Crown OC-150A User manual

ADDEmM SHEET FOR BC-1SOA INSTRUCTION mNUAL
Starting with sesfal nmber 2326, we introduced a new canvenlence
feature in the AC fine moniLor swiechLng,
The new circuitry nat only
swigches he line voltage Ants the meter cixcuie, but alss changes the
meser range EO 14QV* This eliminaees the need $a separately engage the
range %%itch and insurea the meter needle wcrn8tPle accidently damaged,
The redram schemtic pargial enclosed illustrates
the wiring
changes, There are no changes in the parts list, The foLlowing changes
way be inserted into the manual text,
1, Page 2, D, METER/MONITBB SWXTCR
delete SentencE within parenthesis
2, Page 7, 4, AC Z~NE HONITORING
ffrst seneence add: . , . AC line vsltage, and
the meter range is switched ts 140V,

INTRODUCTION
FIG, 1-1
With the purchase of a CROWN OG-150A, you have
g~~atly expanded the flexibility OF your Hi-Fi system,
Ysu now have output flexibility camparable %a the isa-
put versatility made famobas by the CROWN ii@-J,50A,
Once again, this CROWN product offers uncom-
promised value, not in frilly gimmicks, but in honest-
tg-goodness function; all at an attractive price,
Thio is nd to say that the priee is the only attraction.
The esthetics of ths Q3C-1508 sma&ly mat& the un-
eiueered styling af the acclaimd "^150A7? iiine, the D-
ISOA and the !C-1568, "t"he new f~ature~ are not
offered on any of our other products, and bring the
ultimate in output switchingand monitoring right to
your finger tips,
Even if thr; unit arriated in pedect condition, as most
do, it is advantageous to saw the packing materials.
They will prove valuable in preventing damage
shauld there ever be an occasion to transport or ship
the unit.
CROWN guarantees this equipment to perform as
specified. GROWN also warrants the components
and workmanship of tl-8i.s equipment to be free from
defects far a pesid af 3 years from date af purchase.
This warranty does not @&end to fuses, and Jar com-
panent or equipment damage due ta negligence,
misuse, shipping idamage or accident; or if the serial
numkr has been defaced, altered sr removed.
A copy of the FULL WHREE-EAR WARRANTY is in-
Please inspect the control center for any damage in-
cluded with this manualv The WARRANTY is subject
currgd in transit. Since the unit was carefully in-
t, the conditions contained therein, Upon receipt of
s~eaed and tested at the factor~r it left
the registration form, CROWN
issue a WARRAN-
unmarred. If damage is found, notify the tra~spoea-
~y TITLE. This title applies to the original end-
ti~~ company immediately* Only the consign@@ may
purchaser 3% well 3% subsequent purchasersh
institute a claim with She carrier for damage d~rin~
shipment. However, CROWN will cooperate fully in
You, the purchaser(sf, are responsible for accurate,
such an event. Be sure to wve the carton as evidence
complete records (sales siips, invoices, etc.) for
erf damage far the setippgr" inspeetian,
FULL coverage!

QUICK SUMMARY
The GrC-15QA is an GIUTPUT Ca3faaTFSBt CENTER. It is conneded in a hi-fi sl/slem
fier(~) and the speaker sys.$.em(s),
P. The meters rgad ~i%.ser VU in dB, ar rms equivalents a4 true peaks, in mEb,
2. Output fmm one, two, or three amplifiers can be monitored on the meters, one at a time, switch selected.
3. Up to three spaker systems, in any combination, are switch-selected fram Amp #1 input
4. From input #2, three headphone outputs are evailable; the rear panel electrostatic strip is direct; front panel
pcks 1 and 2 are switch-selected and fed through the attenuator switch on the rear panel.
Details blow:
A, HOLD BMnE COMTWBCS
O, MmEWMOWfTOR SWITCH
1,2 -deternine haw larag the metem wifl hold a 1 --VUPPEAK - when depressed, meters read
vo!bge reading when in the peak mode. rms eguivalenb af true signal peaks, ira volts,
Variable from rera %a infiniw.
When disengaged, meters act as 'BbU meters.
8, METERS
Meters calibrakd i~ dB,
1,2-can be used $0 monitor output signal ievels,
eithgr in VU 01" PEAK, Meter scales are
calibrated in dB and volt$, CAUf Never
adjust the mechanical adjust screws on the
meter Branti since they are adjusted as pae
of -$Re calibrathn procedure.
C. HMDPHCJaNE JACKS
1,2 ---connscted through headphone ssiector
switch and the @$%nuator switch to Amp #2
input, tf inbnded for use with Amp WP input,
an external jumper must be used bebeer?
Amp #1 and Amp #2 inputs, $&e Caution,
Page 42
2 --AC hl N E/AU D IO --- when depr~ssed, meters
are connected t:s monitar the AC rine ~~Ibge,
in volts* (The RANGE SWiTCM, E, will have %a
h swit~ hed ts the 146V scale to properly ad -
just the meter sensitiviv for the AC fine,)
When disengaged, the meters are canncctd
to moa itar thc noma f audio pragrams. NOTE:
BOTH metes display the Iina voltage when
AC LINE is dspressed* Additionally, when the
OC-lSQA is connected far 246VAC speratisn,
the two meter readings must be added (or
either meter multiplied by two) far%h@ actual
valtage read irng. St igRt variations ar@ normal
due to circuit bler~nees,

