Emulator II: Technical Description

Architecture The Emulator II is an 8 voice polyphonic digital sampling keyboard, which uses two Z80 microcomputers to reproduce 8-bit digital samples of any musical sound or instrument. The EII is entirely controlled by computer software which is loaded from disk when it is powered on. Both the Z80 processor's run at a clock speed of 4 MHz.

The first Z80 is utilised as a scanner CPU to regularly check the status of the keyboard, the control panel buttons, the control wheels and the footpedal and switch. The main Z80 runs the EII operating system, which is always loaded from disk, after the initial boot program has run directly from EPROM (Boot in Progress). The primary CPU takes commands from the scanner CPU, and controls the micro controller, generates envelopes for the analog circuitry and interfaces directly with MIDI and SMPTE. The micro controller replays the samples from memory into the analog processing output channels. Seven of the eight channels are identical, however the first channel has additional circuitry to create the sampling function.

Sample Memory The 512 Kbytes of sample memory on the EII consists of 64 x 64k bit DRAM's fitted on 2 circuit boards. Memory prices had dropped by the time of the release of the 1 MB EII+, and 32 x 256k bit DRAM chips were used instead.

Engineering Changes The Emulator II has had a number of minor circuit board changes to address early problems with MIDI, SMPTE, display and power problems. EII's built since June 1985 (serial numbers above 455 and 900), seem to have had no subsequent engineering revisions.

Analog Filters The EII has analog 4-pole 24dB filters (SSM2045) for each of the eight voices. They sound very pleasant - although the bass drops off when they are driven into high resonance values. They do not sound like a Moog filter ladder ! The main Z80 generates software envelopes for the filters and VCA's - they are therefore consistent and they can be fast. The minimum envelope attack time was reduced by 4ms as an upgrade to the EII.

That Sound The EII has a distinctive quality sound, which belies the use of 8-bit sampling. It does not sound like a Mirage or an E4 Ultra set to 8 bits! The warm analog filters and the grit of the low sample resolution gives the EII a desirable character from acoustic guitar to bass synthesizer. The EII is best suited as a keyboard instrument, rather than a sample wrench.

Digital Sampling The EII samples at 12-bit resolution, but stores the samples into memory (and disk) as 8-bits. This is done by using hardware bit compression and expansion, from a DAC chip used in telephone communications. Remember this is before CD players made DAC's cost effective. The digital to analog converters are 6072 companding DAC's. Analog to digital conversion for sampling is done via successive approximation with one of the DAC's. There is no ADC on the EII - except for reading the analog controls.

Sample RAM had to be used efficiently due to its very high cost in the mid 1980's, and is therefore limited to 512 or 1024 KB. 16-bit sampling would have made the EII too expensive to produce.

The EII makes extensive use of CMOS/TTL integrated circuits, with over 150 chips spread across the memory boards, the digital board and the analog output board. No custom chips were utilised - except for the filter chips which had already been designed by E-mu with SSM some years before. This large number of chips makes the EII a warm instrument with a large internal power supply. It also means it is less reliable than modern day electronics (which have a small number of surface mounted components). The EII should no longer be gigged or moved about - and temperamental problems often develop on well used examples. Take care of this baby.
 

The Emulator II uses 5.25" floppy drives, which are well past their designed life span. Replacement drives are no longer manufactured, and 5.25" DS/DD media is now hard to find, and less reliable than 3.5" diskettes.

A replacement 3.5" floppy drive is an attractive option. We have researched and proven a solution using new 3.5" drives, and we sell a complete upgrade kit.
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The EII uses DS/DD soft sectored 5.25" diskettes, High quality diskettes are recommended. Do not try and use HD diskettes, or DD diskettes that are hard sectored or IBM formatted. They will not work.
We recommend and use Imation DS/DD soft sectored diskettes.

Why not High Density ?
There is a difference between double density media and high density media, and they are NOT interchangable. High density diskettes have different magnetic properties; a higher coercivity, requiring a higher write current from the disk drive.

Formatting HD media as DD is not a good idea; the media will be too weakly magnetized, and your data may be completely unreadable or may fade away after a while. These problems are worse on 5.25" disks than on 3.5" disks because the difference in coercivity is greater for 5.25" media, but they exist for both types of disk.

You cannot reliably distinguish between 5.25" HD and DD media if they are not labelled. There are a couple of ways of guessing: DD media usually has a hub reinforcing ring (but not always), while HD media generally does not. The color of the media also tends to be different; HD media is darker.