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PreSonus DigiMax FS (8-chan mic pre with ADAT/analog I/O) - Now with Conclusions


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First rule of a Pro Review: Don't schedule one to start on Halloween when you have a pre-teen daughter about to have her friends over for a Halloween party.

 

I like to start a Pro Review with pictures that you don't find in brochures and manufacturer web sites: The insides, the construction, the parts that are used, and so on. However, as I watched the natural light slip away into darkness and still hadn't finished putting up the Halloween decorations, I realized okay...the photos are going to have to wait until tomorrow.

 

So what's the DigiMax FS? The PreSonus web site files it under "Preamp," which is accurate up to a point. It's actually eight preamps that feed either an ADAT out (standard or SMUX to accommodate sample rates above 48kHz) or eight analog direct outs. There are also analog inserts for the eight ins. However, there's also an ADAT input that terminates in eight DAC outs.

 

While waiting to do the photos, though, as is also customary with Pro Reviews, I like to refer to where you can get background, specs, and the like. That way we don't have to re-invent the wheel here, and can concentrate on the user experience.

 

There are several pieces of useful information at http://www.presonus.com, including an overview, a video that covers the basic philosophy behind the unit, a typical hookup diagram, and a complete set of specifications. You can also download the user manual if you want to get a pretty good idea of what the unit's about.

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Companies have different reasons for wanting to do Pro Reviews - from something as simple as showing they stand behind their product enough to subject it to the scrutiny of the HC community, to gathering feedback they can incorporate in future products. But I'm assuming that PreSonus wants one because of the application-oriented nature of the Pro Review process.

 

The DigiMAX FS is clearly more than a simple preamp, and is intended as an "expander unit" for ADAT-compatible mixers and interfaces. (Of course, PreSonus would want you to use it with their FireStudio, but as we'll see, it's well-suited to many other pieces of gear.) They wanted to make sure, for example, that I had sufficient gear sitting around with ADAT I/O and work clock, as well as the ability to handle 44.1kHz to 96kHz, so I could test out the various options. As it so happens, I sure do - and in fact, I'm very interested in reviewing the DigiMAX FS because it might be a good solution to some limitations I've experienced with otherwise very useful gear.

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I just wrote a column for the October 2006 issue of Keyboard magazine about simplifying your life in the studio, and one aspect of that was advising that people use multi-input interfaces. Here's what I said:

 

You do need an audio interface with multiple inputs. "I'm a solo performer, so I only need a couple inputs." Wrong! You have a condenser and a dynamic mic, right? And at least a couple of keyboards . . . and if one of them has multiple outputs, that's at least a half dozen outs, all desperately seeking inputs. You don't want to re-patch; it's great to have everything ready to go, so all you need to do is record-enable a track to make music. Incidentally, this is also a raison d'être for the new generation of Firewire-compatible mixers: Mixers aren't just about mixing, but about routing.

 

The two main interfaces I use for my computer are the Creamware SCOPE system and E-Mu 1820m interface. Both have ADAT I/O (the SCOPE has two sets for 16 channels, the 1820m one set), but the complement of mic pres is only two for the 1820m, and none for the SCOPE. Although the SCOPE card has a breakout cable with SPDIF, analog in/out, MIDI, and SPDIF, all I really use are the ADAT connections in conjunction with my Panasonic DA7 mixer, and of course, the MIDI connections.

 

But the DA7 doesn't handle sample rates over 48kHz, and the DigiMAX FS seems like a good way to add significant "input power" to the SCOPE system (which handles 88.2/96kHz sample rates) independently of the DA7. Similarly, although the 1820m has much more accessibly I/O thanks to its "dock" (breakout box), again, if you want to have multiple mics set up the box alone is not enough.

 

Both the DA7 and the 1820m also have word clock options, lending themselves to further experimentation with the DigiMAX FS.

 

So that's basically the direction I'm going to take: Checking out the DigiMAX FS with these two interfaces, as well as using it to expand the number of analog aux buses in the DA7 (I'm a fan of using it with external analog gear...more on this as the review develops).

 

That's enough for tonight. I'll be back tomorrow, camera in hand, and take the sucker apart. (Note to PreSonus in case anyone's reading this: No, I'm not going to give it the same "drop test" I gave the Inspire 1394, so no worries there!)

