ADA-7551
Audio Distribution Amplifier
AM-7551-03
ADA-755I AudioDisributionAmplifier
ADA 7551BLOCKDIAGRAM
OUTPI'T
STACIS
u4c
INPUT AYP
GAIN
OUT I+
STAGE
OUT 2+
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OUT 5+
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OUT 7+
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OUT IINVERTER
U38
OUT 2-
OUT 3-
OUT 4-
PO'ER
REGUL.I,TORS
ouT 5+ 15 Volts
+ 16 Volt3
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- 16 Voltr
ouT 7-
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ADA-755 I Audio Dishibution Amplifier
Introduction
The Ross ADA-7551 Audio Disbibution Amplifier provides a meaxr of mplifing
and distributing
program-levelaudio with virtually no loss of quality, Use of the latesttlpes of integratedcircuits vrhich
are developedspecifically suitedto professionalaudio ap'plicationsassunx,avery low level of distortion
andnoise.
Installation
The card TRAY TYPE jumper (JPl) settingsmust be set beforeuse. All jumper plugs must be set in a
vertical row correspondingwith the tray type designationasfollows:
RossTrays
GVG' Trays
CAUTION:
If JPI is not set correctly for a GVG tray, damageto the integratedcircuits may occur.
Operation
Controls are provided for setting the gain of the amplifier,
The GAIN jumper plug is to be set for the desired gain range. In most installations it will be set to the
0 dB position to obtain unity gain.
The GAIN potentiometer provides a fine control of the gain and has a range of +/- 6dB.
There is no need to set the common mode BAL adjustment as it has been precisely factory pre-set and
sealed. This amplifier incorporates an advanced type of input stagethat does not have to be balanced for
each installation.
Circuit Descriotion
The input stagq U6, performs the firnction of converting the balanced input signal into an unbalanced
(single ended) signal for further processing.
This stage is unique becauseit functions exactly as if the amplifier had a floating transformer input. This
means that it responds only to the voltage difference between the two input lines and ignores any
imbalance to ground- This gives the distribution amplifier the very desirable ability to accept any
out-of-balance input signal and produce a perfectly balanced outpul As a consequence,it also has an
exceptional ability to reject common mode hum and noise over the whole audio band.
The input circuit includes diodes to protect the amplifier againstdamaging input noise spikes.
The amplifier gain is provided by circuit U3A.
vernier gain adjustment-
l-3
JP2 selects the desired gain range and RVI provides
ADA-755I AudioDishibutionAmplifier
The positive line outputsare driven by unlty-gain stagesUl. and U4. These circuits are designedto be
very stableand not oscillateat any normal line load.
The negativeoutput stagesU2 andU5 are driven by unrty-gaininverterU3B.
The power input voltageof approximately+l- 16 volts is reducedto +/- I 5 volts by transistorsQ2 and Ql .
_ This lower voltage powers the input and gain stageswhile the output stagesare fed directly from the
power supply.
.
-- Alignment
The only alignment controls provided are for balancing the common-mode rejection of the input
amplifiers. To adjustthe BAL eontol, makethe indicatedconnectionsto the terminal block associated
with the particularamplifier.
OTE:
this control hasbeenpreciselycalibratedat the factory, it must not be adjusted
U6 hasbeenreplaced.
t.
2.
5-
4.
5.
IA
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Placethe amplifieron the extenderboard.
Use a shortjumperwire to connectthe tray "input *" and"input -" terminalstogether.
Connectan audiogeneratorbetween"input *" and ground. Setthe generatorfrequencyto I KFIz
andoutputlevelto +20 dBu.
Connecta balanced-inputsensitiveaudio level meteror distortionanalyserto a balancedpair of
amplifier outputs.
With the output level meter set to the most sensitivescale,adjustthe INPUT BAL potentiometer
to obtain the lowest possibleoutput level. It shouldbe possibleto obtain an output level of at least
-80 dBu. (l00dB below+20 dBu). Sealthe pot.
Disconnectthe testsetup.
ADA-755I AudioDisEibutionAmplifier
Specifications Input
Dutput
Iqimlmpedanoe
>3SKohs,bahoced
MaxInptkvel
+34dBu [+30 dBln]
CommonMode Rejection
>l00dB @60I'4'
>80d8 @z0KIlz
Nrmberofotrputs
Max Outputlevel
E
+2EdBu[+24ffim]
OntputImpedance
48 ohms, [ 600 ohms]
OutputIsolation
>70 dB
S/N Ratio
>100dB (unity gain) relative to
+t dBu
Gain Range
FrequencyResponse
-lt to +34dB
[+6dBfineadjustment)
+l- 0.V2dB20IIz to zOKIlz
Total HarmonicDistortion
4.AU)% f0.ffi7o/ol
Intermodulation
<0.002yo[ 0.006%KSMPTE)
CrosstalkbetweenAmplifi ers
>100dB
PowerConsumption@ +8 dBu
output
l.6w [2.6w ]
All testsperforrnedat +18 dBu andcover20 Hzto 20 KHz unlessotherwisespecified.
All measurements
madewith an Audio hecision SystemOnetestset Performanceof
:he600 ohm versionis similar, exceptwhere indicated I J.
l-5
ADA-755I AudioDistribution
ADA 755I
Bill of Materials
7551A-00t
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ADA 7551-600
7551A -001A (600 ohmversion)
Bill of materialssameasper 75514,abovewith the following exceptionshcrn l:
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CoeyrightO f 995by RossVideoLinito&
PrimedinCmada
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Atl spccificdios aresrbjectto changowithort notico.
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Rossil ac Trademalcs
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RossVideoLimited
- EtohnS'trcet
Iroquois,Ontario
KOBIKO
No partof thismanualmayberepoducedin my form
withoutprioruniten pemissi,on
fromRossVideoLimircd"
DISTRIBUTION PRODUCTS
WARRANTY andREPAIR POLICY
l. Roo Video Limited (the Courpany)warana ia produca to be frec from defectsin worhanship and material
under normaluse and servicefor a period of FIVE yearsfrom tto datc of ship,me,ntIf, within the warranf pedo4
the customernotifies the Compmy that a product is defective,the Companywill correct the defect,eithcr by
productto the customer,as det€rmbed by the
repairing tbc defectiveproduct or by $ipping a replaceme,nt
Company.
2. li"bilitio rmderthis warranty is limited to the repair or replaccmentof the product asdeterminedby thc
Companyarid is in lieu of all otherwarrantiesexpressedor implird.
3. thir *"r"-ty doesnot extendto any product which hasbe€nsrbjectcd to mlsnse,nejlect, accident,improper
instatlationor application,na doesit orrcnd to productswhich havc becnrcpaird c altcredoutsidethe factory by
personnelgther thm thosc of tbe Comp,ay, rmlessexpresslyauthsised in writing by lbe Compmy.
4. W"rr"rrty repairswitt be madeat thc Compan/s plant rmlessofterwise specificd in writing by the Company.All
packing shipping;and specialhandling costswill be paid for by tte customer.
5. Noo-*"r"-ty repair serviccmadeat the factory will be at custom€rexponsc.Cost of repain will be quoted
following examinationof the product by Companypersonnel.
6. h no eventshatl RossVideo Limited be liable for direcr, indirect,special,bcide,nta! or consequentialdarnages
(including lossof profits).