Mini-review of Coleman Audio M3PH mkII line/monitor switcher

[mhschmieder]

I originally began a discussion of the Coleman Audio M3PH mkII line and monitor switcher over in the main DP forum as part of a proposed long-term solution to someone's problems with hot-wiring different topologies during mixdown and other contexts (the traditional solution is something akin to a Mackie Big Knob or Presonus Central Station).

Last week, I bought a demo copy of one of these units from Sweetwater, but only this night finally had a chance to check it out in detail, as I had a very intense period of gigging and subbing for multiple bands, which thankfully came to an end (for now) in the wee hours of the morning.

The unit arrived damaged and will be sent back with no problems, but I of course wanted first to make sure it's even the right solution for my studio setup, and the lessons learned from this testing may be helpful to others considering a similar solution to a complicated multi-purpose setup.

My main goal was to avoid having to rewire things when I switch modes from recording/mixing/mastering to playback of pre-recorded material, mastered CD's of my own material, cassette and vinyl legacy material, and also when inputting analog material for conversion and/or audio restoration. The icing on the cake was to also have monitor switching and related functions, for long-term studio growth (not of short-term necessity).

For the past 20+ years, I have been using a Bryston .5B no-frills preamplifier (more of a line switcher with built-in RIAA phono preamp). Bryston is a Canadian company of high repute and are used in studios everywhere (though their power amp designs tend to be more popular than their preamps, and I sold my 2B power amp when I switched to active monitors a couple of years ago). Bryston stands by their product and guarantees for 25-30 years (I forget which), with partial lifetime guarantee atop the basic warranty.

But by now, most gear has moved over to balanced connections (whether TRS or XLR), and at least a second pair of outputs. Thus integrating high-end hi-fi equipment with recording studio gear has become ever trickier -- especially if trying to avoid level balancing.

Devices such as the Coleman Audio unit, the Central Station, Mackie Big Knob, and higher-priced units from Dangerous Music, Great River, Grace Designs, and others, seem like overkill for a semi-pro project studio, but the lower end units looked tempting for a studio that intends to eventually transform into more of a pro-level project studio.

After much research on Gearslutz and audio magazines, I dismissed the PreSonus and Mackie units and gravitated towards the Coleman Audio unit. Irts simplicity and elegance impressed me as being inspired by Bryston's ethos, with an uncluttered interface and controls that are unlikely to wear over time. Sound-On-Sound has given all of their stuff excellent reviews.

So when I put it through its paces tonight, I was pleasantly surprised when it opened up the sound on pre-recorded CD's and even moreso on quality home-made cassette tapes. I had noted similar improvement in clarity, transparency, and evenness of frequency spectrum when comparing to my Ashly LX308b line mixer fairly recently, but that is an active device and I would need a second one for the studio as my current one is for gigs.

The difference in quality using the fully-passive Coleman unit is many steps beyond what I noticed with the Ashly unit. But going from RCA to XLR is non-ideal, and requires the volume knob to be at near max for what would be considered moderate to borderline loud playback of hi-fi material. This could pose a problem for some material -- especially very old material which was typically recorded at much lower levels. For this reason, I do not feel the Coleman Audio unit on its own is ideal for integrating hi-fi and studio gear. They make a powered version but it wouldn't be as transparent. I am back to looking at audiophile preamps, with a later purchase of a dedicated single-source monitor switcher once I get around to buying the Avantone MixCubes and have a need.

As for the unit's main purpose as a big knob for digital audio interfaces, such as the RME Fireface 800, $800-$900 is a lot to pay just for that, but certainly it does that job well, and when I compare digital sources on my computer with the Fireface Mixer set at -12 dB and going straight from the Fireface to my KRK Rokit 6's and Rokit 10 subwoofer vs. the Fireface Mixer set at 0 dB and going through the Coleman Audio unit using its trim knob, the difference is noticeable but minor. More startling is how boxy things sound if I plug the analog 1-2 outputs of the Fireface into the Bryston preamp and take that boosted output to the speakers. So the Bryston preamp as a "Big Knob" for the Fireface would not be acceptable.

Although this is not documented per se, my theory is that 0 dB is nominal for D/A on the Fireface unit (it allows a gain of +6 dB going out, but this introduces overs and thus distortion). Just as iTunes sounds better at max volume and trimmed at the analog stage, I believe the optimal level for the RME is 0 dB as any trim in the Fireface Mixer is probably applied pre-conversion and thus scales the D/A in a way that diminishes the analog output quality slightly.

