Well-well-well, how's this for a "blast from the past"? I hadn't come into possession of one of these even close to when they were actually relevant (having jumped straight into the 896 mk3 Hybrid), but a few weeks ago i stumbled upon a ridiculous deal for this and an 8pre, for a price i literally could not refuse. So without further ado, let's take a peek in there, shall we?
Lots of ins & outs to be had. That being said though, despite this belonging in the same generation as the 828 mk2, there's no hardware-accessible way to manipulate the internal mixing. Granted, i have no idea which came first etc, but just thought it worth mentioning. The CueMix software does though work just fine, of course, and i'm assuming it saves the last state it was in, on power-down.
Well... construction is a wee bit different than the mk3, i can tell you that much. Still a few years before they swapped over to the switchmode power supplies, so they had to shoehorn the "heavy metal" somewhere. Come to think of it, that's likely (also) the reason for the additional cast-aluminium supports that the side panels also bolt to.
The transformer is a similar R-core as i think(???) i've seen in an 8pre at some point, perhaps? But either way, quite a chunk of steel. Not too sure how effective that thin shielding around it is, but there you go. All Meritek capacitors, par for the course. But now, for a closer look inside...
Even disregarding the separate power supply, this thing is stuffed at least as full as the later mk3. Quite a bunch of sizeable silicon (or, well, at least many-legged packages).
Quite the old-school processing center - very similar to the 828mk2, albeit this has a separate microcontroller only for handing the front panel (at least going by the label on the DIP-packaged chip). That being said, unlike later products, they interestingly left pretty much all the component values and/or part numbers visible on the silkscreen!
The PLCC-packaged processor is (most likely) the same SST (now Microchip) SST89V564RD - just about confirmed by the lettering poking out from under the edge of the socket. If you squint enough... The front panel microcontroller is some flavor of 89C54 - possibly an Atmel AT89C54, since that small label covers all the markings, and Atmel's were concentrated in the middle there.
As pointed out by the silkscreen, the little daughterboard hosts a Texas Instruments TMS320VC5402 DSP for the mixing duties.
Obscured by the DSP daughterboard is an Altera Cyclone EP1C3T144C8 FPGA likely handling all the various signal routing features, clock signals etc.
Staying in the processing realm, the Firewire interfacing is dealt with by a Philips PDI1394L40 and a classic Texas Instruments TSB41AB2 interface chip.
Before moving towards the audio silicon, it may or may not be worth mentioning the few 74HCT595 shift registers, for driving the myriad LEDs on the front panel.
A lone Crystal Semiconductor (now Cirrus Logic) CS8420 digital audio transceiver & sample rate converter handles the AES/EBU interface.
Nearby lives a Texas Instruments TLC2933 PLL chip.
Moving on to the converters - the ADC's are four AKM AK5385's, while the DACs are no fewer than six AK4382's (four for the eight outputs on the back, while the "main" and "phones" outputs each have their own too).
That being said, in case you doubted this was related to the 828mk2, here we can also see the (infamous and prone to failure) custom dual potentiometers for the gain adjustment. Both reverse-log taper ("C"), one 20k while the other is 2k, and with the ridiculously long shafts. Good luck finding a replacement for those... Maybe if you can MacGyver a shaft extension, and find a dual rev-log 20k pot, and solder a 2.2k in parallel with the pot that's replacing the 2k?
Since we've reached the preamp area anyway, these are built around Texas Instruments / Burr-Brown INA163 instrumentation amplifiers.
Most of the opamps are "classic" JRC / NJM / Nisshinbo NJM4580's.
The odd ones out are the pairs of Texas Instruments / Burr-Brown DRV134's in charge of the all the analog outputs on the back (ten of them, to be precise).
Power-supply-circuitry-wise, nothing exactly space-age going on. The analog rails are whatever comes out of the transformer, while the converters are supplied with 5V from a Texas Instruments / Burr-Brown REG103.
The digital 5V is provided by a National Semiconductor (now TI) LM2940CT-5 low-dropout regulator.
An LM317HV regulates the 48V for the phantom power.
And that about wraps it up for this one. As soon as i bolt it back together and test all the ins & outs, i hope to find a nostalgic cheapskate that might be willing to offer this a good home.. Any takers?
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