Audio Research Dual 50 (1969-73)

Performance

Ultra-stable -

Ideally suited for complex loads such as electrostatic speakers. (May be operated into open circuit or any combination of reactive and/or resistive load.)

Unique circuitry -

Delivers superior performance under dynamics of music .

Overload Stability -

And lack of crossover distortion provides clean effective loudness of much larger amplifier.

Features

Exclusive new circuitry (U.S. Patent No. 768,460)

Conservative specifications

Quality construction

-1/8" anodized aluminum chassis

-Silicon power supply

-Thermistor controlled warmup

-Choke filtering

-Heavy duty epoxy-glass circuit board

-Conservative design

-Many precision parts

-Extra quality components

Unique guarantee

Although the information presented above provides definite clues to its outstanding performance, this amplifier employs design concepts for performance that does not readily translate from conventionally offered criteria.

Such common amplifier ills as crossover distortion, poor push-pull coupling, and power supply weaknesses are not necessarily revealed by conventional sine wave testing. In the Dual 50 design, special emphasis has been placed upon the ability to handle complex - wide dynamic range musical information into complex loads, resulting in definition previously unattainable.

Definition is not a characteristic normally associated with audio amplifiers. It cannot be measured as a identifiable quantity; it cannot be expressed in dB, watts or hertz. Definition in audio can be compared to "resolution" in photography. It is the accurate portrayal of teh original image, the faithful reproduction of both shape and texture. A high definition amplifier will reproduce the featheryhalo high of the tumpet, the delicate rasp of the violin and the sharp instantaneous attack of the piano. It will recreate characteristic tone and color not only when the instruments are played individually, but when played in combination as well, whether that combination be a jazz quartette or a full symphony orchestra.

The Dual 50 amplifier employs a partially cathode coupled output stage, providing tighter coupling and lower distortion than conventional circuitries. This is preceded by a unique new cross-coupled circuit which provides (a) very tight push-pull coupling, (b) balanced low distortiondrive, and (c) very stable long-term automatic balance. Push-pull feedback is employed around these stages. The phase inverter is also a very low-distortion automatically balancing circuit and is voltage regulated (together with the first stage of the cross-coupled circuit). It is also excluded from the overall feedback loop. Finally, an oversized power supply is used. These provisions insure its ability to perform properly regardless of signal levels or external load conditions.

Specifications

Power output: 50 watts RMS per channel, 30 Hz-15 kHz

Frequency response: 25 Hz - 20 kHz ±1 dB at 50W RMS

Input sensitivity: 1.15V RMS for 50W RMS output

Input impedance: 500 kΩ

Output taps: 4, 8 and 16 Ω

Load regulation: Approximately 1/2 dB/1 kHz - 1 dB/15 kHz

Damping factor: Approximately 14 to 1 kHz

Internal impedance: Approximately 1,1 Ω/16 Ω tap to 1 kHz

Distortion: Less than 0.1%, 1 kHz/50W RMS

Rise time: Approximately 20 µs

Hum & noise: 90 dB below rated output

Power requirements: 117 V 50/60 Hz, approximately 200 watts at idle, approximately 325 watts at full power

Tube complement: (2 matched pairs) GE6L6/KT-66/EL34, (3) 12AX7, (2) QA2, (4) 6FQ7

Dimensions (W x D x H): 16" x 9 1/4" x 7 1/2"

Weight: 38 lbs. Net, 45 lbs. Shipping

Technics SU-7300 (1978)

Constructed by technical standards usually reserved for sophisticated separate pre-amplifier and power amplifier units, the SU-7300 provides superb performance at a very reasonable cost. The excellent specifications only suggest the pure, natural, transparent sound this unit is capable of, when combined with components of equal caliber. Not to be overlooked are its elegant, brushed aluminum front and luxurius cabinet styling, which give it an appearance to match the beauty of its sound.

Current Mirror Loading Attains Extremely High S/N Ratio in Equalizer and Low Distortion in Power Circuits

A classic dilemma in amplifier circuitry is that higher operating current (for gain), produces a correspondingly higher level of noise. To solve this problem, Technics employs current-mirror loading in the differential amplifier first stages of the equalizer circuit and the power amplifier. The results are a higher S/N ratio in the equalizer and lower distortion in the power stage.

78 dB S/N Ratio (IHF) at 2,5 mV Phono Input Sensitivity.

