Marantz Model 2

 The Marantz Power  Amplifier has been designed and constructed to give a long, trouble-free life of line listening quality. Here is the type of performance and workmanship that previously was found only in high quality Broadcast or Laboratory equipment. A built-in metered test instrument permits simple, accurate adjustments for optimum performance.

 "The Model 2 power amplifier followed in 1956. largely completed by Sidney Smith, it was a very successful tube design using EL34's in ''ultra-linear'' (push-pull) configuration.

… some sources cite the Model 2 as the beginning of Smith's exclusive concentration on power amplifiers while Saul focoused his attention on preamplifiers,…" (from Marantz History)

 40 Watt / 20 Watt Switch

This unit has been designed primarily as a 40 watt ultralinear amplifier. Speaker systems of a lower power rating could easily be damaged by unwanted pulses coming through at full power. To protect these systems we have incorporated a switch which changes the output connections to Triode operation limiting the power output to 22 or 23 Watts. This control, located near the output terminal strip, is marked '40 Watt UL' and '20 Watt TRI'.

 Input Connections

There is a choice of three input connections to the Marantz Power amplifier.

Pre-Amp: This input is recommended for most preamplifiers. At this connection a 2 volt signal will drive the amplifier to it's full output. A subsonic filter rolls off frequencies below 20 cycles so as to supress speaker "breathing" and other subsonic disturbances.

High Gain, Filtered: For preamplifiers that have a low output voltage capability. Also may be used where loudspeaker has very low efficiency. A signal of 0,7 volts is required here for full 40 watt output. Subsonic filtering is also in effect.

High Gain, Unfiltred: Same as above in sensitivity but without the subsonic filter, response being maintained to below 2 cycles. This input is direct to the input grid and is used in testing frequency response or for special applications where subsonic response is needed.

 Output Connections

When not using Variable Damping:

Use "Ground Return" (center terminal) on loud speaker output terminal strip together with impedance tap on right which matches speaker.

Variable Damping control must be switched off for proper operation.

To use Variable Damping:

Instead of usual ground return, connect to corresponding "Variable Damping Return".

Turn "variable Damping" control on and adjust to desired damping factor.

Specifications

Power Output:  40 Watts ( 80 Watts peak). "Ultra-Linear" operation.

20 Watt Triode Operation. Switch changes output connections to protect speaker of low-power rating.

Output Connections:  4, 8 and 16 Ω from Ground Return. 4, 8 and 16 Ω Variable Damping returns.

Input Sensitivity for 40 Watts:

Two High Gains Inputs:  0,7 V RMS into 105 k Ω

Pream Input: 2 V RMS into 285 k Ω

Response (has been deliberately rolled off approx. 5 dB at 100 kHz to control transient response):

At 40 Watts : Within 0,1 dB from 20 Hz - 20 kHz, within  1 dB from 15 Hz - 45 kHz

At ½ Watt : ±1 dB from 2 Hz - 50 kHz

Subsonic Filter: In Preamp and High-Gain Filtered inputs, response is slowly rolled off below 20 Hz (less than 1 dB at 20 Hz, 10 dB at 3 Hz; etc)

Distortion

Total Harmonic Distortion at 40 Watts: 

less than 0,1% at mid-frequencies;

less than 0,5% from 20 Hz to 10 kHz;

less than 1,5% at 20 kHz with resistive load  (for less at equivalent voltages with inductive speaker loads)

Intermodulation Distortion at 40 Watts (equvalent 80 watt peak):  Less than 0,5% (60 Hz /12 kHz  4:1

Distortion below 30 Watts is largely of 2ad order and reduces rapidly with signal level.

Damping Factors

Greater than 20 from 20 Hz to 20 kHz (without Variable Damping connections)

Continuously Variable from 5 to ½ with Variable Damping connections

Inverse Feedback and Stability

23 ½ dB of overall feddback (20 dB in triode position). Great care has been taken to ensure stability and low distortion under widely varying loads, both resistive and reactive, such as are encountered in loudspeaker systems. Power supply surges are balanced out of signal channels providing excellent recovery from strong transients. Will not oscillate under any condition of open circuit capactive load.

Hum

Better than 90 dB below 40 Watts (containing proportionately little of high order components)

Meterd Tests and Adjustments

Bias, D.C. Balance, A.C. Balance (drive).All accurately adjustable with built-in D'Arsonval meter and test switch

Power Supply

The use of a transmitting-type oil input condenser, choke, telephone quality electrolytic and the new type 6AU4-GTA as heater-cathode rectifiers provide, protection from starting surge voltages, improved regulation and thorough filtering

Power Requirements

Design center; 117 volts, 60 Hz. Range 105 -125 volts. 150 Watts at Zero signal, 200 Watts at maximum signal

Tube Complement

1 x 12AX7 / ECC83

1 X 6CG7

2 X 6CA7 / EL34

2 X 6AU4GTA

Size and Shipping Weight:  15" x 9½" x 6½" / 47 lbs