Arp quartet service manual

Page 1

GQUWW

INTRODUCTION

The ARP Quartet is a compact, preset/variable syn-
thesizer with four selectable voices-polyphonic
brass, string, organ and piano. While the voices
alone are realistic, combination of voices simul<
taneously chOsen do not always maintain their
individuality. The new sounds which appear add
greatly to the flexibility of the Quartet.

Most of the circuitry in the Quartet is fairly simple.
For that reason, the circuit descriptions have been
kept succinct, dwelling only on areas that may
prove new or confusing. '

SCHEMATIC TERMINOLOGY

In the Quartet schematics, a Boolean mnemonic
code is employed to identify logic control lines
running between circuit boards. For example,
where 3 Brass voice control line was identified, it
was represented as mnemonic FE) . Everywhere
3 mnemonic is shown it indicates a physical
connection to all the other identical symbols. A
. connection is indicated only if the contents are
identical in the different flags. That is, the_s'ymb_ol
E) is NOT connected to the symbol [1 TR) .

In addition, the flags give an indication oi the expect-
ed logic levels that Will appear on that line. On the
line beering this flag, [30?9 , a logic 0 will appear
whenever String voice AND Solo have been select~
ed. (A plus sign indicates an OR lunction. An
elevated decimal indicates an jiNVD function.)
Even the complex flag LVIB fSQ SI) trans-
lates to "A Logic 1 will appear wheritlie Vibrato
switch and either Brass or the combination of
the Solo and String swttches are closed."

Using the Boolean mnemonic code makes it possible
to .follow control lines through the combinatinnal
logic to see how they are "assembled" for differ~
ent voices. Let's take the example where, by design,
the vibrato circutt is enabled when Brass or Solo
Strings is selected.

The flag for solo Strings is SQ;S>, indicating
a Logic 1 will appear if both String voice AND Solo
switch have been selector],

The flag for Brass BE) .

with the use of an OR gate, a new flag is created,
3+ 50 ~ 8} , indicating a Logic 1 will appear if
Brass is selected OR String voice AND Solo switch
are, both selected. This new line is used to enable
the vibrato circuit.

MNEMONIC CODE TABLE
Push Switches

Plan =P
BraSSZB
Strings=S
Organ=0

Tab Switches

TromboneTB
Trumpet=TFl
CellrFC
Violin=V
Percussion=PZ
Solozso
Organ=OR
Celeste=CS
Piano=Pl
Honky Tonk=H
Vibrato=VB

NOTE: Flags shown on the schematics are present
when only one push switch is selected at a time.
Troubleshooting should be done on one voice at
a time.

The connector numbers also help in tracing paths
through the Quartet. Connections are shown in
this. format:

PlI-4C

connector nunibci pin nuiiibei--destination board

Pl Ill will be connected to J] 1-4 on Board C.

For those who alt: unfamiliar with European schema-
tics, grounds aru shown as a connection to a single
horizontal bar. A 5.6K resistor Will be written as
5K6. Sonie capacitors tire listed in NANOfaruds.
An 4n] capacitor translates to a .0047 microfarad
capacttor.

CIRCUIT DESCRIPTION
Board C

The ARP Quartet uses a master oscillator and top
octave divider to generate the pitches for the 49 note
keyboard. Located on Board C, the master oscillator
sends a ZOOIMHZ signal to an MK50242 divider. This
generates the twelve pitches of the highest octave,
which are routed to their respective TDAiOOB pro-
grammable gated divttleis, one for each note of the
octave, Depending on the gate selected by the. key
contact, different levels of division (octaves) are

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selected and sent to another set of internal dividers to Board F
be converted to separate 2', 4', B, and 16' pitches

of that note In addition, the keying envelope is On Board F1 le3 is a two pole VCF for the Brass
used to control the voltage level of the signals being velces. The String voices are sent to the three delay
fed to the final divider stage. This results in a very lines. Signals are shifted and clocked through the
flexible keyboard gating system for convincing TDA1022 "bucket brigades" by their respective low
POIYPhonic voices. The 2, 8', and 16' pitches leave and high frequency oscillators. Honky Tank and
Board C and are sent to Board F. Celeste voices are also routed to the delay lines but

one delay line is disabled for these voices by the
flag at J10-4B.
- c PIYCH Jlfl

'"° W m" m The strings squelch circuit shuts off the string signal
when the input level to the delay lines is low enough

to cause noise problems.

(KY
comm 2'

I All the Slgnals are sent to the Mix Preamp and then to
the Output Stage (THO).

Board B

be

._ ,_..I Loglc levels to control channeling oi the signals to
the proper circuits, along with envelopes to control
the Brass VCF and the delayed vibrato, and the Key-
board Gale signal for the keyboard buss rod are all
generated on Board 8.

Boards A, D, E

tango; The Power Supply (Board A) and the Controls Switch
Board (Boards 0 and E) are sell explanatory.

ENVELOPE BOARD

lU llU
powen ll 7 7 7' I I
SUPPLY II J) .I'.1 Jll)
BOARD m .H F
. FILTER/DELAY LINE BUAHD
A l l'l'. P13

.l,

KEY CONTACT BOARD
(under keyboard]