attain similar levels.
Although the .5 was pretty good to start with the external power supply helps in reducing overall noise, and the internal layout improves the signal to noise ratio so that the subtler nuances of the recorded signal are better perceived.
What this adds up to is a more natural musical presentation, which becomes more obvious as you improve upon the rest of your audio chain.
This may not apply, but the most obvious improvement I found was with the phono section of the BP25P over the .5.
Also if you were to go for a BP25 over the BP20 you’d also benefit from remote control and a headphone out, or bite the bullet and go straight to home with a new BP26 and never worry about the “what if”.
Or as vegasdave recommended, the BP6, for a more rational budget, but still excellent pre-amp.
Robert
