What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Audio Research SP11

 The SP11 is a hybrid unit, utilizing both vacuum tubes and FETs (Fiel Effect Transistors). It is not intended that this product should somehow continue the controversy of "vacuum tubes" vs. "solid-state". Rather, in keeping wit Audio Research's design philosophy of advancing the state-of-the-art., each type of device is used where it performs best.
One important result, aside from the dramatically improved quality of sound reproduction, is the use of only six vacuum tubes - tubes which need not be selected low-noise types. A significantly longer time between tube replacement is also expected.
As a last word, this preamplifier may well change your thinking about music reproduction. Because it is so incredibly "open" sounding, much information not previously sudible is available, providing new insight and enjoyment from many sound sources. To be appreciated, the SP11 preamplifier must be personally experienced; it cannot otherwise be adequately related.
 Operational Features:
Automatic warmup, brown-out power-line interruption muting and manual muting at all preamplifier outputs, with new shunt circuitry.
Subsonic phono filter with 6 dB /oct rolloff (to eliminate ringing) with transition to 12 dB/octave.
Bypass switch for use with "audiophile quality" program material.
Absolute phase switch for main outputs, plus unswitched inverting and non-inverting outputs.
Full tape functions; two inputs, two recording outputs, plus tape copy and tape monitor functions.
Input/output connectors have heavy gold plating and connect "ground" before "hot".
Level set control in addition to normal gain control. Allows essentially unlimited input signal range while preserving optimum gain control usage.
Toroid power transformer for low mechanical noise and low external magnetic field.
 In Octobr of 1985, Audio Research Corporation introduced the SP11 preamplifier. During the first year, our introductory claim of "a new reference standard" has been confirmed by reviewer after reviewer throughout the Free World.. It is improbable that any audio product, including previous Audio research products, has ever received such unanimous acclaim. We believe that once you hear the SP11 reproduce music, you will find that acclaim justified.

Frequency Response:
High Level Input :  0,2 Hz to 100 kHz ±1 dB (-3 dB below 0,1 Hz and above 200 kHz)
Phono Input:  20 Hz to 40 kHz ±2 dB of RIAA (±1 dB of RIAA, 1,0 Hz to 100 kHz)
Harmonic Distortion:  less than 0,005% at 2 V RMS output, 5 Hz to 20 kHz (Typically less than 0,001% at midband, phono or line input)
Intermodulation Distortion:  less than 0,003% at 2 V RMS output
Gain (aat 1 kHz , bypass mode):
Phono Input to Tape Output :  46 dB (0,2V output from 1mV input)
Phono Input to Main Output :  75 dB (0,175 mV input for 1 V output)
High Level Input to Main Output :  29 dB (36 mV input for 1 V output)
Inputs:  Phono, Tuner, CD, Video, Spare, Tape 1, Tape 2,
Outputs:  Tape 1, Tape 2, Main 1, Main 2, Direct, Invert
Filter:  25 Hz Hi-pass phono subsonic 6 dB/octave rolloff (to eliminate ringing) with transition to 12 dB/octave at 10 Hz. Front panel switchable, phono only
Controls:  Gain, level (to set gain Range), balance, Mode, Input, Impedance
Switches: Tape Monitor, Copy, Tape 1/2, Tape 1 to 2/2 to 1, Mute, Invert Phase,Bypass, Filter
Input Impedance:
Phono :  47 k Ω, 100, 30, 10, 3 Ω (front panel selectable)
Phono Input Capacitance:  150 pF at 10 kHz
High Level:  20 k Ω or higher, depending on switch functions
Maximum Inputs Level Undistorted:
Phono :  350 mV RMS at 1 kHz, 1200 mV RMS at 10 kHz (0,1 second maximum duration, 6 dB less if continuous)
High Level :  25 Volts RMS
Output Impedance:  250 Ω main, direct, invert outputs, 500 Ω tape output. Recommended load 60 k Ω and 100 pF (25 k Ω minimum, 1000 pF maximum)
Rated Output:  2V RMS 1 Hz to 100 kHz main, direct, invert outputs (Maximum 80 V RMS output at 0,2% T.H.D. at 1 kHz into 60 k Ω load with 2,85 V RMS high level input)
Tape Outputs, Direct Output;  Non-inverting
Invert Output :  Inverting
Main Outputs :  selectable non-inverting or inverting. All outputs may be used simultaneously.
Noise (IHF Weighted, shorted input):
Output (Gain down) :  6 µV (110 dB below rated output)
Input High Level) :  3 µV equivalent input (110 dB below 1 V input)
Phono :  0,15 µV equivalent input (76 dB below 1 mV input)
Tube Complement (Hybrid FET/Tube Audio Circuit, Solid-State Power Supply):  6 - 6DJ8/ECC88
Power Requirements:  95 - 135 V AC 60 Hz (Export 190 - 270 v AC 50/60 Hz)
Power Consumption:  130 watts maximum
Dimensions (W x H x D) Each Chassis, EIA Rack panel Mounting:
480 x 134 x 260 mm (19" x 5,25" x 10,25")
Weight Net:
SP11 :  6,4 kg (14 lbs)
SP11PS :  6,8 kg (15 lbs)  

