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Audio by Van Alstine ABX Comparator Review
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Sokel
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Even better.
Relays and passive attenuators have been elevated to myth status these days.
A silent room is the absolute basic if one wants the benefits of all these nice numbers we see at the results.
Clicking relays, fans, etc, are not the best idea when they make this noise floor going like if was back at the '50's with some self-audible gear.
Interesting, if vexing, results. I wish I had kept my ancient ABX switcher and test results but they are long, long gone. I cannot remember what op-amps I used to buffer, and the test equipment I had access to at the time (ca. 1980) was nothing like what you can get today, but I think was around 0.001% (-100 dB). It was not an AP; I had access to an HP audio analyzer and Nakamichi audio test system back then. I used unity-gain op-amps (voltage followers) right at the inputs, followed by the attenuators and switches, then another follower on the outputs to reduce loading effects at either end. The line-level switches were reed relays, not as low resistance but I figured it did not matter for buffered line-level sources, and they were very quiet. The (unbuffered) speaker level inputs used high-current relays that were fairly loud (as long as the music wasn't playing), but IIRC I switched both sides (relays) every time, so there was no "tell". I used power resistors to ensure the amp was loaded during switching (after previously discovering that amp recovery could be an issue for some amplifiers if they were unloaded even briefly).
Wiring layout was critical and required several iterations to get right. I also tried putting the control circuit and relay drivers in a separate chassis to prevent any logic circuit noise coupling but that actually had no impact on the test results that I recall. It always had the power transformer in a separate box so only DC went to the switch box. The logic was SSI chips, combinatorial and simple latches/flip-flops, no clock circuit inside. I would do it much differently today, natch, with digitally-controlled attenuators, CMOS/FET switches for signals so no clicks anywhere, etc.
Wiring layout was critical and required several iterations to get right. I also tried putting the control circuit and relay drivers in a separate chassis to prevent any logic circuit noise coupling but that actually had no impact on the test results that I recall. It always had the power transformer in a separate box so only DC went to the switch box. The logic was SSI chips, combinatorial and simple latches/flip-flops, no clock circuit inside. I would do it much differently today, natch, with digitally-controlled attenuators, CMOS/FET switches for signals so no clicks anywhere, etc.
I repeat.. why listen to clicks when you have the source LED telling u whether A or B is active. It's there in the Pic.
It’s just as open or closed as it ever was.
As solderdude pointed out, the attenuator used already had distortion at the same magnitude as Amir measured. That’s not a revelation.
Probably the relays. But we don’t have any evidence of that yet, other than conflicting testimony. Could be phase. Could be fabrication. Could it be filters? Seems incredibly unlikely, especially with the HF rolloff and presumably some if not most of those DACs used used the same filters on the DAC chip.
By far the most parsimonious explanation is that there was something wrong with the methodology, but then that was always the case.
welwynnick
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No it doesn't. This has already been explained.
Right. It doesn't need an LED to tell you which one is on. It has a relay for that...ba da boom!
Sure, but that's an individual determination. Josh has written countless articles and to my knowledge there's no prior indication that he operates in bad faith.
Because the LED doesn't tell you what X is.
Again - it is not about good or bad faith. It is about amateurish approach, questionable test method and no valid data.
But clearly doesn't know what he is doing. Uses a useless device. His articles are worthless.
How do you know that.
We never got a thorough description... how do we really know he didn't cable up things himself and knew exactly which DAC was connected to which port? This device was to obscure that, right? Clearly it doesn't and can provide both audible and visual cues.
The one thing I remember is that Josh never claimed this was proof he could hear differences between DACs. Others did turn this into that kind of idiotic "proof".
I also have no idea why suddenly it's claimed Josh sold the device for 1.3k. It was about 3k.
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It totally does if you cable things up yourself.
Whether or not the LEDs were covered up no one really knows.
RandomEar
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The ABX comparator manual says:
So regardless of who cabled up what, the LEDs obviously do not tell you what device is active in ABX testing mode (because they are off). I'm pretty sure this has also already been discussed in the initial thread and it would also make the device immediately and obviously useless to anyone.
Does it really make a difference if a LED is obvious or not, or a click is different or not, concerning a DUT (here: an ABX-Comporator), that is distorting within audible range?
Explain the picture of the device with two big LEDs identifying the source.
I'd rather trust my own two eyes than your third party observations, sorry.
RandomEar
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Obviously, they are not off in training mode because you need to know what you listen to in that case
I am not saying that's the reason, but there seem to be too many things making this a totally useless appliance for the purpose of a real blind test.
His "Best Version Of" articles are gems.
Are you under the impression that when you select 'X' on the remote, the comparator lights up whether 'X' corresponds to 'A' or 'B'? If that were the case, that would be a truly useless device. However, there is no reason to suppose that to be the case.
I guess you were there live, ensuring the testing protocol was executed according to your assumptions.
RandomEar
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If you assume Josh cheated, the comparator doesn't matter, the LEDs don't matter, nothing does. He could have simply made up the results in that case. So this whole disussion about LEDs can only be about the question if they are on or off in test mode. And they are off.
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