The 78 dB signal-to-noise ratio is the eqivalent of a 1/8,000th noise component in the music signal. In real terms, this means that noise won't interfere with your enjoyment of music, even during very soft musical passages. This extreme "quietness" of the phono equalizer is another result of advanced current mirror circuit design.

RIAA Compensation Accurate Within ±0,3 dB.

The playback equalization characteristics of the SU-7300varies by only ±0,3 dB from the RIAA recording characteristic for phonograph records. It will produce no perceptible coloration of sound.

0,08% THD (20 Hz -20 kHz) at Rated Output

Amplifier power is useful only if it is delivered free of distortion. At any powerlevel, from a whispering 250 mW to the full roar of 41 watts per channel, the total harmonic distortion of the SU-7300 is an imperceptible 0,08%. The impressive distortion rating also applies to the low power output of 250 milliwatts. Use of the matched transistor pairs in a single package and the already mentioned current-mirror loading contribute to the low distortion.

Two-Way Dubbing

The tape selector circuit permits two tape decks to be connected at the same time  to the SU-7300. dubbing may be performed between the two decks in either direction.

Additionally, as the tape monitor and recording mode switches operate independently, you can use the SU-7300 to listen to a record or FM program source while tape dubbing is in progress.

41-Step Volume Control

To provide precise, repeatable volume settings, the volume control has 41 click-stops.

High Filter

Cuts down high frequency noise such  as record scratches and tape hiss. Cut-off slope is -6 dB at 8 kHz.

Direct Reading Power Meters

The large scale meters provide direct readout (at 8 Ω) of amplifier output power in watts, with instantaneous tracing of signal peaks. To improve linearity at low output, a germanium diode is uded for rectification. Two ranges are provided (x1 and x0,1) for accurate monitoring of all output levels.

Loudness Switch

Use of this feature boosts the lower and upper ranges of the audio signal to compensate for the poor response of the humen ear to extremes of frequency at low levels. It is useful when listening to music late at night, when the volume setting is very low.

Main, remote Speaker Connections

Two pairs of speakers may be connected. A pushbutton selector permits selection of either pair.

Specifications

Amplifier Section

Continuous Power (1 kHz):55 W + 55 W at 4 Ω (both channel driven); 43 W + 43 W at 8 Ω

Power Continuous (20 Hz - 20 kHz): 48 W + 48 W at 4 Ω (both channel driven); 41 W + 41 W at 8 Ω

Power Bandwidth: 8 Hz ~ 55 kHz , -3 dB (both channel driven at 8 Ω)

Total Harmonic Distortion:

0,08% at rated power (20 Hz - 20 kHz);

0,04% at half power (20 Hz - 20 kHz);

0,02% at half power (1 kHz)

Intermodulation distortion: 0,08% (60 Hz : 7 kHz = 4 : 1, SMPTE)

Residual Hum and Noise: 0,6 mV

Damping factor: 20 (4 Ω), 40 (8 Ω)

Input Sensitivity and Impedance:

Phono: 2,5 mV/47 kΩ

Tuner: 150 mV/47 kΩ

Tape1 Playback: 180 mV/47 kΩ

Tape2 Playback: 150 mV/47 kΩ

Tape1 Rec/Play: 180 mV/47 kΩ

Phono Max. Input Voltage: 150 mV (1 kHz, RMS)

Signal-to-Noise Ratio (IHF, A):

Phono: 78 dB

Tuner: 97 dB

Frequency Response:

Phono: ±0,3 dB, RIAA standard curve

Tuner: 7 Hz - 80 kHz, +0 dB, -3 dB; 20 Hz - 20 kHz, ±0,5 dB

Tone Controls:

Bass: +12 dB, -12 dB (50 Hz)

Treble: +12 dB, -12 dB (20 kHz)

High Filter: 8 kHz, -6 dB/oct

Loudness control (volume at -30 dB): 100 Hz, +8 dB

Output Voltage and Impedance:

Rec Out (Tape 1, 2): 150 mV/1,2 kΩ

Rec/Play (Tape 1) output: 30 mV/82 kΩ

Load Impedance: Main or Remote: 4 - 16 Ω

General

Power Consumption: 400 W

Power Supply: 110/120/220/240 V, 50/60 Hz

Dimensions (W x H x D): 410 x 139 x 334 mm (16-5/32" x 5-15/32" x 13-5/32")

Weight: 8,9 kg

Technics SU-7700 (1978)

Technics has expanded thier line of integrated amplifier to include this moderately-priced unit.
It features output meters, an effective subsonic filter, elaborate taping facilities and fine overall performance. Technics is rapidly becoming an important factor in the market, and this amp should help to continue that trend.