One big surprise for me using the Coleman Audio unit was that my Rokit 10 subwoofer no longer needed to be turned down to roughly -18 dB to -24 dB for pop material (-24 dB for more recent stuff) and -12 dB for classical, so my horror after buying the subwoofer last year and thinking that modern recordings are too "hot" in the sub-lows was slightly exaggerated (though definitely true). That is a relief on many fronts, and is also good to know going into my next mixing and mastering sessions next month.

My preferred primary recording for testing audio is a 1994 Sony Classical recording of Murray Perahia playing Chopin's ballades and assorted shorter solo piano works. I do sanity checks with other recordings but start with this one, as it is the best-recorded solo piano CD in my collection. I consider piano ideal for judging audio as it is a full spectrum instrument that most of us are not only familiar with but are used to hearing in a fairly intimate close-range setting.

It is now clear that the Bryston .5B preamp is the weak link in the chain, which comes as a surprise in spite of its age, due to how little (if any) the consumer end of the market has improved in that time, and how expensive the once-affordable "smart" high-end was (newer Bryston amps, for instance, are closer to $3000 vs. the $400 to $500 I paid for this amp in the late 1980's). And I even wager that quite a few on this forum have hi-fi preamps (or integrated amps) that would lose out in a shootout with the Bryston. I'm just pointing out that even in current magazine reviews, these older amps still get mention as holding their own.

Nevertheless, using that preamp as a Big Knob for the RME outputs and thus as an additional if minor gain stage, results in the low end becoming boxy and muddled, even boomy. High end detail on fast piano passages becomes brittle.

Using the Coleman Audio unit, every detail presents itself clearly, with even tone, and a realistic image and presence. This is a very impressive unit well worth its street price. I highly recommend it over the PreSonus Central Station and Mackie Big Knob. It also has more useful features in a more readily accessible way. But no digital inputs (a good thing, really).

Just as an aside, in an earlier audio test, I noted that the converters in my Arcam CD73 player (which I bought last year after the non-replaceable lasers in my excellent late-80's Rotel unit finally died), provide far more detail, warmth, and presence, than when taking the S/PDIF output and using the RME Fireface 800 converters. Arcam used to use the same Burr Brown(?) converters as RME, MOTU, and others, but switched a few years ago to Wolfson MicroElectronics as being more musical and open.

My next task is to go to a local audiophile store to try out the Manley Shrimp preamplifier and a couple of others, and to check whether they have adequate balanced and unbalanced input and output connections for a combined hi-fi and recording studio setup (a second pair of outputs would be sufficient as that's the most I would grow as a project studio).

[mhschmieder]

I definitely need an active preamp for the line inputs. Not strictly speaking as line level is sufficient, but just as using a good preamp can improve a keyboard during recording (even though the input is "hot" enough on its own), the low end in particular tends to have more detail when an active preamp vs. passive switcher is used to drive the power amp (active monitors in my case).

So I have decided it is best to split the two tasks, with a traditional no-frills high-end audiophile preamp doing the line switching chores, and a separate passive device doing the monitor switching, mono-summing, left/right muting, and phase switching chores. I can hold off on the latter until I have a second pair of monitors, and can use Fireface Mixer for now in cases where I want to do mono-sum sanity checks (I have to verify it suppoorts this, but otherwise I can do it in Digital Performer with a special Master Fader and mix setup).

Although Coleman Audio also makes an active version of this unit, I have no reason to believe the op amp would be of acceptable quality vs. their specialty of passive switching gear. Op amps aren't ideal anyway, and some designs use MOSFITS. At any rate, I am very impressed by the transparency and overall quality of Coleman Audio gear, and recommend them without hesitation. Once I need a dedicated monitor switcher, no doubt I will line up one of Coleman's output-only switcher devices.

As for preamps, I am currently debating between Manley Shrimp, Rogue Metis, and Rogue Perseus. Maybe even the older Adcom GFP-750. The preamp is in some ways the most important link in the chain and can have the biggest impact on accuracy and transparency.

Today I heard the Rogue Metis and was very impressed, but it has limited connectivity so I may go for the Perseus. The Metis is very transparent with just a touch of unnatural emphasis in the low treble range. Not enough to mess up a mix or to be unpleasant for playback listening. FWIW, I compared vs. a Conrad-Johnson reference preamp and found the latter too coloured, too forward, and not very pleasing. The Rogue Metis has excellent imaging and a very three dimensional sound. A great buy for under $1000, especially as it is all American-made.

[guyreilly]

Thanks for your very detailed and thoughtful review!! I would love to hear the coleman unit in my setup, it sounds like it has added a lot to yours. The RME fireface sounds amazing, and it makes sense that the only way to do it justice is to have a completely passive signal path to you active monitors. It is interesting about how it cleaned up the low end and gave you a more even response with your sub...