Audio Research M300

M300 Hybrid Monaural Power Amplifier - Audio Research Corporation developed and patented new circuitry allowing hybrid utilization of Fets with vacuum tubes in ways which can bring out the best in both devices. This circuitry is used in the relatively new, but already widely-acclaimed SP-11 preamplifier. Drawing from this technology, Audio Research has designed a new hybrid power amplifier, designated the M300 - a monaural unit rated at 300 watts.

Hybrid Monaural Power Amplifier
Most hybrid power amplifier designs use small signal-input vacuum tubes, then rely on FETs for the output stage. Audio Research has chosen instead to eliminate these low-level input tubes - tubes which can be prone to problems with hum, noise, microphonic, drift and, of course, require periodic replacement. The new FET "front end" is combined with Audio Research's long-famous, patented cross-coupled circuit to provide a design offering exemplary stability, reliability (low maintenance), and superior performance.
These design advances have been coupled with yet another Audio Research patent; an output stage utilizing vacuum tubes, and partially cathode-coupled (as all previous Audio Research vacuum tube amplifiers have ben), but with the screen (or accelerating) grids operating with a signal voltage precisely in phase with the cathode voltage. True "pentode" operation and efficiency is thereby achieved; however, all thr advantages of partial cathode coupling are maintained .
Advantages include:
Efficiency up to 60% above. (Class "A" designs achieve 25% to 50% typically 30% to 35%)
Inherently better cross-coupling
Output transformer with lower "turns" and "impedance" ratios, resulting in greater bandwidth.
Partial cancellation of saturation effects of the "DC" inn the output transformer's core
Switching transients essentially eliminated, rendering the question of class of operation ("A", "AB", etc.) irrelevant. The virtues of Class "A" operation without the usual drawbacks
Bias adjustment is essentially non-critical.
Output tubes need not be matched, although slighty better performance will result if they are.
Lower internal impedance improves handling of complex speaker loads.

Operationsl Features:
Front-panel replaceable line and screen voltage fuses, with LED indicators.
Two integral, low-noise fans for cooler operation, longer tube life. Front-panel switch allows "Hi" and "Lo" speeds.
"Standby" switch for lower power consumption and less heat during warm-up periods or telephone interruptions.
Automatic muting circuit provides silent shutdown upon power shut-off or interruption. No "thump" from speakers.
Gold-plated input connectors connect "ground" before "hot".
1, 2, 4 and 8 ohms output taps.
Front and rear handles for easier handling

Tube Saver protection Circuit
The M300 Power amplifier contains a remarkable new circuit called the :Tube Saver" it's a small secondary circuit board located on the back side of the main board in the amplifier. Primarily, the "Tube Saver" reduces stress to tubes and associated driving Fets. As an overload protection circuit, it is triggered only when abnormal current is sensed from a cause like those listed  below. Under even extreme conditions of normal use (i.e. extremely high playback levels), the circuit is designed to remain inactive. When triggered, the circuit immediately shuts down th eoutput stage and indicates protection mode by dimming the "Screen" LED. At this point, the amp should be manually switched off, then restarted after a period of 30 seconds.