4'
3 -Amp #1 --- when depressed, signal from in-
F, SPEAKER SELECTOR SWiTCM
put #I is fed to meters,
1,2 -- HEADPHONES --. select headphone jack
4 ---Amp 82 --. when dep~essed, signal from input
1 and/or 2,
W2 is fed ta meters,
3,4,5 -SPEAKER SYSTEMS --- select arcysraif (in
5 --.Amp #3 --- when depressed, signai from input
parallel) of speaker %yst@ms L, 2 and 3.
#3 is fed to meters*
Routes signal from inpu"t.1 to selected
E, RANGE SWOYCH
ou tput(s),
1,2,3,4,5-determine the sensitivity of the me-
6 -. BNIOFF - AC power to meter circuib.
te~, bath in VU and in PEAK mades,
Full scale ranges are expressed in dB
and ssott~~ (See Impedance vs. Vof-
tage, Pawsr graph, page 17,)
FIG, 1-3
@. HEADPHONE AnENUATOR SWITCH
1 -Amp #I --. Signa I fed ts meters (when AMP #I
(Fed from Input #2)
is depressed) and to speaker seteclor switch,
then to selected speaker syslen3.
1 $2 ---selects the amount sf &Benuation desired
(see page 6) for either headphone jack (1
2 ---Amp #2 - Signa! fed to t~eters,(when AMP and 2) sn front pane[+
#2 is depressed) to electrostatic headphone
ELECTRQgT&Tbe
barrier stpip (D) I and through the aBenuator
switch (C) ts haadphsae selector switch, then
Barrier strip type campatible with ~elf-powered
ts headphone jacks on front panel,
~OXGS common to many types of eleetrosfatic
3 -Amp #3 -+ Barrier strip type - signal fed to
headphones* Connected directly to Amp #% input
meters anfy {when AMP W3 is depressed),
with no auenuatian.
Be SPBKER BUTPUTS
E. AC OUTLETS
U ngwltc bed, ava ila bls far pawering accessory
I
(Fed from Input 81 through speaker seiector
switch,)
equipment (1250 watts maximum),
1,2 - Dual binding post type
3 --. Barvier strip type
F. AC FUSEHOLDER
Use on!y type MDL 1/8 Amp fuse.

Amp inputs #I, tf2 and #3 all have isolated grounds, both channel-tom
channel, and from the chassis. Amplifiers with balanced outputs may be
used without problems.
Amp #2 input is connected to the front panel headphone jacks via the
headphone selector switch. Mechanically, these stereo jacks have
cammpn grounds. To keep input #2 balanced, the ground return for
channel I has been deliberately eliminated. (Strap "c ,see schematie, MI*
264.) Thus input#2 can k usedasa balanced input for metering only; no
signal will be present on channel 1 at the headphone jacks. The e1ectra.o-
static barrier strip may be used as a balanced output.
Most present-day amplifiers have a common ground between channels.
Thus strap "X" is not needed for normal operation. If single channel
operation is desired, then strap "X' must be installed, Additionally, a
similar strap could be added to all inputs, and thespeakt3rcables could be
reduced to 3-conductor ea bles.
-. Any load connected to a balanced output must have isolated grounds! Just
because electrostatic headphone boxes have four wires does not mean the
set has isolated grounds!
Never parallel the OCm150A input terminals, except in the case of using
one amplifier for speakers and headphones. Any time an unbalanced in-
put is parallsled to another input(s), all inputs involved become un-
balanced!
$5 PY
-- With strap
X connected, you cannot use a balanced amplifier (such as
any CROWN amp operating in mono) into input #2.
For special hook-up diagram for CROWN mono amps, see INPUT
CONNECTIONS FOLDOUT. This hook-up provides full power to the
speakers and half power to the headphone jacks.
- Never adjust the mechanical zero adjust on the meter fronts.