50 watts per channel, minimum RMS, both channels driven, at 8 ohms from20 Hz to 20 kHz, with no more than 0,08% THD.

Amplifier Section

Continuous power (1 kHz): 70 W + 70 W at 4 Ω (both channel driven); 53 W + 53 W at 8 Ω

Power (20 Hz - 20 kHz): 60 W + 60 W at 4 Ω (both channel driven); 50 W + 50 W at 8 Ω

Power bandwidth: 8 Hz ~ 55 kHz , -3 dB (both channel driven at 8 Ω)

Total Harmonic Distortion:

0,08% at rated power (20 Hz - 20 kHz);

0,035% at half power (20 Hz - 20 kHz);

0,01% at half power (1 kHz)

Intermodulation distortion: 0,08% (60 Hz : 7 kHz = 4 : 1, SMPTE)

Residual Hum and Noise: 0,6 mV

Damping factor: 25 (4 Ω), 50 (8 Ω)

Input Sensitivity and Impedance:

Phono: 2,5 mV/47 kΩ

Tuner, Aux: 150 mV/47 kΩ

Tape1 Playback: 180 mV/47 kΩ

Tape2 Playback: 150 mV/47 kΩ

Tape1 Rec/Play: 180 mV/47 kΩ

Phono Max. Input Voltage: 150 mV (1 kHz, RMS)

Signal-to-Noise Ratio (IHF, A):

Phono: 78 dB

Tuner, Aux: 97 dB

Frequency Response:

Phono: ±0,2 dB, RIAA standard curve

Tuner, Aux: 5 Hz - 80 kHz, +0 dB, -3 dB; 20 Hz - 20 kHz, ±0,5 dB

Tone Controls:

Bass: +12 dB, -12 dB (50 Hz)

Treble: +12 dB, -12 dB (20 kHz)

Equalizer Subsonic Filter: 30 Hz, -12 dB/oct

High Filter: 8 kHz, -6 dB/oct

Loudness control (volume at -30 dB): 100 Hz, +8 dB

Output Voltage and Impedance:

Rec Out (Tape 1, 2): 150 mV/1,2 kΩ

Rec/Play (Tape 1) output: 30 mV/82 kΩ

Load Impedance:

Main or Remote: 4 - 16 Ω

Main + Remote: 8 - 16 Ω

General

Power Consumption: 450 W

Power Supply: 110/120/220/240 V, 50/60 Hz

Dimensions (W x H x D): 410 x 139 x 334 mm (16-5/32" x 5-15/32" x 13-5/32")

Weight: 9,7 kg (21,4 lbs)

Maxell UD Reel-to-Reel Tape (1977)

Maxell UD

Ultra-Dynamic Master Quality High Fidelity Tape

Maxell UD permits a frequency response from 20 Hz to 24,000 Hz - limits that are beyond the range of many recorders. The dynamic range, too, is so wide as to allow high input signals to be recorded without distortion, while low strength signals are captured with full fidelity.

The binder system guarantees uniform coating of the oxide, which means virtually no dropouts along the lenght of the tape. Special surface polishing to a mirror finish means better tape-to -head contact for maximum fidelity.

The tape that's too good for most equipment.

Maxell tapes are not cheap. In fact, a single reel of our most expensive tape costs more than many inexpensive tape recorders. Our tape is expensive because it's designed specifically to get the most out of good high fidelity components. So it makes no sense to invest in Maxell unless you have equipment that can put it to good use.

The reason our tape sounds so good is because it's made so carefully.

Every batch of magnetic oxide we use gets run through an electron microscope. Because if every particle isn't perfect, the sound you hear won't be either. And since even a little speck of dust can put a dropout in tape, no one gets into our manufacturing area until he's been washed, dressed in a special dust-free uniform and vacuumed.

We clean off the crud other tapes leave behind.

After all the work we put into our tape, we're not about to let it go to waste on a dirty tape recorder head. So we out special nonabrasive head cleaner on all our cassettes and reel-to-reel tapes. Which is something no other tape company bothers to do.

Our tape comes with a better guarantee than your tape recorder.

Nothing is guaranteed to last forever. Nothing we know of, except our tape. So our guarantee is simplicity itself, anytime you ever have a problem with any Maxell cassette, 8-track or reel-to-reel tape, you can send it back and get a new one.