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Okay, let’s look at the front panel. I have mixed feelings about all the inputs being on the front; it’s of course very convenient (particularly for the two instrument inputs), but you’d probably want to put the DigiMAX FS pretty low in your rack so that the cables don’t trail in front of other units. The other possibility would be to leave a single space above it, and feed the cables in over the top of DigiMAX FS, and then plug them in to the front.

 

In any event, the point is moot because as we’ll see, the rear panel is pretty packed and there wouldn’t be room for paralleled input connectors on the output anyway. The only option would be to have put some connectors on a breakout cable, which I would definitely not prefer.

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The Gain controls are physically offset, which makes it easy to adjust one without brushing against another one. The feel of the knobs is worth noting: They feel very smooth, with a just the right amount of resistance, and have click detents.

 

Note that the gain settings are screened separately for the line and mic levels – a nice touch. Mic gain ranges from 0 to 60dB, while line covers –20 to +20dB. Also note that there’s a clip indicator to the lower right of each knob.

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The sync section is very simple: You have one button to cycle through the various sample rates (44.1, 48, 88.2, 96kHz) and another button to cycle through internal sync, external sync to work clock, and external sync to ADAT.

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The first two inputs are mic/instrument inputs; and by the way, I’m a big fan of Combi connectors that do XLR and 1/4” J. Anyway, the instrument ins are spec’ed at 1Megohm (the manual says “1 MegaOhm,” but we’ll let that slide!). I consider that to be pretty much the ideal input impedance for guitars with standard, passive pickups.

 

Also note the +48V phantom power switches. The good news: They really do put out +48V. The bad news: You can only enable phantom power for two groups of inputs, 1-4 or 5-8, not for individual inputs. So if you use one instrument input for, say, guitar, then you’re down to have four mic ins with phantom power (5-8) – not six. While this probably wouldn’t matter much in the studio, for live use – where even eight ins might not be enough – you don’t want to have to write off any more inputs than needed.

 

Of course, you could put other mics through an external mic pre and use inputs 2-4 as line inputs, but that kind of defeats the purpose of having nice mic pres in the DigiMAX FS.

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I thought you might like seeing a shot of the back of the input connectors. I like their “chunkiness,” and the fact that those big barrels keep out dust and other contaminants. The downside is that if you do ever need to clean the contacts, it’s more difficult than having exposed jacks. Still, it’s not a big deal as you can just put contact cleaner on a plug, and twist it around a few times…or if you’re brave, spray a little bit right into the 1/4” input hole, then plug in a plug and twist it.

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I like to take things apart and photograph the innards, but the DigiMAX FS makes that pretty difficult. There are two screws on the top and bottom, and once removed, you can take off the side rack ear panels, as well as the front “cosmetic” panel. Click on the attachment to see the DigiMAX FS with the front and side panels removed.

 

However, this still leaves an upper and lower shielding panel in place. To remove this, you would presumably need to unscrew the lock nuts from 24 1/4” jacks, 2 BNC connectors, and a wall wart connector. Now, I love you guys and all that, but that’s a lot of work! However, if y’all really want to see some serious inside views, let me know and I’ll deconstruct the unit further.

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Even though I couldn’t take the unit apart completely, this shot shows the insides behind the front panel, so you can see the pots and pushbutton switches used for sample rate selection. Interestingly, the pots are 10k – I’m not sure how they’re configured in the circuit, but I do know from my analog design days that 10k from input to ground is pretty much the sweet spot for bipolar integrated circuit amplifiers in terms of obtaining the lowest noise. Yeah, that’s kinda trivial, but it might give some clues about the circuit design.

 

If someone from PreSonus is listening, is the schematic for this posted anywhere online? I’m curious…

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As you’ll see from the photo, there are two sets of direct outs: Analog direct outs from the inputs, and DAC outputs that carry the signal from the ADAT light pipe input.

 

The analog inputs also terminate in an ADAT out (more on this later), but the direct outs have their uses. One that comes to mind is sending them to a separate recorder as a safety. Another is that if you have a recording setup or interface with an ADAT in and line ins, you could feed the “main” preamp signal in digitally through the recorder’s ADAT input, but also feed the direct ins to the line inputs, set for a lower level. Then, if distortion occurs with the main feed, you’d have an alternate set of signals at a lower level for “backup” that you could gain-correct and paste over the distorted section.