CROWN MONO AMP HOOK-UP
--.The ground ream fw channel 1 l@ through the
c@mman @@und of the input linesto the rvva amplirfi-
em.
-- This hmk-up applm ta CROWN amplaemon&! V@u
must be certginof haw the~;poundsilrecannmta b-
fam you cannsctany atkr arn- In this configurntian.
MOTES:
FIG. 1-4
-. Add ma-conduetov jumpers from tnput #1 to tnput It2 far headphone and
SV-~F?~ ~~fpuf fram one ampiifleu,

-0bsewe proper phasing of speakers.
If you are using a power amplifier other than a
CROWN, be very careful that you don't exceed the
amplitlets power capabilities by deereasing the
load impedance too far. For example, by depress-
ing two speaker selector switches and a headphone
sat at the same time, the resultant impdame
would be 27 ohms, if all three were 8 ohm sys-
tems*
-Be certain to fuse speakers according to the manu-
facturer's recommendations.
--Use headphone jacks cautiously to avoid overpower-
ing headphones or damaging hearing.

FIG. 1-5

Your OC-150A has many possible uses. The folfowing
NOTE: if you desire to eliminate all t~rn~on
discussion can be usd as 3 guide kr possible
lh~s~nps and noise, simply &%engage all
I
appticatians, Your own specific equipment as well as
swa ker! headphone $witches before turning
!
i
your peawplai listening habits wit! d@Permine exadly
on the pawr amplifier, Allow 5 seconds for
I
how YOU use She 0@-15QA, warm-up, then select your chaice of
I
1, SYSTEM SWltKCnlHE
A, SPEAKERSJHUDPHBMES
With a speaker system hmked ta each af the
three sets af outputs on the back panel, you
B. AMPtlFIERS
can select ogle or all the systsms by
depressing the apgrapriafe button(s) on the
fraot panel selector switch. Thus from an@
Iscation you can contrsl m~ia ~waker~ and
two sets of remate swakers.
IF: you
want to add headphones ta your
~y%t@rn~ UP 90 three mirs an h add~d; two
with the front pasoel jacks, and one with the
ternpal strip an t hc back panel. Either of the
two jacks can k seleded with the front panel
sele@^Ear. The terminal strip is '%gllnf"afl thc
time*
%nee high power at the hsadphone jacks
represents a p~tenbial health hazard, (such
8s shaaer@cf ear drums) your OC-1508 isf-
etudes atterauator switches which fed the
two Oleadphone jacks on tha fmnt panel. If
you turn up the volume ts drive ine8icSen"c
speakers, and then switch to an efficiant
headphone set, you wiri raed ts u* ane sf
A
the aBenuator positions,
It is goad practice ts always ttgl~a dawn the
volume, switch to an attenuator positi6n, then
carefully increa~ the volume for a csmfo~
table listening level+ Hww switch ts
headphones white wearing $he set,
The ""MAX" psitian of the attenuator switch
patches %he signal straight thraugh ts "&he
phones, The center position ipasefis a 17 db
gad, and the "MlN" position inse~s a 24 db
pad, With these combinations it should be
possible lo balance behwn swakers and
headphones, rsr Wa h~adpho~e sets, for corn-
Soflable listening tease!s.
The 06- 150A has three "amplifier-output"
inputs. The monitor switch on tha lmnit panel
$witch@$ thaw inputs into tha m~tsrinp cir-
cuit, These thme switches only progrtrm the
meterg, they do nat =lac% amplifier ~utputs,
Sa fog example, you can wled any d thrgs
amplifiers ta monitor sat the meters, but yaks
wifl rad change the autpaat to ths speker%,
(The swar%er ~wit~fit is tied dirr?ctly to Amp
#1 input),
Amp #1 input is the "main" 'input. It is m-
neeled ta the $maker $@lector switch,
Amp #2 in~ut is the headphone amplifier in-
put, and is hmked directly to the electrastatic
head phone terminal, and through the
aiMenuatcar switches ta the headphone $@lee
tar $witch.
Amp #3 input is ooly far metering, and is
hooked to the manitor switch.
If you have only one amptifier, and want: to
use speakers and headphones, a jump~r
must b6 crrnrrecterf betwen Amp #I and
Amp W2 inputs. The amplifier may then k
cannscted to either input.
CAUTION: Never cannect tw amplifier out-
puts in parailel. If a jumwr is used htween
aasy amp input terminals, ONLY ONE
AMPCllf lER MAY BE CONNECTED TO THOSE
iNPUTSI Also &cause sf $h% comwxcar*r
gfound~ at the headphone jack$, BALANCED
L!NES MAY NOT BE USED WtTH AMCaBtPg2: IN-
PUT, QR fN ANY f NPUT PARALLELLED WITH
AMP #2"

