After spending time with the Altmann courtesy of miklorsmith, I finally had time to write up some thoughts.
Pardon the link to a discussion on AC but it's tightly related.
I have been fortunate enough to participate in the demo tour of the Altmann Attraction DAC run by Mike Smith.
First a little bit about my values, goals and objectives in regards to audio reproduction. First and foremost is tonal quality. If the instruments and voices don't sound realistic it doesn't matter what else the system does well as I can't get past artificial tone. Of course all systems are artificial but many can get the basic tone correct.
The next thing that causes me happiness or distress is the high frequency presentation. This is the area where most digital front ends fail for my tastes. My current digital source is a very heavily modified (analog section) Squeezebox 2. While I like it better than any other digital I've owned and most that I've heard it pales in comparison to my analog source in this regard. Even good digital sounds pretty lame IMO compared to vinyl.
During my time with the Altmann a few friends came over with some additional toys to play with, so I had the opportunity to compare the Attraction DAC to a few other devices. My primary comparison was with my much modified SB2, this was one of the first ones modified by Bolder Cable and I have since modified it several more times. As I'm friends with Wayne at Bolder he's been kind enough discuss his mods with me and as I'm a DIY type I generally do all my own work. My SB2 and power supply are essentially the same as Bolder's top offerings in regards to the analog outputs. My SB2 does not have any of the digital output mods as I don't have a stand alone DAC. I used my SB as the digital source for nearly all of my listening with the Altmann. I also had the opportunity to compare it a fairly heavily modified Slim Devices Transporter and a Monica II non oversampling DAC. There is quite a bit about the comparisons to the other devices in this thread:
http://www.audiocircle.com/circles/index.php?topic=37662.0I listen primarily to Jazz but also have a lot of other music depending on the mood but for this I used pieces I listen to or have heard numerous times.
Since I can't get past bad tone I'll start with that. Tonally I found the Altmann to be very good, in particular vocals and stringed instruments sounded very good, very rich and full. It was one of the first things I noticed so we were off to a good start.
Regarding the bass, I found the Altmann and the SB2 to be very similar. Others have mentioned the Altmann had better or more extended bass than their Squeezeboxes. In my system this was not the case. Looking at the circuit board I noticed that the Altmann uses 3.3uF output caps, this is the same value as my SB2, so the -3dB point should be the same.
In the area of high frequency reproduction I had the initial impression of less extension in the Altmann but after a while I decided this was not it, the difference was more like a softer HF presentation. I suspect this is a result of the non oversampling architecture and I can see why people are fond of this. In a less damped room or with aggressive speakers or electronics I would find this much easier to live with in the long term.
Then there is imaging and spatial presentation. This seems to be an area where there is less agreement on what is important in a system. For me I enjoy a system where the sounds of the instruments and singers escape the speakers and where it has the ability to present the low level ambiance cues. For me those low level cues affect the reality of the presentation, even though I know many of them are artificial. I just enjoy the sense of a hall or space. I found the Altmann to do quite well in this area, depending of course on the recording. Interestingly, the SB and the Altmann were somewhat opposite in regards to how the spatial information was presented. On some recordings the Altmann presented layers to the music hat I hadn't heard before but on others it was closed in while the SB would remove the speakers. The caused me to wonder if there is something in the way the music was encoded that makes it somehow different when decoded by an OS vs Non OS DAC. I don't know of anything that would cause this but it popped into my mind while listening.
In the previously mentioned thread there is much discussion of running the Altmann on an expensive linear power supply VS a battery. As part of that listening session Wayne connected a capacitor bank to his SLA and to me it sounded better with the cap bank connected than it did off of straight battery but not as good as the linear supply. As I was still curious about this after Wayne took his toys and went home, I built up a cap bank to use with the Altmann. This consisted of a 15,000uF cap, a 220uF cap and a .1uF cap in parallel along with a switch to connect and disconnect it to the power supply.
I found I preferred the sound with the cap bank engaged. The sound seemed less constrained and more open with the caps turned on. With Mike's permission I've included this with the DAC so that others can experiment with this as well and hopefully report their thoughts.
Did I prefer the Altmann to my SB overall? No but there are some things I like better about the Attraction, in particular the way it has with vocals and stringed instruments. I could be quite happy with the Altmann but I like by current setup a bit better.
Thanks again to Mike for making this possible. It was great to listen to the Altmann Attraction DAC and I very much enjoyed my time with it and had no desire to remove it from the system. For me that is a very good thing. I've put entirely too many components in the system that make we want to remove them, either immediately or after living with them for a few days. The Altmann never did that and that is a very good thing. Very much worth the time for an audition I'm sure it will find many fans, I count myself as one.
System Info:
Source - much modified Slim Devices Squeezebox 2 with gold Bybees.
Preamp - none, connected direct to Marchand XM-44 electronic crossover.
Amps - mids/highs - R.E. Designs LNPA 150, bass - Rotel 1080
Speakers - Meadowlark Blue Heron 2 modified for active amplification. XO from bass to midrange is at 275Hz, 4th order LR active, mid/high is at 4kHz, 1st order passive.
ICs - DIY design using Neotech shielded twisted pair silver cable with the shield connected to ground through a low pass filter.
Speaker cables - 10GA twisted pair for bass and Analysis Plus Oval 9 for mid/highs.
Power - BPT BP-2.5 Ultra balanced power unit. PC's are assorted DIY stuff. The seem to work well.
Mike
