[art]

Someone asked me recently why I thought our amp fared the way it did.

Accoding to Gary Dodd, the soundstage was well-defined, with a solid image. But the soundstage was narrow, and a bit too forward.

Ooops.........the last guy that auditioned the amp wanted one that way, so he heard one that was tweaked in that way.

I forgot to "un-tweak" it. Hey, it happens.

Pat

[avahifi]

Question about the amplifier tests.

How did you adjust for gain differences between the various amplifiers?

How did you actually affect the change from one amplifier to another?

Methinks there may be some unaccounted for variables here.

Frank Van Alstine

[Danny Richie]

How did you adjust for gain differences between the various amplifiers?

We used our ears and turned them up or down as needed. I think the guy in the center seat had the remote for the volume.

How did you actually affect the change from one amplifier to another?

How did we effect the change? Do you mean compensate for loudness differences?

Methinks there may be some unaccounted for variables here.

Actually there weren't. The amps compared in the first round weren't that close or in other words were very different.

It seams that the host of the event spent a great deal of time listening to the various amps before hand, and unknown to the participants, stacked the first round in a way that amps that were close, and would need a greater level of scrutiny to discern, would not meet in the first round.

It wasn't until the end that comparisons got close and became a subjective assessment of a toss up.

Match ups in the first round were unanimous.

[ctviggen]

You simply must perform level matching using a wide band signal and a meter.  Anything less than that means the test is flawed.  It's very easy to turn one amp up a few dB (especially when you're taking amps in and out of a chain) and then to say that this amp sounds better.  You have to place each amp on a level playing field and letting one guy set the volume up or down to his likely does not do so.  Audiophiles are the least scientific  people (other than people who believe cholesterol has anything to do with coronary heart disease) I know.  No wonder there are power cords for thousands of dollars.

[avahifi]

Whoops, without precision matching of the amplifier levels, your tests have no value, no matter how much you want, hope, or think they did.  Sorry about that.

As I have reported here before, when we test new circuits, we first of all know the gain and keep them identical for test purposes.  Then we listen to just one changed channel vs: one original channel in mono into a pair of side by side matched speakers and simply use the balance control to switch back and forth.  We randomize the preamp and speaker connections so nobody, not even the tester, knows which is which before or during the test.  We have to do this to keep ourselves honest, otherwise we would be sooooo tempted to like the "new and improved" circuit best, even when it is not best. Matching "by ear" introduces variables that will affect the listening test results.

We don't proceed to full stereo listening unless and until blind mono comparisons tells us we are actually on to something worthwhile musically.  Even then, it better be better on bench tests too (we use square waves into difficult loads).  If it tests bad, it is bad, no matter if we think it sounds good.  To be good it has to test good and sound good both. It is pretty easy to like something (for a while) that really is not very good at all.

Frank Van Alstine

[avahifi]

By the way, don't think I am picking on you.  Those "scientific" ABX box tests are flawed too.

In these tests, the two amplifiers are connected to a common preamp source and the amplifier outputs are switched to the speakers.  

The usual result is "all the amplifiers sounded the same."

No kidding, here is why.

We have shown that with almost all amplifiers, output non-linearities are reflected back into the amplifier's feedback loop, and can actually be observed at the amplifier's input jacks too.  When two amplifiers are tied to a common source through the input connections, then the non-linearities of both amplifiers are summed and fed to both amplifiers.  Of course they are going to sound the same, and usually never good.

I suggest you repeat you tests, using a preamp with carefully matched channels, a repeatable balance control, and only one channel each of the amps you want to test. Measure the gain of each amplifier first, and pre-mark the balance control to make up for differences in gain.  You are going to be surprised how different your results are going to be when you eliminate the unknown variables.

Frank Van Alstine

[marvda1]

so you're saying every common joe has to go through this when they want to upgrade their equipment or else they are shooting in the dark and wasting a lot of money. why not just program all this into a laptop with microphone and let it tell us which is the best equipment!  

sorry, just stirring the pot a little.

[Danny Richie]

You simply must perform level matching using a wide band signal and a meter. Anything less than that means the test is flawed.

Whoops, without precision matching of the amplifier levels, your tests have no value, no matter how much you want, hope, or think they did. Sorry about that.

Ha, ha, ha...  

Who said they weren't level matched?

Are you questioning our instruments?

Frank, I have been there and done that. I do it with speakers all the time. I even had a custom high quality A/B switching device built. Mono to mono listening is a good tool, but not the whole story.

Guys, I had these amps here for several weeks. I was able to listen to all but one of them extensively. They were very different and consistently different.

I listened to some of them enough that there were times you could have blinding played my reference music back to me on one of the them and I could have told you which amp it was.

Some of these amps sounded different enough to notice the difference in the first few seconds, and it had nothing to do with level matching.

Some had completely different sound stages. Imaging is different. Noise floor is different. Space between the notes, different. A sense of air and space around instruments, different. Lushness, hardness, or smoothness of the vocal region, different again.

And  lot of this you just don't get from listening in mono to one speaker.

I saw no real surprises in the outcome.

Some amps sounded good regardless of source material, and some sounded bad regardless of source material.

Trust me, it just wasn't that close until we got down to the end and then it was give and take.

[avahifi]

"So you're saying every common joe has to go through this when they want to upgrade their equipment?"

No, that is not what I am saying.  I am saying however that when you read a comparison review, you should be able to trust that the review setup did do its very best to eliminate uncontrolled variations.  This amplifier test did not do this.

I am also not saying that there will not be significant differences in musicality between the units tested.  I simply am uncomfortable with making the decisions without level matching.

I also would like to have seen the actual waveform output of the various amplifiers under test under stress conditions (a half power 10K square wave into an 8 ohm load in parallel with a 0.1 uF capacitor for example).  Sometimes it is really nice to see what you are hearing.  This is also a good way to see just what your pet speaker cables are really doing. Its hard to say that your cables sound really wonderful when the scope tells you they are making your amplifier go bezerk. When you see all the HF garbage being dumped into your speakers by various Class D switching amps that might slow down your love of them too.  Do the tweeters and your ears really like that?

Regarding tests in mono, we do that first to most easily eliminate variables.  Of course the survivors are evaluated musically in the stereo mode too.  Again, makng sure levels are matched exactly.

I have only been doing this for over fifty years. Been there, done that, heard that too.  Before you trust your ears too much, see how much a one dB level mismatch can screw up your judgement.  Do you want good results or simply a sanction of your assumptions?

"We don't need to level match because we can really hear big differences" seems to me to be no different than claims for audiophile grade AC outlet wall plates or Ming Shu dots.  Do it right, don't be down to that level of audiophlake nonsense.

Frank Van Alstine

[Danny Richie]

Well, I haven't been doing this for fifty years, but I have been doing it long enough to figure out that the customers of these amps and of yours are not going to compare them with your test equipment. They are going to listen to them to make their own comparisons.

Maybe you can talk all of these amp manufacturers into sending you their amps so you can compare them the right way, by measuring them all. I am sure that whichever one measures the best will be the best right?  

Maybe you would like to send some of your amps on tour down here and we'll put them through our vigorous testing (I mean LISTENING), and we'll let you know how they compare.

I'd be willing to bet that your potential customers would be more concerned with how they compare to other amps after a week of listening to it and comparing it to other references than would be interesting in hearing about how they compare in any other way, and especially if the feedback came from a group of well respected audiophiles.

Oh yea, who says we didn't level match?