Give our tape a fair hearing

You can hear just how good Maxell tape sounds at your nearby audio dealer. (Chances are, it's what he uses to demonstrate his best tape decks.) You'll be surprised to hear how much more music good equipment can produce when it's equipped with good tape.

Maxell UD Compact Cassette (1977)

maxell UD

Ultra-Dynamic Professional Choice for High Fidelity

There are a number of reasons why professional recordists working in the cassette format choose, and prefer - Maxell UD cassettes. Foremost among these is the ferric oxide particle itself, a micro-fine coating of PX gamma-hematite for very wide range high fidelity reproduction.

The exclusive maxell thermal-hardening binder system is responsable for the notably smooth oxide coating, finished to a mirror surface for ideal head-to-tape contact and elimination of drop-out causing irregularities. Maxell UD cassettes are well known for extra high output lower noise, low distortion, and very wide dynamic range.

No wonder audio laboratories select Maxell UD cassettes to test the abilities of new recorders.

Any critic who wants to do a completely fair and impartial test of a tape recorder is very fussy about the tape he uses. because a flowed tape can lead to same very misleading results. A tape that can't cover the full audio spectrum can keep a recorder from ever reaching its full potential. A tape that's noisy makes it hard to measure how quiet the recorder is. A tape that doesn't have a wide enough bias latitude can make you question the bias settings.

And a tape doesn't sound consistently the same, from end to ebd, from tape to tape, can make you question the stability of the electronics.

If a cassette or 8-track jams,it can suggest some nasty, but erroneous comments about the drive mechanism. And if a cassette or 8-track introduces wow and flutter, it's apt to produce some test results that anyone can argue with.

Fortunately, we test Maxell cassette, 8-track and reel-to-reel tape to make sure itdoesn't have the problems that plague other tapes. So it's not surprising that most critics end up with our tape in thier tape recorders. It's one way to guarantee the equipment will get a fair hearing.

Our cassettes are put together as carefully as our tape.

Other companies are willing to use wax paper and plastic rollers in thier cassettes. We're not. We use carbon-impregnated material. And Delrin rollers. Because nothing sticks to them. A lot of companies weld their cassettes together. We use screws. Screws are more expensive. But they also make for stronger cassettes.

Maxell. The tapethat's too good for most equipment.

Nakamichi BX-125E

The BX-125 follows the Nakamichi BX series design philosophy of pursuing the highest performance at the lowest cost.

Employing a special Sendust laminate core record/playback head and a single capstan transport, the BX-125 provides wide, flat frequency responsenout of 20 kHz. Dolby B and C noise reduction are both included guaranteeing excellent signal to noise ratio. And like any other Nakamichi deck, 30 critical parameter adjustments are made on each unit to provide the accurate record/playback performance you have come to expact from, nakamichi.

Utilizing the most useful features from both the BX-150, the BX-125 is further testament to Nakamichi's committment to creating the best sounding beat quality cassette deck at an affordable price.

Features

Microprocessor Controlled Sisngle Capstan Silent Mechanism with remarkably low flutter.

Sendust Laminate Core record/Playback Head for exceptionally wide, flat frequency response.

Dual-Gap Ferrite Core Erase Head with excellent high-frequency characteristics

Low-Distortion, Low-Noise Recording, and Playback Amp.

Dual-Speed Master Fader Control for professinal fade-ins and fade-outs fingertip control>

Auto Repeat playback for repeat listening of the entire side of a tape or any section between a preset "000" tape counter position and of the tape, when used in combination with the Memory Stop function.

Memory stop for stopping the tape automaticay fromrewind at a preset "000" tape counter position

Dolby B-Type NR with ca. 10 dB noise reduction in the high frequency range and Dolby C-type NR with ca. 20 dB noise reduction in the critivcal 2 kHz - 8 kHz range, the range where the human ear is most sensitive to noise.

LED Pek level Meters with wide range of -30 dB to +7dN

MPX Filter to cut the 19 kHz Fm broadcast pilot signal (defeatable)

One-Touch Record Standby

Left/Right Record Level Controls

Timer Recording/Playback

Output Level Control

3-Digit Mechanical Tape Counter

3-Position Tape Selector

Output Level Control

Headphone Jack

Black and Silver versions available for matching other components.

Specifications

Track Configuration: 4 tracks/2-channel stereo

Heads: 2 (1 x erase, 1 x record/playback)

Motors:

Tape Transport:

1 x DC servo motor (capstan drive),

1 x DC motor (reel drive)

Power Source: 100, 120, 120/220-240, 220 or 240V AC; 50/60 Hz

Power Consumption: 23 W max.

