Philips 22 rh 53

Page 1

THE QUALITY OF
THIS MANUAL IS

THE BEST THAT
l IS AVAILABLE

l PHILIPS

L MFE SYSTEM
LouusPEAnR Box anti-fin

Everybody knows the problems cropping up when a loudspeaitsr
C box must he designed. The msnniacturrr aims at the best
possible sound quality but there are several hindering tactors
tor which a solution must be round. on the one hand. the housing
,e oi a loudspeaker system must not he too lsrgei on the other
hand. the distortions in a loudspeaker system also play an
\- important role. When a small housing is made. the reproduction
oi the lower ireouencies is limited. With the introduction oi the
new Motional-FEEG- Back system one had succeeded in Elimi-
( hating the drawbacks oi a small luullspemter housing. in the
lowennre raitee where the cone oi the bass loudspeaker causes
i largo amplitudes. the dlslarclon is greatly reduced. Besldes.
one has succeeded in increasing the iraouency characteristic
" in the low-cote rungs considerably. ha a consequence. now
[ small boxes can be used ior n sound reproduction in which up
to how large boxes were required.

If

MFR-SYSTEM
HamALEnKABlm-n' ZZRHSJZ

MF )3 SYSTEM
HOGTALARE 221114512

Alla hanner ahltert do problem aom lnilnnei- sig uhr en hugialar-
knmhinotion altall knuatrucras. Man lulvu' unturiigtvis eiter
basis nihiliga lludkvalite men del iinus mango iaittnrer tlu vilkl
man mine to hhnayn. lesn lair iute bli mr star. men sanitidlz!
iiir lute iyudkvaliten enersattsa. Med en liteii li'ida minaltnr
mnjligheterna ati hterge de 1363 irekvsnserna pii rhlt slit.

ldet nya MFB-sysiemel Motional~reed-Bacit med dynnmlslt
hterkoppling hot man lyckaks ellminera tie olugeuheter aom an
liteh lads annars ior med slg. ldet llga registret dlar hashing-
taloreus ken rot sig med stnra umpiltuder hr dulnnlnnen
starltr reducerad. araautom her man lycltsu tilts lreitvens-
omrddet betydligt. Resultant har blivit nti man erhi'illll strict
ltldor med en liudltvaiite som tidigsre epdaat uppndtta med
hyhlp av stora lfidor.

\_.

F
Ms.

De demo or bekendt med problemstiltiten ved koostruhtlonen ai
et hdittalerltabinet. Fabrikanten adger at optiil den bedst mullge
lydlivslitet. nten (model: or der adsltilliee tnrhindreode ialttorer.
som md nyervindea. Pd den ene side this kabinettet lions were tor
start; pd den aided side spine: innrteuglngeui et hdlttalep-
system ogsd en vsesentllg rolle. Smu habinetter hegrienaar som
heltendt geogivelsen at de lave ireltvenaer. Mod lntroduittloncn iii
den iiye Motionsi-Feed»haclt system or cat lyklaedes st eliniiuere
dot lille hdittnlentabinctn ulainpar. l det lave ireltveneomrade.
hvor vandrlngen at buhdittalersnn memhrsn u meget stor. er
torvrmngnitgen reduceret gansire vesentllgt. Desiiden er det
lykltedes at gdre traitvenagspgen (or do lsveste irekvemmrider
hetydcllgi mere ratllnet. nette hetydsr. at man in er i stand til at
anveade stall Mittalerltahinetter i stcdet inr the store. som indtll
nu har vneret anvendt.

lndlx: cum. (1330411. cad-1321x3379

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Suki-ct (a wading-fin
1822 125 ill-ls

print-d In tho Netherlands

I To explain the working oi the new audio system. we shall iirst
. desi with general upects. Then we shall go into details.

. The box accommodates two output amplifiers: one far the has-

~ loudspeaker, and one tor the medium and treble lundspedkel'.
The ampllller tor bus reproduction is terminated with a
1 n impedance. the :lnumldil power being to w iioii l-izi. in
point oi tact. one and are same ampliller ia used ior medium

; and treble reproduction. However. this ampliilcr is terminated

, with a a-h load; thus. the sinusoidal power is limited to 20 w

. (1 kHz). aehitid the latter ampliiier there have been titted a
high-pus and a low~paas iiitcr each with a crossover point

l at about lsua lit. All ireouencies exceeding also Hz are applied
to the trehle loudspeaker; the trcouencics irom 500 Hz to
1500 Hz are applied to the medium loudspeaker. heinre this
ampultcr. a high-pass tiltcr with a crossover point ol sou Hz
clips the treouencies heiow sou Hz.

