Audio Pro A4.14 Zero User manual

LIST OF CONTENTS
1. TECHNICAL DESCRIPTION
1.1 Power Supply Circuits
1.2 Autom tic ON/OFF
1.3 Overlo d protection for Midr nge & Tweeter
1.4 Sign l Amplifier Circuits
1.5 B ss Circuits
1.6 Ace-B ss Circuit
1.7 Midr nge & Treble Circuits
1.8 Power St ge for Woofers
1.9 Power Amplifier for Midr nge & Tweeter
2. FAULT FINDING
3. ADJUSTMENTS
4. SPARE PARTS
5. ENCLOSURES
5.1 Circuit di gr m 2-141502 (A4-14, S/N through 12399)
5.2 Component l yout 3-141504 (A4-14, S/N through 12399)
5.3 Circuit di gr m 5520991-01 (A4-14 Mk2, S/N from 13400)
5.4 Component l yout 4-80150 (A4-14 Mk2, S/N from 13400)
1. TECHNICAL DESCRIPTION
1.1 Power Supply Circuits
Unregul ted volt ges +30V & -30V supply the Power
Amplifier & lso regul tor for ±15V
-15V supply tr cks +15V in order to void tr nsients
& oscill tions when power is switched on or off. The
positive supply must dec y f ster th n the neg tive
supply when power is disconnected, which is ssured
by 2k2Ω dummy lo d (R101) on the +30V c p citor.
1.2 Autom tic On/Off
The Auto ON/OFF circuits re powered vi D201,
D202 & C201. The power tr nsformers & the uto
ON/OFF circuits re powered s long s the spe ker
A4-14 is plugged in to live outlet. The rem ining
circuits re powered only in "ON" st te when rel y
K101 is closed.
The udio sign ls enter vi pins 3 & 5 in DIN
connector J301. The other A4-14 in stereo p ir
receives sign ls vi pins 3 & 5 in DIN connector
J302. The sign ls enter the mplifier circuits vi
push-button switches S301-S302 which select Left
or Right Ch nnel.
The input st ge of uto ON/OFF, Z202 (1,2,3) works
s mplifier with g in -7 determined by feedb ck
network R204, R205. D208 & D209 limit the mplifier
sign l to ±7V. The second st ge, Z201 (1,2,3) works s
n mplifier with g in of ~2,000 t 500Hz.
The sign l t pin 1 is limited to +7.0V/-7.0V. Z201
(5, 6, 7) plus tr nsistor V201 works s Schmitt
trigger with ON level pprox. 7V & OFF level
pprox. 5V. The input, pin 5, senses DC volt ge
which is obt ined vi diode D211 & c p citor C206.
Tr nsistor V201 drives rel y K101, which connects
power to the udio circuits in A4-14. When switch
S201 is in "AUTO" position, rel y K101 will open
bout 5 minutes fter the sign l t the input
dis ppe rs. The time rel y is determined by C206 &
R210. During testing you m y shunt R210 by 100kΩ
to obt in shorter OFF-del y.
When switch S201 is in "ON" position, the uto
ON/OFF circuits re byp ssed & A4-14 rem ins
perm nently ON.
A thermistor TS3-75 senses the temper ture of the
he tsink. When this temper ture is too high, the
thermistor resist nce becomes so low, th t rel y
K101 opens.
1.3 Overlo d Protection For Midr nge And Tweeter
Z202 (4-13) cts s n overlo d protection device
which is ctu ted if there is risk for d m ge to the
midr nge driver or the tweeter.
The volt ge cross the voice coils re rectified in
diodes D220, D219, & the rectified volt ges ch rge
c p citors C212, C211. The time const nts for
disch rge re longer th n the ch rging time
const nts. If the volt ge t Z202 pins 5 or 6 exceeds
threshold v lue ( pprox. 3.4V), the mono-st ble
flip-flop Z202 (8-13) is triggered for 10 seconds.
This c uses V201 to be shut off, so rel y K101
opens & A4-14 is de-energised for 10 seconds.
