Ross Martin Audio PCM1794 Dac - $250 Overachiever
I like to have music available at my desktop. I have a very well built out Macbook based system in the main listening room but have a more moderate system in the office. I have all of my music on a drive connected to the Mac via firewire and use this library to feed a Logitech Squeezebox Touch in my office. I use the Touch when I want to listen to high quality files from my library either via my desktop amp and speakers or through my Shure SRH-840 cans.
I was using a Hat Peed Thingee from Blue Circle Audio as my headphone amp. It was a good device and had a pass through output to feed my amp so I could listen to speakers or headphones without disconnecting anything. You notice I say “was using” the Blue Circle headphone amp. That is because the designer in his infinite wisdom to get the price point of his creation low enough (as if $500+ was low enough) decided to use PVC pipes for the enclosure of this audio device. It worked fairly well as it was certainly cheap had lots of room for components and was lightweight for shipping. Just one problem! He encased the components, circuits, power supply, etc. in Silicone. That’s right everything that would normally go into a case went into the pipe along with a big old tube or two of silicone.
I did not mind the looks so much and the sound was decent enough but one day I started to hear some distortion in one channel and after a few emails with the designer in Canada, I fired it up one day and found the entire channel dead. He instructed me to send it off to his US repair facility and in turn he would pick it up in few weeks. I saved some shipping costs as opposed to shipping to Canada and I was not in any big hurry since it was out of warranty and they would have to look at it to determine repair costs. Long story short, I got the email one day saying that it could not be fixed because of all the silicone encasing the components. They could save the power supply and reuse it since it was in a separate outboard pipe but the repair cost would be over $450. No accommodation or offer to help since they built an un-repairable device. Essentially when you buy one of these “pipe bombs”, it is assumed to be a disposable piece of equipment should something fail. Not too bad while it is under its short warranty perhaps, but after that you have a non repairable unit. I told them to toss it in the dumpster rather than have to pay freight back from Canada with it in whatever state of dis-repair.
Back to the dac. As I thought about my experience with the Canadian Blue Circle Audio and the Hat Peed Thingee, I began to think about dac purchase options and what the market offered. I also thought about budget and my intended use of the dac. I wanted to keep it below $500 and I did not want the headphone amp to be part of it. As I was looking at budget I came to find lots of dacs were available from Asia that met the price criteria and a few that were available from Pro Audio suppliers. I quickly ruled out the off shore stuff simply because I am not willing to spend the freight dollars both ways should something fail either under warranty or not. Several years ago fellow headfier ASR told me of his philosophy of only buying from American based companies. At the time I thought it was a narrow view, not now. And the Pro Audio stuff had fewer options for connectivity and in many cases had functionality that had to be used with a separate computer software program. Many also had analog to digital conversion included which meant they spent less of the remaining budget on the other parts of a dac. So I started to look at US companies who either made the final product here or had a good reputation for after sales service.
Ross Martin PCM1794 Dac
My personal need to find a good quality dac to serve a variety of functions led me to the Ross Martin Audio dac. Ross Martin runs Ross Martin Audio out of a town just south of Omaha, NE. He builds Dacs and other pro audio styled gear and offers a fair amount of customization for low prices. My particular dac features the TI PCM1794 DAC chip and TI’s DIX 9211 receiver chip. I have optical and RCA Spdif inputs as well as USB input via the TE7022 chip. It has balanced XLR outs as well as single ended RCA outs. I selected the excellent National LME 47910 and LME47920 opamps, although Burr Brown models are also available. The output levels set to +8db on the balanced XLRs and 0DB on the RCA outs. These can be factory set to your spec. The Dac will decode 16/44 through 24/192 via spdif and up to 24/96 via USB.
I am not a big technical guy so bear with me as I try to describe the topology of the dac. It uses 4 internally regulated supply voltages powered by an external heavy duty AC power supply. This provides 16.5 volts AC to the internal half wave rectifiers which is filtered and is a bi-polar design. This feeds linear regulators which provide a tightly regulated DC supply of +3.3, +5, +15 and -15 volts DC. The power supply was designed with plenty of head room. The dac uses a 10ppm crystal for the receiver chip. The line driver uses an lme49720 as a cross coupled inverter to achieve the balanced output. The entire output circuit is direct coupled with no coupling capacitors used in the signal path from dac to balanced outputs. When using the rca outputs, the signal is coming off of the 2nd order filter and bypassing the line driver. Each channel's filter is composed of an lme49710 (you have to have the filter to remove any out of band noise). So you have one less op amp in the signal chain.
I ordered my dac with all connectors on the back but he also offers them on the front for some versions. On the front is a power switch, USB Switch, Optical / RCA switch, Filter 1/2 switch and a locked indicator. The only thing I need to point out is that the Filter Switch allows either fast rolloff in position 1 vs. slow rolloff in position 2.