2 SYSTEM MQNfTBRIWG
A. SWAIKERSIHWDPHQNES
With the 8C-TSOA, you can monitor the
voltage levels Xa any lraudrpeaker or
headphone in your system,
When the meters are proprly programmed
aad the readings c~srectf y interpreted, you
can determine the drive signal to any
spa ker, By using the speaker/ headphane
switches ysu c8n chsose any toad for
monitoring the signal Bevel. Thus it is easy to
compare relatiwe efficiency of difierent
headphones rap spakes in your system,
For example, if a given swaker prsduces a
ca&ain sound pr~%sur@ level at a meter
reading of 25 volts, and another speaker
produrns the same sound pressure level at
0n1y 15 vaft~, you know the latter is the mare
efficient.
The honitoring system can also be used for
balancing channels. Turn the pre-amp ta
msna, and ad just the amplifier input centrals
far equal mtgr readings on both ckanl-refs. 18
the smakersare identicsl, this will accurateiy
balance the channels,
NOTE: The meters axe programmed as
$01 !am:
%%ect $ha desired tyw of reading, VU or
BEAK, f$ PEAK, adjust the hold time controls
for desired len@h of time at which voitage
wilt be displayed an metes,
&lec"E:~~rreet range wjf h range switch,
@% AMPLlFlERS
The amplifier switch on the frorat panel
switches $Re outpub from any sf three
amplifiers into the m~tering circuit. The
applicatisu of this feature is the abilib %to
monitor leveis from any amplifier in the
sy%t@m, For exampfe, yau could monitor the
levels from the headphone amplifier, or from
the rear channel amplifier in a quad system.
You could also check the levefs to diflerent
elements of a bi-amwd system.
"%"his monitor switching does a& a#ect the
prarngram to the speake~, but aged5 only
whet the meters read.
With %he metering circuit& of the OC-150A it is
possible ta pedarm an objective evaluation of
program materials, With the unique peak catch
and hold circuit, yau can actually "'catch'bsjgnal
peaks.. These readings sr~ sent the m&cs where
they are dispiayd %s rms @quivaien"lvottag@s, (If
you want true wak valljles, mul'LipEy the meter
readings by %,414,6 With a known foad, this is
readiiy conve&ible to power. (Refer 48 Section il,
Techoical i nforma"rioug),
A careful observation of peak and averag@
readings wit[ reveal a 1st of informatisaa abut
pragram material. FOP exampie, how does the
peak poaiacer prduced from e Iarg~ orchestral
passage csmpsre ts thatof a rock baud at a givgn
loudness level From the speakers? You might
want to examine which frtqueneie~ seem to k
producing the pak powr from different
sources, bes a wide- band source (such as a ful t
archestra) produce the same Isudness, at a
given meter reading, as a single ff&e?
"4au san see thc many appficilllisns for careful
metering af signal levefs in comparing programs.
Your imagination is the next step in actuatly using
$BOUT OC- 3 50A..
4, AC LXNE MONiTORlNG
By depressing the AC LINE/AUDIQ switch, the
OC- 15QA meters are automaticalily eonn~fd ts
the A@ line valtage. This is a useful feature for
evaluating the AC line voltage when the A@ line is
spmbjeded lo heaw load conditions. For warwple,
if your system amplifier is being driven hard, you
can qlr ickly check the urns equivalent Era true
maks at the AC input to the amplifier, Since the
amptifier is rated far power of I2BVAC (or the
peak equivalent 0;5 a 120886 rms sine wave) yw can
immediately tell if the A@ line is capable of
skappiying the input power neeessay for full
amplifier output,

Thare are fsur basie; ways to display your 8C-%5QA;
custom mounted, maunfed in the accesme 5-R
walnut cabin~t, standard 19"' rack mounted, or free
standing in its aaractiwc vinyl cover.
GUSTOM MOUMTED - The OC-15OA is shippd with
endbars installed. Whese endbars are used for
~~st~dm pasnel mounting, sr $re@-standing, A full -
sized ternplats of the 8C-150A t'sarrclss@d in the rear
sf the mar"ruaO, "9"his template aloa includes dimen-
sions for the shetf whish is recommended,
ACCESSORY CAB! NEVI BACK MOUNT1#6 -- Angle
brackets are ussd far rack mskarclting and for"insta&la-
tion into the 5-8 sr other larger CROWN "'rack""
cabinets. Ta prepare for such an iustallation, firgt
remsve the bur swket screws retaining the andbars.
1
Align the angle brackets to tha unit and reie?wfi the
socket screws. (Rate: Sckel scr8ws may fwk $3
though they are cmrs threading but will str";raighterr
1
apprawimatejy halMay through,) 1
Next remove the Csur ~ubber feet from the boQom
cover. Save the feet and four screws. (Mots: The front
right screw is a machine screw; the other three are
sheet metaI screws.) Slide the OOC-158A carefully into
the frant opening ofthe 5-8 and secure to the cabinet
side rails lasing the four thumbscrew-washer assem-
bfies supplied in the accessow pack, (Be sure ts use
a nylon washer under each thymb Screw to prevent
damage $0 the surface sf the rack eats.)
FIG. 1-6

