Ensoniq EPS

Ensoniq EPS

The EPS (Ensoniq Performance Sampler) was one of the first few affordable samplers on the market. It was manufactured from 1988 to 1991 by Ensoniq in Malvern, Pennsylvania, USA. It was an update to the Mirage 8-bit sampler, as the EPS used a 12-bit sampling architecture.

The EPS had a straightforward interface that was easy to use, with configurable controls geared for live performance. The user interface was a 22 character single line vacuum fluorescent display. It booted from an integrated floppy disk drive (sourced from Sony or Matsushita), or from a SCSI drive connected to the expansion bay. The EPS came with 512Kb of RAM onboard. Ensoniq offered both a 2x (1Mb) Memory Expander and a 4x (2Mb) Memory Expander with SCSI interface. A company called Maartists offered both 4x and 8x memory expanders, allowing a total of 4Mb RAM. Extra RAM offered longer and higher quality samples. Because it used two processors, you could load and play up to eight instruments simultaneously, with up to eight instruments on reserve.

The EPS uses MIDI and can be used as a controller of other instruments, or linked to a PC or Macintosh.


The keyboard is of thick plastic construction of a dark gray color with 61 weighted keys. There are assignable pitch, modulation wheels, and two patch select buttons. The interior of the unit is accessed through by removing four hex screws and swinging open the the control panel.

The whole unit was configurable through a custom operating system (latest version: 2.49). After the system boots from the floppy drive, it flashes a "Hands Off" message while it calibrates its polyphonic after-touch keyboard.

An optional Output Expander module allowed you to access eight discrete mono outputs on the machine, allowing you to separately mix levels and effects for each loaded sample.

The key limitations of the EPS were its proprietary disk format, and a lack of support from Creative Technology, the current owner of Ensoniq. A 19" rack-mount version, the EPS-M, was also available in limited numbers.

This model was superseded by the Ensoniq EPS-16+, released in 1991. The EPS-16+ was pretty well identical to the EPS, with the addition of integrated DSP effects.


The EPS is a performance sampler -- it contains two processors -- so you can continue playing while loading another sample. The one processor handles the IO while the other is responsible for keeping the audio running without interruption -- this made the EPS especially useful for live performance situations.

The interface, although operating through a single line fluorescent display, offered rapid access to all functions by the intelligent way that functionality was broken into "Modes" and "Pages".

Modes were: Load, Command, and Edit.

Pages were: Instrument, Sequence, MIDI, and System.

In addition to eight soft instrument buttons, it had a number pad (0-9), four cursor buttons, a value slider, and 'Yes' - 'No' buttons.

Users could access pretty well any function with less than three clicks: Mode - Page - Number Pad.

There was also a dedicated button for Sampling, and setting the Keyboard range.

Three buttons (Record, Stop, Play) controlled the built-in sequencer (named sequences could be built into a Song)


Instrument pages would be prefixed by clicking a Mode (Load, Command, or Edit) -- yielding functions relating to loading, editing, and tweaking EPS sampled instruments. Instruments could contain a number of discrete samples which were patched into Layers - each with their own ADSR envelopes and keyboard ranges. A simple loop editor that allowed you to define envelopes, cross-fades, and sample start-end, and loop points in real-time made the instrument flexible enough to recreate just about any sound you could hear.


The Sequence pages allowed you to define sequences and songs. Simple quantitization was available, and a crude step-editor to tweak individual sequence elements. Sequences (with up to eight instruments playing simultaneously) could be assembled into Song Steps. In assembling songs, you could define the number of repetitions of each sequence that comrprised a song step. This made it relatively easy to score and arrange a song.

Sequences depended on having instruments being loaded into one of the eight instrument banks in the right order. You could save Banks of instruments which could be loaded in by a song sequence so that loading the song loaded up all the appropriate sounds into the right places so everything would just play when you started the sequencer.


The EPS supports polyphonic-aftertouch on its 61 keys, and therefore allows a fair amount of expression as a MIDI controller. It allows sys-ex messages to be passed over MIDI, and can transmit and receive on multiple MIDI channels simultaneously.


Because the EPS contained two processors -- sound generation and disk IO were handled separately. You could boot the EPS, load some sounds while playing the ones that are already loaded. Then sample in a new sound, only to find that you're out of floppies to save your precious sample to -- the EPS OS will allow you to go ahead, format another floppy disk, and save your new sound without the system function getting in the way of playing the audio.

One of the nice things about the EPS was that the boot disk contained everything needed to duplicate itself. You could create a bootable Ensoniq disk with a single command from the System page. Thus, if you had one boot disk, you had everything you needed to make another boot disk.

Repair Tips

Persistent key calibration (tuning) errors are usually fixed by reconnecting the interor connecting cable.

Problems with the cold solder connections can disable the vacuum fluorescent display; this is remedied by resoldering.

Since the ROM chips were in sockets -- sometimes after a couple years, the unit would fail to boot, and give strange characters on the display. Simply opening the unit and reseating the two ROM chips has saved it on more than one occasion.

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