Tape Speed: 1-7/8 ips. (4,8 cm/sec.) ±0,5%

Wow-and-Flutter:

Less than ±0,11% WTD Peak;

Less than 0,06% WTD RMS

Frequency response: 20 - 20,000 Hz

Signal-to-Noise Ratio:

Dolby C-Type NR on [70 μs, ZX tape] Better than 68 dB (400 Hz, 3% THD, IHF A-WTD RMS)

Dolby B-Type NR on [70 μs, ZX tape] Better than 62dB (400 Hz, 3% THD, IHF A- WTD RMS)

Total Harmonic Distortion:

Less than 1,0% (400 Hz, 0 dB, ZX tape);

Less than 1,2% (400 Hz, 0 dB, SX, EXII tape)

Erasure: Better than 60 dB (100 Hz, +10 dB)

Separation: Better than 36 dB (1 kHz, 0 dB)

Crosstalk: Better than 60 dB (1 kHz, 0 dB)

Bias Frequency: 105 kHz

Input (Line): 50 mV/40k ohms

Output

(Line): 0,5 V (400 Hz, 0 dB, output levelcontrol at max.) 2,2k ohms;

(Headphones): 2,2 mW into 8 ohms (400 Hz, 0 dB, output level control at max.)

Fast-Wind Time: Approx. 80 sec. (with C-60 cassette)

Dimensions: (WxHxD) 430 x 100 x 250 mm, ( 16-15/16 x 3-15/16 x 9-7/8 inches)

Weight: 5,0 kg, (11 lbs.)

Luxman PD 444 (1978)

Quartz-Locked Direct Drive Turntable with provision for mounting 2 tonearms (1978-80)

Quite frequently we encounter strong demand of audio buffs for a turntable which can use a long type tonearm or 2 tonearms.

Strange to say, however, there is no adequate one available on the marketplace.

To cater for such requirements, Luxman decided to develop an epoch-making turntable with provision for two tonearms, including a long one.

The Luxman PD444 is a direct drive quartz locked turntable, and its most outstanding feature is its ability to remove all kinds of external load variation thanks to our exclusive load free spindle system.

Additionally, the PD444 is made extremely resistant to howling and mechanical vibration by means of insulators of a 2-step brake system with the lowest resonant frequency, and an ultra heavy chassis of sandwich structure made from 2 thick iron plates and a high density chipboard.

Needless to say, all the necessary conditions for a high grade player are satisfied.

Load-Free Spindle Motor

Though basically quartz-locked direct drive system, a newly developped motor is employed to alleviate the load of the turntable platter applied to the bearing, which is named "Load-Free Spindle" system. The platter is made to float by offsetting most of its weight by repeling power of magnetics in the motor, which makes it possible to reduce the platter's weight on the bearing to about 1/5 of its actual value.

Even the best quartz-lock system is not a cure-all, and it is effective only in the suppression of external disturbing load variations ranging from DC to 1 Hz. To reduce those of relatively higher frequencies (5 - 10 Hz) that cannot be controlled by the quartz lock system, the flywheel effect of the platter must be utilized. The heavier the platter and consequently the larger its moment of inertia, the better.

But here arises a problem with respect to the life of the bearing. A prominent feature of this turntable lies in the beautiful solution of this problem. With the Load-Free Spindle system, the motor itself has the repelling power to float the turntable platter is made floating by an additional magnet device.

2 Step Brake Insulator

generally speaking with an insulator the lower the minimum resonance frequency (f₀) and the higher the sharpnes of resonance (Q), the better the cut-off characteristics. If "Q" is simply made higher, however, the turntable becomes unstable against vibrations of large amplitude in the vincity of "f₀". To cope with these incompatible factors, a new 2-step brake insulator was developed. The neoprene rubber supporting the shaft of the insulator works against vibrations of small amplitude which cause acoustic feedback, and good cut-off characteristics are procured. White to counter the vibrations of large amplitude effective are the spring and viscous brake of neoprene rubber with silicon grease are effective. In other words, both cut-off characteristics and stability of operation are made compatible.

Slim yet Ultra Heavy Chassis of Sandwich Structure

An unusually effective counter-measure against howling is hidden in the slim, compact appearance - an ultra heavy chassis of sandwich structure consisting of 2 pieces of 3,2 mm thick iron plate and a high-density chip board. The iron plate itself is heavy in weight but susceptible to resonance, and therefore a high-density chip board which absorbs resonance is inserted between 2 iron plates. Thus we realized an ideal solid and resonant-free chassis for a disc player.

