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June |
June 16 QSC POWERLIGHT 6.0 PFC ARRIVES! I've been swamped with work on an unrelated project, so not much to report until the first of the QSC Powerlight 6.0 amps arrived. This one's a trial/checkout. If I like it, I will buy additional units to drive the Bassmaxx subwoofers to their full potential. I researched this amplifier extensively, including analyzing the 15-page schematic diagram at length before making a purchase decision. When the amp arrived, I was amazed at how much it weighed, for a switching power supplied amp. It's built like a tank. The schematic indicates the use of high-precision 0.1% tolerance resistors in critical gain stages, and 1% tolerance resistors in other parts of the amp. No expense was spared in the design of this beast. I first need to rewire part of the rack to accommodate the special power plugs that these amplifiers use. This will likely be a weekend or late evening project or a rain day project. The amp was purchased used from a major west coast sound company for about 28 cents on a dollar. It was meticulously-maintained, and is clean inside & out. Hopefully it will work as well as it appears to have been maintained. The gain controls are step attenuators--very precise. There are individual switchable clip limiters for each channel. The rear features binding posts that can accept 6AWG wire, as well as the newer Speakon connectors. Inputs accept balanced signals from XLR/TRS combo connectors and Phoenix connectors. There's also a data port back there and a remote standby connector. The amp is all MOSFET output stages, so it should sound good, as well as be a terrific bass amplifier. Power supplies are power factor-corrected switching supplies, which are fully-regulated. These photos open in a separate browser window: Front View of QSC Powerlight, click HERE. Rear View of QSC Powerlight, click HERE.
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REMAINING BASSMAXX ZR18 WOOFER ARRIVES! This has been a busy week! I'm engaged in some unrelated projects which are taking up 14 hours of my day, and Monday welcomes the arrival of the last of the Bassmaxx drivers, bringing the total to four. At the end of an already busy day, I set myself to the task of removing the Altec 3182s from the Destroyer cabinet and moving the EVX-180Bs from Earthquake to Destroyer, making room for the ZR-18s to be installed in the Earthquake subwoofer cabinet. I accomplished that task in my usual slow and methodical way. Now everything is ready at the front end. I just need to buy some 10AWG stranded zip cord for the new subs. I ordered a second QSC Powerlight 6.0 PFC 6,000 watt amplifier on Monday. Hopefully that will arrive Friday. All that remains to be done is to add wiring and twist-lock outlets for the QSC amplifiers. So far, I've mounted the metal outlet boxes to the bottom of the rack. I need to buy some SJ type power cable to make the hookup to the breakers. In about a week, the system conversion should be about complete. I'll be running 12,000 watts on sub-bass, 4,000 watts on mid-bass and 3,000 watts on mids/highs. Total system power output, a conservative 19,000 watts. That will really test the construction quality of the house! As my friend reported to me last weekend, it was the concussion that killed Al Quaeda's commander last week, not the actual missile. Such an example illustrates the danger of huge and rapid changes in air pressure. Telarc's "1812 Overture" ought to be quite something on this system. I'm somewhat behind on photos. The photos are quite outdated now. I hope to have some more time next week to take some new ones and update this site.