The input signal is applied lists the box to this high-pass {liter
and to a low-pass iiiter having also a crossover point oi son l-la.
in this low~pass (liter all lrequencies higher than soil Hz are
clipped. Because an audio system still iunctioning below as it:
may cause problems irumble by the record player. elm). n
high- pass illti-r has been titted behind the low-pass ititer.

This high-pass rilter clips all ireouencies below 35 Hz. subse-
quently. the signal is applied. Via an adder circuit and an output

-ai-npiilicr. to the ioudspesitcr. The purpose oi the adder circuit
will be discussed later on.

The bass loudspeaker is made up at a normal t" ivooier incor-
porallllg a "rag-order". This recorder" is the moat. impel-tin:
ieature or the entire system. iiecause the level at the sound heard
is proportional in the acceleration oi the cone, this acceleration
must be measured. This is done with the accelerometer. Behind
this ucceletallng recorder there is an amplilier stage wttti
which some mar! ireoueacy currecllons can be achieved. The
signal is then led touch to the aioremsnttoned adder clrcu .
isciore going iurthur mm the circuits. we shall he concerned
with [he worklng of the nectleralil'g recorder. Over the speech
and e no. board (I) has been titted. This pic. board has a hole
in which a ceramic element (2; is clamped with two rubber
blacks. Consequently. the element can "away" and react to cone
accelerations. with each acceleration. the element will supply
a voltage depending an m- accelerallnn. The ccrlmk: element
is on both sides provided with s droplet ol solder is). thus.
the wires are fixed.
Because the element must have an exactly deiined mass. the
weight oi the solder droplets has been exactly determined. A:
can be seen In thl circuit (9111 503) YJIO 9.3. Baud ll provided
not only with the scceleroioeter but also with a PET and two
resistors. With the ill-Mi: realstnr the element is kind oi
capacllive generator) I. tel-initialed with A huh-ohmic manta-ma.
owing to which the ireoueucy characteristic will be horizontal.
Owing to this high terminal impedance. the puliiblmyrol hum.
however. increases; consequently, the PET is used as an impe-
dance converter in this case. Contrary to the normsi method,
has actual method is based upon the isct that the signal is tilten
oil the drum; that is why a third connecting wire is not required.
To maintain the gate impedance oi a lunctiomFET at a high
level. the draimsource voltage must not exceed a certain value.
For this purpose the zener diode use has been iitted in combi-
nation with Ts-iih lesrtbcd basin circuit).
Now that the working oi the accelerometer with its appertaining
components LI itnnwn. we can devote our attention to the other
circuits - in the same sequence as in our iirst general approach
trig. at. The LC~mmhlnAuon $482-$549 iorms a Iowan: illtcr
ior the medium loudspeaker; the CLecembln-Y-(on 0551-5483
iorma a high-pass iiltnr tor the treble loudspeaker. The amplliier
is at the well-known type. To ovoid cross-over entirely. this
ampuliier hns been an adjusted that up to about i w it works as
a close A smpliilor. Upwards at l w. the Idllnlmem drilts tn
itmuiuABnn-lpufle.
The output atego accommodates completely complementary
Dariiugton transistors. To ensure the thermal stability 0! the
Burlington transistors, the quiescent current circuit includes
an NTc-rrsiator on the cooling plates ol those transistors.
Diode man has heen added to prevent any hsanucoiiecmr current
oi 442. This ourrem could ilow because the base voltage oi
T3442 coitid be increased so much by the bootstrap site can
I. it exceeds the Cuuelllnr VOIIIIE.
On the W at the scapililsr there is an active highepau filter.
which is connected between the bass and the emitter oi Issue;

the slope oi this characteristic is is dB/ocl. The input signal
Irons the box is appued to the input oi the lllter - either directly
os via R582 according to the position oi $107. The desired input
sensitivity can b. idyusted with Sim. The two input sockets are
in pulllel; in this manner the left-hm and the right-hand box
or seven! loudspeakers can he looped through.

The lat-rim switch sK-B cnaurrs that the box may he used
.- s left-hand and no a right-hand reproducer.
The input oi the low channel is provided with a low~pass lilter.

rw

which is connected between the bone nnd the emitter oi T5421.
The circuit is the mirror image oi die son-its mhepul iilter
with Tsaas. The slgnll la talten oil the Thou-emitter. which is
connected as an emitter iollower; the slope oi the characteris-
tic oi this illter is also is dB/ocl. The signal is applied to a
high-pass filter consisting 5! caps. case. itssz, 1655,5556
and T5422. This high-pans (titer has the iunctiop or a rumble v
iilter. and clips all ireoueiieies lower than about 35 K1 with .
12 dn/oct. The Ireoueary characteristic is. consequently, the

same as that at a inuospeaitcr with a natural irsqueocy oi is lit. _,
subsequently. the signal, now having a ireoueocy range iron-i

about as H: to son iii. is applied to the adder circuit. Besides.
the iredhaclt signal. ohtaiood from the accelerometer. is

applied to this circuit.