Sliding Arm-base for Easy Replacement of Tonearm

precision arm-rails make it possible to instal any of your favorite tonearms with "one-touch" operation. It is constructed so as to fix the tonearm firmly at the optimum position by simple operation of a lever while sliding the arm-base in line with the over-hang gauge on the panel. The arm-base is made of die-cast zinc resistant to howling. Also a 5 mm thick extruded aluminium plate is employed as the arm panel in view of elegance at the surface and easy provision of various tonearms.

Platter Mat to Hold Disc Firmly

A platter mat fit for the shape of the disc is employed to ensure the closest possible contact between the mat and disc. The surface of the mat is specially treated to realize smoothness, and the mat is made of high-density rubber to damp the platter itself.

Other Features

Acrylic plates of 4 mm thickness are put together to form a dust cover, which is resistant to howling and external vibration. Also the hinge for the dust cover is incorporated into the slim chassis to provide a compact appearance. A semi-free-stop type hinge is used so that the total weight of the dust cover is applied to the turntable when it is closed. This also helps improve anti-howling characteristics.

Specifications

Phono Motor Section

Driving system: Direct drive

Motor: Crystal control, load-free spindle system, flat brushless DC servo motor

Platter: 300 mm (12") aluminium die-cast 2.5kg

Rotation: 33⅓ and 45 rpm

S/N ratio: no less than 75 dB

Wow and flutter: no more than 0.025% WRMS

Torque: 1 kg/cm

Temp. characteristics: below 0,00003% / C⁰

Turning accuracy: 0,002%

General

Acrylic Resin Cover: 4 mm thick (1,6") detachable with semi-free-stop hinge , 2,5 kg

Insulator: Low "f₀", 2-step brake type by means of spring, rubber and grease, height adjustable (range: 10 mm )

lock Indicator: Blue - 33⅓ rpm; Orange - 45 rpm

Arm Base: detachable, die-cast

Toneram Selector Switch: tonearm -1; tonearm -2 interchangeable

Power requirement: AC 120/220/ 240 V, 50/60 Hz

Power consumption: 16 W

Dimensions (W x H x D): 664 x 392 x 160 mm (26¼ x 63 x 154 inch)

Weight: 22 kg, (48,6 lbs) net

McIntosh MC 500 (1994)

The Mclntosh MC500 is a 500 watt per channel stereo power amplifier created in a stunning new contemporary industrial design. Two 5½ inch True Power Output meters are mounted behind the ½ inch thick glass front panel. The high efficiency of the MC500 circuits together with oversize heatsinks utilizing convection cooling eliminates the need for internal cooling fans. Typical Mclntosh attention to detail includes the use of 1% metal film resistors and polypropylene capacitors throughout. Internal heatsink module connectors use gold plated contacts to ensure reliable operation. Gold plated Balanced as well as Unbalanced Input connectors ensure reliable signal transfer.

A rear panel MODE switch is also provided to change the MC500 output configuration from a 500 watt per channel STEREO amplifier to a 1000 watt bridged mono amplifier The patented Mclntosh Power Guard circuit in each channel eliminates the possibility of overdriving the MC500 amplifier into clipping distortion. Mclntosh Sentry Monitor Output protection circuits are also included. You ensure maximum amplifier reliability and long operating life with absolutely no sonic limitations or compromises.

Each channel is coupled to the loudspeaker loads by a Mclntosh Output Autoformer with matched impedances of 2, 4 and 8 ohms. Each channel of the MC500 can produce a peak current output of more than 112 amperes, the highest ever for a Mclntosh stereo power amplifier. The MC500 can successfully drive any type of loudspeaker. With a distortion limit of less than 0.005%, the MC500 power amplifier is absolutely transparent, ensuring total sonic accuracy.

Features:

Two 5 inch illuminated output wattmeters read the True Power Output by measuring output voltage and current simultaneously.

Includes two McIntosh Output Autoformers

2, 4 and 8 ohms output impedances

Bridge Mono capability

Gold plated, multi-way output.

