Emax, Technical

Overview The Emax I is an 8 voice, 12-bit, mono polyphonic digital sampler. It is a major revision and update to the Emulator II design. Unlike its predecessors, it makes extensive use of VLSI (very large scale integration), as well as a 32-bit microprocessor for the main CPU. It also sees the introduction of PAL (programmable array logic) micro chips, and the first custom DSP that E-mu Systems ever designed. Thanks to Dave Rossum !!

Processing The main processor is a 16-bit National 32008, clocked at 8 MHz. This rather overloaded processsor can result in MIDI timings being a bit slow for drum sounds. The Emax is entirely controlled by computer software (the operating system) which is loaded from disk at power on, into 2 DRAM’s with a total of 64k bytes (alot smaller than the total size of the Operating System.) The small amount of OS RAM means that the Emax software is loaded in overlay mode, which means there is a short delay as specific software modules are loaded from disk each time they are used.

The scanner CPU is the standard E-mu part, a Rockwell 6500/2 (a 6502) processor running at 4MHz. The 32008 main processor boots the initial firmware from a single 2732 EEPROM with a total size of 4k bytes.

The E Chip To simplify the design and to reduce costs, E-mu Systems developed their first custom Digital Signal Processing chip – The E-chip (Emulator on a chip – nearly !). It contains over 50,000 transistors, and had some curious teething problems. It provides four functions:

  • low distortion pitch shifting
  • data expansion
  • volume contouring
  • keeping track of which channel is playing

This frees up the main CPU from these core tasks. Sample replay is also improved by the E-chip, over previous designs, by enabling lower distortion pitch shifting. The chip cost $226.40 to replace.

e-chip

Sample Memory The Emax has a fixed sized sample memory of 512k bytes fitted to the main board. It cannot be expanded, as the addressing chip (PAL) is limited to this size. The sample memory consists of 16 x 41256 DRAM chips (32k bytes each). Emax sequences as well as samples are stored in this memory. The total memory cost $221.76.

Digital Sampling The Emax samples monophonically, at 12 bit resolution via discrete ADC circuitry. This is includes a DAC and comparator, and a 7 pole anti-aliasing filter. The Emax replays eight voices via eight channels at 12-bit resolution. It uses eight Analog Devices 6012 DAC’s. The analog filter (see below) acts as the reconstruction filter to smooth the “stairsteps” of the signal.

Analog Filters The Emax was launched before E-mu Systems developed their high quality digital filters DSP chips. Traditional 4-pole 24dB low pass filters are implemented, using the SSM2047 combined VCF/VCA chip. They are very nice, but don’t expect fat Moog filter sounds !

OS The Operating System is similar to the Emulator II, but with enhancements. It saw a number of improvements over the years, so get the latest copy. This varies depending on model.

Support Chips One standard 6850 UART chips provides MIDI and RS422 serial interfacing. The floppy disk gets the usual WD1772 controller. The floppy drive is the most expensive single component in an Emax at $250. Unbelievable !

Hard Disk The optional internal SCSI hard disk requires a SCSI upgrade, which is possible with later versions of the Emax. The drive is a Miniscribe (later Maxtor) 8425S with 20 MB of space.

Engineering Changes The Emax has had a number of engineering changes.

Circuit Board Versions There are 3 main circuit boards in the Emax, the digital board for the processors, memory and E chip (sometimes this sits on a daughter board), a front panel board for the controls, and an analog output board. The digital and analog board went through three main versions, as the Emax was developed with further hardware features and as bugs were fixed in the electronics.The digital board versions are important as they determine whether a SCSI interface can be added.

  • Version 1 – initial digital board found in just the first few basic Emax’s – it cannot be upgraded to take a Hard Disk or SCSI
  • Version 2 (PC326) – has 24-pin boot ROM, SCSI controller chip socket and can be upgraded to HD/SCSI with modifications.
  • Version 3 (PC333) – already has a SCSI controller socket and 28-pin Boot ROM. Easy to upgarde to external SCSI, especially if the Emax is already a HD model.

The PCB’s have a couple of humorous comments on them, a gun holding Emu – Rambird (aka Rambo) is on the digital board, and “Emax HD no more floppy seconds” on the HD analog board!

Verdict The Emax brings the Emulator II sound to a much wider set of owners, with 12-bit sampling technology at a lower price point. This was the first use by E-mu of a custom DSP chip (forming the basis for future Emulators). However the memory could not be upgraded, and the sound was not quite the same as the Emulator II – even though the designers kept may of its unique characteristics. A very desirable sampler, if you can cope with the memory limit!

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