METER RESPONSE
+Ql -14 db fram 20 Hz ts 20 KHz; En peak
mde eapabte of measuring (within 5%) a
single cycle at TOKHz,
METER ACCURACY
?5% adaf full scale, all ranges.
GROUNDING
HEADPHONE JACKS
Adjustable at front panel; miniurn hsld
approximately 600 mi9liseconds; maximum
hold essentially permanent while OC-15OA
is turned on - driR in maximum hold
(limited by device tolerances) sf less
than f 8,5 db over 20 minutes,
LEB aawd right speaker as?d amplifier
grounds isalat@d, so that amplifiers with
for witfP~k~"g isolated channel ground%
may be used safely,
Rear panel swikkes a!!ow 3 levels of
attenuation of amplifier signal apgDied
to headphones; 8 db, -17 db, and -24 db,
SEMICONDUCTOR COMPLEMENT
Four sp-amps i~ quad IC packages; 2 BI-FET
ap-amps as meter drivers; 12 signal dides;
2 Zener diodes; 12 bipslar transistors,
AC OUTLETS
Four, kenswitched. Total current capability, 15A.
POWER REQUIREMENTS
1261240 VAC, 40-400 HZ,
5gfl Hx 17'" x 8%'"ehind panel,
10 Ibs.; with Girate-nut enclasure, 19 Ibs.

he OC-150A is essentially a mechanical
As such it should greatly enhance the output
evice, designed with simplicity and precision.
flexibility of your hi-fi system.

IkNPUT/OUf Pm SPECS
Since it is a mechanicat (~~"stelhing) device, the DC-
150A dwr not alter the output fram an amplifier in
any way. The swikhing Is pr~ckse and uses break-
before-meke coo~rbe% to protect $ha assxiafed
ampiif ier eaurtputs from aeeidentsl shafiing, Bn addi-
tion, the amglifi~fr i~puk hawe analgctricai Imk~ut to
fu~hef guard against aeeiden&l paralleling*
AC pwer is plrmid~d br Xhla OC-15OA only to power
Eh rn~tering ~ireuifs, Th@ swlt~hing mmhanibm wiII
hfiabon
wgh the mwr turn& 8@.
In add Rim, faita r conw;nienee outjets are prov*@ad an
the rear panel ta PGWQ &CC%SQT~~~ qui pmant . P he*
outlets are unswitch~d and remain an as la~"rgnsths
86-1 5QA power plug is plumed into
""live" murca A
ve~ conmagiant wurca is alt"lsei? sf the $w&ch& OUEI&S
on the pfg-amp.
METER RESPONSE!INTERPRETATIOMS
Wny HI-Fi sptcms include a mehring system which
reads the output voltage acrass the amplifier tgr-
miinail%, The tendency far most users is to make
some tym of assxiation ktwen mter readings
and pawr sutpuk White a relationship does exist
w voltage and wwr, it is oat a simple ma%@r
to det~rmina in a hi-fi system - paflicularly when a
complex waveform, such as musie, io used as a
program source, So 3% a takeaR pint, w n~ed $0
review the basic eharacteristies of measuring cir-
cuits and meter mavements, t&erns~tv~$~
As the frequency of a signal iner~ases, it bcsms in-
creasingly didaicuit far a meter mowm8nt ta follow
the sodden changes of signal i@v8lx In fact if an A@
signal of abo& 10 Hz or higher w~e applied to a
center-zero, dc meter, the wiflX@et.~~~id only manag@
to vibrate arsund zero, Because of the physical
pram&ies of ths movement, it simply $=au not "Ilfow
%ha rapidly changing voltage. The srssuit is a
smmthing aut sr simpliving 04 the w~vefarm~ the
reading bing an avemge* If that wawefarm is a sine
WVE, the av8rage is zeqo, sa the meter, king en
average reswnding meter, reads zero.
We could try to use a dire& AC reading
again because sf mechsrnial di@icu&ies,
frequency limit is En the viciniw af 400 Ht,
If we would rectib a sine way8 with a ful! wave rm-
tifieu, end connect a DC m@t@r to this o~tput, the
metgr w~ufd smooth out Zhs wev~faa*m and indicab
an avarage value of about .637 times the mk wt-
put. flhe rectified waveform consis& of positiva
halv~s only af the sin@ wave; NO ~sitive halves mr
cycle of input*) W@ couM calibrate the scale ta rwd
snflhixag w8 wanbd, gueh ar av@r1g@, @#web'
(rms), w paak. As ktng as the signal rgmains a L%@*
~ioe wave, we can make accurab ~W@P earn-
partations when meaguring acrws a knwn ia~d
where:
P Powr in w%$
Ez
(BV@MB, fm, ~8k, @tee); of &b %~@Q%JII
in w~it3
F@ R~gistance 02" the load in ohms
fl
What hapmns &e~ the 8ig~al iti na Imger ar %t@ady
sine wve'? LetP$ Iwk at OLLP mter when the inp& b ;a
mudc pFogYa me
Even thaugh our mter i$ &cclilmt@ty c;alibrat@gS b
read rns or peak voltages with a sine ww , msn -8b
cornpi@x musie signal is rrs&ifi@d and applied ta the
mter, the &st tha sfu~ish mter can ds is indim&
some tym sf ayerag8 readirrg* We tatally miss aXI tb
quick waks aF the high frequencies, QWr@ an eSm
G~~~QSGOW muld k the only masuring &vice
capable of responding fast enaugk to catch snd die
play these =&s. ~wveu, our eye is nd alw~s %st
enough to sw ths wak, so ewn this 1% wok gr?;stiy
secumte,) At this paint, whet katl hap~$s@d OM$
vohap readiugs and pswr corwap&atioras!
It takes a 10t af camplieated mthamtits to versg~der
~RQSIE?! witage readings US~U~ for mwt CO~
putations. Using an analysis tmif ebfied the &ussiran
didributian cuwe, it is possible to pr@di& (mr a
Bong prisd of tim) what the signal iewl% @fa ~US~C
prognm will be Most of US IV~W~? g"Bi-fiT@r$ an%
have the mathematical know-howor the patience to
'
use this prscsss, 98 for us the mekr readin@ ;are

