|Class D Switching Power Amplifiers and Power D/A conversion|
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|23rd July 2006, 10:49 PM||#1|
Join Date: Feb 2003
Ref-T review part 2
Well I will skip the amp descriptions since that has been covered by Michael already. Over the past several weeks Ive given the AMP3, Charlize and the Ref-T fairly thorough scrutiny and have found that they indeed, are very similar but also quite different is some very specific areas. Since engineering isnt my forte, I will only offer my observations into the sound of each.
My auditioning is somewhat different from most peoples since I use a pair of Stax earspeakers for much of the listening. Ive found that since they are devoid of crossovers, room accoustics and most ambient noise, they allow an unbelievable portrait of the clarity, articulation and resolution of the music. They dont reveal the soundstaging or lower octave bass performance, but after using them for so long, I have been able to convert the "headphone sound" into what the speaker sound will most likely be. And they can be directly connected to poweramp, making a passive system possible. For the rest of the listening, Ive used Fostex FE166ES-Rs sealed with BR woofers, tweaked Klipsch Heresys and Braun mini monitors.
I powered all the amps with a 60VA 18VDC(for the Ref-T) supply, with 4400uf capacitance. I have a RCA Isotap mains supply that allows be to dial the AC to 85V, to give 13.5VDC for the AMP3 and Charlize. So all use the same supply. All where operated passively through an Alps pot using a Rega Planet and Pioneer DV563 for SACD.
My music consisted of mainly jazz and some rock. I generally listen to one track several times and then switch to another amp and do the same. Swap time is less than a minute.
All three amps sound excellent and are similar but the differences do exist. I have found that the amps vary in just a couple of areas. Their overall signatures are almost undisernable, but the details vary. The first is in sharpness of detail or clarity. The second is soundstage or "soundscape" for the headphone listening and the last, LF performance.
I should make it clear that Im a resolution freak and that the more I hear, the better. This is the case with the AMP3. As many have noted, it can be fatiguing over time, but Ive found that it is due to the reproduction of everything that passes through it- you get the good and the bad. I hate the word clinical so I will call it precise. It adds nothing but passes everything. It also has the poorest soundstage of the three. The LF is very controlled but not the deepest.
The Charlize is the reverse of the coin. It offers a wide soundstage, and a softer presentation. Although less fatiguing, I find it less revealing too. It lacks just a touch of clarity and the sharp, defined edge to strings and percussion that I like. The LF is very good, but less controlled.
The Ref-T seems to do it all. I found that the resolution and clarity to be excellent. It offers the best soundstage of the three and borders on superb. I found it totaly 3-D and able to present a huge soundstage. Even on the Stax, it is so wide and depth, there is very little "head congestion" in the sound. Separation is fanastic and Im assuming why the clarity and soundstage both excel. The LF is the best of the group too. Solid and controlled. It seems that first impressions can be fairly accurate since this only confirms my initial listening.
As an example, trying to pull David Crosby and Graham Nashs vocals out of the backround on Joni Mitchells "Free man in Paris" is tough. The Ref-T did it the best because of the wide soundstage. It opened up the vocals and separated the timbres of their voices better (for lack of a better explanation). This is also a nice trick on Peter Gabriels "Mercy Street" How many of him are there overdubbed for the backing vocals? Better count.
On Spyro Gyras "Yosemite", the vibes stand out as if in the room and the reverberant qualities are lifelike. The Charlize was better than the AMP3 at this, but lacked the 3-D placement and ambience.
The track "California" from Wendy MaHarry is another example of the clarity and soundstage acting in unison. The strings in the backround, that lay below a clarinet and piano are not defined on most amps, but the Ref-T pulls them out and layers them between all the other instruments rather than sounding intertwined with them.
Overall, I would say that the Ref-T is my favorite and provides a lush and articulate presentation of the music. In particular, it excels at reproducing the decay of strings and percussion and the micro detail that I love. The AMP3 has a slight edge in overall clarity, but its not as perceptable without the large soundstage in complex stuff. The Charlize is my least favorite, but only because it doesnt have the steely edged resolution. This is probably a good thing to many, but its just a bit soft for me. So Im guessing that the dual supply has alot to do with the larger soundstage and apparent separation. Ive not been overly concerned with the soundstage performance of my amps but I see now that it can open things up and provide a less congested sound, all other things being equal. This really helps with older, less well recorded rock (which I love and hate at the same time)
Brian is doing some great investigative engineering here and is providing a great sonic service to all of us! Thanks for allowing me the use of the amp. So you want to sell 'em huh?
|24th July 2006, 12:50 AM||#2|
diyAudio Moderator Emeritus
Join Date: Jan 2005
Hey Art, thanks very much for posting your listening impressions on here. I value your opinion and thank you for taking the time to really compare the amps you had available. It's certainly fun but it can also be quite time consuming!
I've only been able to compare the Ref-T and the AMP3 and have come to similar conclusions with regards to how they sound. I love the wider soundstage and detail (especially with stringed insturments and percussive instruments) that the Ref-T offers over the AMP3. I found the AMP3 only slightly fatiguing because, like you said, it reproduces a lot of micro detail - it's very noticeable with cymbals. And if you use 8 ohm speakers (like I do) there will also be a slight bump in the frequency response in the 17-20kHz range which would seem to add to the fatiguing factor due to the extra "brightness". The Ref-Ts output filter is better suited to 8 ohm loads (like my speakers - what a coincidence ) and won't have that bump in the upper range of the frequency response.
Anyway, I've only built three Ref-Ts so far. I have the first one, Art has the second one, and the third one is up for sale in the Trading post. I plan on making some parts and layout changes to reduce the cost and hopefully increase the performance a bit, but that's further down on my project list at the moment.
Thanks again for the review Art.
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