Thiel Owners

@tomthiel   I know you have a lot of experience using the Benchmark AHB-2 with Thiel CS-2.2 speakers, and I'm hoping you can answer two questions about the AHB-2:

1. Are you satisfied that the AHB-2 has sufficient power to drive the 2.2s with ease in stereo mode under any real-world listening conditions in a medium sized room?

2. Do you know what kind of distortion profile the AHB-2 has in relation to second and third harmonics compared to higher order harmonics?

Distortion profile is an issue that Nelson Pass has studied a lot in relation to Class A and A/B amps, and it is also being discussed in relation to Atma-Sphere's new Class D amp that uses GaN-FETs. The Atma-Sphere amp is supposed to have the sweetness of a tube amp with lower distortion, greater transparency, and better masking of higher order distortions. The Atma-Sphere amp has similar power ratings to the Benchmark amp at both 8 and 4 ohms.

Jeff - you may be in for a big treat! If your woofers are indeed mis-wired, that wreaks havoc with the phase coherency of the whole system. The most certain way to get it right is to get a 6 volt battery (lantern) or 9 volt is OK for woofer with a short-duration test. Connect + to + and the cone should move outward. If wrong, change the leads. I think your 03 woofers are Eminence and I would love to know the model numbers on those. Likewise for the mids and tweeters if you don't mind.

Regarding tweeters, I (seem to) recall the 03 was Polydax and the 03a was Audax which may have been an upgrade or a merger, etc. Rob at CSS may have a more definitive answer. Stay away from an old tweeter. They wear out via fatigue of the tinsel leads. Let us know what you learn.

The silliest question is the necessary one unasked.

TT

tmsrdg - yes sir!

sdl4 - remember, I’m an electronics layman

1. Yes, an AHB-2 should drive your 2.2s. Medium-size and real-world are vague and subjective terms, but here’s why I say yes. The (clipping) protection circuitry is so fast and sophisticated that I can see the lights flickering without hearing any dropouts. That takes 100dB in my functionally rather large room. In case you don’t know, my room was weird. I built a resistive-wall (leaky) 4000 cubic foot room within an 11,500 cubic foot floor of a 38,500 building with various openings between the floors. Virtually no modal interactions, but hard to characterize its "size" since the direct space was moderately sized and the larger spaces were acoustically secondary. All that said, my preference and regular use mode was each speaker driven by a bridged AHB-2. But, a single stereo amp was adequate for moderate (85dB peaks) listening.

2. The AHB distortion profile is extremely clean, but I lack technical fluency regarding your specific question. I point you to the Stereophile and AudioScience reviews, among others, to see their qualitatively (stunningly) low distortion. It took me some time to realize that the bass balance was not thin or dry. Other amps (of my experience) add harmonics, especially noticeable in the bass. On a related note, the Benchmark DAC3 and Preamps-4 take additional measures to reduce second and third harmonic distortion. John Sieu’s essays on Benchmark’s site are quite informative.

I don’t know the Atma-Sphere amps, but I do know that the Benchmark class H topology acts differently than do ’normal’ amps, even full class A. JS sent me some distortion graphs illustrating that the 1 ohm profile is virtually identical to the 8 ohm profile. No, that’s not normal, and no, I can’t lay my hands on those graphs or explain the technicalities. But, yes, the amps do sound that way. With JS’s coaching, I rigged an experiment to account for my initial perception of ’better’ sound in stereo than bridged. The output impedance drops to half, lowering the damping factor. I shortened the speaker cables from 12’ (stereo) to 6’ (bridged) and the SQ difference seemed to vanish. This THX amp topology is amazing as tmsrdg said - all that weirdness goes away leaving only the music. Sorry to gush, it’s just hard for me to believe.

BM has a generous return policy in case their power doesn’t meet your needs. Or, if your budget can be stretched, two of them make for serious audio nirvana.

tomthiel wrote " your 03 woofers are Eminence and I would love to know the model numbers on those".

Yes, the "67" in the date code indicates the manufacturer is Eminence. Markings: 10KZHG8GX Date Code: 67-7920

 I'll send you more info/photos soon. Thanks!

^The Benchmark amps are at the very top when it comes to a lack of distortion within their load tolerance. They are also somewhat special in that their input allows for a variability that is somewhat uniquely accommodating for system matching.  Regrettably, many Thiels have impedance loads that is outside the window of ideal operation for them. The Benchmarks are not designed to work optimally with many Thiels. While I'm hardly the one to make such a supposition, I don't believe that Jim Thiel would have traded his Krell for the current (or lack thereof) Benchmarks. They could very well be the very best amps for different speakers.