Adcom power amp comparisons
The two Adcom GFA555s arrived yesterday and I compared them to each other, to the GFA555 II, to Sennheiser HD800S headphones, and to the Benchmark AHB2. Brief report to follow.
A fair prior question is ’why’. My present odyssey includes long-standing riddles among which is why some users experience classic Jim Thiel products as some combination of hard or harsh, up-front, analytical, etc. while others hear little of these issues and love them. Among myriad interacting potential causes are:
• Room, listener position
• Inferior signal chain and/or recordings
• Cable/wire with time-domain problems exposed by phase coherent presentation
• Crossover location behind the woofer. Later progressed to behind passive radiator, cabinet bottom
• Less than best diffraction and wavelaunch control
• Other including high-frequency balance, driver and floor coupling, etc.
Today we’re examining Amplification. These Adcom amps were well-regarded and popular in Thiel’s mid-cycle product development. If some amps don’t like some cables or speakers (such as low impedance). Let’s say those issues are settled with the amps presently under consideration. Historically, Thiel graduated to top-tier amps because we got excellent dealers who used those amps. We never tested our speakers with anything less than the Krell-Levinson league. Even Audio Research and Classe washed out due to Jim’s assessment of off-neutral (AR) or less-than-best (Classé.) Bryston was our 'entry level' recommendation.
My present rack: Reference: All Benchmark stack with AHB2 power amp driven by HPA4 by DAC3B from Philips CD80. Benchmark interconnects. StraightWire Octave II speaker cables.
Known amp: Adcom GFA555 II
New amps: Adcom GFA555 (original) (2) All amps bridged mono
Speakers: Thiel CS1.5 stock
MO: Patty Griffin – Impossible Dream skipped through full album for 10-15 minutes total per amp under test. Album is pop vocal with simple to orchestrated instrumentation, and various pop production effects. Without apology, the Benchmark has become my reference. Adcom 555A is early production. Somewhat up-front, simple, direct, ’no mic windscreen’ sound Adcom 555B is late production. Slightly more ’refined’, ’mic windscreen’ sound. Adcom 555 II. More controlled, safe, less ultimate detail and dynamics. Differences are fairly subtle. Family resemblance is the over-riding quality. Family sound is very similar to HD800S headphones.
Benchmark AHB2. Solid, quiet, clean. Studio reference quality both technically and aurally. Note, the original 555 sounded closer to the AHB2 in their shared direct liveliness, than the MkII. I am sending 555B to Jim Williams for upgrade. Another comparison will ensue on its return. I support with Harry Lavo’s recommendation. The 555 II is the safer bet for unknown upstream components and source material, and within its power capabilities, should drive any Thiel speaker well.
