An Xciter Journey!
When Dennis Had, the mad scientist and owner of Cary Audio, told me they were designing a new Xciter line of products to include a very versatile Headphone Amp, A Dac and later a Transport, to say I was excited, was an understatement. The Cary Audio Cad 300SEI Integrated/Headphone Amp has long been my reference headphone amp. It is my all time favorite single ended dynamic headphone amp. The 300B tube is God's gift to the audiophile. The magic it can provide the listener is breathtaking but that is a whole other topic to be discussed. Today I would like to talk about the Xciter Amp and a journey I have taken and will continue to take as time passes with a complement of different tubes and how these tubes match up with different brands of headphones. First, let me tell you about the amp.
The amplifier has the following features. 5 watts per Channel, Single Ended Triode design, Pure Class A, Integrated Stereo Amplifier with 6L6 Power tubes and 12ax7 input tubes. 3 stereo input pairs. Standard with remote volume control. Metallic black chassis with clear coat finish. Silver or Black faceplate available. ZERO feedback design. Headphone output and Speaker binding posts. Subwoofer outputs for left and right channel.
You would think that a 5 watt channel amp would easily crumble under the strain of a pair of speakers, but during our review multiple speakers at different sensitivities were used. The amp never fluttered. An increase to 10 watts per channel is accomplished with the swap of the 6L6 tube to a KT88. The amp is self-biasing and multiple power tube options are available. 6L6, EL34, 5881, 6550, KT88 and any other power tube with a matching pin arrangement. The input tubes can be 12ax7, 5751, ecc803 or ecc83
The stereo vacuum tube power amplifier has a great history at Cary Audio Design. The superb lineage of CAD power amplifiers and integrated amplifiers have consistently garnered fantastic reviews for stable power output, incredible value for the money and sound quality along with ‘Best Buy’ and ‘Class A’ ratings from magazines and reviewers worldwide. Building on this storied legacy, we are releasing the CAD Xciter Integrated stereo vacuum tube power amplifier. This innovative stereo power amplifier was conceived to be a small desktop integrated amp to be companion to the new CAD Xciter Digital to Analog Converter. In the Cary tradition, it features a gorgeous cabinet and has a subtle touch of translucent blue LED back lighting to complement the natural beauty of the vacuum tubes. Although it may be small in physical size it is imbued with the full spirit of Cary Audio. Its 5 watts per channel in class A triode mode plays much bigger than you might expect and its sublime musicality is just what you would expect from Cary Audio. For headphone lovers, a standard ¼ inch diameter, 3 circuit output jack is conveniently located on the front panel to pipe the music to your favorite set of cans. The circuitry is optimized to provide a good match for all high quality headphones. A front panel switch allows the user to select between the speakers or headphones. Additional features are the subwoofer outputs - one for each channel, and the motorized remote control function for adjusting listening level and mute. You will absolutely enjoy listening to this lovely amplifier – it truly is an Xciter! The input circuit is a single-ended design with three (3) switched RCA stereo inputs per channel. The vacuum tubes in each channel consist of one (1) 12AX7A (dual triode) for the input gain and for the driver stage and two (2) 6L6GC output power tubes. The filaments of the 12AX7A stages are direct heated with filtered and regulated 12 VDC for lower noise performance. The first section of 12AX7A provides the low level preamp gain stage and the second section provides the phase inverter and differential driver stage. Both sections of the 12AX7A are operating in Class A with minimal feedback. The 6L6GC output tubes are configured as triodes and operated in a class A push-pull configuration and are continuously auto biased through cathode auto biasing circuitry. The laminate output transformers are customized to match the output circuit requirements and have a signal handling capacity well beyond the amplifiers demands to avoid any problems with linearity and saturation. Five-way Gold plated speaker binding posts provide reliable connection to your speakers. Frequency response at full rated output power is from 17 Hz to 23 kHz with less than 2% total harmonic distortion.
The circuitry for the entire amp is designed into a high-grade two-layer printed circuit board with extensive ground planes and heavy copper circuit traces on the power bus circuitry. Shielded coaxial cable is used for critical signal path component interfaces. This design approach imparts an extremely clean layout and a very high performance level. A toroidal power transformer provides the foundation for a compact, yet high efficiency power supply. The power supply features seven (7) 100 micro farad low impedance low profile electrolytic capacitors which yields an abundant total of 700 micro farads of energy storage and provides an excellent dynamic performance capability. The high voltage power bus is further enhanced with a power choke in a pi-L configuration for additional filtering to the preamp stage and with two (2) high speed .22 microfarad Kimber Kap polystyrene by-pass capacitors to further enhance the superb transient response characteristics under demanding musical passages.
The CAD Xciter integrated Stereo Amplifier is the perfect match for the CAD Xciter Digital Analog Converter.
Now on to the headphone/tube journey. I assembled quite a stash of tubes to play with, and these are just the cusp of what is available. I tried as many different tubes with different headphones possible to find some matching combination. While I would not use this as a cut and dry direction of which tube to use with each headphone it at least provides a starting place for experimentation. Here is a list of the tubes I have acquired in no particular order and average prices.
