Ampex 601 Manual

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I AMI
EX
^ ^MiDEL601
Operation
Maintenance
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AiMPEX
CORPORATION
.•14CHARTER STREET
BEWOODCITY • CALm>BMA

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AMI
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EX
MODEL 601
Operation
Viaintenance
Manual
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AMPEX
CORPORATION
934CHARTER STREET
REDWOOD CITY - CALIFORNIA

3rd EDITION
OCTOBER 1958
TableofContents
Page
I. DESCRIPTION AND SPECIFICATIONS I-l
GENERAL 1-1
SPECIFICATIONS 1-2
n. PRINCIPLES OF OPERATION 2-1
THEORY 2-1
HI. INSTALLATIONANDOPERATION 3-1
GENERAL 3-1
POWER 3-1
LINE INPUT 3-1
MICROPHONE INPUT 3-1
REPRODUCEOUTPUT 3-1
INTERCONNECTING 3-2
CONNECTORS 3-2
STUDIOINSTALLATION 3-2
TAPETHREADING 3-3
RECORDING WITH HALFTRACKMACHINES 3-4
REPRODUCING WITH HALFTRACKMACHINES 3-4
RECORDING 3-4
REPRODUCING 3-5
REWIND AND FAST FORWARD 3-5
ERASING 3-5
MIXING 3-5
SYNTHETICREVERBERATIONS 3-6
IV. TAPETRANSPORTASSEMBLY 4-1
GENERAL 4-1
STAND-BYOPERATION 4-1
PLAYMODE 4-1
REWIND MODE 4-3
FAST FORWARDMODE 4-3
ROUTINE MAINTENANCE 4-4
V. ELECTRONICASSEMBLY 5-1
GENERAL 5-1
RECORDCHANNEL 5-1
REPRODUCECHANNEL 5-1
BIAS AND ERASE OSCILLATOR 5-1
ELECTRONICALIGNMENT 5-2
ALIGNMENT AND TEST EQUIPMENTREQUIREMENTS 5-2
VI. PARTS LIST 6-1,
ListofIllustrations
Fig. No.Caption Page
FRONTISPIECE
2-1 TAPEMAGNETIZATION 2-1
2-2 RECORDINGHEAD 2-2
2-3 MAGNETIZATIONCURVE 2-3
2-4 OUTPUT VS. FREQUENCY 2-4
2-5 ACHIEVINGFLAT RESPONSE 2-5
3-1 SPACE REQUIREMENTS 3-2
3-2 TAPETHREADINGANDNOMENCLATURE 3-3
4- 1 MECHANICALOPERATIONSIMPLIFIED 4-2
4-2 ROUTINELUBRICATION 4-3
4-3 TAPETENSIONMEASUREMENTS 4-5
4-4 TAPETRANSPORTEXPLODEDVIEW
5-1 REPRODUCEAMPLIFIER RESPONSE 5-4
5-2 RECORDAMPLIFIER RESPONSE 5-7
5-3 SCHEMATICDIAGRAM

