Frank, I agree that it was a WAY overdesigned / underpriced unit in its' day. I've talked to David a few times in the last two years or so. I have his current phone / address and he's probably not too far from you. He currently designs and markets safety / monitoring equipment for Nuclear Power plants. From what he told me, he basically has the market cornered in several surrounding States and is working his way towards me in Illinois. He is still quite interested in audio and repairs his units. From what i gather, i think that he still dabbles in audio on a personal level as he mentioned doing some swapping for Madrigal gear, etc... I just wish (REALLY, REALLY wish) that he would have put an amp into production back then.
As to the lack of dimensionality, i hear where you're coming from but also tend to disagree. I've found that the unit SEEMS to be somewhat "2D" but not really. Most of the time, this is a limitation of the amplifier being used. The preamp will give you whatever is there. On good recordings, there is a definite sense of ambience, depth and spaciousness. On a specific Loreena McKennit disc, it is quite astounding when using a good DAC with this pre and a "reasonable" power amp. Quite honestly though, i have very FEW recordings that offer this type of depth, space or ambience. When it is present though, this preamp lets it through in spades.
I have compared these preamps to several others WAY above their price point and they have always held their own, actually stomping quite a few units along the way. So long as they are properly matched with amps, cables, etc... they truly are wonderful. As a case in point, I temporarily replaced my Fathers tube preamp ( while i repaired his ) with one of my AGI's. When i told my Mother that their preamp was ready to go and i would be bringing it back soon, she told me "keep it. That one sounds like junk compared to this one." My Dad simply said that the AGI was much cleaner, clearer and offered far better detail with better bass resolution. He never mentioned any loss of spacial characteristics or ambience during this time even though the system had been dialed in with the other preamp in mind. He later prompted me to find him an AGI to replace his "highly reviewed" tubed preamp once i brought his back. Once he was able to do direct comparisons, the differences were even more obvious. Keep in mind that his preamp was not a "bargain basement" model, as it used an external power supply, wonder caps, wonder solder, teflon wiring, was loaded with gain matched tubes from Roger Mojeski, etc...
In a direct comparison to my Marsh in three different systems, the Marsh sounds slower, somewhat murky, lacks pace, the bass is less distinct and the treble is slightly splashier. While this description makes the Marsh sound like a piece of junk, it is not by any means. It is just "different".
In terms of "mods" or "upgrades", most of the pots on these units are about shot or going the way of the wind. Channel balance and volume tracking on these controls are no longer up to spec even though they were pretty much the best that you could buy at the time. These can be replaced with other current design potentiometers. I'm even thinking of putting in a remote control volume in one unit.
The BIGGEST improvement that one can make to these units is to remove the entire sub-board that holds all of the RCA's to the back panel. You can chassis mount much higher grade RCA's and hard wire them to the board using higher quality wire. You have then removed the standard RCA's ( which cost WAY less than $0.20 apiece wholesale ), the circuit traces on the rear board, the ribbon cable that consisted of low grade tinned wire and two molded plastic connectors. The slight amount of brightness or hardness that these units might tend to exhibit is removed and you end up with a much smoother, fuller and more dimensional product that has greatly improved midrange lucidity. Bass has more impact and offers better extension also. You retain all of the clarity, speed and detail and simply add more "warmth" and "musicality" to what was already one of the most revealing preamps ever made.
You can also do some simple upgrades to the power supply rectifiers, increase filter capacitance, etc... This too can help quite a bit, as most of the caps are beginning to dry out or have lost a large percentage of their rated value. The power cord was also pretty cheap, as it even said something to the effect of being manufactured for a toaster : ) David put the money into the parts that he thought were the most important. Other than the power cord, RCA's and internal ribbon cable ( which were all industry standard back then ), i can think of nothing that he skimped on in terms of build quality.
Jason, can you direct me to the websites that make mention of modding these units ? I'd like to compare notes with others that have done this and see what we can come up with. Sean