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There are inserts for each of the eight ins that occur prior to A/D conversion, so you can patch in compression, effects, limiters, whatever. These seem to be oriented toward line level signals, what with a 51 Ohm output Z and 10k input Z, but you could probably put some guitar pedals in there if they had enough headroom. Note that unlike the TRS inputs, the send and receive connections are unbalanced, and appear on the tip and ring of the insert jack with a common ground.

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You’ll note from the photo that there are two ADAT connectors for the input, and two for the output. Why do you need two for an 8-channel unit, anyway? Because when the ADAT optical interface was introduced, it could accommodate eight, 24-bit data streams at 44.1 or 48kHz – but not higher sample rates. To deal with higher sample rates, various companies came up with multiplexing schemes, and SMUX is a common protocol that basically splits the data stream over two connectors. So, when operating at twice the sample rate, each light pipe line carries half of the samples. This allows for 88.2 and 96kHz sample rates.

 

At lower sample rights, you use only one of the connectors (the one marked 1-8). At higher sample rates, you use both. Of course, whatever you’re feeding into needs to accommodate the SMUX protocol as well. For example, my Creamware interface goes up to 96kHz and has two ADATs in. I don’t know if it will be possible to feed in the two ADAT lines from the DigiMAX FS and do 96kHz sample rates, but it’s something I’ll test (unless someone from PreSonus reads this and tells me it won’t work and I’m wasting my time).

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The DigiMAX FS has word clock in and out, and is meant to be daisy-chained with other systems. PreSonus makes a big deal of their “JetPLL” technology, which supposedly gives extremely low jitter. I’m assuming that might make some sonic differences with the conversion process; as to using the DigiMAX FS as a master clock, I’m a little less clear as to how that process works…when it’s a master clock, do the slave clocks re-clock internally based on what they receive, or follow the master clock exactly? Hey, I don’t know everything…

 

In any event, you can terminate the input to 75 Ohms if the DigiMAX FS is the last device in the chain.

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Yup, it’s made in China – check the label next to the wall wart adapter input. And speaking of the wall wart, it’s actually of the “line lump” variety, but of the same ilk as typical laptop adapters. In other words, one end plugs into the DigiMAX FS, and the other end has a non-captive line cord that plugs into the wall. Presumably, this is so that when shipping to non-US destinations, all you’d need is a different line cord going to the wall to accommodate different physical AC connectors. The adapter itself handles 100-240V at 50/60Hz, and runs at about 45 Watts.

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This seems like a good stopping point, as we’ve covered the major gozindas and gozoutas, as well as a bit of the physical construction. The next step will be to feed the ADAT out into something with an ADAT in, crank up those mic pres, and see what they sound like.

 

And as always, remember this is an interactive review format. Got questions? Got answers? Care to illuminate us all about how the master clock thing affects slave units? Is there a a schematic online somewhere? Stay tuned!

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Originally posted by Anderton

The DigiMAX FS has word clock in and out, and is meant to be daisy-chained with other systems. PreSonus makes a big deal of their “JetPLL” technology, which supposedly gives extremely low jitter. I’m assuming that might make some sonic differences with the conversion process; as to using the DigiMAX FS as a master clock, I’m a little less clear as to how that process works…when it’s a master clock, do the slave clocks re-clock internally based on what they receive, or follow the master clock exactly? Hey, I don’t know everything…

 

Craig,

 

I won't attempt to pretend to know everything on this subject but there are a few things I know. The JetPPL in DigiMAX FS is developed by TC Applied Technologies, a division of TC Electronic. Its the same technology found in the DICE II chip. This chip is used in the TC Electronic's Konnekt 24D interface as well as Presonus's new FireStudio. I'm not certain that this product has the DICE II chip, since it doesn't have 1394. I suspect is just has a component of it for JET (Jitter Elimination Technology).

 

In the case of the Konnekt 24D, I've been told that any incoming digital source will be "corrected" to have the same jitter spec as the Konnekt regardless of which of the units is the master clock. In our own tests, the jitter spec of the Konnekt 24D and likewise the DigiMAX FS will be very hard to beat even compared against dedicated clocking products.

 

Mike Martin

TC|US

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>

 

That's a neat trick. Just to make sure I understand...so you don't have to use the DigiMAX FS or Konnekt 24D as a master to gain the benefits of the JetPLL technology?

 

>

 

BTW I think it is extremely cool when a "competitor" paticipates in a Pro Review in a neutral, helpful manner. And yes, I'm looking forward to starting the Konnekt 24D Pro Review next week :)

 

Now excuse me while I get out my ADAT cables and set up my mixer for testing with the DigiMAX FS....