I.Description& Specifications
TheAMPEXModel 601isa lightweight,portable,magnetictapeGENERAL
recorderdesigned for professionaluse, andis available inany combina-
tion of theseversions:
Power Input 117 volts, 50or60 cycles
persecond (cps)
Tape Speed IY2 or 3 -M inches per
seconds (ips)
Head Assembly full or halftrack
Anaccessorytransformer(CatalogNo.17331-1)featuringconvenient,
quickplug-inchangefromhigh tolow impedancemicrophoneinput is
available foruse withthismodel. The machine canbe operated inthe
horizontal or verticalposition. Itis packaged ina durable,luggage-type,
saddle-tanSamsonitecase, oris obtainableuncased for custominstal-
lation.
TABLE 1-1
EQUIPMENTSUPPLIED
TAPESPEED TRACK LINEFREQ AMPEX DIMENSIONS
UNIT (ips) WIDTH (CPS) CAT. NO. (Ins.)
Complete
Equipment
(incarrying 7-1/2 Half 60 7948-1 16-1/2x13-3/4x8.
Case) 7-1/2 Full 60 7948-2 16-1/2x13-3/4x8.
7-1/2 Half 50 7948-5 16-1/2x13-3/4x8.
7-1/2 Full 50 7948-6 16-1/2x13-3/4x8.
3-3/4 Half 60 7948-101 16-1/2x13-3/4x8.
3-3/4 Full 60 7948-102 16-1/2x13-3/4x8.
3-3/4 Half 50 7948-105 16-1/2x13-3/4x8.
3-3/4 Full 50 7958-106 16-1/2x13-3/4x8.
TapeTransport 7-1/2 Half 60 6200-14 9-5/16x12-1/2x5.
7-1/2 Full 60 6200-10 9-5/16x12-1/2x5.
7-1/2 Half 50 6200-15 9-5/16x12-1/2x5.
7-1/2 Full 50 6200-11 9-5/16x12-1/2x5.
3-3/4 Half 60 6200-121 9-5/16x12-1/2x5.
3-3/4 Full 60 6200-122 9-5/16x12-1/2x5.
3-3/4 Half 50 6200-123 9-5/16x12-1/2x5.
3-3/4 Full 50 6200-124 9-5/16x12-1/2x5.
Electronic 7-1/2 17416-1 6-1/8x12-1/2x5.
Assembly 3-3/4 17416-101 6-1/8x12-1/2x5.
PowerCord CS-5
96.
MatingConnector,MicrophoneInput PL-33P
MiniaturePhonePlug,LineInput PL-450
MatingPlug,Output PL-445
Notes:
1. All matingconnectorsaresuppliedwithoutwiring asa convenience
fordiversifiedinstallation.
2. Hardwarekits are available to facilitatemaintenance. (See Sec-
tion VI.)

SPECIFICATIONS
Tape Width
Reel Size
Tape Speed
Playing Time
Reproduce Timing
Accuracy
Flutter and Wow
Starting Time
Stopping Time
Fast Forward Time
Rewind Time
Frequency Response
Signal-to-Noise Ratio
Record Inputs
Reproduce Output
Operating Controls
VA inch.
7inch,RETMAreel(maximum).
IV2 ips, lull track.
IVj ips,halftrack.
3Mips, full track.
.3Mips,halftrack.
Full Track—32 minutes witii 7 inchreel,
IV2 ips,1200 feet.
Half Track—64 minutes with 7 inchreel,
71/2ips,1200 feet.
±0.2%,oran accuracy of±3.6 seconds in
a30-rninuterecording.
71/2ips—Below0.17%rms.
ips—Below0.3%rms.
The tape attains full speed in less thanone-
fifth second ineithertheplayorrecordmode.
Less thanone second.
90 seconds for full 1200footreel.
90 seconds for full 1200footreel.
71/2 ips—40 to 15,000 cps±2db50to
10,000 cps down nomorethan4 dbat 15,000
cps.
3M ips—±2db50to 7500 cps.
Full Track—over55dbbelow peak rec-
ord level. Peak recordlevelisdefinedasthe
point of3%totalrmsiiarmonicdistortion,
measuredwhileusinga 400cpstone;and
peak recordlevelincludes bias, erase andre-
produceamplifiernoise.
Half Track—50 dbbelow peak recordlevel.
MICROPHONE:Accommodatesanyhigh
impedancemicrophone,andcanbequickly
convertedfora lowimpedancemicrophone
with the plug-in accessory transformer(Cat-
alogNo. 17331-1).
LINE: 0.5 volt requiredfornormalprogram
level.
1.23voltsrmsinto600ohmsatprogramlevel.
PLAY—REC:Theplaymodeis selected by
placing theswitchinPLAYposition.
Therecordmodecanbe selected onlybyde-
pressingthe safety buttonatthe same time
the selector switchisplacedinRECposition.
The safety button,a flattoppedneonlamp,
remainslightedwhilethemachineisinthe
recordmode.
REWIND—FASTFWD:This selector
switch ismechanicallyinterlocked with the
PLAY—RECswitch.
1-2
Reproduce Output
Operating Controls
Miscellaneous
Monitoring
Head Assembly
Power Requirements
Accessories
MIC RECLEVEL,andLINERECLEVEL
are separate mixingcontrols.
TheMONITOR SELECTOR switchisused
for monitoringasdescribedinthe following
paragraphs;butitfunctions also asanoper-
ating control.InthePLAYmode,the MON-
ITOR selector switchmustbeintheTAPE
position inordertobringthereproducehead
signaltotheOUTPUT.
A toggleON—OFFswitch,locatedonthe
control panel,turnspoweronoroff.When
placedintheONposition,thistoggleswitch
will cause the capstan torotate;butthe tape
will notmove until oneofthetwooperating
switchesisturned from itsneutralposition.
TheMICROPHONE input, a threecircuit
connector,isconvenientlylocatedonthecon-
trol panel.
ThePHONESoutputisa twocircuit jack,
locatedonthefrontpanel.
TheLINEINPUT connector isa twocircuit
jack recessed intothe right sideoftheequip-
ment.
TheOUTPUT connector isa threecircuit
jack also recessed intothe right sideofthe
equipment.
Mating connectors aresupplied(see Table
1-1).
TheMONITOR SELECTOR switchallows
monitoring ofprogram input, orreproduce
output. A phone jack andilluminatedv-u
meterareonthefrontpanel.
WhentheTAPEpositionis selected, there-
produceoutputcanbemonitored.
WhentheINPUTpositionis selected, the
headphones andmeterreportprogramsignal
level.
Separate erase, record,andreproduce heads
arecontainedina singlehousing.
117volts,50or60cps;0.52ampere,61
watts.
MaintenanceKit: 6392-1
Speed ConversionKitsto:
3M ips,60cps 7556-0
71/2ips,60cps 7556-1
3%ips,50cps 7556-2
71/2ips,50cps 7556-3
SPECIFICATIONS
1-3

