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  1. Very true, but IMO it's a good thing to eliminate the loudspeaker impedance variable from the amp shootout so that the difference between the sound of the amps alone remains, if any. Not to eliminate the loudspeaker magnitude response differences (caused by amp output impedance differences) would make the test results applicable only to the amps under test into the specific loudspeakers used in the test. IMO. : ) Edit: I think I see your point now. If one were doing an amp shootout in their home with their loudspeakers, neither of which they planed to replace or modify, then you're absolutely right. I'm always thinking about other folks using the results of my foolishness measurements. : )
  2. Level matching is a big deal if the amps being compared sound similar, which will almost always be the case unless something is broken. As Greg infers, it's impossible to meet Claude's spec using a single frequency tone - or any other stimulus type for that matter. What would have to be done is to place a fancy 2in/4out EQ in front of the amps to remove these linear distortion differences. Non-linear distortion differences, if any, are helpful differentiators and shouldn't (and can't) be removed. The proper measurements would be at the loudspeaker input terminals. The difference in level and magnitude response (phase ignored) would then be equalized throughout the spectrum of interest within the tolerance of interest using standard minimum phase filters and gain. Then you run the ABX test on a different day when you've recovered from doing all the prep! : ) The following plot isn't an illustration of the above, but it makes the point that different amps are going to have different responses into a variable impedance load. After restoring a MC275CE tube amp I measured the output into an 8Ω resistor and then into a Danley SM100 loudspeaker. The measurement was taken at the amp output terminals. God bless you and your precious family - Langston
  3. I agree! : ) I'll get around to doing the ABX test again before too long - for the full 25 trials. I started working out with a personal trainer about a month ago that also trains soldiers at the local Naval base and the pain he puts me through reminds me of the ABX test. From the QSC ABX manual. Sorry for the poor quality, but it's the best I'm aware of. Edit: after pasting the above from the QSC ABX manual, I got interested in figuring out the probability math and it turns out that my earlier ABX test where I got 8 right out of 11 trials results in a confidence of 92% that I heard a difference between the amps. If you are interested in the math I just added it to the original post.
  4. I think that's a good sign, my guess is that the NC400's near zero output impedance has removed the slight bass boost that typical AB amps provide, and that tube amps significantly provide. The load impedance (loudspeaker) independence of the NC400 may be the best available. It's also a magnificent laboratory amp.
  5. Looks like a very good deal to me. I built a pair of these amps from the diyAudio kits without modification and they sound wonderful, particularly in parallel mode which requires one amp per channel, such as offered in this sale. You'll need very efficient loudspeakers due to their low power, but that's what we have around here. : ) I made (5) posts on the diyAudio forum including measurements of my amps beginning here. God bless you and your precious family - Langston
  6. A few things of note re: the SBAF Loki measurements: 1. The ARTA measurements are single channel (the second is used in loopback to remove the sound device transfer function errors), so you can't judge channel balance with them. They were performed nicely - I can tell that even the max. boost traces are undistorted and noise-free. The guy makes no mention of the drive voltage(s) used, thus we have no idea if the Loki can output undistorted EQ boosts in the neighborhood of the 2V RMS standard for home audio. 2. The Audio Precision measurements have the advantage of showing both channels, but the guy made several mistakes that make the results much less useful. The first mistake is that he selected 100dB Y-axis scales for a device that can affect gain by +/-12dB at most, thus it's very difficult to see channel imbalances or anything else. The second mistake is that while the Audio Precision system is an integrated (software and hardware) platform, the guy doesn't bother to tell us the drive voltage(s) used. Thus the Loki might not be able to get anywhere near the 2V RMS standard for home audio equipment, or maybe it can exceed it like the EQ570, we can't tell. The third mistake is that he didn't provide results (as seen in the ARTA plots) of each knob position an end-user is likely to use, but instead shows a few useful results along with some simultaneous mixing of the EQ's which is interesting, but far less useful. The forth mistake he makes is he drives the Loki significantly beyond its linear range into distortion and doesn't seem to realize it (post #29). The heavy fuzz on Ch1 is one example as are the wiggles in the midrange traces (500Hz - 2kHz). Both are tell-tales of non-linearity caused by distortion and/or high noise levels and/or inappropriate FFT parameter settings in the measurement. 3. The ARTA measurements are the most useful because they show how the EQ behaves at various knob positions. From them I can see: Like the Bellari EQ570, the Loki has a low frequency shelving filter. Unlike the EQ570, the remaining (3) filters are peaking types. While I slightly prefer the Loki's high frequency filter bandwidth, the lower (3) filter designs are so bad that it makes the unit a non-starter regardless of any other specifications it may boast. The low shelf filter affects a bit too much of the spectrum above 100Hz at likely in-use settings, but the real deal breakers are the critical mid-band EQ's around 400Hz and 2kHz. Those two bands show useful shapes only at their max. and min. gain settings. At the lower settings where they are much more likely to be used, the curves flatten out to the point of uselessness and affect way too much of the spectrum. IMO, the Loki is useful for its bass and treble knobs alone. I'm amazed this thing ever got off the bench. After reading several reviews with measurements of other Schiit products, I am at a loss figuring out what they're up to. Some stuff appears to be quite good, while other stuff is mediocre or worse. Fascinating. God bless you and your precious family - Langston
  7. Good observation - we're been spoiled by a digital world where everything is spot-on. With most analog stuff, variations between L/R like this are common, though the EQ570 is probably better than most, maybe better than all near this price range. Still it doesn't matter. Worse case is less than 0.5dB and loudspeakers with L/R differences less than 2dB are rare. Then you have room modes and reflections and non-symmetrical furniture arrangements and imperfect listening positions and... I think it's reasonable to consider the EQ570's channel balance flawless considering all that other stuff. : ) God bless you and your precious family - Langston
  8. 4Ω Is the probably the closest answer if you don't want to experiment. Your amp can dissipate much more power than the Cornwall will ever need, thus I'd suspect that the 2Ω output terminals will sound best because it will result in the least frequency response variation due to the amp having the least output impedance. Then again, the frequency response variation may sound nice, thus I'd consider the 8Ω output terminals as well. You can measure it yourself very accurately using the Dayton Audio DATS. God bless you and your precious family - Langston
  9. I don't know. : ) I do know about the original product from Aphex called the Aural Exciter, and the Bellari gizmo is likely a simple distillation of it. Don't read past this point if you value your time or sanity. : ) Background The WWII battleships were some of the loudest places on earth occupied by people and they had a terrible time communicating with the crew. Thus they trained the heck out of them to minimize the need, but the need to communicate changes in the theater of action was still there. Sound system power was quite limited at the time, but they found that if they pushed the system pretty hard into distortion (10%+ 3rd harmonic), they could get the equivalent of about 10dB+ louder communication ability without additional voltage from the amplifier or excursion from the compression drivers in those reentrant horns. The clipping amplified the consonants in speech aurally (perception), and it is the consonants that provide understanding (articulation) in speech. It wouldn't be until the 70's that Peutz would develop a speech intelligibility metric he called the Articulation Loss of Consonants (ALCons), but the major ground work had been laid during the war. So. We learned we could make huge apparent increases in communication based power without actual increases in electrical or acoustic power. Radio and the Loudness War The 80's saw a distinct change in the way music was broadcast over FM. Whereas the earlier decades of radio worked from fairly fixed definitions in broadcast technology and end-user reproduction systems, the 80's saw wild advances in both domains. While the earlier decades had to compete based on content, the 80's had the advantage (?) of maturing processing capabilities that the Beatles pretty much started in the 60's with multitrack and large scale concerts. Thus compression and hard limiting was used by radio to increase the apparent loudness of their transmission, but this initially brought complaints from both