Power Output:  300 watts minimum continous at 8 Ω, from 16 Hz to 25 kHz with less than 0.5% T.H.D. (typically below .005% at 1 watt).
Approximate Actual Power Available at Clipping:  330W at 1 kHz, nominal.
Power Bandwidth:  10 Hz - 60 kHz (-3 dB Points)
Input Sensitivity:  1,5 V RMS for rated output
Input impedance:  60 k Ω, nominal
Output Regulation:  Approx. 0,3 dB, 8 Ω load to open circuit (Dampping factor approx. 30)
Negative Feedback:  20 dB
Slew Rate: 25 volts/microsecond
Rise Time: 3 microseconds
Hum and Noise: less then 2 mV RMS 90 dB below rated output (broad-bandwidth unweighted, inputs shorted)
Power Supply Energy
Storage:  approx. 350 joules
Power Requirements:  105 - 125 V AC 60 Hz (210 - 250 V  AC 50 Hz); 900 watts at rated output, 450 watts at "idle" - 130 watts at "standby"
Dimensions (W x H x D):  480 x 270 x 410 mm (19" x 10,5" x 16")
Weight:  50 kg (110 lbs) net

Tubes required:  8 - 6550 Power Output (matched pairs will yield marginally better performance)

Ampex ATR 100 Series

In the three decades since Ampex introduced the first commercially feasible audio tape recorder in the U.S., many newer and improved recorders have come along. None of them, however, represented as great a step forward as this newest Ampex triumph , the ATR-100 Series.
The ATR-100 is a different means vastly better performance by any measurement.
Look at the specifications. Some of them are as much as an order of magnitude better than any other recorder now available. Look at the all-new matrix-type control panel, designed to be used as efficiently as a hand-held calculator. Look at the editing capabilities, unrivaled by any audio recorder.
Look at its adaptability to any world recording standards and techniques. Look at its maintainability, requiring only a handful of tools.

Incredible as it sounds,  ATR-100 performance specifications are as much as an order of magnitude better than any presently achievable on any other audio recorder. A bold claim, especially in view of the conservative approach that Ampex traditionally takes toward quoted specifications.

Distortion - Third harmonic distortion and intermodulation distortion are both at least an order of magnitude better. Third harmonic distortion is less than 0,3% at a recorded flux level of 370 nWb/m (0VU). Intermodulation distortion is less than 1,0% at the same recorded flux level.

Signal-to-Noise - This specification depends, on tape speed and the particular technique of measurement used. Any way you measure it, ATR-100 Signal-to-Noise is significantly better than any other audio recorder. For example it is in excess of 80 dB at 30 in/s, ANSI "A" weighted.

Frequency Response - Ferrite heads and fluxgate head design deliver unbelievable response. Again, specs depend on tape speed and the range of frequencies measured, but look at ATR-100 response at 15 in/s over the commonly used range of 100 Hz to 15 kHz just ±3/4dB.
You can actually see the superiority of the ATR-100's semi-automatic phase equalization by observing on a scope how remarkably well it makes square waves. This outstanding phase response is achieved by a unique record circuit.

Flutter - this specifications also depends on tape speed and measurement technique, but consider a worst case. At 30 in/s the ATR-100 achieves full flutter spec in 0,5 second.

Speed/Timing Accuracy -  The triple servo transport and unique capstan combine to deliver superb speed accuracy. Speed variation from the beginning to the end of a full 2400-foot reel is just ,02% maximum.
These specifications are only a few examples of the unprecedented performance of the ATR-100 also allow it to use higher coercivity tape than any now available. When better tape is here the ATR-100 can take full advantage of it.

It even looks dofferent. Any ATR-100 Series  recorder is built around the basic machine, consisting of the transport with audio and transport electronics. There is an unbalanced input-output circuit with no meters and no operator adjustments, and in some places and some applications , that's enough. Yet all the advantages are here.
There is nothing traditiona about the transport except Ampex quality. A super-rigid aluminum transport casting supports the fully servoed tape handling system. Both reel motors are servoed, as is the capstan, which has no pinch roller. You're assured of precise speed accuracy with constant tape tension at all times. With no tension adjustment , the ATR-100 handles any reel size from 2 inches to 14 inches in diameter.
The ATR-100 also treats your valuable tapes with a special brand of kindness. When you thred up a tape and engage the servos, constant tension takes over to insure that you never stretch a tape. You have positive gentle control of tape motion in either direction at any speed, with complete confidence.
Dynamic braking on the ATR-100 also contributes to smooth tape handling, and also takes over in the event of a power failure to prevent tape damage. The ATR-100 always stops in a programmed manner, even without ower.
Ferrite heads, unrivaled fro performance and long life, are used in the ATR-100. ceramic tape guides help provide precise tracking accuracy with gentle tape guidance. For additional protection, there is also a unique head gate that can be raised and lowered.
Four standard record playback speeds are available on all ATR-100 Series recorders, any two of which can be selected - or changed - by the user. The speeds do not even have to be adjacent. Choose any pair from 3-3/4, 7-1/2, 15 or 30 inches per second. You can order a 7-1/2 - 15 in/s version, for example and later set it up for any other speed pair, even 3-3/4 and 30 in/s if you wish.
A speed selector knob for all four speeds is located on top of the head assembly cover. If a speed is selected other than the pair for which the machine is set up, the machine won't start, and a lamp near the selector knob illuminates as a reminder.