SPECIFICATIONS Accessories
ConversionKitto:
50cpsoperation,714ips9738
60cpsoperation,71/2ips9739
50cp"soperation,354ips9740
60cpsoperation,354ips9741
Adaptor forrackmounting9684-1
Spare parrs kitsfor:
714ips,60cpsmachine9742-1
7V2 ips,50cpsmachine9742-2
354ips,60cpsmachine9742-3
354ips,50cpsmachine9742-4
Minor hardware Kits: 7802
SeeSectionVIfora complete parts list.
II.PrinciplesofOperation
If a material capable ofbeingmagnetizedisplacedinthe proximity Magnetic Tape
of a magnetic field, themoleculesofthematerial will beoriented
accordingtothedirectionofthe field. Anyofseveralmethodscanbe
used toproducethemagnetic field, butofmostinterestinmagnetic
recordingisthat field producedwhena current flows througha coil of
wire. Thecurrentmaybederived from a transducer—forexample,a
microphoneconvertingaudiosoundwavestoelectriccurrent.
Magneticrecording tape consists of finely divided iron-oxide par-
ticlesdepositedupona plasticbacking.This tape ismovedthrougha
magnetic field in which themagnetizingforceisalternating,andthe
iron oxideparticlesarealignedaccordingtothe instantaneous direction
andmagnitudeofthe field (SeeFig.2-1).
Fig. 2-1. Tape Magnetization
2-1

Magnetic HeadThemagnetic field isproducedinthegapofa recordinghead,
over which therecording tape passes. Therecordingheadisa ring-
shaped electromagnet(SeeFig.2-2).It consists ofanincomplete ring
of highly permeablematerialinsertedina coil of wire. Thediscontin-
uity inthe ring formsthegap,andthe ring isthecoreoftheelectro-
magnet.
GAP
TAPE
e
Fig. 2-2.Recording Head
Magnetization CurveThemagnetizationcurveofthe iron oxide utilized astherecording
medium issimilartothatshownastheheavy line inFig.2-3.Atpoints
nearthe origin, thecurveisextremelynon-linear,andthesignalrecord-
edonthe tape would notbe directly proportionaltothesignalapplied
to thehead.This would resultina high degree of distortion uponre-
production. This distortion isgreatlyreducedbytheapplicationofa
high-frequency constantamplitude bias signal which ismixed with the
signalbeingrecorded.Thefrequencyofthis bias isgenerally selected
to befivetimestheupperfrequency limit oftherecordertoprevent
beatingbetweenthe bias andharmonicsoftherecordedsignal.
Bias While the tape isintherecordinggap,the bias causes themagnet-
ization characteristicsofthe iron oxideto follow the dashed line loops
shown inFig.2-3, known asthe MINOR HYSTERESIS LOOPS.As
the tape leaves thegap,theinfluenceofthemagnetic field createdby
the bias isreducedtozero,andthe tape assumes a permanentmagnet-
ization, known asREMANENT INDUCTION, determinedbythegap
flux atthetimethe tape leaves thegap.
After therecording process, there exists onthe tape a flux pattern
which isproportionalinmagnitudeand direction tothesignalrecorded
on it.Ifthe tape isthenmoved past thegapofa reproducehead—
which issimilarinconstructiontotherecordhead—themagnetic flux
of themoving tape will inducea voltageinthe coil ofthereproduce
2-2
Fig. 2-3.Magnetization Curve
head.ThisinducedvoltageisproportionaltothenumberofturnsofInducedVoltage
wire onthehead,andtherateof change of flux, expressed inthefol-inHead
lowing equation:
E= N(d0at)
WhereE isthe induced voltage
N isthe number of turns ofwire
d0tlt isthe rate of change of flux
It isdesirablethatthegapinthereproduceheadbeassmallas
possible, sothatthegap will intercept less thanonewavelengthof
the signalonthe tape atthehighestfrequencytobereproduced. How-
ever,asthegapis made smallertheinducedvoltage decreases, sothere
isa practical limit in decreasing thegapand still maintainingan ade-
quate signal-to-noise ratio.