The enclosure is a simple metal affair with wood ends. They have a cnc machine that can be used to modify the enclosure for a number of configurations thereby keeping customization affordable. Fit and finish are what you would expect for an item that is essentially custom made at this price point. You may find some Pro Audio Items with a bit more fit and finish finesse and you can find some that use cheaper plastic materials. The enclosure is functional and looks somewhat old school. It is compact and does not appear to radiate any noise. The 2 blade AC power adapter is wired at the end of about 6 foot of cable to the unit. All output jacks are good quality and well spaced. I also like the switches as they are metal and have a positive action.
The Test Systems
Main Listening Room
DIY power conditioner- power conditioning for the external disk drive and Macbook
Apple Macbook – 4GB Memory dedicated to playing music
External Disk Drive- 1TB disk connected via Firewire 400 to the Mac
Blue Circle BC-509 – 192 kHz – 24 bit capable dac
Bel Canto EVO4- four channel amp run in bridged stereo mode
SP Technologies Timepiece 2.0 Monitors- speakers
JDS Labs – Cmoy with various opamps
Moon Audio RCA to Mini Cable made with DH Labs BL-1
Westone UM-3X earphones
Shure SRH 840 headphones
Element Cable Titan copper- XLR cables from dac direct to amp
Element Cable Titan Silver – RCA Cables from dac to amp
Copper Flat Cable- Proprietary speaker cables similar but much better sounding version of Goertz M series biwired to the tweeters
Luminous Audio Synchestra Signature Speaker Cable – Biwired to the bass driver
Halide Design Bridge- Async USB to spdif bridge used for comparison
Empirical Designs Coax- Coax cable to connect UC-192 to dac
Wireworld Ultraviolet USB cable – used to connect Dac to computer
Virtue Audio – Amp
Logitech Touch – Source of digital signal playing native files from the Macbook
PSB Image B25 Speakers
Belkin OCC Copper speaker wire
VH Audio Pulsar- SE interconnects from dac to amp
I guess it is best to disclose here that I have no relationship with Ross Martin Audio other than that I purchased the dac from them. I also want to point out that this entire post is copyrighted and should not be re-posted anywhere without my permission.
The first place I tried the dac was with the Logitech Touch which is probably where it will spend most of its time eventually. I connected it via coax to the spdif coax input and via RCA outputs to the Virtue amp. My first reaction was very good with a slight emphasis to the high end and a little thinness in the mids, all of which pointed to burn in time. It was burned in 48 hours at the factory but I feel this is not enough to let the circuits settle. I did not listen after the initial 30 minutes and let it decode a stream from the Touch for several days. After about 30 hours or so it sounded fuller and the mids and highs were in balance. With my PSB speakers the Ross Martin dac sounded more open up top than I remember with my Benchmark DAC1. Frequency balance across the range was excellent and detail retrieval was also very good with the Touch. The one thing you notice with this dac compared to other that I have used is that is it digs out all the details without making it sounds hyped up top or glaring. It also presents a wide soundstage with good depth and attack. I had a TC Electronic BMC-1 dac ($450 street) in the office system for a while and the Ross Martin dac is so much more musical with solid bass and better detail up top, better dynamics and every bit as quiet as the dice chip in the TC Electronic. Compared to the Purepiper dac I had, it was no contest at all, with the Ross Martin outperforming it in every area. Even with the optical out of my built in soundcard on the HP tower PC, it gave life to Spotify and really showed that lots of their material is not even 320k. I have not tested the USB directly from the PC yet but have with the Macbook and will discuss a little later.
With the Ross Martin Dac feeding the Blue Circle HPT headphone amp it was open and very clean across the board. Noise free and really made the Shures sing. Later with the Kenwood receiver the match was also very good. The Kenwood gave a bit more of a tube like feel to the mids and upper bass. Even the JDS Labs Cmoy with its stock opamp sounded great with the Shures. I took the Ross Martin Dac and my Blue Circle Dac along with the Kenwood and JDS labs CMoy to the Westone meet a few months back and spent the most time listening to the Ross Martin with the Kenwood and JDS.
The Touch, as good as it is, is not a perfect source with a bit of leanness in the mids or a peak in the lower treble with some tracks. With some songs the cymbals had a little bit of crunchiness with the Touch that was not present in the main system. The Dac will reveal any faults or tonal differences in your source. When the Touch was used in the main system it revealed that it could not substitute for the superior sound of the Macbook and Halide Bridge as a transport. With some songs the filter set to position 2 or slow rolloff helped to smooth the lower treble out a bit and added a bit of texture to the mids. This is a really nice feature even though I mostly keep it on position 1. With some 24/96 material I again preferred the slow rolloff. Yet on a great 24/192 track I preferred it in fast rolloff. I also found that I preferred some classical material on the main system with slow rolloff. Play with it!