1% metal film resistors and polypropylene capacitors used throughout

Balanced and Unbalanced inputs

Exclusive McIntosh Power Guard non clipping circuit

Peak output current of 112 amperes

BRIDGED (MONO) OUTPUT

In BRIDGED Mono configuration the outputs of the two channels of the MC500 will combine to produce 1000 watts. All performance specifications for the stereo configuration will be exactly the same in BRIDGED Mono configuration, but with double the power. In BRIDGED Mono Configuration, only the BRIDGED Output terminals marked +4, +8, +16, -4, -8, and -16 are used. The COM (Common) terminals are not used.

DESIGN PHILOSOPHY

The design philosophy incorporated in the MC500 involved many different techniques, all based on sound scientific logic. Every stage of voltage or current amplification is designed to be as linear as possible. Negative feedback is then utilized to enhance the performance.

Mclntosh engineers know how to properly design negative feedback circuits so they contribute to the extremely low distortion performance expected from a Mclntosh amplifier. The typical Mclntosh owner would never accept the approximately 100 times higher distortion

of many so called non-feedback designs. All transistors are selected to have nearly constant current gain (Beta) over the entire current range they must cover. Output transistors in particular, must have matched uniform current gain, high current-bandwidth product and large active region safe operating area. Resistors and capacitors in the signal path are carefully selected to have exceedingly low voltage coefficients, (change of resistance or reactance with applied voltage). Precision metal film resistors, low dielectric absorption film capacitors and premium audio grade electrolytics are used in all critical circuit locations.

PROTECTION CIRCUITS

Some power amplifier manufacturers claim that their products do not need or do not use protection circuits and that such circuits compromise performance. Mclntosh feels that protection circuits are desirable and necessary to prevent amplifier or loudspeaker damage due to abnormal circumstances. The genius of Mclntosh engineering has resulted in protection circuits which do not effect or compromise the normal performance of a power amplifier. Six different types of protection circuits are incorporated in the MC500 to insure it a long, safe and trouble free operating life. This is just one of the characteristics of Mclntosh power amplifiers that have made them world famous. The SENTRY MONITOR circuit is a good example

SENTRY MONITOR CIRCUIT

All power transistors have limits for the maximum amount of power they can handle. The MC500 output transistors and power supply have been designed to allow very high current flow into properly matched load impedances. However, if a short circuit or very low load impedance were connected to the MC500 outputs, destructive current levels could be reached if it was not controlled by the Mclntosh SENTRY MONITOR circuit. This circuit senses the dynamic operating time, voltage and current of the output stage, and controls it to safe operating limits. The SENTRY MONITOR circuit does not limit the power output available from the amplifier.

There is absolutely no compromise in sonic performance and it ensures safe operation of the amplifier under even the most extreme operating conditions.

THERMAL CONTROL

All power transistors have limits to the maximum amount of heat they can safely tolerate. The MC500 uses a highly efficient amplifying circuit which produces relatively little heat from the power transistors for the output power produced. The amplifier uses large area heat sinks with an area of more than 2800 square inches to efficiently dissipate the transistor heat. Natural convection air flow is sufficient for safe cool operation. Cooling fans are not required. If the cooling air is blocked, or the amplifier operating temperature is forced too high, thermal cutout switches will turn off the AC power to the amplifier. When the problem is corrected and the amplifier cools to its normal operating temperature, the AC power will turn back on.

POWER GUARD

The MC500 includes the unique patented Mclntosh POWER GUARD circuit on each channel. POWER GUARD eliminates the possibility of ever overdriving the amplifier into clipping. Clipping occurs when an amplifier is overdriven past its output design capabilities. An overdriven amplifier can produce both audible and ultrasonic distortion levels approaching 40%. The audible distortion is certainly unpleasant, but the ultrasonic distortion is also undesirable, since it can damage tweeter loudspeakers.

The Mclntosh POWER GUARD circuit acts as a waveform comparator, monitoring both the input and output signal waveforms. Under normal operating conditions there are no differences between these waveforms. When an amplifier is overdriven beyond its maximum distortion free output, there will be a difference between the two signal waveforms. If the difference exceeds 0.3% (equivalent to 0.3% harmonic distortion), the amber POWER GUARD indicator will light. If the difference continues to increase, the POWER GUARD circuit controls an electronic attenuator at the input of the amplifier to reduce the gain just enough to prevent any further increase in distortion. Distortion will not exceed 2% with as much as 14 dB overdrive.