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Originally posted by Anderton

That's a neat trick. Just to make sure I understand...so you don't have to use the DigiMAX FS or Konnekt 24D as a master to gain the benefits of the JetPLL technology?

 

That is correct

 

Originally posted by Anderton

BTW I think it is extremely cool when a "competitor" paticipates in a Pro Review in a neutral, helpful manner. And yes, I'm looking forward to starting the Konnekt 24D Pro Review next week
:)

 

Presonus makes great stuff! I've known those guys since my Kurzweil days. Plus the DigiMAX FS would make a great expansion for the Konnekt 24D. :thu:

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Even though I couldn’t take the unit apart completely, this shot shows the insides behind the front panel,

 

I think it would be interesting to see what's going on there. I have been thinking about cracking open my Firepod (now that they're not quite as expensive to replace) to see the possibility of upgrading opamps, but of course, I should probably talk to Rick Naqvi first... does he hang around these forums?

 

I'm interested to hear how the preamps stack up against the Firepods... apparently, the Firestudio sounds significantly better, which would be impressive for a sub $100-per-channel pre amp. Obviously, the improvement in AD/DA is of interest as well.

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>

 

That's one vote. If I get a dozen votes, I'll get out the nutdriver and camera!

 

 

He posted a lot in the Inspire 1394 thread, and was very helpful I might add...maybe he'll put in an appearance here when he gets a chance.

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I have been thinking about cracking open my Firepod (now that they're not quite as expensive to replace) to see the possibility of upgrading opamps, but of course, I should probably talk to Rick Naqvi first... does he hang around these forums?

 

Upgrading opamps on the Firepod will be a bit more challenging than on our transformer balanced pres (Eureka, MP20, M80, VXP) because the opamps on the Firepod are not socketed. However, that challenge hasn't stopped some from trying....

 

However, since this ProReview is on the Digimax FS, we should probably let Craig do his thing. Feel free to email me if you have any other questions relating to your Firepod.....

 

Carry on Craig!

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I figured I'd test out the ADAT connections next. So, I hooked up a light pipe cable from the DigiMAX FS ADAT out 1-8 (not the 96kHz SMUX out) to the E-Mu 1820m ADAT in, and the E-Mu 1820m ADAT out to the DigiMAX FS ADAT 1-8 in. So far so good.

 

I wanted to sync the 1820 from the DigiMAX FS clock at 44.1kHz, so I just hit the DigiMAX FS internal clock button until the 44.1kHz light came on.

 

Next up: Setting up the 1820m. I called up the PatchMix template for 48kHz ADAT transfer, which opens up four stereo ADAT strips for the eight tracks, and also four stereo strips for ASIO for good measure. I set the PatchMix DSP external source to ADAT, which seemed like the right thing to do :)

 

Then I booted up Sonar 6, and did the proper input enabling routine to recognize the signal coming in from ADAT channels 1/2. Success! The mic sound came through clean and clear.

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I also tried running off the 1820m's internal clock, and synching the DigiMAX FS to it. Again, the DigiMAX FS operation was obvious: When you hit the External Sync button, it's either unlit (which means that internal sync is on, or with successive presses, it glows red (ADAT sync) or blue (word clock sync). I also set the PatchMix DSP's clock to internal sync.

 

I was pleasantly surprised by the fact that switching sample rates around didn't produce horrible pops or clicking sounds. What's up with that? There was something beneficial happening somewhere, because Sonar's input channel would mute as soon as the sample rate changed, and wouldn't carry signal again until I re-enabled direct monitoring. Does the 1820 mute when it doesn't see a clock, maybe? That seems unlikely, because I assume it would just switch over to its internal clock. Or does Sonar lose direct monitoring when its clock goes away? I don't know if this was the result of conscious thought or just a happy accident, but it was nice to know that if I forgot to down down the monitors before changing sample rates, my ears (and monitor) would survive.

 

So, could I hear a difference between running off the 1820's clock and the DigiMAX FS's clock? Well, doing an A-B comparison just doesn't hack it because of the time required to switch over from one mode to another, and there was no hugely obvious difference. So, I think I'll record a track with the first part done with the 1820's internal clock, and the second part synching off the DigiMAX FS clock. Stay tuned, I'll be back in a couple of minutes...

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