Thiel Owners

Regarding amps: In addditon to my hotrodded learning labs of Classé DR9s and Adcom GFA555s, my reference amp is the Benchmark AHB2. A single stereo amp may not have the oomph you need/want, but in bridged mono a pair might. Power aside, the distortion and noise characteristics of this amp is extraordinary and its unique feed-forward topology pegs the output signal profile as nearly identical whether stereo or mono. The only difference is that the damping factor goes to half in mono, but chopping your speaker cables to half length corrects that. They maintain their operating characteristics to below 1.5 ohms.

It took me awhile to get comfortable with their operation and differences from 'normal' amps. I'm hooked. You can read all about it at

@tomthiel 

That's good to hear because I can't see Adcom amps as being used as a reference when you're designing or refining previous speaker designs. From my own experience with an Adcom amp many years ago, they just aren't that good.

roxy54

Since the mid 90s, I have used a pair of Classe DR9s in mono for my professional studio and consulting needs. They were more than adequate, especially via RCA inputs rather than the OpAmp quasi balanced mode. After I bought Thiel' Audio's ashes in 2018, I migrated to a Benchmark stack (DAC3B, HPA4 headphone/preamp, and a pair of AHB2 power amps.) They meet my present playback and research needs very well.

Along this recent path I wanted ways to power Thiel's difficult loads at prices musicians could afford. To that end I've tested a lot of gear that comes across my radar - much of it via this forum. Adcom was such an exploration. Here's a snatch of what I learned. Some of the Adcom gear was designed by Nelson Pass, whom I adore. Much other of their gear is more ordinary. In particular the GFA555 (straight) was Nelson's shot at simple, clean, innovative design that checked his boxes of voltage/current stability, short signal path, stability into low impedance, etc.

I bought a low serial number GFA555 and later a higher number 555 and then (on recommendation) a 555 MkII. My evaluation was the low# 555 was clean and direct, the higher# 555 was somewhat shouty and jittery and the MkII was smoother, less engaging, more ordinary.

Jim Williams of Audio Upgrades in Carlsbad rebuilds/ upgrades studio recording consuls. He hotrods the GFA555 (not MkII) and informed me that Nelson's 555 depends on high quality parts to shine. The early 555 renditions featured best of form Japanese components assembled in Japan. Later they went to Taiwanese parts and board assembly. The MkII was a French outsourced design that shared only the chassis from the original 555 plus the name.

I sent one of my 555s to Jim. The upgrade was wonderful. Increased bandwidth on both ends, better transient speed and settling time, noise floor, etc. all substantially improved. For a few hundred bucks. That amp went to Bill Thalmann of Music Technology for audiophile tweak recommendations. Then back to Jim for implementation including best of form film resistors, etc. Point of exercise is to create a no-excuses solution with under $1K investment for folks in my world.

The Adcoms don't perform at the Benchmark level. And the Benchmark might be  outclassed by high end gear, usually at prices beyond the reach of most.

I'm thrilled with the Benchmark's performance and price; plus the Adcom GFA555 (modified) and Classé (modified) ground me to my personal history with performance that I judge as really fine, especially considering price.

@tomthiel, The Benchamark amps set the bar for SINAD when first intorduced. It has been surpased by a few since then. But it's become rather academic, as those in the know claim that some where between -115 to -120 dB SINAD becomes inaudible to human hearing even in anechoic conditions. The Benchmarks also allows for user adjustabillity to permit playing nice with a variety of accompaning components. All in all, a rather very, very good prouct....In the right applications.

Benchamark does not spec their stereo amp to below 3 Ohms, and their bridged monos to below 6 Ohms. Neither of these amps meet Jim's recommended minimums into the actual load of a speaker like the CS 2.4's. I'm not sure what ..."They maintain their operating characteristics to below 1.5 Ohms."..actually means? Is this similar to the marketing techno babble of "stability"? I don't think halving the length of speaker cable in domestic situations is going to change that. And, I don't imagine such advice is all that practical in most domestic situations.

I don't know how much using uniquely customized amps to address the need for inexpensive amps for musicians to drive the more difficult Thiel loads really is?

I get it...ultimately we are in this for enjoyment, and if these amps provide that, so be it. But the Benchmarks, while less expensive than many competitiors, is still not cheap, especially in bridged mono mode. At these prices I think there are better reccomendations available to maximize the potential of the more difficult Thiel loads.

unsound - the 1.5 figure is from John Siau, the amp's designer. Their feed-forward topology maintains stability until it doesn't - when it interrupts the circuit. BTW: I'm all ears for your 'better recommenddations'.

The 6' speaker cables came from my feedback to John re the looser bass of the bridged mono configuration. Clearly audible improvement chopping my Straightwire Octave 12' cables in half. I use my 6' cables from my centered amp stack.

I suppose the old amp thing is my personal hobby. There are so many GFA555s out there for a couple hundred bucks and with a few more hundred bucks, they greatly outperform whatever these 'normal', non-audiophile people are using. That solution appeals to me.

I wish two things. Larger BM amps, which John Siau rejects the need for, and higher impedance loads from Thiel speakers, which Jim Thiel rejected the need for. That's a long talk in itself.