Control Panel
No other features of the ATR-100 is more visually and functionally up-to-the minute than the new matrix-type control panel with LED indicators. With channel selectors and mode controls so conveniently arranged, any operator will soon find himself working more smoothly and efficiently than ever. What's more, the control panel can be mounted on either the right or the left side of the transport.
All transport controls have international symbols. There is no restriction on sequencing you can go from any transport mode to any other without going through Stop and without waiting for the machine to slow down or speed up.
An optiona remote control panel with a 25-foot cable contains all functions except Dump Edit and deactivable servos.
An extremely accurate integral tape timer is standard equipment on the ATR-100. its bright display reads in hours, minutes, and seconds, or you can set it up to display minutes, seconds, and tenths if you wish.

If your application requires more than just the basic ATR-100, then you can add optional input-output modules for a full capability one, two or four-channel recorder (ATR-101, ATR-102, or ATR-104, respectively). Each I/O module include the normal balanced input and output circuitry and its own matering. You can even switch the metering between ASA balistics with VU indication, or EBU balistics with Peak indication.

Along with all its perormance benefits, the ATR-100 offers a number of features that make editing faster and easier.
First of all, the Ampex PURC (Pick Up Record Capability) is standard on all ATR-100 Series recorders. PURC gives you perfectly timed edits by eliminating the overlap at the beginning and the hole at the end of an edit.
ATR-100 machines can wind tape at speeds that you have to see to believe. You can wind a full 2400 foot reel to another reel in just 60 seconds. Spoot Mode alows you to spool tape off for storage at 60 or 180 in/s in either direction.
Once you reach an edit point, using the integral tape timer as an aid, you can position the tape precisely by turning the knob on top of the capstan, using just one hand. You don;t have to rock the reels by hand.

To split tape, the ATR-100 can be placed in Dump Edit mode. In this mode, the takeup tension arm is employed as a pinch roller, allowing the operator to split tape in a controlled manner.

