Roland Vocoder SVC-350 Service Notes page 3

MOUII
IIUIM -Deiail-
uec. 8,1979
CCMPR3USCR
After ampi— fled by 14-54d3 through Mic Head Amp or. Ar-127,
Mic 3ignal ijoea to id i,pin3 5-7) whoje gain i3 reversely
proportional to she control current from Q5 emitter.
The aic 3i,sr.ai coming from IC2 pin 7 La full-wave rectified
by IC3 (pir.3 5-7), Dl and D2, peak-voltage detected by IC3
Ipins 1-3;,D*, jncothed to DC voltage by IC5 (pir.3 1-3), ani
7-1 converted by IC4 (.pins 1-3),Q5 • Connected acros3 IC4'3
pins 6 and 7 in parailed with feedback resistors is IC1 3A6CJ.
As the mic si-gnai increases, Q5 output current increases,that
causes 3A662 conductance to increase, lowering the gain of
IC4 (pins 5-7; to retain either half peak output from $oing
above 10V (2OVpp).
In thi3 7oc oder, there are two other compressors similar to
the Mic compressor ir. configuration: in Guitar preamp ohain
and synthesizer filler output channe-.
SXPAIJDSR
Ihe output -voltage at pin 1 of IC5 io al30 received oy
3x?ander3 IC17-20, 322 and 32;. The current from 322 ^323)
varies in the same direction a3 in the Compressor, but with
thi3 fashion, 3igr.al flew rate through IC13 (IC2G/ is ii-
reciy proportional to the control current; the more current
flows, the moire signal flows through IC13.
ANALYZER FILTSR
Ten 3?Fs witri a nign Q consisting of ICs (s. g. IC<?G and
IC55; covers most of the audio spectrum - 3peech signal.
The 3ignal from the compressor is pre-emphasized through
IC5l?in3 5-7) and fed to the filter bank which slices up the
3pectrum. Each. 3lice goes to a iiode(e.g. D37) where its
peak is letected, 3moothed and is fed to the 7CA in the next
3tage filter -Synthesiser filter. This i3 a control voltage
that is proportional to *.he jtrer-ght of that slice.
J "/:.rTHE JIZEli ? IL :2h
Trie Jyr.th^ji»'.«r f-itor u a jet ^f oar.'i?-^ filr-jr, .ier.-
ticai to tnose of the Analyzer 3ection,iJfed by tne o.^n-
■ii •-•oming througn either IllSTRUMENT or joJAR preaap and
IlAiuMCIIICS circuit, i'he filter bank 3lice3 Jp instrument
3ound jpectrua into banas :n the 3aoe way Analyser filter
ioea on the jpeech 3pectrua. Each 3lice tr?n connects to
•/oit'dge— :ontroiied amp -7CA.
7CA
During an absence of signal in Analyser 'ilterie.g.IC5O
IC55.-C63), negative peaks of trian^alar *ve jn pin 1J of
IC33 is kept positive -determined by 7?.3 • with respect
to the pin 11, disnabling 3witcnir.g gata -iC;2.
When the voltage from ICc3 increases to . scae extent, it
exceeds lower portion of trianiguiar wave,au3ing IC33 pin
13 turns to "H" wnich in turn gates 1C32 :. When pc3itive
going triangular wave reaches above the /ctage on pin 11,
pin 1; tum3 to "L" and IC32 turns off. Ths signal flow
rate througn IC32 aepend3 sn the width of lulse :*r:a 1C33
and pulse width is proportional to -Co; ;;trcl ventage.
pul3e3ating rectified 3ignal3 are smoothedwhile tr.ey are
passing through the next fixter -IC39.
TOCCDiiR I1CLD
IC33 pin 10
IC33 pin 11
IC63 pin 7
IC33 pin 1
-rj n
HUH CCNSCIIA3T FILTER
This H?F allows only high-frequency cccc'-.ent -n signal
from tne Mic imp :o pass 30 aa to coaper.sa; f^r r.igh-
"requer.cy range .r.oapub^e .:' reprcciuc-.ior. : t.ie • :c :aer
rhu 'jirrj;; .j •: i.-npoj.jd ;f QC.Q3 'lnd Q.X. *hen the
KCLD jacit circuit :pen3, and 5Cm3 later, the Q2 output
mcrea3*3 in -.r;-* positive-going to turn on tne gate Ql
and to jnunt 175 0 input to the ground. On the other hand,
a 3ignal supplied through D7 turns FST 3witch IC53 (pins
10-12) on, turning 1C53 (pins 3 and 9) off, disconnecting
H3O7 from iiscr.argir.g path, increased discharging time
constant can r.old previously charged C135 for 7-10sec.
7CICS JHARACTCR CONTROL
Because resi3*or3, -R726,728, 730 connected to
wiper terminals of CHARACTCR CONTROL pots, are different
in value; the higher the frequency, the ^arger the value:
overall frequency response offer3 de-emphasized charac
teristics .
SOUNU DETECTOR
During an absence of musical instrument's signal,7cccder
3hut3 inadvertent 3ignal3 in under the coordination of a
system. The sound detector i3 the first 3tage of the
3y3tem.
IC45 (?in3 ~-~}, D51 and D52 make up a full-wave recti
fier, the average output voltage is peak of the 3ignal
ielivered by IC21 pir. 1, then IC45 (pins 1-3) provides
adequately smcctn ^C output from pin 1.
•hen this vc.tage - at pin 4 of IC37 - exceeas voltage
at pin 5, pin I goe.s to negative, cutting Q29 off, removing
the ground rrea pin 2 of 1C17(IC19J. Expanders are now
ready to function.
IC37 pin 7 al3o 3ees Sound Detector's output and deter
mines pin 1's output pulse rfidth which in turn regulates
H?F sigriHl flaw rare. While Synthesizer filter 7CA re
sponds to s^e-izr. 3 peer rum, H?F .'CA to tne instrument' 3.