Monday, June 29, 2015

The balancing act continues

I've found I can balance both main power amplifiers pretty close to the 0.1dB spec simply by using the Behringer DEQ 2496 image "tilt" control.  My current adjustment is 1 degree Left for the Krell, and 0 degrees for the Aragon (the Aragon already now being balanced to .15dB or better).

So then level matching the two amps comes down to level, and my current level setting is +1dB for the Aragon.  That's as good as I can do through the DEQ because now I find out it can only set gain in 0.5dB steps.  Fortunately, that almost matches the Krell.  Actually the Krell seems to change it's gain any about 0.3dB during the first hour of warmup.  The +1dB setting puts the Aragon at the low end of the range of the Krell, almost identical with the first minute of warmup.  If the DEQ had finer control, I'd likely set the level to 1.1dB or 1.2dB.

This 0.1dB matching for ABX testing is much more stringent than usually done in audio, notably more stringent than I've been doing for electronic balance (which I hadn't been paying attention to and just assuming it was correct since I have no variable resistance elements in my system…and now I see I had unintended differences larger than 0.3dB) and in setting up crossovers for triamplification (which I've done since around 1979 btw).  For many years I used a Pioneer D21 crossover (a Series Twenty beauty) and thought of it as about as perfect as such a thing could be, and it is only settable in 1dB steps.

For a few minutes, I was thinking my project of using DEQ's as crossovers was doomed because of the limited "tilt" balance control and 0.5dB steps.  But now I'm thinking "close enough for crossover" since even with the 0.1dB adjustability of the DCX units, I can't say my adjustments are anywhere near that accurate and I often play with changing levels by 1dB or more to see if a new setting would be better.  I recall differences of 1dB as being hard to tell apart and have never expected my crossover adjustments to be better than 0.5dB.

Strangely, IIRC, small differences in timing are more audible, with 0.5dB in level difference being not unlike 0.5 msec of delay, with even 0.1 msec being important (more important than 0.1dB).  0.1 msec is close to the difference of moving speaker or listening position 1 inch.

I just won a Denon 5000, my 3rd new R2R DAC.  I now have enough of them to do all three ranges in the living room system if I'm willing to use the same DAC for both midrange amplifiers, which I now think I will do since I have useable digital level adjustment with sufficient accuracy for a crossover (and almost sufficient for ABX).  I could even control the DEQ settings with a trigger voltage via a trigger-to-midi device.

I think I will implement a level-box as my ultimate Y adapter for the two amps, but in the meantime an Audioquest Y adapter will do, with low cap cables possibly from Blue Jeans.   None of the cables I am currently using are particularly low cap, though I could have done worse.  I was shocked to find that the 4 meter Monster 1000i or something like that (it was over $100 if not $200, IIRC) had 800pF and I decided that made it totally unusable.  But even the Straightwire 1m cable I have for the Krell is 300pF, and the combination of cables I have to the aragon is over 400pF.

I will need to get a rack.  The piles of equipment behind each speaker are already too high, and I needed to stack the turntable above the Aragon amp already…with a rack I can also support a couple of boat anchor DAC's and other stuff.  I've picked out a very nice audiophile grade rack and turnable stand, it will put the turntable at 48 inch height which is about all I can deal with.  Before finding the one I want now from Mapleshade in solid maple, the previous ones I was looking at had glass shelves.  It's looking hard to find the Lovan Sovereign I used to lust after, and even the Lovan Legacy that is even featured at Houzz.  There is a four point stand by VTI that looks OK for a mere $400, and even $100-200 glass stands at Wayfair look tolerable.  I don't much like the Sanus stand I have now under the keyboard.

I've been matching the Aragon to the Krell + Audio GD level because the latter has sounded so good, despite being different from my last DEQ Calibration in January.  I think I'm playing the midrange at a higher level now by about 2dB or so and that sounds better because it dominates the subwoofer bass, giving the sound a tighter electrostatic bass sound.   Or perhaps I should say it now equals the bass, whereas previous the bass dominated giving everything a plate-amplified subwoofer sound.  This adjustment needed to be done by ear anyway, it's hard to say precisely where one terrain of 10dB hills and valleys should be joined to another.

And so if I was wrong by 2dB during an actual calibration--with careful measurements and listening, just how critical is it to set level better than 0.5dB?

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