InducedVoltage
inHead
Thevoltageinduced across rheheadiscomputedbythe following
equation;
E= B V sin TTcj/
m /x
WhereE istheinduced voltage
B isthemaximumfluxdensityoftherecording
material
V isthevelocityofthe tape over thehead
w isthegapwidth
Xisthewavelengthofthesignalonthe tape.
From thisexpressionitcanbe seen thatthevoltage across thecoil
increases directlyasthevelocity increases andasthewave-lengthde-
creases (frequency increases). Ifrhetapevelocityandgap width are
assumedtobeconstant,the output voltage from theheadisdirectly pro-
portional tothefrequency,aslongasthewavelengthonthetapeis
largecomparedtothegap width. Thisresultsinan output vs.frequency
characteristicsuchasshownincurveA ofFig.2-4.Thevoltage does
not continuetorise indefinitely. Aselectrical losses inthe core mate-
rial increase, andasthewave-lengthonthetapeapproachesthe same
dimensionsasthereproduceheadgap,rheactual output resembles curve
BofFig.2-4.
OUTPUT
(db)
+25
+20
+15
+10
+5
0
-5
-10
-15
-20
-25
1
1
(
J^__.
1
1 A!/
1
1
1- +
1
t
1B
t
1B
——
10 100 1000
FREQUENCY
lOKC
Vig. 2-4.Output vs. Frequency
2-4
In ordertoprovideanoverallfrequency response thatis flat (see FrequencyResponse
Fig. 2-5)anequalizationcircuitconsistingofa series resistance and
capacitance isinsertedinoneoftheearly stages ofthereproduce ampli-
fier. Thisequalizerhasa high-frequencydroopcharacteristic(curveB,
Fig. 2-5) which istheinverseofthereproduceheadcharacteristic
(curveA,Fig.2-5).Inordertoextendthehigh-frequency response,
additional equalizationisincludedintherecordamplifierinthe form
ofa high-frequencyboostcircuit,designedtocompensateforthedroop
in reproduceheadcharacteristics caused byhead core losses, gap losses
and recording losses.
Fig. 2-5.Achieving Flat Response
2-5

