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 Post subject: ABX comparator
PostPosted: April 4th, 2014, 10:32 am 
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Joined: February 28th, 2013, 3:31 pm
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QSC used to make an ABX comparator box to do double blind testing of audio components. I have had one for a number of years and used it sucessfully. Years ago they stopped manufacturing that device because as you can expect the demand was low.

Now there is a new ABX device available. Here is a link if anyone is interested:

http://www.monoandstereo.com/2014/04/au ... rator.html


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 Post subject: Re: ABX comparator
PostPosted: April 4th, 2014, 11:29 am 
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Joined: April 11th, 2013, 3:17 pm
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Seems like it would be a good device for the club unless someone wants to built a DIY version. Perhaps either split the cost among interest club members or the club could charge a weekly rental fee. The unit could be retained by any club member who hosts a meeting until the next meeting then it would be transferred to the next host member.


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 Post subject: Re: ABX comparator
PostPosted: April 4th, 2014, 12:42 pm 
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If someone only wants to borrow one on an occasional basis I have the QSC version that you can use. It has an IR remote and I have adapters for almost any kind of input or output.

Tom


Attachments:
Finished display on top of ABX box.jpg
Finished display on top of ABX box.jpg [ 186.66 KiB | Viewed 18517 times ]
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 Post subject: Re: ABX comparator
PostPosted: April 4th, 2014, 2:52 pm 
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How do the features and capabilities of your QSC version compare to the Van Alstine ABX Comparator Switchbox? For instance, the Van Alstine ABX supports two sources, two amps and three pairs of speakers either with or without subwoofers. It can also be used to evaluate cables and component parts. The Van Alstine is controlled by a remote and states it has precise volume level matching within 0.1dB.

This is what I got off of AudioCircle:

“For you DBT fans, rejoice! Audio by Van Alstine has just completed our very own ABX test box. Originally, we just wanted something to allow us to compare circuit ideas in house, but as word as got out about it, the requirements have grown and thus so have the capabilities.

The box allows you to connect two preamplifiers, two power amplifiers, three speaker system pairs, and a subwoofer (with both in and out connections). You can mix and match any pair of components and speakers (with or without subwoofers), and control the selections from the supplied remote control.

Output levels can be matched exactly and easily with the use of a simple digital meter reading AC volts. You can either set the level of both systems under test by matching output levels with the meter, or simpler yet, simply adjust to null the differences with the meter.

Then you can use the setup simply to switch preamps, amplifiers, and or speakers and keep track of what you are listening to, or - - - you can enter the test mode.

To do this you would want to set up one component in each signal path that is different. System A might consist of preamp A, power amp A, and Speaker set A for example. Then set up system B as preamp A, power amp B, and Speaker set A. This case would allow comparison of power amps only. Match levels exactly with the meter and you are ready for true DBT time.

Enter the test mode and all the indicator lamps are turned off, the starting point is randomized the dispaly lights up saying "Test 1". Listen away, make notes, and when you want to, press the test button again. This will then switch to Test 2 and the power amp under test will switch to the other power amp, or -- maybe not. This depends upon the random number generator making life difficult for you. Listen again, make notes again, and press test again and switch to Test 3. Repeat for the entire 8 test program session. Each test either switches or does not switch the component you are listening too. At the end of 8 tests, you can keep going, repeating the cycles as long as you want. Or you can then switch out of the test mode and the displays will light up again. Now going through the 8 cycles once more will tell you exactly what you had been listening too.

This allows you to take all of the huge audio sugar pills out of the listening process and provides some interesting and often humbling results.

There are absolutely no active components in the ABX box, nothing to "mask" or "ruin" the system sound. What you have set up is exactly what you are listening too. With identical components in the test chains, you can use the ABX box to listen to interconnects, speaker cables, or even high end fuses too. Even more fun.

The tests can be absolutely stress free. Listen as long as you like to one test sequence yourself. If it takes half a day to really "learn" what a given component sounds like, take that long if you desire. Its just your time.

We think that this really transparent ABX box might be useful to a variety of listeners. Audio clubs, speaker builders, electronic component builders, audio stores, even interested audiophiles. We don't have a price for the unit yet, probably under $2000.

The ABX box even has a computer connection to allow future programming updates and revisions.”


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 Post subject: Re: ABX comparator
PostPosted: April 5th, 2014, 8:13 am 
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The QSC comparator spec sheet is attached. It will do pretty much the same as the van Alstine. The large display that I made allows placement of the comparator near the equipment minimizing lead length while still providing high visibility.


Attachments:
QSC ABX1.jpg
QSC ABX1.jpg [ 275.04 KiB | Viewed 18499 times ]
QSC ABX2.jpg
QSC ABX2.jpg [ 233.88 KiB | Viewed 18499 times ]
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 Post subject: Re: ABX comparator
PostPosted: April 7th, 2014, 9:54 am 
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Joined: April 11th, 2013, 3:17 pm
Posts: 65
Tom, thanks for the detailed info and offer. If we have a room at the Capital Audiofest it might be fun/instructive to use your QSC comparator. If not maybe we can get together later this year and you can show me how you've used it in your system choices.


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 Post subject: Re: ABX comparator
PostPosted: April 7th, 2014, 11:05 am 
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I would be happy to provide it for use in our room. I will mention that setting up a proper test takes time and consideration to details. The prupose is not to decide if one component is "better" than another but simply to see if there is a difference in the sound of the devices under test.

Test conditions can also vary the outcome. As I mentioned before when David Berning and I did the double blind test using the ABX comparator between a 300B SET compared to my Crown Macro Reference amp we could not tell them apart at normal listening levels. David had previously tested the box to make sure it did not cause any non-linear artifacts. This test was done with my RD75s which are purely resistive. If the speakers were very reactive with large impedance swings I would expect an audible difference between the amps due to power delivery capability differences in the amps into various impedances. This is the kind of stuff that makes double blind testing very important as it helps you get to the repeatable root causes of differences in components.


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