only relative voltage readings, and airnost
meaningless For accurate pawr eomputatians.
This hefps us to make an observation: (Ruleof thumb
# 1 .) Unless the input is a 5teady sine ansave, you can
farget a bout taking a reading and deciding precisely
how much ~wer autpbot your ampiifier is delivering,
This abbemation aSss applies ta VU meters (and the
so-called peak reading VU met~rs since wcke
already dceided that a meter can? ~QSS~ btyfoIIaw the
ma ks in a complex wave farm). AVU meter is simply
a BC meter with a s~ciat fudge factor built into the
calibratisn ss that it rgads Volume Units. A Volume
Unit: is essentially the saw as a db. VU's are always
ref~r@ne@d to a defioed wwer 1ev@/, (One mEiliwat
across a 606 ohm load,) I6 addition, a VU meter must
canform to a defined r@spstse time.
At this wint you are pprobabiy wondering what useful
purpose mcetefs cauld ~ssibiy have, As Iang as you
keep rule af thumb WJ, clearly in mind, the meters
can sew@ 3% a valualsls aid in program comparison.
Far examp%@, it is generally safe ta assume that a
higher average voltage reading means mare gswr*
Notice we didn't say &ow much power! This assump-
tion esufd be used for comparing amplifier outputs,
with different toad cglmbinatianr;, sr different types of
music
The 0C-1568 aH~rs this type sf relative cornparisan
with the meters functioning in the Vlb mode. And this
is only the &ginning, "Th QC-I$OA also offers a
PEAK mde, or $0 describe this Functian compj~tely,
a peak ""ckeh and tsoBdv"ml@,
If there were same way ts actually measenre peaks,
even with comp tex wave forms, we would have a lot of
US~~UI infarmation on our hands, Far exsmgte, the
peaks tell us whether the amplifier is clippirrmg and
thus what [eve t af di6tofiisn to expect. Accadrats peak
vaffages help us to determine the peak power, if
the load is known,
The OC-15OA in the peak catch and hold mode wit1
pravide accurate starage of peak voltages. The cir-
i
cuit is designed sa that all $he inherent limitations af
a meter movemsnt are by-passed, Here" how it
works,
The waveform is sampied efectronieafty using a sen-
sing circuit which measuqes eventhe fastest. peaks.
"T^is measurement is stored aleetr~nically, and then
sesrt to%he meters, The hafd ti me controls determi me
haw long this sts~ed informatian 1s held at the meter
terminals, "Pe bald lime is adjustable from nrerafo in-
finity, so the slow meter movement can take all the
time in the world getting up to the peak reading.
When the pointer $taps movement, you are observing
a vattag@ peak that occurred some fraction sf a see-
ond previously. The meter scales are calibrated to
yead urns equiva8ent values, SO if you want a peak
value, muitiply the meter reading by 1.414,
Once a peak is caught and held, the meter wi 19 re-
main a$ that level until a peak of higher vatu@ comas
afsng, If you want to see as many peaks, at different
levels, as possibie, a sRo& hs\d time is necessary.
Remember, 8s long as the metercowlestoa stop, it is
reading an rms equivalent to a true peak. In essence
we have trickily outwitted the pr&~ve~biaJ ofd slow
meter movement. Rather neit. eh?
Up $0 this paint we have assumed a test-bench situa-
tion when relati~lgvsltage readingo ts pswer, That is,
we have assumed that th@ toad was naa-reactive;
and the resistance vatu@ was known, Power
calculations fsllow wjth Ohm's law; P = E?.
R
What happens ts power output if we substitute a
swaker (reactance and resistance) far our resistive
load?
When an amplifier supplies power to a purely
~esistiwe laad, "re current through the resistance,
and the valtage across it areexactly rn phase& That is,
waks and zeros sf the current and voltage wave
forms occur simultaneously. If a pure reactance is
substituted for the resistance, the GWTTEM~ is
longer in phage with the voltage, but leads sr lags by
90"depending on whether the reactance is
capacitive or inductive,
In any practical Isad, such as a loudspeaker,"ehe toad
is camplex, consisting of both resistance and reac-
tance. These two quantities are added by a technique
using phasors (quanti"ries which include both an
amplitude and a phase angle) and the resultant,
called impedar-ice, ix the real bad the amplifier
" sees".

