After summarily deciding to blow off yard work, I decided to do a little side by side testing of the Yamaha C40 preamp and my venerable Adcom SLC 505 passive preamp. You all can look up the other gear I use so I'm not going to go through repeating it.
My initial impressions of the Yam (cosmetically) were pretty favorable, using the Dave as a basis for comparison. Simple black face, solid feeling knobs for volume, bass, treble. Yamaha insisted on using the crappiest wide plastic buttons for power on/off and source selection. Seems like something that you would find on a Fischer Price Speak and Spell. The connections in the rear are seem adequate if unremarkable. All around it's got a good, hefty, solid feel. Overall, I'd give it a B. Those plastic buttons kill me.
Ok, I ran through of my few old standbys (William Tell Overature, Magnificent Seven, Texas, Crash, Bittersweet, Ordinary World) first on the Adcom and then hooked up the Yammie. The most noticeable thing is that the Adcom has a much more laid back (natural to me, but that's what I am used to) sound than the Yammie. I'm not saying it's unpleasant or fatiguing but the Yammie definately has a more "in your face" kind of sound. Bass with the Yam in more demanding tracks (William Tell Overature) is noticeably faster with the Yam. I did find that the discontinuity in speed that I have noticed between the high/mids and lows with the DQ's is less pronounced with the Yam. Again, I don't know if this is a good thing or not.
One thing that I will say with the Yam is that from recording to recording is a more uniform sounstage and image. With the Adcom I find that they soundstage and image reflect the quality of the recording. The Yam sort of levels the playing field if you will. Preference here is a six to one, half dozen to the other. It hurts some, helps others......
The high end brightness that I have come to expect from Yammie was noticeably absent for the record. All in all it's a pretty transparent preamp. The things that I have noted are generally things that you really have to listen for as opposed to hit you over the head differences. Thumbs for the Yammie. It's certainly not going to replace the Adcom, but I wouldn't be ashamed (other than those damn buttons) to have it.