III. InstallationandOperation
Thismachine canbe operated in either the horizontal or vertical
position. Inthe carrying case, installation consists only of making up
and connecting the required cables (See "Connector" in thissection).
Forstudioinstallations, an adaptor(Catalog No.9684-1)is available
which permitsmounting ina standard19-inchrelayrack.
GENERAL
Thepowerrequirements are117 volt a-c,50or60cps,0.52 ampere,
61watts. A nameplate onthe bottom ofthecase adjacent tothe aper-
ture for OUTPUT, LINE INPUT and117v.a-c indicates the proper
line frequency.
POWER
Theline input isan unbalanced bridging input of100,000 ohms.
Any unit connected tothe LINE INPUTconnectorshoulddeliver a sig-
nal ofat least 0.5 volt whenrecording from consolettes,mixers or other
taperecorders.
LINEINPUT
Therecorder is wired fora high impedancemicrophone, but pro-
vision for internalmounting ofan accessory plug-in transformerimme-
diately changes the machine foruse with low impedancemicrophones.
Tomakethisconversion,remove the four screws onthe panel ofthe
electronicsassembly. The panel and assembly can then be removed.
A. High Impedance--adummy plug J107P shown onthe sche-
maticdiagram(Fig. 5..5) must be plugged
into socket J106S for high impedance op-
eration.
B. Low Impedance — remove the dummy plug J107P. Acces-
sorytransformerAMPEXcatalognumber
173.51-1 (shown asT103on schematic dia-
gram Fig.5.3)is thenplugged into J106S
for impedance inthe range of150 ohms
to 250 ohms.
C. 30ohmto50 ohm — Installtransformer T103as shown on
the schematic diagram (Fig.5.3)by plug-
ging the transformer into socket J106, and
removing the jumper as shown in Note 7
on the schematic.
MICROPHONE
INPUT
Theoutput ofthe machineshould be connected toa unit having 600
ohms input impedance. Ina situationwherein the recorder will work
into a high impedance line, physicallyterminate the OUTPUT connec-
torwith a 600ohm resistor and bridgethisresistor with the high im-
pedance circuit. A threecircuitOUTPUT plug is supplied. A twocircuit
plug canbe used, and will work; butit automatically makes an unbal-
anced line. Ifan AMPEXamplifierloudspeaker is used plug it into the
MONITOR jackonly.
REPRODUCE
OUTPUT

INTERCONNECTING
Regardless ofapplication observe therequirementsunder"Line Input"
and"ReproduceOutput"wheninterconnectingthemachine with any
other piece ofequipment.
CONNECTORS A power cable andmatchingplugsfortheMICROPHONE (JIOIS),
LINE INPUT (J102S), andOUTPUT (J104S) connectors aresup-
plied with theequipment.
Shielded,low-capacity cable isrecommendedformakingup input
andoutput cables. Makesuch cables asshortaspossibleforintercon-
nectingunitsinaudio systems. Refer tothe schematic diagram(Fig.
5.3),todeterminecorrectpinconnectionforallplugs.
STUDIO Thereproducehead cable isdoubleshielded,insuringagainstr-f
INSTALLATION pickup. Cable capacityandlength have been minimizedtoavoidhigh
frequency loss. Ingeneral,mounttheelectronic assembly and tape trans-
port nomorethanonefootapart.Ifthereproducehead cable islength-
ened for greater separationofthecomponents,highfrequency response
will beaffected.Intheeventaninstallationabsolutelydemandslength-
eningthis cable, a verylowcapacitytype (RG-62/U) isindicated,plus
theadditionofanoutershield. High frequency losses cannotbekept
•'toa minimum ifthe cable length exceeds three feet.
Space requirementsforcustominstallationaregiveninthe accom-
panying illustration(Fig.3-1). Allow sufficient clearance atthe right
sideofthe electronics chassis for easy access toLINEINPUTandOUT-
PUT connectors. Ifdesired, these connectors canbebroughttoa patch
panelmountedat some moreconvenientpointintheinstallationtopro-
vide readyaccessibility.
Fig. 3-1. Space Requirements
3-2
The tape threadingpathdescribedbelowisthe same forall modes TAPE THREADING
ofoperation;butspecialattentioniscalledtothe notes dealing with
halftrack heads.
Step 1: Place a reelof tape ontheleft-handturntable,andanempty
reelontheright-handturntable,makingcertainthatthepins
around the base of each spindle engage corresponding slots on
thereelhubs.
Step 2: Press a reelhold-downknobin place on each spindle.
Step 3: Threadthe tape asindicatedinthefrontispiece.Make sure ,
theoxideor dull surface isagainstthe heads.
Step 4:Anchorthe tape intheslotontheemptyreelhubifdesired,
but a full tape turn counterclockwisearoundthereelhubis
usuallysufficient.
REEL
SUPPLY HOLD-DOWN TAKEUP
MICROPHONL MnNllLP LINE MICROPHONE
RECORD SELECTOR RECORD INPUT
LEVELLEVEL
Fig. 3-2. Tape Threading and Nomenclature
NOTE
Because machines usinghalftrack heads
recordorreproduceonlyhalfthe tape width,
the tape supplymustbesoorientedthatthe
halftoberecordedisfarthest from the tape
transport surface. Aftertheentire tape has
been woundontothetake-upreel from a re-
cording run,for instance, thetake-upreel
mustbeturnedoverandthe second halfre-
corded—orindentifiedfora laterrun.For
example: