Hello all - back from away for a few days. Jon - was it you looking for grille fabric? Rob at Coherent Source Service has original grillecloth. Note that it got more sheer over time, so you might need a matched pair.
Re amps: What a trip - I have some potentially relevant experience with the AHB-2, Classe DR9 and Adcom GFA555 II. My setup includes 4 four pole knife switches plus locking bananas on their output jacks, driven by two pairs of amps, so that I can rig direct comparisons with simple switch throws and banana swaps. My test crossovers are outboard with no-solder access to separate driver outputs. Two CS2.2s are wired with two direct runs to each driver, swappable at the crossover outputs for comparing cable runs and the effects of cabling on the 3 different driving amps.
The GFA555 is a known to be decent mid-level amp. The DR9 performs above its price class. David Reich used Thiel CS3.5s as a design load. According to Atlantic Systems, the eastern US MacIntosh warranty service station, the DR9 output circuit is ’the same as’ the MacIntosh solid state circuit. Good amp. The AHB-2 is a THX licensed implementation of a class H amp regulated by a small Class A regulating circuit - new type of topology. I have appreciated discussion here of the AHB-2 among its peers. I agree with the observations that its bass leaves something to be desired. John Siau says that it is correct and "everything else" is bloated or loose or too big. That may be true. It is also true that B&W’s big bass would complement the AHB’s leaner than most bass balance. The AHB-2 is a winner, but might have deficiencies in the deep bass.
My test allows a CS2.2 woofer-only fed through a knife switch driven by the closely level-matched bridged DR9 or bridged AHB-2. The 2.2 crosspoint is 800 with first order rolloff, so there is musical content all the way up. Using a variety of sources, and with the absence of mid and highs, I consistently hear the following:
The AHB produces upper reaches which are cleaner, more detailed and more articulate. The lower reaches are drier, with the deepest transients sounding somewhat limp. The fundamental seems diminished. That diminishment might be in time-duration, but it sounds like transient imprecision and reduced level. Sounds like a hole in the bottom of the harmonic sequence.
One iteration of my test was with Dana Cunningham’s ’Live at Stone Mountain’ concert on a Yamaha concert grand, with Jeff Oster on horns and Max Dyer on Cello. I attended the stunning concert and assisted Dana’s evaluation of mixes and masters for production, so I feel comfortable with knowing the producers’ intentions. In this case as in general, I judge the DR9 to nail it much better than the AHB. The DR9 (bridged) delivers solid onset transients and well integrated fundamental bloom. I admit that the AHB reveals more nuance and space around the trumpet and cello. Similarly, the growl of the lower cello tones are authoritative with the DR9, and easily un-noticeable with the AHB.
Even if I accept Benchmark’s claim of ’rightness’, which is plausible given their company’s excellence, there remains the problem of the sonic jungle. Even for this live performance with minimal processing, the original musical event has gone through multiple stages of tweaking, and all of that tweaking used "normal" amplifiers with sonic signatures closer to (or actually being) the DR9 rather than the leaner, drier AHB.
Just for grins, my setup allows the following very appealing setup. The tweeter and midrange each has its own channel of the AHB. No contest winner over the GFA555 and noticeably more articulate and detailed than the DR9. The woofer can be instantaneously switched between a bridged DR vs bridged AHB. After all the note-taking and head scratching, I selected ’Flying over Water’, with Piano, Flugelhorn, Cello and Congas, for its beauty and complexity. Played full length with each bass amp, the DR9 always took me there and made me smile. The AHB left me in my chair analyzing the mix. Note the same result even with the SmartSub engaged; the sub-bass didn’t supply enough bottom for satisfaction.
I guess that’s my report for today.