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QSC POWERLIGHT 6.0 PFC INSTALLED This morning was a new milestone: the monster amplifier from QSC is installed in the power amp rack! I finished wiring the twist-lock outlets and got the amp positioned on top of a shipping container, in front of the rack, fed the massive power cable through and then slid the amp into position in the rack. It's wonderful how everything works out when you've done your homework! Installation completed at 2:00AM, so any real testing will have to wait til tomorrow. But I have some observations about noise levels and acoustics. The amp is silent. Not a trace of hum in the subwoofers, even with the gain on the amp cranked all the way to 32dB. The amp idles cool. Much cooler than one Hafler 500. The four fans are pretty quiet. Much quieter than the rack's squirrel-cage blower at 60 volts drive (it's throttled down because it's way too loud at 110v). In this configuration, the amp will push close to 3,000 watts to each Bassmaxx dual 18" cabinet. Another QSC amp, identical to this one, will arrive hopefully later this week. I will switch these to bridge mode at that point and then each Bassmaxx dual 18 will have 7,000 watts on tap. EVENING: TRASHIN' THE PLACE Insanity. I may have gone too far this time. How much bass is too much? Normal people would have said there was "too much" bass long before I did these upgrades. I didn't get to run the QSC all-out--the building itself was crying out in agony. It was also getting hard to breathe the air for two reasons: the barometric pressure was rapidly fluctuating (sound) and there were billions of particles of fiberglass acoustic insulation floating in the air. Scores of chunks of acoustic insulation were scattered all over the studio floor after just one song. Dust rained down from the suspended panel ceiling, as the acoustic tiles ground themselves into a fine powder. In just five minutes, my Roland A-80 keyboard looked like it hadn't been dusted in 30 years, where normally I keep it spotless. This is the first time I had both Bassmaxx pairs operating. "What a difference" would be an understatement. I had to leave the building and stand outside, about 70' away and get some fresh air, while listening to some selections. Usually, it is impossible to get a 16Hz fundamental to escape the building and be audible outside. Tonight illustrated just how useless the conventional woofers are at producing enough clean subsonics to "brute force" its way to the outside through concrete walls up to 3' thick in some places. But it's a totally different story with the Bassmaxx woofers. Even at very low frequencies, they shake the concrete slab with ease, and by shear brute force, produce a very loud fundamental on the lower organ pedal tones, outside, at the edge of the property line. I got to thinking, if this system were outdoors, and there were seating for thousands of people, we could hire a virtuoso organist, set up the Kurzweils with Post Organ Toolkit samples, and have an organ concert under the stars. Outside my house, I was experiencing better bass than I experienced inside the Cathedral of St. Joseph in Hartford--the organ the Berj Zamkochian himself once played--when the mighty Austin Organ was demonstrated for me as a prelude to a recording session. Deep in my imagination, I thought of moving everything out on to the patio just to try this, but the amount of work involved would be enormous and it would not take long to get a not so nice police investigation going on for the mutha' of all "breach of peace" calls. Fantasies aside about organ concerts, stars and setting up outside, I did find the low end, as heard outdoors, to be a surreal experience. There's that certain "pressure" you feel on your ears when a very low frequency is present in copious quantities, and that feeling was quite intense from a distance away. Listening to a digital copy I made of the direct to disc LP of Marcel Dupré's Poème Héroique, (Crystal Clear Records CCS-7011) the lowest notes came through as if the whole house were a giant woofer. The tables are turned completely, as compared with the way this system used to sound outdoors. The lower the bass note, the better this system sounds. The real fun lives below 30Hz. Listening to a J-Pop tune that has two dominant bass notes at 19Hz and 17Hz, the volume just cranks and cranks with no sense of effort at all, until it feels like the concrete slab under my feet is about to crumble. Oh yeah.. this rig is on the ground floor, below ground. I seriously doubt that a wood frame structure of conventional build would last more than a few seconds at the SPLs and frequencies I tested at this evening. Well, what about that QSC? It's a beast! It just cranks along without breaking a sweat. It blows luke warm air from it's front during some real heavy bass that would have overheated the Haflers that were bridged in mono mode, but I don't think the fans even had to kick up a notch. I was lighting up the -10dB LEDs on the Powerlight 6.0 and it felt like the whole house was going to come down on top of me. The Bassmaxx ZR-18s just cruised along with no effort under the most intense bass that used to fry the coils on other speakers I've had in here. No wonder I was recommended to use TWO Powerlight 6.0s in bridge mono to drive the sets of ZR-18s. I may be inclined to employ the other Powerlight to drive the six EVX-180Bs, to bring the mid bass up to par with the sub bass. As it is right now, it's a quantum leap over last year's configuration. What a difference to be free of power compression! My next project is to repurpose the two Hafler 500s that are run in bridge mono mode as drivers for the mids and tweets. These will provide a lot more power into 8-ohms than the Phase Linear D-500 did. Probably on the order of well over a kilowatt of continuous power. With the highly-acclaimed sound quality of the Haflers and their MOSFET signal paths, the mid and high end may even improve some in terms of spacial imaging, not ot mention an extra 3dB of headroom. Oh and... next time I listen to bass this intense, I'll put a cover over my music equipment.