I am curious about why you're find the Big Knob and Central Station to be unsuable. I haven't been able to find any review where they are A-B tested, unfortunately. I understand that mackie is loaded with opamps and IC chips that color the sound, but the central station is totally passive. I don't see the need to pay for d/a converters though... aside from that it seems to be a decent value. Is there also a concern for coloration here or something with the feature set?

Clearly the Samson unit is a noisy POS. When I think of Samson I think of Taco Bell. There are some places I just won't go.

It is becoming apparent that having some sort of attenuator when monitoring directly out of a DAW is important. I will probably order the SM Pro Audio box I mentioned in the other thread and report back. For $149 it may prove to be a great buy.

[mhschmieder]

Well, the actual conclusion was that the op amps in my current gear are not as good as they could be, and therefore the fully passive signal path of the Coleman Audio unit was more transparent.

In thinking it over more, I realised I was also losing some bass presence and that the lack of muddiness that I got when using the Bryston was confusing me about what the real implications were.

Preamps vary quite a bit in what they deliver, both in terms of gain and of course quality. The Rogue preamps mentioned above add up to 12 dB of gain. I think the Manley Shrimp provides up to 24 dB of gain. My Ashly LX308B line mixer, mentioned earlier, can boost up to 30 dB (36 dB?). I don't recall how much gain is available in the active version of the Coleman unit. Some units provide up to 8-12 dB of trim as well, but most provide only gain. Passive units of course provide only trim and no gain.

Ideally an amp is not driven past 50% of its potential, in order to leave enough headroom for transients and also to prevent driving the amp at max (which could cause overheating and also distortion if the amp has no time to settle down). Much of today's music is so compressed that there is almost no dynamic range whatsoever, so it can probably be driven slightly louder as there won't be any transients. And yet the paradox is that it becomes fatiguing even at minimal volume.

Of course bear in mind that these are all opinions. Although they are based on varying levels of audio knowledge and are shared by many, there are others who bring up valid arguments for other points of view. Those who feel strongly enough about their opinions often start their own company and sometimes even turn the industry on its head . There is so much psychology involved in audio perception that even when people think they can fully quantise it beyond any ambiguity, there are few true absolutes.

Anyway, regarding the Mackie Big Knob and the PreSonus Central Station, I feel that both have a lot of features I wouldn't use (such as talkback mic) and flimsy construction (relatively speaking -- they are not shoddy, but merely not up to my preferred standards for something I would hope to buy once and keep in my studio for 20 years or more like my Bryston gear). Once I see so many features listed, I figure at that price point it's unlikely anything of true use to me would be maximised for quality. The talk on Gearslutz is pretty down on both these units, but I hesitate to say they are unreliable as it isn't valid to draw a statistic from such a sample. Most importantly though, neither seems to preserve transparency, which of course would have a negative impact on your mixing decisions.

Here is a budget option for those who need more flexibility and may not have the best preamp currently but also don't want to spend $1000 or more: Adcom GFX-750. What is interesting about it is that it has a switch for passive vs. active mode, lots of parallel outputs and input options, and is based on MOSFET designs vs. Op Amps. A former co-worker back east has had one since it came out, and although this remains his opinion that it is the best preamp under $1000 (if not higher), he is the most knowledgeable person I know about audio and electronics and isn't an audiophile snob so has gotten real smart over the years about finding best value within a budget range. He recommends this amp to me even now, and I may even go for it. I have heard it on my visits, but never in an A/B situation with slightly higher-end gear. Or against my Bryston .5B.

There's a current eBay auction for the Adcom preamp (item #300164179478) that ends in six days. They also show up on audiogon.com now and then. Look at the specs: you might be surprised how well a well-spec'ed audiophile hi-fi preamp can address the connectivity needs of a project studio.

And many manufacturers argue that RCA connections are better than XLR due to fewer issues with longer cable runs, and even a cleaner internal circuitry with less signal interference both internally and externally. I know this goes against the usual intuition about the superiority of a balanced signal. But my friend mentioned above has opened up many a unit as he does his own mods all the time (usually just swapping out cheap capacitors with $8 capacitors that can make a prosumer-level device sound fully pro), and he surprised me when he said that lots of high-end audiophile gear uses op amps to convert XLR inputs internally to match the RCA's!

This is yet another example of why it's so difficult to issue absolutes when evaluating equipment. Even many high-end manufacturers don't publish the specs I really want to know. MOTU tends not to publish any at all, and certainly not circuit diagrams. I'm almost at the point where I won't buy a piece of gear unless it has a fully divulged spec sheet showing exactly how things are routed internally and where things are buffered, etc.