|
Emulator I : Technical Architecture
Architecture The
Emulator I is either a 2, 4 or 8 voice polyphonic digital sampling keyboard, which uses one Z80 microcomputer to reproduce 8-bit digital samples of any musical sound or instrument.
The EI is entirely controlled by computer software
which is loaded from diskette when it is powered on. The Z80 processor runs at a clock speed of 5MHz. The Boot PROM is 1kbyte.
The Z80 is utilised as a scanner CPU (descended from the Prophet 5 and Oberheim designs created by E-mu
Systems in the 1970's), to regularly check the status of the keyboard, the control panel buttons, the control wheels and the footpedal and switch.The Z80 also runs the operating system, which is always loaded from disk. This program is 8k
bytes, leaving 120k bytes of memory for samples.
Sample Memory The
128 Kbytes of sample memory on the Emulator consists of 64 x 16k bit DRAM's (4116's) fitted on the left hand side of the CPU board. The memory can not be upgraded. There are five Direct Memory Access (DMA) chips (the AMD9517A), that read
the samples straight out of memory and deal with pitch shifting.
Voice Cards There are up to two 4 channel voice cards for converting the digital signals to analog. These cards are fitted to the base of the instrument
on the left hand side. The samples go via a COMDAC digital to analog converter chip and then the SSM2044 filter chip and 5534 Op Amps.
Digital Sampling The Emulator I samples at 27.777kHz and at 12 bit resolution, but stores samples into memory (and disk) as 8
bits - by using hardware compression and expansion. This ups the dynamic range from 42dB, to a more respectable 72dB.
A tracking filter further reduces high frequency noise at the outputs, by closing down a low pass filter
(SSM2044) as the pitch played descends down the keyboard. The SSM2044 is more familar as the VCF in the Korg Poly Six and PPG 2.2.
Hum that Again
Our Emulator I has a rather noisy output, well around -50dB of mains hum on the output to be precise. It's worse on the jacks, than the XLR's.
Diskette Drive The EI uses a full height Shugart SA400L 5.25"  floppy diskette. This drive can store up to 180k bytes on
a Single Sided/Double Density diskette. The Emulator I makes use of 128kbytes on the diskette. The format of the diskette is unique to the Emulator I, and requires the Emulator I formatting program. We have brand new Shugart SA400L drives
in stock, email us for details.
Diskettes The EI uses SD/DD soft sectored 5.25" diskettes,  although DS/DD soft sectored 5.25" diskettes can also be used. 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 Imation DS/DD.
There is essentially no difference between single and double density media, however high density media is very different, and
should not be interchanged with single/double/quad density media. It has different magnetic properties (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.
Revisions The Emulator CPU and Output boards went through a number of revisions. The last known revision was Rev 4, which is
used in serial number 440. Most Emulators will have Rev 3 or Rev 4 circuit boards. If you have one of the first 20 Emulators manufactured, you almost certainly will have the Rossum kludge
retro fit - which adds the envelope release (Rev 1 ?).
Schematics The Emulator I schematics, service and operation manuals have been kindly denoted to The Emulator Archive. These
are available for service problems, contact us via email. The Audities Foundation is a non-profit organisation that also has copies of these manuals. You can visit them at
www.audities.org
|
Site Options
Diskettes
* Debug EPROM's
* Fuseholders