1.4 Input St ge
When the B ss-Blend switch is off, the sign ls enter
vi R302, C302, R303.
When the B ss-Blend switch is ON, the b ss
frequency sign ls in left & right ch nnels re dded
vi filters C301, R301 & R304, C303, R305.
C301, R301 is high-p ss filter with cut-off
frequency 100Hz. Lower frequencies re ttenu ted
by f ctor of 2.
R304, C303, R305 is Low-p ss filter with cut-off
frequency 100Hz, & ttenu tion 1:2 rel tive filter
R302, C302, R303.
The sign ls below 100Hz re summed t Z301, pin
9. Bec use of the ttenu tion introduced in e ch
ch nnel, the b ss level is the s me s when B ss-
Blend is not used.
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The g in is djusted by potentiometer R306 in the
feedb ck circuit of oper tion l mplifier number
one. After this mplific tion the sign ls re Split to
b ss circuits & midr nge/tweeter circuits.
5 B ss Circuits
The sign l p sses the b ss control circuits R311,
Z301 (12,13,14), which controls the sign l level to
the woofers. The b ss control circuits ffect higher
frequencies (e.g. 100Hz) more th n low frequencies
(e.g. 30Hz).
The b ss sign l then p sses vi low-p ss link
R313, C306 which forms one p rt of the crossover
filter between b ss & midr nge.
The next link is high-p ss filter, which cuts
frequencies below 30Hz 12dB/oct ve, & is p rt of
the woofer's tot l tr nsfer function.
1.6 Ace-B ss* Circuit
The power mplifier for the woofer, together with
Z302 (1,2,3,5,6,7) forms the ACE-BASS*, mplifier,
which c n be represented by the di gr m below
R412 & Z302 (1,2,3) sense the voice coil current in-
the woofers. Z302 (5,6,7) cts s b nd-p ss filter &
sums sign ls from & Ⓓ Ⓕ
The power mplifier for the woofer is inverting &
cts s dder for sign ls from & .Ⓔ Ⓕ
The p rt of the current sign l which is fed b ck Ⓕ
positively produces the neg tive output resist nce R
S
.
The p r llel reson nt circuit Lp, Rp, Cp is formed
by neg tive feedb ck of the current sign l vi the
b nd-p ss filter.
*ACE-BASS = Amplifier Controlled Euphonic B ss.
1.7 Midr nge And Treble Circuits
From the g in control the sign l is lso fed to the
midr nge/treble mplifier. Z301 (5,6,7) cts both s
high-p ss filter for the crossover (C502, R501,
R502) & s treble boost filter (R505, R506, C503).
The high-p ss link C504, R507, R508 forms the
second p rt of the crossover filter between b ss &
midr nge.
The power mplifier is of the inverting type, & cts
s, oper tion l mplifier for the treble control R510,
which is ctive bove 5kHz.
POWER AMPLIFIER CIRCUITS
1-8 Power St ge For Woofers
The sign l is coupled vi C703 to the input of the
power mplifier.
From the output, the sign l is fed b ck neg tively vi
R 709 & C704. When the sign l mplitudes re l rge,
neg tive feedb ck lso is provided vi network of
resistors & diodes. The output sign l is comp red to
the supply volt ge, & couple of volts before
clipping will occur, the sign l will be rounded by the
diode network so the clipping is soft.
The input st ge consists of differenti l st ge V702
& V707 fed vi const nt-current gener tor, V701.
The output st ge is of D rlington design with
tr nsistors V710-V711 & h s AC g in -1. V707
senses the temper ture of the output tr nsistors so
th t the bi s current is const nt.
V705 & V709 filter the supply volt ge for the input
st ge, elimin ting hum & other kinds of noise. (If
A4-14 "pops" when switched on, one of these
tr nsistors is prob bly shorted).
No-sign l DC-levels of volt ges & currents re
shown in the circuit di gr m enclosed.
