Adcom amps - a fair question is why. In a world with new low-distortion amps and Benchmark’s AHB2 selling for $3K, why bother with vintage amps? We recently recommended an Adcom GFA 555 mkII as a viable, low-cost choice. I compared my 555mkII to an available 555 (straight), and bought a second 555 to keep while the original 555 was upgraded by Jim Williams of Audio Upgrades in Carlsbad CA. Turns out the newer 555 sounded a little more threadbare / forward than the older unit.
I got that older 555 back from Jim yesterday and did some listening. He replaced some caps and transistors with high-performance, low noise ones. I asked for a run-down of his upgrade (which hasn’t come yet). However we know he increased the bandwidth from its previous 3Hz-150KHz to 1Hz - 300KHz. The noise floor went from quite noticeable to hardly audible. The charge and decay speeds are faster.
As I’ve mentioned, Jim rebuilds / upgrades recording consoles and other pro devices. His parts choices are best-of-form ’conventional’ choices with a goal of improving the technical performance and sound quality toward ultra-clean at ’affordable’ cost. This upgrade cost $225 plus freight.
I listened via StraightWire Rhapsody 3 throughout. Speaker cable is Octave II. SW has survived my trials as extremely good, plus I know it from years of use. So I side-stepped the newer Iconoclast offerings in favor of familiarity.
The overall character of the GFA 555 (stock or upgraded) is similar to the BM AHB2, that is clean, clear, no-nonsense, factual and without editorial character. JW’s upgrade brought the 555 closer to the AHB2 by a lot. I could not claim to differentiate between the AHB and 555 in blind testing. However, I could easily blind-pick the stock vs upgraded 555. Stock is less definitive, less authoritative and less satisfying while having a slightly looser bass and slight upper midrange glare / shimmer that obscures detail.
I have not yet found time to compare the 555 mkII. I will report on that when I’ve put it in the mix. The only Adcom amps Jim upgrades are the GFA 555 and GFA 545.
Back to the question of why Adcom. Someone looking to supply a clean signal to any Thiel speaker would do well with the Adcom GFA555 with Jim Williams’ Audio Upgrade. Although Adcom was barely hi-fi, this may be its best amp, and this upgrade increases its performance considerably; and its high sales count supports multiple service and upgrade possibilities in the marketplace.
I’ll be sending my second 555 to Jim for more magic. Who knows, I might take one to Virginia when I visit Bill Thalmann at Music Technology in October.
Cheers, Tom