Without POWER GUARD, the distortion could easily reach 40% for the same operating conditions. A Mclntosh power amplifier with POWER GUARD will always deliver its maximum distortionfree output. This power is always well above the rated power due to the Mclntosh philosophy of conservative design. You will never experience the harsh and damaging distortion due to clipping when using a Mclntosh MC500 amplifier with POWER GUARD

TRUE POWER OUTPUT WATT METERS

Two illuminated 5½ inch WATT meters are provided on the MC500 front panel. The meters are peak responding and their circuits are constantly reading both voltage and current delivered to the loudspeaker loads. The load impedance of a loudspeaker may differ at various parts of the audio frequency range, resulting in a change of output current requirements. The MC500 meters react to these changing current and voltage conditions and indicate the true amplifier power output of each channel at all times.

in the METER WATTS position, the meters respond to the musical information and read the amplifier output of each channel on a continuous basis. In the METER HOLD position the meters will lock to the highest power peak in a sequence of peaks. If no higher power peaks are reached the meter pointers will slowly return to the lower power level. If the music stops, the meter pointers will return to the rest position. The meter pointer decay rate is approximately 6dB per minute. The MC500 output meters are extremely accurate, and will respond to 9 5% of full scale, with only a single cycle of a 2,000 Hz tone burst. In MONO operation, the two meters will read identical power levels. The total mono power output of the amplifier will be the sum of these readings.

THE VERSATILE McINTOSH OUTPUT AUTOFORMER

All transistor power output circuits work best into what is called an optimum load. Depending on the number and configuration of transistors used, this optimum load may vary considerably from what a loudspeaker requires. In the case of more than one loudspeaker connected in parallel, the impedance load reflected to the power amplifier may drop to two ohms or even less.

A power amplifier connected to a load that is lower than optimum causes extra current to flow and extra heating of the power transistors. This means the amplifier will run much hotter, with a corresponding reduction in operating life.

The output signals from the two channels in the MC500 are coupled into the autoforrner at the point on the windings that is an optimum impedance match for the transistors in the output circuit. The MC500 amplifier output circuits are always operating at their highest possible efficiency.

The MC500 autoformers include output impedance taps for exact loudspeaker matches of 2 ohms. 4 ohms and 8 ohms. Loudspeaker performance will always be at its best Any Mclntosh power amplifier with an autoformer is especially well suited for stereo installations that require multiple speakers, since it is possible to have a very close impedance match.

The frequency response of a Mclntosh autoformer exceeds that of the output circuit itself, and extends well beyond the audio range. Its distortion level is so low it is virtually impossible to measure. The Mclntosh Autoformer is quite simply a significant engineering advance in power amplifier performance and reliability. The unequaled expertise of Mclntosh in the design and manufacturing of autoformers is legendary in the high fidelity industry. In the rare event of output circuit failure, the Mclntosh autoformer will conduct any speaker damaging DC (direct current), directly to circuit ground. This will protect your valuable loudspeakers from possible damage.

ADDITIONAL FEATURES

Heavy duty high current gold plated output terminals will accept speaker cables up to 0.204 inches (5.18 mm) in diameter. It is easy to connect speakers using any of the currently popular speaker cables

Both Balanced as well as an Unbalanced input jacks are provided for complete flexibility in any installation.

SPECIFICATIONS

Power Output:

500 watts per channel into an 8, 4 or 2 Ω load is the minimum sine wave continuous average power output

1000 watts Mono into a 16, 8 or 4 Ω load is the minimum sine wave continuous average power output

Rated Power Band: 20 to 20,000 Hz

Total Harmonic Distortion:

0.005% maximum harmonic distortion at any level from 250 milliwatts to rated power output

Dynamic Headroom: 2.1 dB

Frequency Response:

+ 0, -0.25 dB from 20 to 20,000 Hz

+ 0, - 3.0 dB from 10 to 100.000 Hz

Input Sensitivity:

2.2 volts, Stereo Balanced and Unbalanced

2.2 volts, Mono Balanced

3.2 volts, Mono Unbalanced

A-weighted Signal-to-Noise Ratio: 85 dB (115 dB below rated output)

Intermodulation Distortion, SMPTE: 0.005% maximum if instantaneous peak power output does not exceed twice the output rating

Wide Band Damping Factor: 200 at 8 Ω output

Input Impedance: 10,000 Ω

Power Guard: Clipping is prevented and THD does not exceed 2% with up to 14 dB overdrive at 1000 Hz

Power Requirements: 120 volts. 50/60 Hz, 12 amperes UL/CSA

Dimension including front handles (W x H x D): 438 x 264 x 511 mm (17¼ x 10⅜ x 20⅓ inches)

Weight: 51,7 kg (114 pounds)