Thhe net resu ll: of this csmplex impedance cau*s t he
voltage and current waveforms to be out of phase by
some angie Bess than 9@, %e figure 2-2.
$300 1800 270-600
(B) Current wavefg~~m with pure is?ductiv@ reac-
tance. Current lags voltage by 90%
(C) Current wavefaam with camplex im-
pedance, a cowbi nation af inductive reactance
and resistance. Current lags voltage by some
angle less than 90).
FIG. 2-2
Now back to our original question, Let's took at a
typical loudspeaker, a complex load, consistiugaf in-
ductive reactance and resistance. it has ken deter-
mined that this speaker repre-nts an 8 ohm im-
pedance a$: IKHz,
We wifl set up our test by using a lKMz input signat
to %he arnpfifier of sufficient !@vet to cause an out-
put voltage of 10 vasts across the swaker terminals,
"8
I
t
I
f
f
1
f
I
With this information, we can compute the power to
Si
be P=F
Z
I
p"@ #,A [.
+A -- 12.5 mtts
8
Oses this mean that the speaker is dissipating the
12,s wa@s as acoustical mwer across the comptex
impedance, in a simplified analysis, we can account
for the total power (12.5 wags] From the amplifier,
being dissipated in four argas.
(15 %me OI the power is dissipated as heat across
the resistive pae of the immdancc. This is es-
sentiall y wastc?c% power since if. dms nat produrn
any acoustical r~soit, Resistance is found in
such places a5 in the wir@ ofthe s~ak~r" waice
csi t .
(2) Same af the po~er is dissipated 8% heat in the :
amplifier itself because of the reactiv~ cornpa-
nent of the impedance, One af the
cha~acteristics of pure reactance is that ikcannat
dissipate any pwer.
Rather it semes as an enera storage device,
This stared energy wili be returned to the
ampiifier and wasted as heat. Lwk again ad:
Figur~ 2-2, Notice that in each cycle &a periods
s;tl time exist when the uoitage is positive while
the curreut is negative. (This is due hcs the
reactive component causing a phase shift.) tt is
during these WQ psriods kaf time that negative
power is produced, and the ~tar~d power in the
~eactance is returned to the amplifier to be
wasted as heat It should be clear from this, that
to drive ;a pure reactive foad weauld be pointless
as it would only cause amplifier heating.
(3) am@ sf the tatat wwer i~ transformed and dis-
sipated as acsusticaf enerB. This is becausethe
ind~aefive reactance (voice coil) BS situated in a
magnetic field, The applied AC WWFC~US~S the
voice csil to move, Since the voice coil is at-
"caehed ts a large diaphram which in turn causes
'
campressions and rarefactions of the surrsun-
ding air, acsustical energy is produced.

$4) %me power is last due to inefficiencies in the
doudspeaker, Interaction of the voice coil with
the magnetic field causes heating af the
magnetic care. nki sheat is all wasted, producing
no acokastica t effect,
It can be seen fram this, that perhaps anty a
smaif paWPian of the 12-5 WBBS total has been
transiated into actual aeaugtical energy, HOW
much reactance is present, how march resist-
ance, and ather factars such 3% speaker ef-
ficiency dstermine the nst result, !a: should be
clear the6 highly reactive speakers (such as clec-
trortatic system%;;) rgpresent a difficult load and
severely limit the amplifier's efficiency,
Motim the V-l auwuf graph, Figure 2-3. The
straight line through %he middle represents the
toad fine for an 8 ohm resistive toad, Notice that
no negative power is produced (voltage and
currgnt are in phase). "I"@ ellipse in the center
represents an 8 ohm impedance laad line, (The
8 ohm impedance consistsof 3 ohms re~i~fance
and 9.42 ahms inductive reactance at 1KHz.)
Notice that because af the phase shrift, 68"n this
case, the straight fine has became an ellipse,
and then far WO p% riod5 af time through the 36Q0
cycie, negative power is produced.
UP
FIG, 2-3
It should be clear that tb ideal laad in terms of
producing aceustiea9 enerw would be one which
minimize% the reactive camwnant (high amplifier
efficiency) while optimizing the desired dissipation
campsnsnt , $Isw inductance high efficiency
spaker).Aiss the resistance sf the load shagaid h
kept at a minimum. Iln practical terms this ideal is difw
ficult to achieve and amplifiers shoufd therefore !x
designed to handle high reactances without aver
heating,
At this win.%: the obsgwant raader has probably notie-
ed ahat wrs have employed only osle frequaasey in
daaribing complex laads. WC have one pa&ing poiut
to mnder kfore W@ can be satisfied in knowing what
the OC.150B"s voitags rgading~ are &bring us* (You
didn? texpeet anfiRing simple with so wphisticated a
system , , , 2)
Notice the*graph sf Figure 2-4. This is a plot of a 3ypp-
icaf" 'speaker system impedance aver the audi~
bandwidth,
Since reactance varies wi"r frequency, the ratia af
reactance to resistance, and thus immdal-rce, varies
with frequency also.
When a music program is used as a wurce and is
applied ts speakerterminals, the impedance seen by
the amplifier becomes vey complex, king siightly
different far each frequency component present.
Since
the impedance varies, the amaunt of ww@r at
difzfecent frequencies atso varies.
Swaker manufacturers have "Eied many schemes

