Thiel Owners

Funny side note

I was looking at HiFi equipment sales in Portland Oregon 

and at Fred's sound of music they still have Thiel Audio 

listed under New Components !

I think you're right to question where in the chain to try to fix or compensate for problems in music reproduction. It would seem to make sense to fix things as far upstream as possible, but that isn't always easy to do. 

With regard to Nelson Pass, I watched a YouTube video of an interview he did with Steve Guttenberg that mentioned the distortion profile issues briefly. Nelson was careful to state that he didn't actually add second or third harmonic distortion to some of his amps. Instead, he simply chose not to suppress those lower order distortions as much as he could have in the circuit design. 

For my own listening, I don't look at ultra-low distortion specs in an amp as a sign of sonic purity if those specs are associated with any harshness or brightness in the sound quality I hear at the downstream end of the chain. But adding in a lot of extra distortion doesn't seem like an ideal design strategy either.    

@tomthiel, the impedance limits of an amp depends on the speakers attached to it. Most later floor mounted Thiels from the 1.7's / 2.3's / 3.6's / 5's / 6's / 7's have a  minimum power recommendation of 100 Watts per channel into 8 Ohms. The nominal impedance of all these speakers is at least 4 Ohms. We all know the actual minimum impedance can be less than that, and quite often for more than just a slight dip.

Models | The Coherent Source (wordpress.com)

The Benchmark amp in stereo mode is spec'd at 100 Watts per channel into 8 Ohms and is not able to keep up with doubling down even into 4 Ohms, just missing the minimum recommended 200 Watts into the nominal impedance. Things get a bit worse as we work down into actual minimum impedances, as rather than reaching the recommended 300 Watts into 3 Ohms the Benchmark comes up short at 240 Watts per channel. In Bridged mono mode the Benchmark isn't even spec'd below 6 Ohms.

Benchmark AHB2 Power Amplifier - Benchmark Media Systems

With the right speakers the Benchmark might well nigh be the most perfect amps available. They might work beautifully with some older legacy Thiels, or with the Thiels that are not floor standers, but I think there are more suitable options for the more recent Thiel floor standers. 

usound - Thank you for your thoughts. I share your concern about the power ratings, especially into low impedance loads like the (maddening) Thiels. To learn more about the discrepancy between the AHB-2 non double-down performance vs. my intensive auditioning experience with it, I engaged John Siau in conversation. Among the lessons Iearned was Benchmark’s eccentric power measurement protocol which goes like this:

They rate the amp at 0.0003% THD+N into all loads. In other words if it doesn’t shut down, that running spec is met with no allowance for additional distortion. The amp exceeds that 3 zeros spec at the power limits you cite (which obviously decrease into decreasing impedances.) But, if the traditional 1% THD+N spec were used, it would double-down as we want and as I (among others) experience it doing. It sounds and acts like it is doing what John says it is, and BM is very conscientious about its claims. Their internal tests go to 1 ohm continuous and their customer service tells me they are viable to 1/2 ohm resistive loads. All Thiel models are extremely resistive via Zobel networks on all drivers - which push the amp limitation from distortion-limited toward heat-limited. I have shut down the AHB-2 via overheating, but it required louder levels than my comfort zone. Admittedly, my installation maximizes radiation and convection cooling. When John evaluated the load graphs of Thiel models considering phase and impedance, he recommended stereo-only except for the CS7/7.2 = stereo or mono. Due to the BM feed-forward distortion reduction the only advantage of bridged mono is 4dB greater headroom before shut-down, no increased distortion as in all other amps.

I recognize that these claims run counter to everything we know about amp behavior. Have you seen any second-party lab tests using the traditional 1% distortion limits? I would love to see those results. Note that I (among others) have requested a higher-output AHB-2, but John is firm that ’it isn’t necessary’. Perhaps from BM’s perspective of primarily pro market and inability to meet demand, he has a point.

Note I am not arguing that better and more suitable amps aren’t out there. I imagine they are. My personal situation is needing an amp that drives the loads while telling the truth. The AHB-2 does that for me, at a price I can afford.

Here's the AudioScience Review