Roland SDE-3000 Service Notes

FEB. 6.1984
SDE-1000/3000
n
SDE-3000 DESCRIPTION
The following sections concentrate to the circuits particular to SDE-3000.
For other circuits not described, refer to those in SDE-1000.
HEAD AMP
Has a gain range of 2dB(1.26) to 30dB(31.6).
DELAY OUT/PHASE SELECT
This stage has 9.9dB gain. When TR78 is conducted, the delay out is 180°
out of the direct signal.
MIXED OUT
Changes its gain with UNIGAIN settings:
7dBwithUNIGAINat +4dB
-3dB with UNIGAIN at -20dB
CVIN
Level shifts 0 to +12V inputs to ±4V.
INV OUT
Level shifts ±4V inputs to 0 to +12V.
MOD DEPTH
Controls the amplitude of CV from CV IN or LFO with 0 to +5V coming via
IC27Afrom RM8..
CV LINEARIZER
The output voltage at IC49A pin 1 is normally 0V.
Has a unique voltage response curve to compensate for nonlinear V/C charac
teristic of D62 varicap in VCO circuit.
IC31 MAIN CONTROLLER
DBO, DB1 Address offset data fx companding RAMs.
(See COMPANDING RAMs.)
DB4 Strobe . Latches data from companding RAMs into IC32 on
rising edge.
DB5, DB6 Signals D/Aor A/D cycle.
Cycle DB5 DB6
D/A H L
A/D L H
DATA COMPANDING
Audio signals are digitalized with a 12-bit Analog to Digital Converter before
stored into RAM. In ordinary D/A conversion, the number of significant
digits decreases as input signal level decreases, lowering relative resolution.
The reason is well illustrated by comparing A/D system to a voltmeter.
Suppose the voltages ranging from IV to 100V are read with 100V scale,
smaller voltages cannot be read accurately. The meter has to be switched
down to lower ranges to allow the pointer stay around the middle of the
scale. The same concept, named companding, is applied to SDE-3000 A/D
conversion circuits.
Companding
Input Signal
Q
Peak
Hold
IC2, IC3
Comparator
IC6, IC7
isr
■
RAMs
IC1
I
IC12
Companding
RAMs
IC41
IC43
Fig. 2
The ideal companding system will work as follows:
With 100V, 10V and IV input applied to the comparator (IC8) at different
time, the D/A converter outputs the same successive voltages which are
attenuated by IC10 by 1, 10 and 100'respectively before comparison. Conse
quently, the A/D converter has a higher resolution 100 times that of direct
conversion at 1V input. The same procedure takes place, when RAM stored
data are D/Aed as a delay signal, to correctly restore the voltage to the origi
nal level. Examples of companding effects are shown in the photos below.
Note that waveforms at TP-1 will change drastically as the input varies in
level, especially at a border of ranges where companding system works even
for one waveform cycle of low frequencies.
These phenomenons should be made familiar to the eye of observer to avoid
misjudging.
INPUT
100Hz
TP-1
5V/div
■ A/D cycle
- D/A cycle (RAM stored data)
INPUT
40Hz, +5dBm
IC8 pin 2
2V/div
TP-1
10V/div
5ms/div
INPUT
40Hz, +5dBm
IC8 pin 2
2V/div
TP-1
10V/div
5 /is/div
11

Roland SDE-3000 Specifications

General

Type	Digital Delay
Output Impedance	1 kOhm
Inputs	1/4" phone jack
Outputs	1/4" phone jack
Total Harmonic Distortion	0.05%
Power Supply	AC 117 V