To void on & off-tr nsients, the b ss mplifier is
ctive only when the supply volt ges exceed +17V,
so th t the oper tion l mplifiers lw ys work
properly when the b ss mplifier is ctive, When
diode D712 st rts conducting, the const nt current
gener tor V701 st rts working, & vi V712 ctiv tes
even current gener tor V706. The mplifier is
in ctive when these current gener tors re shut off.
1.9 Power Amplifier For Midr nge And Tweeter
The power mplifier is simil r to the b ss mplifier
but the diode network for soft clipping is not
included. The volt ge del yed on-function is lso
elimin ted, so this power mplifier is ctive t low
supply volt ges.
The sign l from the power mplifier is split in
p ssive crossover filters L602, C616, C617 to
midr nge & C614, C615, L601 to the tweeter.
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2 FAULT FINDING
A4-14 does not work
2 Set uto ON/OFF in position on
2.1 Check th t both the green & red LED re lit.
2.2 Check the power fuses & fuses F601, 602, 701, 702.
2.3 Me sure supply volt ges +33v ±2.5V, -33v ±2.5V,
+15v ±2V, -15v ±2V
2.4 To loc lise the f ult, connect test instruments s
follows:
-Tone gener tor to J301 pins 3 & 5. Adjust till B
is 42mV. Sensitivity in M x position, b ss &
treble pots in centre position. Comp re to
volt ge levels ccording to v lues in circuit
di gr m.
2.5 If fuses F601, 602, 702 blow during
me surement per Section 1.4, you m y
disconnect the woofers & repl ce midr nge
driver & tweeter by 5-10Ω resistors. Test g in
per Section 1.4 (sign l levels in points , , , ⒺⒻⒼ
& will of course be different). Ⓚ Ⓙ
2.6 Auto ON/OFF c n lso be tested with set-up per
1.4.
-Set uto ON/OFF in AUTO. The sign l t 2201
pin 1 should be 7Vp-p, & the sign l Z201 pin 7
should be 15VDC.
Rel y K101 Should close t 15mV/500Hz in
(R210 m y be shunted by 100kΩ to reduce the
off del y)
3. ADJUSTMENTS
3.1 Bi s Current In Power Amplifiers
After repl cing ny output tr nsistor in ny of the
power mplifiers, the bi s current must be
re djusted. Setting of bi s current should be done
while he tsinks re t room temper ture, th t is
immedi tely fter A4-14 is turned on.
Set potentiometer R722 or R617 till DC volt ge
between emitters of V710, V711 re ds 10mV Or
volt ge between V610, V611 re ds of 20mV,which
corresponds to 23mA bi s current.
NOTE: When output tr nsistors re repl ced, he t
sink compound must be pplied to both sides of the
insul tion w shers & to the temper ture
compens ting tr nsistors.
Check th t insul tion is dequ te & th t the power
tr nsistors re mounted fl t g inst the he tsink.
The he tsink must be screwed on to the PC c rd
before the tr nsistors re soldered in.
3.2 Neg tive Output Resist nce
After repl cing Woofer, or ny of the current
sensing resistors R408-R412, the neg tive output
resist nce must be re- djusted.
The woofers must be properly mounted in the
c binet, their voice coils must be connected, & the
b ss djustment potentiometer R311 must be in
centre position. Voice-coils must be cold ( t room
temper ture).
Apply n input sign l of 60Hz ±1Hz & djust sign l
gener tor till test point ( re ds 0dB (=0.775V). Ⓖ
Ch nge frequency to 180Hz +3Hz without ch nging
the sign l level of the sign l gener tor, & set
potentiometer R410 till volt ge t test point is Ⓖ
-5.5dB (5.5dB below 60Hz),
Go b ck & forth between 60Hz & 180Hz & re djust
if required until the difference is st ble t 7.3dB.
4. SPARE PARTS
Sp re p rts c n be obt ined from Audio Pro
Sweden, or from Distributors & Service Centres.
When ordering sp re p rts, ple se refer to seri l
number of spe ker, & component number per
Circuit di gr m 2-141504 resp. 5520991-01
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