I have been a member of the AV123 forum since 1/23/05. I had joined when a subwoofer they had announced, looked like a candidate for purchase. I subsequently found out that I had been fan of the company president, Mark Schifter, but did not know that at the time. It seems he had been involved with some companies and products I had either owned or admired and only found that out till after I'd joined. I might have been predisposed to be favorable to the X-Amps. I also bought the sub, a UFW-12, and have been very happy with it. The preceding statements are in the interest of full disclosure.
I had pre-ordered 2 mono-block X-Amps spring of '08 at a pre-introduction price. Due to more than a few production problems they did not arrive until 1/9/09. These are 150 watt Philips/Hypex/UcD based class H(or D, I'm not sure) "digital" amps. Each amps weighs 7lbs. Not a misprint, 7lbs!
I quote the designer of the X-Amp, Doug Goldberg from the AV123 forum "The X-Amp has a very sophisticated switch-mode power supply. Its fully regulated to max current and is power factor corrected. Its by far the most expensive piece of kit in the X-amp." The X-Amp input impedance is 100K Ohms and the gain is 34dB. There have been complaints of rattling inside the amp. I quote Doug Goldberg again "As far as the "rattle" is concerned the picture points to the fly-back transformer. The only way it can rattle is if its not mounted properly on the PCB. I have never seen one have this issue. It should not effect electrical performance. The large metal "shield" is in fact the heat-sink for the switching transistors in the switch-mode power supply. It should get rather warm. This is perfectly normal. Later production units have a revised power supply with a new perforated heat-sink that provides a bit better airflow inside the chassis". Link to pic. http://av123forum.com/showthread.php?t=39842&highlight=fly-back&page=2
One user reported a loose screw inside his amp. There have also been several reports of intermittent lighting of the, rather bright, blue LED on the front. One of my amps rattled, the other was silent, when shaken. Both LEDs work fine. There are no ventilation holes on the amp which helps isolate it from RFI and EMI as well as prevent those nasties from emanating from the chassis. The dimensions are 8"W X 2"H X 12"D. During my time so far with them they have remained only warm to the touch either at idle or after being driven hard for 5+ hours of auditioning. There have been complaints of hum and/or hiss coming from these amps. The amp comes a with detachable IEC, C13 power cord and cheater plug. I plugged mine into my PURE/AV(Belkin) PF60 power conditioner and experienced noticeable hum. Plugging in the cheater plugs substantially reduced the hum, but didn't completely eliminate it. Determined to reduce this even further, I started to unplug all unnecessary equipment from the PURE/AV unit, to eliminate any possibility of parasitic power supply gremlins, and rearranged my interconnects away from power cords and other electronic components. This further reduced the hum to levels below those I had experienced with my previous amps. Now, I can only hear the hum when my ear is within 6" of the woofer. I then remembered that Mark Schifter, president of AV123, had recommended the amps be plugged directly in the wall. Doing this resulted in a further reduction in hum. I now have to put my ear within 2" of the woofer to hear any hum. This is at full gain. There are those that decry the use of cheater plugs as dangerous. I would submit that, that is only the case if the cheater plug in question is non-polarized, allowing the flipping of the ground. Since the plugs that are supplied ARE polarised, this cannot occur. The other alternative would be to hard-wire a polarised cord and plug to the amp, preventing the use of third party power cords. That does not sit well with a great percentage of the potential customers that the X-Amp is trying to appeal to. To my knowledge, the IEC, C13 standard does not come in a 2 prong iteration. My take on the hum issue, or lack thereof, is that when a power supply is implemented correctly, it shouldn't need any external treatment. There are, to my surprise, a number of audiophiles who feel differently, and are disappointed when power treatment doesn't substantially improve a component. Whatever. The only hiss I heard was when I put my ear INSIDE the waveguide of the Timepiece Minis, at full gain, and none from the VMPS Ambiance tweeters. Something that needs to be remembered is that these are very high gain amps, and will amplify any upstream noise in a dramatic way. Run of the mill preamps or receivers that do not have extremely quiet output will be rendered in an uncomplimentary way. Since I use no preamp, and have extremely quiet source components, I was able to appreciate the X-Amps at their best. I cannot over-emphasize enough the fact that the X-Amps will exemplify the acronym GIGO, or, garbage in/garbage out. By extension they will also exemplify QIQO, or, quality in, quality out.
So how do they sound? They don't sound at all, really. They are utterly neutral and get out of the way and amplify. From mid-bass to cricket chirps, they convey whats fed to them. They really showed me how great the 2 new DACs I was auditioning were. Compared to my previous amps, they allowed me to hear the sense of space around each individual instrument instead of a homogeneous sound of the hall acoustics, on recordings made in real time in live venues. Micro-acoustics, if you will. No glare, artificial sheen, boom, tizz, over, or under emphasis of any part of the audio spectrum were present. I did not test their low bass capability, as my system is setup with a passive line level filter, and I have no desire to rewire, so the X-Amps only had to work from 70hz on up. Low level details were presented in away I had not experienced in such affordable amps. The sound of spittle in a sax mouthpiece, the chiff noise of a violin bow being moved across the strings when changing direction, the inflection of emotion in vocals, all were revealed in familiar recordings heretofore obscured. Keepers, and a helluva bargain at $299.99 MSRP(I think). The main disappointments with this amp have nothing to do with performance. There were no owners manual, spec sheet, or warranty card in the double boxed cartons that I received. While the lack of documentation is disappointing, my subjective reaction to this amp is that I will be very surprised if independent testing does not confirm that this amp possesses some of the lowest distortions and highest signal to noise ratios around, at any price. The only unique performance issue I noticed with the X-Amp was its overload characteristic. When pushed past its output capability, the sound is interrupted. Its akin to hearing a CD skipping. Right up to this point the output is clean and distortion free. The SP Tech Timepiece Minis' sensitivity is 87.5db and the overload did not occur until north of 105db. Being an old school hard rock fan, I'm looking forward to a higher output version of this amp, if and when available.
Sources: Red Wine Modded SB3, Toshiba SD6980
DACs: AVA Insight, Bryston BDA-1
Passive Pre: Creek OBH-12
Amps: Kenwood K-MX1000s, AV123 X-Amps
Speakers: SP Tech Timepiece Minis, Rocket UFW-12 sub w/RDES, VMPS Ambient Tweeters
Power Conditioner: Pure/AV PF60