This adder stage gains by about a inctor l. The signal. combined
in this stage. is then applied to the «in-W output ampliiier. The
circuit ol this ampliiier is almost equal :a that oi the zo-w
umplliier tor the high arc the medium signal.

Contrary to the iii-w amphiier. the lo-w output ampiiiier
includes a dliierentiai ampiiiier on the output in order to avoid
problems With the extra feedback behind C519.

Moreover. it should be noted that :his ampliller la ndjltsled in
class a. As. however, only the bias loudspeaker is driven and
the ireouency range does not exceed 500 Hz. the signal hardly
contains higher harmonics. Thus. crossover distortion will not
tithe place.

The luudspeaker 'llh the accelerometer has already been dealt
with so that there remains to he discussed the ireoueocy
correcting stage iistli Tsutt anti T5s35.

The input signal t'or this circuit is supplied by the collector ot
Tsuai. in the collector CircuiL ci this transistor. the true: diode
msv serves to smooth the supply voltage. ii a normal elenlmlyflc
capacitor had been used. t circuit would have heen oscillating
in the low-lrequenci rouge o to about 75 Hz. the correcting
stage has a list frequency aracieristtc trig. 4). Below about

75 Hz the characteristic oi the signal has a slope oi s dis/oer:
this is to be attributed to the natural trccuency oi the
lcudspeaucr which is also ahout 75 iia. Below the resonant

point oi a loudspeaker. the frequency range decreases by

12 dis/pct. when the signal is led back in accordance with such

a characteristic. the smpliiier may become unstable. However.
when the slope of the characteristic within the loop oi the
circulating signal is E dis/ocu. the iustahillty problems have dis-
appeared. When then the irsquency characteristic ll ted heels

by less than 5 dn/oct. with 11552551 and can. the decrease at
the loudspeaker is reduced to s its/net. The gun oi the cit-riot

is law: in the straight part at the characteristic the signal
ampliiied only a iew times. Below 15 Hz. the gain increases to
about a iactor 20.

A measuring error on point a with regard to the acoustic powr
output oi the lwdlpeaku compensated by 3841.650. cm

and c522. Vin c523. the signal is taiten oi: the couector oi
T5435. The signal which is applied directly to €506 at the adder
circuit. muy he adyusted with trimming potentiometer disc.
Finally. there is a special detail shout the switching on/oli oi

the boat. Ful- this purpose. a circuit consisting oi TS(-45...TS-uo.
has been titted; this circuit regulates switching on/ou in com-
bination with the mwly unit. This unit can he switched on and

oil with the mills switch. To the bass oi The. the input signal
is applied directly.

This signal is nmplilled and reclined in the circuit. when the
input signal exceeds 145 mv. the Schism-trigger iTSi-ia.
Tsssu) changes over. and actuate a relay. Where no input

signal is applied. the relay remains in its rest position. How~
ever. it may also ocour that. alter some time. no signal is
applied. Than. the SchmittLtriggor changes over again alter

about 2 minutes. so tbst the relay returns to its rest position.
Relay RE actuate] the relay contact as which. in turn.
switches oil the voltage in the supply line «ll-As. sis long as the
supply unit remains switched on. the lines o6. .7 and .5 remain
line.

So it means that the prenmplliiers receive o voltage when the l
bolt is switched on. As soon as an input signal is being applied

in the box. RE changes liver: thus. the output ampliliers also

receive directly a voltage. These ampiiiiers keep their supply
voltage as long as the boxes are being used ior reproduction

and (or at most 2 minutes alter the reproduction has been

iinished.

in both cases - with an output amplifier switched on or oil -

a pilot lamp in the box is hunting. The lamp is burning weariy

when the output anipliiler is switched on, and normally when

the output amplifier is switched oil. .

The aupply unit is norm-I; in it. only the supply voltage [or the
pro-amplifier (.7) is smoothed electronically (1545135452);
besides. this circuit accomplishes by means oi can mat this

voltsga gradually receives the desired level. This is necessary

to prevent undesired switch-on phemmeul. In particular with .
circuits having a iroqusuey range with very low values. this
[actor should be taken into account.

cshuno