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SECOND QSC POWERLIGHT 6.0 PFC ARRIVES! I've decided to put this unit in service driving the six EVX-180Bs. That's over 1,000 watts for each of them! I think this derives the most bang for the buck, given that it: a) eliminates two Hafler 500 amps, and, b) fills in a gap in the midbass SPLs and smoothes out the system response by adding some kick to the midbass. The bottom end is crazy loud now, with ridiculous amounts of headroom. For instance, playing the final movement of Camille Saint-saëns' Symphony Nr 3 <Organ> at levels 15-18dB louder than life, the thunderous bass drums summing with the organ pedal tone at the finale just barely light the signal present LEDs on the QSCs, even though the house is quaking and the air is solidifying with vibration in a very tactile manner. Playing pop music from Japan and Korea and 'club levels', once again the signal present LEDs only flicker on peaks now and then, while the place is really rockin'. The 'signal present' LEDs light when signal power reaches -40dB below maximum output. Rock music with typical 4-string electric bass and distant miked kick drums barely lights the signal present LEDs, even at ear-shattering levels. I ran a 20Hz tone last night at a level too low to light the 'signal present' LEDs and everything was shaking. The SPL measured throughout most of the room was around 105dB. It was quite uncomfortable pressure on the ears, too. There's something different about this 20Hz--it's so pure with no overtones that the ear sensation is akin to diving into the deep end of a swimming pool without earplugs. My next task is to take the two Haflers that I wired for differential inputs via 1/4" TRS jacks (bridge mono) and install them as drivers for the mids and tweets, replacing the Phase Linear amplifier. Into 8 ohms that will more than double the available power to the upper range of the system. And finally, I need a bigger circuit breaker in the rack. That 20 amp breaker powering one QSC is not going to be adequate. |
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HAFLER 500s MOVED TO MID/HIGH AMPLIFICATION I've repurposed the two Hafler amplifiers that used to drive the Earthquake subs for mid and high range application today. Gain staging was quite important here. I wanted to maximize the s/n ratio coming out the the DCX2496, so I had been using cables with tapped attenuator networks that I carefully soldered into the plugs. Since the Haflers were modified a couple months ago to accept TRS plugs with tip being right channel and ring being left, driving them differentially with the balanced output of the DCX2496 provides a bridge mode, where the load is placed across the two POS terminals of the output, right channel being the "+" signal. All that needed to be done was to increase the gain of the attenuators slightly, since the Haflers would be driving a more modest load and less prone to supply rail sag. I carefully matched the drive level, increasing it by 1.45dB by changing the plug resistor divider network. Using a pulsed 1.5KHz tone, I set levels into a bank of power resistors totaling 8-ohms, which were placed across the amplifier output. An H/P 1740A oscilloscope was also connected to the output, running off a ground lifted power connection (very important with bridging amplifiers where the outputs are floating!) With the pulse signal applied, I measured a short term voltage of 290 v p-p across 8-ohms resistive load. That worked out to over 1300 watts. After 450 mS, the amp output decreased to about 260 v p-p, somewhere in the 900 watt range into that load. The gain increase over the D-500 is about 4dB, based on the 1300 watts per channel. This increased the mids and highs by that amount, balancing out the spectral range so that the system is not quite so bass-heavy. Listening to some jazz selections, I'm of the impression that the tonal balance is just right. So we have a dynamic headroom of about 2600 watts on midrange now. That should provide plenty of pop for snare drum hits that have gone through the dbx 4bx expander's "impact restoration" process. With the E120's ultra-high efficiency, each driver should be hitting 134dB quite easily with that much power for short-term peaks. I've snuffed out the last little trace of 60Hz hum by reversing the ac power plug on one of the Haflers, so now it is just about impossible to tell if the system is powered on, even with one's ear inches from any of the drivers. The system is silent with no program audio present. Wow! Things have come a long way from the days when I tolerated a 45dB residual hum.