for smadsthing out the effect of frequency on im-
pedance, For instance, by careful design of the
swa ker enclosure it is wssi ble to smooth out some
sf the wide variations in impdance, But speaker im-
pedance ss still not linear with frequency. Many
variables a&ect I mpedanse, such as cabinet
resonance and C~QSSOY~~ characteristics. These and
sther factors lead 40 the Qpe of impedance curve it-
lustrated in Figure 2-4,
Speaker impedance is usuaily given as a nominal
value, such as 8 ohms or4 ohm%. This is a rough ap-
prsxsmatzon of an average immdance fsr the range
sf audsa frequencies.
The overall effect af uneven pswer response [Ae ta
varylnp smpedance) may not be as dismaying as it
appears. Here by the application of inverse Murphy's
Law, we end lap w&t-1 a beeseficia! tw~st sf fate,
A taudspeager ss largeiy voltage sensitive ra"ther than
power sensitlve Since an ampiifier WI fl defiver a con-
staant voltage over a range of impedaoces, the audi ble
effect oft he cbnging power is not at ways notices ble,
Even though the impedance of a speaker may drapat
a cedain frequency, in many speakers, tbeefficieracy
drops at that frequency as well, The net resuit is th%t
while more power is produced at that frequency,
rnore of it is lost as heat, and the acoustical output
level is unchanged,
All sf the preceding indicates the diRicul%ies involved
in aeeuaately interpreting 06- 150A voltage readings,
using a magic pr~gram $S $OUTC$, with 8n amplifier
driving a campiex load* It is apparent that you must
be satisfied with relative ar comparative inter-
pretations. For specific computations you must use a
test bench set-up. (Sine wave and resistive laad),
Each depa~uie from this test situation inlrduces
new variables which require very carefadli $and Gem-
plicated) analysis+ By the time you have tuned in an
FM stereo signal and hookd up your favorcite
speakers, the voft~ge readings an the QC-1SOA are
chiefly usefut a$ a camparabive analysis tmf*
Ysu might try computing power lasing the oaminal
rated impedance af the speaker system, Ihshoanld be
clear from the above discussion, however, that the
resu its may be far from accurate, If the laad is a pure
resistance, then the graph of Figure 2-5 may be used
ta compute pswer, Look again at Figure 2-3, Nstiee
that the mare reactive the Isad becomes, the fa@her
the graph depa@s from a straight line. Because the
reactance produces negative power, the ampiifier
loses efficiency, Thismeansless of the total pclwer is
defivered to the laad.
Now 4x1 examine the usefulness sf the OC-JSOA
voltage readings* In Figu~e 2-5 the veeicai calumn
repre%enXs voltage, The horizontal ca9umn repres-
ents power. We have drawn three laad lines sn this
graph, Yacr must pick the line that comes the cfasest
to your load impedance*
IF ysur impedance is a pure resistance, you will kx? ap-
proaching 100% eeff iciency. (This won't praduce
I
much acatdsticai energy, but it's great far heating
your room.) As your load impedance becomes reac-
tive:, your amgIifier efficiency goes down. However, it
is f t785 reactive component which prg3duee~
acoustical energy, So WE are looking at a trade-off
between high inductance fgosd enera transfer) and
the corresponding high reactance (amplifier inef-
ficiency),
If we $16uid take an 8 ohm speaker, and vary the ratias
of reactance to resistance from pure resistarace to
pure reactance, the amptlfier wa~Id supply the same
Power through the entire range. At tkteextremee~ld af
pure resjslanee, the load would dissipate all the
power, with 1QO'3& amplifier e^EFiciency, At the other
extreme of pure reactance, the amplifier wauld dis-
sipate all the pswer for an efficiency of 0%
Somewhere in between these extremes, we would
find a campromise between amplifier efficiency and
maxi mum acsadsfi~al energy,
As yau use the graph of Figure 2-5, keep the a bove
discussian in mind and you will not be enticed into
making erroneous sbtements about how much
power your speake~ are pradueing.