This came up on eBay the other week as faulty - inputs 1/2 and outputs 1/2 seemingly dead. First instinct was, 'obviously', look up photos online in the hope of finding some internal shots. A few minutes later, bingo: four CS4272's in there. Now, what're the odds one of them is handling the bad pair of ins & outs? Quite a bit higher than the analog input of one, and the analog output of another to be bad, wouldn't you say? But let's not get ahead of ourselves (too much), and take things one step at a time...
From what i could find online, this thing retailed at four-figure amounts, back in the day (well, 10-12 years ago). And i got my grubby mits on it for a measly 10% of that. Well, there's something to be said for "right place at the right time" and "choosing your battles" and whatnot. Slightly unfortunately, one end of the front panel got a bit bent in transit, but that should be recoverable without (too much) trauma. Hopefully, anyway.
Inputs 1 and 2 have high-impedance inputs on the front panel, as well as a send and a return on the back (if one wished to insert, say, a compressor after the mic preamp, but before the A/D conversion), while 3 and 4 only have high-impedance input options (for electric guitar or bass). Four more line inputs, eight line outputs, S/PDIF, ADAT, MIDI and wordclock ins & outs, and a pair of Firewire ports add up to a considerable complement of features.
Surprisingly generous venting on both sides, though - you don't see that too often. Well, not outside power amplifiers, anyway. The top lid's quite substantial, a good 1.5mm of steel sheet.
Once that's off, here's the money shot. Sure, one side-effect of the venting is dust ingress, but since there's no real power being dissipated, a slight whiff's no big deal. But yup, this is quite a sizeable unit, right up there with the Focusrite Saffire Pro 40 or Scarlett 18i20; a good 30% deeper, in fact. Not exactly the most tightly-packed design ever (and i'm willing to bet there's almost no components on the bottom), but hey, if it works...
The power supply's been outsourced (as so often happens), but is a reasonably good quality unit, by the looks of things. Rated at 24V and 1.67A, that adds up to 40W. The "0816" label on the transformer sounds to me like 2008, week 16, so the whole unit can't be older than that vintage (despite the 2006 copyright on the main board). I do appreciate the Japanese electrolytics, though - both the big primary one and the four on the secondary look to be Nichicons.
Moving on to the rest of the power section, things get a wee bit more complicated. In all fairness, at least five different voltage rails are required: two for the bipolar supply of the analog stages; the phantom-power for the mic channels; a 5V and a 3.3V rail to supply most of the digital circuitry, and on top of all that, very likely one or more lower-voltage rails for the [spoiler alert] FPGAs.
The main mover here is a Unitrode (now Texas Instruments) UC3843, driving an STD25NF10L 25A 100V N-channel MOSFET. A National Semiconductor (now TI) LM2672 is right next to the power input connector - not quite sure which rail that's in charge of (probably 3.3v), but hopefully i'll remember to probe it when i power the thing up. On the other side of said connector, a TI TPS40055 synchronous buck controller drives a FairchildSemi (now OnSemi) FDS6900AS dual MOSFET. This'll likely be supplying the bulk of the current for one of the digital "chunks" - i'd vouch for the FPGAs.
Also, near the top of the picture is a TI TPS70402 dual low-dropout regulator, which most likely supplies the BridgeCo main controller (if only by the close proximity).
The computer-interface side of things is handled by a BridgeCo chip, namely a DM1500E. No datasheet to be found (i believe BridgeCo have gone under, years ago), but according to a press release, this is supposed to be capable of 800Mbps FireWire operation. Since the connectors on the back are the original "400" ones, as is the TSB41AB3 PHY (why they went with the 3-port one instead of the 2-port -AB2 is a mystery to me), they may well have used it for whatever other features it contains. The associated firmware's contained in a Spansion (now Cypress) S29AL032D 32Mbit (4Mbyte) flash memory, and the working memory is a Samsung K4S641632K 64Mbit (8Mbyte) SDRAM chip.
Not quite sure if or how much of the "DSP-enhanced" nature of the BridgeCo chip is actually employed in this design, considering the two Xilinx parts right next door. The "heftier" one is a Spartan-3 XC3S1000 FPGA, along with an XC2C256 CPLD. The firmware for these is contained in an STM27C512 one-time programmable ROM, and an ST M25V40VP flash memory likely contains all the parameters of the on-board mixer / router (which get altered in use).
In the vicinity we have some more digital circuitry - a TI SRC4190 sample rate converter (with the associated 24.576MHz and 22.5792MHz quartz crystals), a Wavefront AL1402G ADAT receiver/decoder for the optical input, and a Cirrus Logic CS8416 S/PDIF receiver. The TI 74HCT04 most likely handles the driving of the S/PDIF output. I'm slightly surprised neither the input or the output is transformer-isolated, though.
Finishing up with the digital side of things (well, almost), we have a quartet of Cirrus Logic CS4272's in charge of most of the analog-to-digital and vice-versa conversion, as well as an additional pair of CS4392's for the two front-panel headphone outputs.
Ok, this time we're really done with the digitals - the mic preamps are four TI / Burr-Brown PGA2500 (as seen in the MOTU Traveler Mk3 and other such units). Most of the opamps are TI TLE2074 quads - not exactly what you might expect in a (relatively) "high-end" unit, but hey, if it works... And/or "it's how you use it"..(?)
Inputs 3 and 4 are a bit simpler in some ways, but have an additional trio of ST LM833 opamps for the high-impedance instrument inputs. Slightly odd choice, given the TLE2074's used everywhere else "already" have high-impedance JFET inputs, but what do i know?
The high-impedance inputs of channels 1 and 2 have a similar arrangement, but right at the connectors, near the front edge of the mainboard.
This big group, i would reckon, is likely the DAC output low-pass filtering, and potentially also some signal conditioning for the ADC inputs as well. Way too many signals to trace, and i personally am not quite THAT curious about details like that. Maybe if i were to employ the use of this unit, but since it's Mac only, that's a no-go. Speaking of which, i still have to get my "Hackintosh" test-laptop set up...
The headphone output section's quite... noticeable (and/or or notable?) as well. in addition to a pair of TLE2074's, the actual output signals are driven by discrete-transistor stages. Not something seen all that often, and a nice touch. Then again, for what this thing retailed for when it was new, you'd sort of expect not-too-many corners cut, wouldn't you?
Last but not least, there's a chunk of circuitry that i've yet to figure out what exactly it does. The largest semiconductor component is a FairchildSemi FDS4895C dual N and P-channel MOSFET. I'm leaning towards some sort of power-switch arrangement for the analog rails, but i can't yet be certain. I may or may not find out later, but don't hold your breath.
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