When I first placed the Ross Martin Audio Dac in the system I used the Halide Bridge to go USB from the Macbook to the spdif in on the dac. I started here because this is what I use on my reference Blue Circle dac. I am a firm believer in using the best possible transport you can to use and evaluate a dac. I first used the XLR outputs directly to the amp using Pure Music’s excellent dithered volume control to control level. The sound was first rate across the board, open and detailed up top with good solid bass. Images were clearly defined like they usually are with the Halide Bridge. Vocals were clear, tonally right and not veiled. Bjork, Johnny Adams and Neil Finn all sounded like themselves with no honk or undue sibilance that often comes with lower costs dacs. This clean, open and accurate midrange is what makes this dac so likeable. Dynamics were above average for a dac of this class, yet remained a bit less impressive than the reference dac.
I then tried the RCA outputs. Since I prefer the sound of the reference dac with the balanced XLRs I thought this would also be the case with the Ross Martin dac. But no! the RCA outs seem to have even quicker speed on the initial attack of notes and better fullness to instruments and bottom end. It must have to do with the one less opamp pair the signal sees before it is output. The bass foundation that the Ross Martin dac has is way above its competition in this price range. As for noise, when pure music was on pause and the volume all the way up on pure music, nothing could be heard from the speaker with ear about 6 inches away, dead silent and that with an amp that can put out 400 watts at that level.
Over several months of listening, the Ross Martin Dac did well indeed in the main system. Compared to the reference dac which is almost 5 times as expensive it was a bit less resolved in the mids and highs and a bit less dynamic. There is a bit more air and spatial cues from the reference dac as well as bit more defined decay on reverb. My notes indicate the minor sound traits between the two dacs, mainly relating to size, tonal texture, treble resolution and weight. And these traits vary by recording, where some instrument presentations on the Ross Martin being preferred in some songs. In absolute terms, presentations of piano could be a little larger with more texture, cymbals could have a bit more brass, highs can be a bit more resolved and a bit more weight to the upper bass. But we are talking subtleties here, for a dac in the half a grand range the Ross Martin dac can stand tall. If you were to leave the Ross Martin in the system and not listen to the reference dac for a few days you would not be disappointed.
I also tested the Toslink and USB inputs and found the dac to be quite revealing of the subtle difference I normally hear with these inputs. With the Toslink input being fed by and excellent Silflex glass cable the bass took on a warmer yet more wooly bass texture with less ambient space around instruments. This is a sound that although pleasing at first eventually lets you know what you are missing with its less focused presentation versus using the Halide Bridge. You still have all the positive attributes of the dac just a little less focused and refined. With USB, I was really surprised. Typically lower priced dacs that do USB are not that good at all. The Purepiper dac was all but unlistenable in my main system as opposed to Toslink and the Halide Bridge. That dac as well as many others have a stark sheen to the upper mids and lower treble even with the very good Wireworld Ultraviolet cable. Bass was not good and dynamics not good either with the Purepiper and its usb input. The Ross Martin dac on the other hand retained a lot of the dynamics it had with the Halide Bridge yet lost just a bit of focus and ambient clues in the low end. Tonal balance remained close to what was heard via spdif with the mids jus slightly pulled forward. Vocals became a bit closer or more upfront and tonal weight got a bit better than with the Spdif bridge. This was a very appealing sound overall and much better than I had experienced in the past. For example this dac tonally beats out the PS Audio DL-3 in my system when both are fed a USB signal.
The Ross Martin dac does an admirable job and is hard to fault overall. One negative needs to be mentioned, though. The on off switch pops when turned off and has a loud inrush type pop and noise when turned on. When used without a preamp this turn on thump and inrush noise is quite loud especially when using a high powered amp and while it may not damage your speakers it will startle you and have you running for the power switch on the amp. It is always best to turn on the dac prior to turning on the amp and turn off the amp prior to turning off the dac. If you follow these rules you will be fine. I asked Ross why he did not put some type of relay in the circuit and he told me that while it could be done it would affect sound quality and add to the overall cost. Maybe that is why many dacs do not even have power switches.
The Ross Martin is a very good dac and a worthy competitor to many dacs in the $500 and under range. The fact that it is only $250 makes it a top contender. It is uncolored and tonally neutral with excellent definition. Compared to many in this range its USB section is strong and is well balanced tonally. It is flexible and should fit in with many systems. If you want a dac that will make your mp3s sound better or sweeten some older cd rips, look elsewhere as the Ross Martin dac is accurate and will not mask any source issues. It mates very well with a variety of reasonably priced headphone amps and sounds way better than many dac / headphone amp combos I have used. If you are considering combos such as the Nuforce Icon HDP, or Centrance Dacport, or Little Dot Dac II, I have heard all of them and feel the combo of the Ross Martin dac and a good Cmoy will outperform all of them. If you are looking at the Arcam rDac, Cambridge DacMagic, Apogee Duet or Minidac or similar dacs, I also have heard them and feel the Ross Martin is a superior sounding dac. I have not heard all the lower cost dacs out there (obviously) but I do believe the Ross Martin Dac can play with most all of the competitors in this range. Overall the Ross Martin dac is a great value and is highly recommended.
Edited by bixby - 9/27/11 at 9:16am