Power Tubes
EAT KT88: Beam Tetroid KT88 Diamond w/gold pins matched Quad : $7-900 Matched Pair
Genalex – KT88 Gold Lion brand. $149.95 Matched Pair
Cary Audio Stock 6L6 Free they come with the amp
Electro-Harmonix KT88 EH $49.95 Matched Pair
Tung-Sol 6L6G New Production $49.95 Matched Pair
Tung-Sol 6L6 STR New Production $29.95 Matched Pair
NOS Sylvania 6L6WGB / 5881 $69.95 Matched Pair
NOS Jan Philips 6L6WGB / 5881 $69.95 Matched Pair
Input tubes:
COOL VALVE ECC 803S twin triode with Cool Damper attached Diamond version: : $450 Matched Pair
Cary Audio Stock 6L6 Free they come with the amp
NOS GE 5751 ?
NOS Sylvania 12ax7 $59.95 Single Tube
NOS Jan Philips 12ax7 $49.95 Single Tube
Lets get this out of the way quickly and then we can move on. Bar none, the EAT tubes blow the competition away. Plain and simple. If you can afford these, buy them. There is not a phone on the planet they don't like. They were effortless with everything I could throw at them. No wonder they cost so much. I would easily take these over any super expensive NOS tube. EuroAudio Team did their homework. So for the most part for each phone I will start with the runner up tube.
Because there would be a million variations of input tubes and power tubes I found in most cases after the EAT tube that I liked the GE 5751 tube the best so my reviews of the power tubes will be with this tube.
Sennheiser HD650 Headphone.
I find the HD650 to be the darkest, laid back, lush sounding headphone ever made. Of course I am not heavily susceptible to high frequencies. I always use silver based conductor cables with these to lift the veil and bring them out of the darkness. I see why classical music lovers are the biggest fans of this phone. It does wonderful things with pianos. So in sticking with that thought I found I really liked 2 power tubes the best. The Senn is a harder load to drive and really needs a KT88 style tube to drive them in a demanding load. Thus the Gold Lion sound the best with this phone. In some demanding passages the other tubes seem to crumble a little. However in quiet listening situations I really like the Tung-Sol 6L6 STR tube. It is very clean and I imagine this a cheaper tube. I found this tube to be the best bang for the buck aftermarket tube in a lot of combinations. It was better than it's bigger brother the Tung-Sol 6L6G with these phones.
AKG K701/702 Headphones.
The K701 or K702 are the most neutral of what I call the big three headphones: Grado, AKG and Sennheiser. The Sennheiser is the most laid back. The Grado is the most forward and the AKG is somewhere in the middle. It is a great headphone for all around listening. It is not incredible sounding in any one music type and nether is it awful in any one spot. It is neutral and natural sounding with not a lot of coloration. I always recommend it to folks who don't flow in one direction musically. It is a great all around performer. Where it lacks is in weight. It does not provide a big impact. I liked the Tung-Sol 6L6G big boy tube with this phone it has a bottom heavy type of quality that is not a bad thing. While the KT88s add more power they did not help to add some fatness to the lower end. Thus this was a good choice for this phone.
Grado GS1000 Headphone.
When Dennis designed the Xciter, this was his main reference phone of choice to tune the circuit. And you can tell, because the amp really sings with the Grado line up. And I think this is why the 6L6 tube is the best choice with the Grado's. This is the stock tube Cary decided to go with and label the chassis with. I love the NOS Sylvania 6L6WGB and have used them for years in a Mac MC240 and so this was the first tube I stuck in the Xciter amp when I first received it. It wonderfully matches the Grado sound. Grado's, more so with the RS-1 on down, are very upfront sounding just like study monitors. Very detailed and crisp and RIGHT THERE. The GS1000 is a little more relaxed due to the fact the drivers are farther away from your head. But regardless it is still a very detailed phone. The Sylvania works well to round this out a little and take some of the rough edge off. I found the clean sound of the Tung-Sol 6L6 STR tube to much with this phone. Some of you that are solid state folks, but would like to own a tube amp too, may like the combination of this tube with a Grado.
Audio Technica ATH W5000.
The W5000 is one of my favorite phones. It is loaded with detail and in my opinion is better matched with tube amps than solid state. I have heard some solid state amps that work well with these, but for the most part they can make the sound edgy and too bright. I always recable these with a big fat copper cable like the Black Dragon. That being said the KT88 Gold Lion was my favorite match with these phones. The W5000 is not a hard phone to drive but there was tones of impact with this tube headphone combination. This reissue tube is my favorite in the KT66/88 power tube section. Just great sound is all I have to say....
Beyerdynamic DT880.
The DT880 is my favorite of the Beyer line up. Like the AKG it is a great all around performer and I would put it between the AKG and HD650 on a neutral to darkness scale. This phone can be easy or hard to drive based on which version you pick. By the way the 32ohm, 250ohm and 600ohm are no finally available in the US. Thank God. As the 600 is my favorite version. And because of the load a KT88 is required in my mind. Thus the Gold line is the must have in a 250 version which I did not spend a lot of time with I liked, the Tung-Sol 6L6 STR.
Well obviously this is not all the phones in my stable but this is a start and as I play some more with different phones and tubes I will update this thread. Bottom line the Xciter amp has made it very easy to tailor tubes to different signature and load conditions. It is a very flexible amp and the fact that it auto Bias's is very nice. Please not warm up times are longer because of this. KT88 tubes can take up to 3 minutes to dial in and get it up to speed so make sure to warm the unit up after changing tubes.