Tape Widths:  1/4 inch (6,3 mm ) for full track and 2 track 2 channel systems , 0,075 inch (1,9 mm ) track width 1/2 inch (12,6 mm ) for 40track systems, 0,070 (1,8 mm) track width
Tape Speeds:  3,75 in/s (9,5 cm/s); 7,5 in/s (19,05 cm/s); 15 in/s (38,1 cm/s); 30 in/s (76,2 cm/s) [any two speeds may be selected]
Reel Size:  2-inch to 14-inch diameter (50 mm - 355 mm )
Reel Type:  NAB
Inputs (with Input/Output system - bridging  input standard)
Balanced, Floating
Input Impedance : 50 k Ω, Resistive ±5,0 %, 5 Hz - 20 kHz
Input level (Variable)
Minimum :  -5 dBm, to produce 1000 nWb/m recorded flux level
Maximum :  =40 dBm
Input clip level, including record amplifier at mid-freq 26 dB above system operating level
Input Level (preset)
-1 dBm to +20 dBm to produce 1000 nWb.m recorded  flux level
Outputs (with Input/Output system)
Balanced, Floating
Output Impedance :  les than 50 Ω, 5 Hz - 20 kHz
Maximum Output Level
With 600 Ω load :  +26 dBm
With 200 Ω load :  +25 dBm
Preset Output Level
Line output level is adjustable over a range of +12 dBm to -2 dBm
Meters are switchable, VU or peak
VU balistics conform to ASA standards
Peak balistics conform to EBU standards
Zero meter reading is continuously adjustable  over a range of +12 dBm to -2 dBm line level
Inputs (without Input/Output system)
Input Impedance:  10 k Ω min., 5 Hz - 20 kHz
Input Level :  -5 dBm, nominal, for system operating level
-5 dBm, input level provides 26 dB clip level margin at mid-freguency
Outputs (without Input/Output system)
Output Impedance:  40 Ω, 5 Hz - 20 kHz
Maximum load Impedance: 5 k Ω
Output level :  -5 dBm, nominal, for system operating level
-5 dBm output level provides 26 dB clip level margin
 at mid-frequency
Overal Frequency Response (within ±2 dB)
At 30 in/s :  35 Hz - 28 kHz
At 15 in/s :  20 Hz - 20 kHz
At 7,5 in/s :  30 Hz - 15 kHz
3,75 in/s :  30 Hz - 10 kHz
Signal-to-Noise Ratio (full tarack format, 30 Hz - 18 kHz unweighted)
At 30 in/s :  77 dB (AES equalization)
At 15 in/s :  73 dB (NAB equalization)
At 7,5 in/s :  75 dB (NAB equalization)
At 3,75 in/s :  66 dB (NAB equalization)
Signal-to-Noise Ratio (full tarack format, ANSI "A" weighted)
At 30 in/s :  81 dB (AES equalization)
At 15 in/s :  77 dB (NAB equalization)
At 7,5 in/s :  78 dB (NAB equalization)
At 3,75 in/s :  62 dB (NAB equalization)
Wow and Flutter (NAB, RMS unweighted):
At 30 in/s :  0,03%
At 15 in/s :  0,04%
At 7,5 in/s :  0,06%
At 3,75 in/s :  0,1%
Basic Machine (including transport, power supply, audio and servo electronics):
(W x H x D) 19" x 15,72" x 12" (48,26 x 39,93 x 30,48 cm)
Cabinet (1 or 2 channel :
(W x H x D) 21" x 19" x 32" (53,34 x 48,26 x 81,28 cm)
Cabinet (4 channel):
(W x H x D) 21" x 23" x 34" (53,34 x 58,42 x 86,36 cm)
Input/Output System :
(W x H x D) 19" x 3,5" x 10" (48,26 x 8,89 x 25,4 cm)
Complete System (including basic machine, 4-channel cabinet, Input/Output system and roll-around pedestal):
(W x H x D) 26" x 46,5" x 34" (66,04 x 118,11 x 86,36 cm)
Basic Machine :  125 lbs (56 kg)
Cabinet :  15 lbs (7 kg)
Input/Output System 2-Channel :  15 lbs (7 kg)
Pedestal :  50 lbs (23 kg)
Power Line Requirements:  90 - 115 / 110 - 135 / 180 - 230 / 220 - 270 V AC; 50/60 Hz
Power Consumption:  0,6 k VA maximum
Environmental Operating Specifications:
Temperature :  10° - 50° C (50° - 122° F)
Humidity :  20 - 95%, non-condensing

Denon PRA-1003

PRA-1003 Control Amplifier was introduced as a control amplifier for the new era, bringing into full play the operation factors of a tape deck which has come to assume an important position as the program source. By introducing new circuitry, it incorporates a high Signal-to-Noise  ratio equalizer amplifier, low distortion, and ultra wide range flat amplifier.

Input capacitorless (ICL)
Low noise FET parallel differential amplifier circuitry in the first stage, current mirror differential predrive pure complementary PP output with emitter follower, 14 transistors on one channel, high Signal-to-Noise 86 dB, and equalizer amplifier
Phono 2 is provided with an impedance change-over switch which will bring out the full performance of the cartridge. Input terminals are all gold plated
Simultaneous recording of 3 tape decks, 1 (2/(3 tape copy possible. Rec Function to meet the are of real recording

Type:  ALL silicon transistor stereo control amplifier
Input Sensitvity/Impedance: 
Phono 1 :  2,5 mV/50 k Ω
Phono 2 :  2,5 mV/30, 50, 100 k Ω
Max. Allowable Input:  320 mV (1 kHz)
RIAA Deviation:  ±0,2 dB (20 Hz - 20 kHz)
Max. Output /Rated Output:  10 V/1 V
Total Harmonic Distortion:  0,003% (20 Hz - 20 kHz, 3 V)
Frequency Response:  10 - 100 kHz +0 dB, _1 dB
Signal-to-Noise Ratio:  better than 86 dB (IHFA network)
Gain Control:  0, -10, -20 dB (0 dB =16,5 dB)
Low :  20 Hz (18 dB/oct)
High : 9 kHz (6 dB/oct)
Crosstalk:  -100 dB (20 Hz - 1khz); -80 dB (20 kHz) - (Phono In - output, defeat)
Power Supply:  AC 120 / 220 - 240 V, 50/60 Hz
Power Consumption:  10 W
Dimensions (W x H x D):  410 x 170 x 270 mm
Weight:  7 kg