record producers and end users. A smart guy at Aphex used the clues in Peutz's work and started clipping audio on purpose and found a range of adding distortion that mimicked the natural harmonics of the bass and midrange in such as way that it highlighted them without actually increasing electrical power dissipation. Thus we tend to perceive more bass and vocal output/clarity even though the actual volume is unchanged. This is exactly what 80's radio wanted because it subjectively offset the heavy handed early compression dullness by "restoring" the liveness of the sound and (perceptually) making it even louder! Of course recording studios applied it to vinyl and tape reproduction formats as both have the same hard limits as radio transmission. Concert sound began experimenting with it as an effect even though they weren't faced with the same headroom limitations. It's in use today via plug-in's in digital recording and concert production, though Aphex still offers the rack mount version. Dave Levine (aka Rat) used it for the Chili Peppers* - he's one of the last of a dying breed that still mixes on analog consoles with outboard racks. 2021 What's old is new again. God bless you and your precious family - Langston * Dave became the first and only (AFAIK) FOH engineer for the Red Hot Chili Peppers decades ago when he rented a modest concert system to them in a small venue before they were known. The bassist (Flea) stripped naked during the show and spray painted the mic stands and a bunch of Dave's other stuff yellow! Afterwards, a very not-rich Dave pleads to the group that he can't afford to fix/replace the stuff and the group paid for all the damage. They fell in love with each other that night and have stuck together since then.
  10. I just posted measurements of the Bellari EQ570 here. Something to note - if you look carefully at the 400Hz and 2kHz plots, you'll notice that the actual peak/dip values shift a bit lower in frequency at the more likely settings of +/- 3dB or so. God bless you and your precious family - Langston
  11. The stimulus for this post came from here. I thought a separate topic would be more appropriate as others may be interested in what turned out to be a well-made, yet inexpensive little analog EQ for those who want to keep things simple. I haven't measured an analog EQ in years and it brings back memories of my favorite console before Yamaha almost single-handedly converted the concert production world to digital. Component quality and PCB layout are very good, switches and knobs have excellent feel and alignment with no play, power adapter has a snug fit, designed and built in the USA by a company I've dealt with for over a decade in the installation industry. American quality at a Chinese price - I am impressed. Front Rear Interior 1 Interior 2 Unbalanced consumer audio equipment is generally standardized to a 2V RMS max output, whereas professional equipment is standardized at 12V RMS max. The Bellari EQ570 passes audio through its buffers whether or not the EQ is engaged and its max output is 3.5V RMS (without boost EQ) before distortion starts to rise. The unit has very little noise as well. The first two plots follow Amir's technique at ASR, which I think is an excellent snapshot of signal vs. noise and distortion at the standardized voltage level. SINAD is the reciprocal of THD+N and probably a bit more intuitive. It is a measure of how much higher a 1kHz test tone is than the noise plus distortion in a device (at 2V RMS in this case). Dashboard with EQ Bypassed Dashboard with EQ Engaged, but Flat Magnitude vs. THD from 100mV to 2V with EQ Bypassed Magnitude vs. THD from 100mV to 2V with EQ Engaged, but Flat 60Hz Low Shelving Filter at 1V (see plot legend for knob positions) 400Hz Peaking Filter at 1V (see plot legend for knob positions) 2kHz Peaking Filter at 1V (see plot legend for knob positions) 7.5kHz High Shelving Filter at 1V (see plot legend for knob positions) All Filters at Max and Min at 1V God bless you and your precious family - Langston
  12. Those things were designed to be rode hard and put up wet, and the multiple coats of paint and wear make it obvious they were used accordingly. Looks like 80's concert tech to me. That's not a compliment. The narrow pattern of the tops will only hold at higher frequencies - you need big boxes to hold those patterns to the transition of the woofer, but it didn't matter for live rock because the venue was screaming loud and the sub arrays were overwhelming anything the woofers in those little boxes were trying to do. That 3 box kit looks like a drum monitor system to me. That means the sub is tuned to dive under 50 or 60Hz. When buying stuff, ignore the "value" of what they're offering if it doesn't apply to you, such as the beat to death road cases. If I bought something like that I'd replace all the drivers unless I had the means to throughly vet them after purchase. Thus I wouldn't pay more than $600 for all of it. With that said, it would be fun to restore that little system to use in small club settings, but I have a feeling it'll be a far cry from satisfactory for critical listening. God bless you and your precious family - Langston
