I hardly know where to begin or where to take this thread. I just finished reading a rave review of an amplifier by a very experienced reviewer. The review ended with the reviewer buying the amplifier even though the timing of the purchase was less than ideal for his finances. I'm going to have start giving some things away here, but I don't have much choice. The review was in Stereophile and JA took measurements of the amplifier. I also want to state for the record that I have heard this amp several times at shows and thought it sounded damn good. I first heard the amp at RMAF 2012 on the Nola KO speakers and I previously wrote about how smitten I was with those speakers.
The amp under review is advertised as a 75 watt per channel tube amp that uses a pair of KT-120 tubes per channel. When JA measured the amp, the amp did not meet its specified power output of 75 watts. I think that many people are under the assumption that when they buy an amplifier, the amp does meet its stated output power and does so at the distortion levels advertised. The amplifier under review could only muster 61 watts of output power into a 4 ohm load from the 4 ohm tap. The kicker is that it could only reach 61 watts into 4 ohms at 1% distortion which JA further defines as driving the amp into clipping. The output power into 8 ohms from the 4 ohm tap was only 43 watts at 1% distortion. When JA drove the amp into 3% distortion, the output power increased to 46.5 watts into 8 ohms and 70 watts into 4 ohms from the 4 ohm tap. So even if you relax the distortion levels to 3%, the amp still falls short of its advertised power output which I find surprising for a number of reasons. When the output power was measured into an 8 ohm load from the 8 ohm tap, the power came close to meeting the specified power. The amp put out 70 watts from the 8 ohm tap into an 8 ohm load, but again it was at 1% distortion.
So here's the kicker: How does an amp that measures poorly in terms of distortion for anything approaching it's specified power output sound so good? Objectivists who love many zeros after the decimal point in their distortion measurements would surely cringe. Frankly, I also have a little problem with a manufacturer saying an amplifier puts out 75 watts a channel when it doesn't and not clearly specifying the distortion levels that will be required in order to approach the rated output power. I think it's called truth in advertising. So here we have a $9K amplifier that is specified as 75 watts per channel at 0.6% THD and it really can only muster 70 watts at 3% distortion. Some of you may remember a rant I went on long ago on this forum about specifications not being measurements and there were some naysayers who didn't get what I was saying at the time. The naysayers were under the impression that specifications in the absence of measurements were just fine and surely they really were the same. Here is a classic example of why this isn't so.
I think there is only two conclusions that can be drawn here as to why this amp sounds really damn good. The first conclusion would be that you are using really efficient speakers so that the amp is never required to deliver enough power to drive it into clipping and the distortion levels stay very low (not SS low though mind you). The second conclusion is that THD is highly overrated and everything still sounds great even if you are clipping the amp. I'm personally going with the first conclusion, the amp has to be mated with high efficiency speakers so that it is never driven hard enough to clip it and raise the distortion levels to 1% let alone 3%. The clue in the review is that the reviewer turned up his system to what he considered very loud levels and the amp was only hitting 25 watts on the VU meters.
The amp in question is the ARC Reference 75 if you haven't already figured it out. The review is in the May 2013 edition of Stereophile.
The amp under review is advertised as a 75 watt per channel tube amp that uses a pair of KT-120 tubes per channel. When JA measured the amp, the amp did not meet its specified power output of 75 watts. I think that many people are under the assumption that when they buy an amplifier, the amp does meet its stated output power and does so at the distortion levels advertised. The amplifier under review could only muster 61 watts of output power into a 4 ohm load from the 4 ohm tap. The kicker is that it could only reach 61 watts into 4 ohms at 1% distortion which JA further defines as driving the amp into clipping. The output power into 8 ohms from the 4 ohm tap was only 43 watts at 1% distortion. When JA drove the amp into 3% distortion, the output power increased to 46.5 watts into 8 ohms and 70 watts into 4 ohms from the 4 ohm tap. So even if you relax the distortion levels to 3%, the amp still falls short of its advertised power output which I find surprising for a number of reasons. When the output power was measured into an 8 ohm load from the 8 ohm tap, the power came close to meeting the specified power. The amp put out 70 watts from the 8 ohm tap into an 8 ohm load, but again it was at 1% distortion.
So here's the kicker: How does an amp that measures poorly in terms of distortion for anything approaching it's specified power output sound so good? Objectivists who love many zeros after the decimal point in their distortion measurements would surely cringe. Frankly, I also have a little problem with a manufacturer saying an amplifier puts out 75 watts a channel when it doesn't and not clearly specifying the distortion levels that will be required in order to approach the rated output power. I think it's called truth in advertising. So here we have a $9K amplifier that is specified as 75 watts per channel at 0.6% THD and it really can only muster 70 watts at 3% distortion. Some of you may remember a rant I went on long ago on this forum about specifications not being measurements and there were some naysayers who didn't get what I was saying at the time. The naysayers were under the impression that specifications in the absence of measurements were just fine and surely they really were the same. Here is a classic example of why this isn't so.
I think there is only two conclusions that can be drawn here as to why this amp sounds really damn good. The first conclusion would be that you are using really efficient speakers so that the amp is never required to deliver enough power to drive it into clipping and the distortion levels stay very low (not SS low though mind you). The second conclusion is that THD is highly overrated and everything still sounds great even if you are clipping the amp. I'm personally going with the first conclusion, the amp has to be mated with high efficiency speakers so that it is never driven hard enough to clip it and raise the distortion levels to 1% let alone 3%. The clue in the review is that the reviewer turned up his system to what he considered very loud levels and the amp was only hitting 25 watts on the VU meters.
The amp in question is the ARC Reference 75 if you haven't already figured it out. The review is in the May 2013 edition of Stereophile.
