THE POWER SUPPLY BACK-STORY
You see, not realizing the Custom Upgrade (D.R.R.T.) was even available, a large percentage of NuForce Reference Series customers were simply coming to us to have their defective amplifier repaired. After informing these customers about the Upgrades and that they were successful in improving amplifier reliability AND sonic performance, many opted to go ahead and have the upgrade installed along with the basic repair. In most such cases only the Amp Module had failed, so it was a matter of replacing it and then installing the Upgrade components. Once in a while though it would be the switching power supply inside the units that had failed, and that was fast becoming a problem.
As things were, the power supply used in the Reference Series amps were not originally manufactured by NuForce, but were an "off the shelf" switching supply made by "Skynet," a company in Taiwan. Well, by late 2015 the existing stock of Skynet supplies at the NuPrime factory (the former NuForce factory) began getting low, and as it turned out Skynet had discontinued the thing a couple of years prior, and with no "drop in" replacement having been made available either. Finally, the NuPrime factory had no alternative but to start shipping defective supplies back to Skynet for repair.
OK, so now TDSS and our customers here in the USA are being forced to wait long turn-around times in order for us to get repaired power supplies back from Taiwan just to finish the repair on their amps. Even then, we're talking power supplies that were overly expensive in the first place. Add to that, they had already been in service for years, had always generated more heat than one would expect/prefer, were older designs and therefore generally less reliable... and now they had already failed at least once and are being “refurbished”??? Oh, man - that just didn't sit well with us so we set out upon a quest to find a substitute power supply that was readily available here in the USA from a few of the major electronic part vendors. As good fortune would have it, we found some that were much more modern and "clean" looking AND exceeded the required power rating by an additional 200-Watts! Not only that, but they easily fit within the space that was available inside the amp chassis. Bingo!
The next step was to acquire a sample pair and give them a try. We took an existing pair of Ref-9s that had already received our Custom Upgrade/D.R.R.T. treatments and installed the new supplies in them. Then we took them "out for a test drive" by connecting the amps to a pair of 4-ohm NuForce S-9 loudspeakers. THEN... "we let 'er rip." What we had thought was going to be a simple "joy-ride down memory lane" turned into the equivalent of an Indianapolis 500 race, and those Ref-9s were leading the pack!!!
Once again a simple "repair" turns into a major revelation, and NOW another major upgrade. Sure, the new power supplies were rated at 500-Watts as compared to the old Skynet supplies at 300-Watts), so the truth is we were expecting reasonable amount of improvement as a little bonus. Then again, any expectations were limited by the fact that the new power supplies did not provide any additional voltage over that of the old Skynet supplies (both produced 50-VDC). So, the additional power provided by the new supplies was only the result of their additional current-sourcing capabilities (10.45 Amps vs. the Skynets at 6.25 Amps).
Therefore, even with the new supplies installed, compared to a stock unit with the original Skynet supply the NuForce amps powered by this new supply would not (theoretically) output so much as a single additional watt of power when driving an 8-ohm speaker load. Any and/or all benefits would (again, based on theory) be seen at lower impedance loads wherein additional current could be helpful.
Nevertheless, we were in no-way prepared for yet another total transformation of these amplifiers, and we don't use that term lightly either. By "transformation" we mean that the improvements were so blatantly obvious such that we could LITERALLY hear the difference within 3 seconds of hitting “play” on the CD Player.
For testing purposes, one of the selections we played was the classic Sheffield "Track & Drum" recording. To our amazement the drums became what almost sounded like miniature "explosions," while at the same time subtle harmonic textures like brushed cymbals sounded as though the drummer was right next to us in the same room. Now, you have to keep in mind that this pair of Ref-9s had already received our D.R.R.T. upgrade, so most of the above other than the far greater dynamics had already been greatly improved. That said, we couldn't have imagined that it was even possible that many of those same qualities could be improved further yet - but they were. On top of that though, now the peak dynamics into the somewhat difficult-to-drive 4-ohm load of the S-9s became something nobody would have ever thought possible. Never before had we ever heard the Ref-9s sound so "real" and incredibly dynamic. At the same time we had never heard the S-9s sound anywhere near that good either. Eureka!!!
Previous to this little "experiment," when using a pair of stock Ref-9s in the same setup, the highest gain setting on our preamp that we could ever achieve before audible "clipping" distortion would set in was about an "88" on the preamp's digital readout. Now we had the preamp cranked all the way to its maximum output with a reading of "99" and could go no further. Yet, this pair of Ref-9s wasn't even breaking a sweat, with no hint of clipping whatsoever.
In fact, we haven't had a chance to go back and try pushing things any further, as we've been too busy ever since to find the time. Besides, during that first listening test the volume was so loud that we literally had to scream at each other to communicate, even though our whole team was standing right beside each other. That said, at this point we'd rather not risk blowing up the S-9s right now... just to see how far these puppies will go. The reason we're a bit "leery" of going there is because at the end of that first test and we were done listening, the aluminum cones of the woofers in the S-9s were almost hot to the touch. So the odds are if we tried that a second time we'd just blow them up. Besides, as it is with the new power supplies installed, the Ref-9s now have more dynamic headroom than most any sane person would ever need - and we’re the type of listeners that like to crank things up LOUD once in a while!!!
Actually, from our "guess-timation" and based on the peak dynamics that we achieved that day, from a "headroom" standpoint that pair of Ref-9s sounded as though they were AT LEAST 500-watt amplifiers - EACH. That makes a certain amount of sense too because if you do the math, it turns out that "IF" the 50-VDC power supply output were to be a theoretically "perfect" Voltage Source (no such thing exists in reality) and powering a 4-ohm load, it would output 625-watts (50^2 / 4 = 625).
Furthermore, when you factor-in the energy storage of the capacitor bank that follows after the power supply AND the fact that the output voltage of these new power supplies is obviously much better regulated allowing them to output more current without the voltage beginning to "sag" (drop), the upshot is that the short-term peak power of the amplifier is being increased quite dramatically as well.
In other words, after having been upgraded with the new power supplies, a NuForce Reference Series amplifier now "sounds like" it has the "dynamic headroom" you might otherwise expect to hear coming from a conventional 600-WRMS "linear" (i.e., non-switching) amplifier.
In full disclosure, we have yet to actually undertake the process of testing to get exact numbers, but for the most part it's pretty much academic because a pair of any Reference Series amps upgraded with these new power supplies become something NOBODY has ever heard coming from a NuForce amplifier before, and that's including the engineers that originally designed them! Let's just put it this way... over our 40+ years in high-end audio we have NEVER heard a better sounding amplifier at ANY price... and we've been around the block quite a few times along the way!!!