  13. DSP is amazing in what it can do, but it's just as good at screwing things up until you go pretty deep into that rabbit hole. : ) In the mean time, I'm convinced that the Heresy IV didn't see the light of day until the Chief and crew felt they had the best result possible for its expected application. Still, you can almost always improve things due to your specific acoustic setting*, tastes, recordings, hearing ability, etc., but I think you're wise to initially take a gradual approach with something like the broad tone control offered by the EQ570. I've never used one of those things, but I trust the company that made it and expect that it will work well. The manual generally specs the EQ offered and I can tell that the designer knew what he was doing. I just ordered one through Amazon since I can return it. It's due to me Monday and I'll post full measurements on it by Tuesday. In the mean time, the guy that's probably measured the Heresy IV more than anyone else outside of Klipsch posted a "spinorama" of it a few days ago. This form of analysis is the brain-child of Floyd Toole and and requires a long trip down the rabbit hole to fully appreciate, but you can just concentrate on the "estimated in-room response" plot to see that a broad (low-Q) reduction around 2kHz, such as the EQ570 provides, may be just what the doctor ordered. God bless you and your precious family - Langston * In live music performance there is absolutely nothing as effective in making an instrument sound good as mic selection and placement. IMO, placement is the most important of the two. There's no EQ or effects or mix (relative level) adjustment in the world that can do what placing the mic in the right spot will do. The mirror image of this is loudspeaker placement within your room. Do that first when your wife isn't home so you can move the furniture as needed. Then when she gets home, catch her before she sees the room and tell her that you have something terrible to confess. When you're both seated, tell her you cheated on her - but very quickly (before you die) correct it and tell her the only thing that really happened was some stuff got moved around in the room with the loudspeakers, "and isn't that way better?!" : )
  14. It is excellent and true. I'm starting to notice fundamental articles vs. their derivatives - your clipping is a derivative of: In contrast, it's fascinating to see attempts to create a small driver with a huge Xmax to bridge the output gap a bit between direct radiators and horns. Xmax to the moon won't aid efficiency and it certainly will increase frequency based modulation. Thus, there's a limit to what they can do even if they figure out how to make the poor thing swing like Duke Ellington.
  15. Interesting post, thanks for taking the time to write it Erik. : ) The voltages are amazing in tube amps, but when you need a given amount of power and can't do current you're stuck with it. This reminds me of an event from my concert production days - 2017 and I'm providing sound for a Warner Bros. event in Ft. Walton Beach FL called Bugs Bunny at the Symphony II with full orchestra and a few muso's that toured with the show. One guy brought the original slide guitar from the 30's they found in a Hollywood warehouse that was used by the original orchestra for the Bugs Bunny opening theme. They spec'd a Fender Twin (the source of that schematic I posted above) for the slide, which I brought along with a backup. So the amp starts buzzing during rehearsal after the cocky engineer with the tour connects it to the slide. I offer one of my cables in place of the ragged thing he brought and he says "nope! it's the amp!" I offer the backup and he says "nope! I got this, this isn't my first rodeo." So he reaches down to the underhung power tubes, amp still on and hot, and then proceeds to fly about 5ft of so backwards before landing. A bit reminiscent of a Loony Tunes episode. I help him up and see his hand and say nothing. Obviously. He's the expert. Turns out it really was the amp, probably a cracked tube glass that fell apart when he touched it. It wasn't the heat that got him - it was the plate voltage! We used the backup. Here's a clip of the opening where you can hear the slide guitar start off the theme that modulates from about 250Hz up to 550Hz: Bugs Bunny Opening Theme.wav Here's the rider I was given for the event for anyone that's bored today: Sinfonia - Bugs Bunny Symphony 2017.pdf God bless you and your precious family - Langston
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