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MIDRANGE/HIGHS LISTENING TESTS I finally got an opportunity to try out the Haflers as mid/high amplifiers driving the JBL units. The conversion proved to be everything I had hoped for. Louder transients, about 3dB more SPL, a clean, open soundstage, freedom from noise. At any volume level, it sounds nicely-balanced. Silky-smooth mids, crystalline highs and lots of "gunshot kick" with snare drum hits that have been boosted through the dbx 4bx impact restoration. I'm continually amazed at how much power those JBLs can handle with very low power compression effect. Just tons of headroom and very natural and clean sound. The transient response seems slightly better too. I think the next project will be to do some cosmetic finishing and a digital jukebox system. I have been dreaming of a 4 RU rack mount computer system with hundreds of gigs of storage and at least a six-channel 24/96 high end D/A converter setup. Perhaps a touch screen LCD display and some custom software for building play lists and sequencing the tracks. Of course, the hard drives would have to be shock-mounted for anti-vibration, and the whole thing could possibly fit into one rack mount cabinet and sit in the preamp rack. My wife also has the jukebox bug--she wants one for her karaoke stuff. She showed me a few that cost two grand, but are basically a $350 computer with a questionable sound card. I haven't decided whether I want to integrate recording with playback in my jukebox concept. Something like a MOTU 896 might be overkill unless I plan to use it as recording equipment with studio mics. On the other hand, if I do playback only, some of the Turtle Beach sound cards might fit the bill. But then again, I prefer to avoid anything with 1/8" mini plugs because they get intermittent. I've had enough trouble with the RCA jacks on the equalizers and preamps to realize that I should avoid those types of connectors. So I guess it will end up being some sort of high end Fire Wire D/A converter. The idea is in the rough sketch phase.
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A "DX" LISTENING TEST REALLY POINTS OUT THE DIFFERENCE Last evening was an interesting experience and somewhat disturbing: I've known the human ear to be a non-linear organ, that is, it compresses the sound pressure levels, reducing the perceived contrast in loudness levels. But I did not realize to what extent until I took a hike up a hill into the woods toward the nearest neighboring (unoccupied) dwelling. This house is located in a sort of "crater" on the top of a mountain. That bowl may have been involved in the phenomena I observed last evening, as I listened to the Korean song with the very deep bass notes, from a block away. What I observed, was that the lowest notes (29Hz) were getting more pronounced as I got further up the hill to the west of my place. The upper bass notes were starting to fade just a little with distance, but the lowest ones seemed to become stronger. I didn't have my sound level meter with me, but I'd say the lowest notes were well over 90dB way out there on the hillside. The contrast from the old system woofers was most startling at this distance: what used to be a dull mid-bass thump, was now like the SPL one experiences when one of those twin-rotor Army helicopters is hovering just overhead, minus all the mid/high frequency noise. I could literally do a thunderstorm recording right from inside the house and have the whole surrounding neighborhood thinking an approaching thunderstorm is eminent. From out there, it sounded as if the whole system were outdoors. Indoors, the SPL was intolerable, even to me. I think I overdid the system buildup this time. It's just too much. No one can actually listen to this thing in the room, when it's at any significant level. And when I did my test, it was at reduced levels, because I knew the 20A breaker feeding QSC #2 would trip in seconds, so I was peaking at -10dB on the QSCs during this hiking expedition. No wonder the music sounded so beautifully clean and sweet. The system wasn't even close to its limits, and yet it was dangerously loud from a block away. This realization has prompted me to curtail my volume levels and shorten the duration for the times when I turn things way up. But this system would sound incredible in a large indoor stadium, no doubt. And no doubt that a large number of people within a couple miles of this place heard at least the lowest bass notes last evening.
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