McIntosh MA-230 Owners manual

STEREO

PREAMP-AMPLIFIER

MA230

TABLE OF CONTENTS

GENERAL DESCRIPTION TECHNICAL DESCRIPTION

Mechanical Specifications Electrical Specifications

FRONT PANEL INFORMATION INSTALLATION CONNECTIONS

AC Connections

Ground Connection

Tape Output Connections

Loudspeaker Connections AC Power Input Connections

OPERATING INSTRUCTIONS GUARANTEE

3-YEAR FACTORY SERVICE CONTRACT

1 1

11 11

11 12 12 12

14 20 20

MA230

MA230 PREAMP-AMPLIFIER

GENERAL DESCRIPTION

The new Mclntosh MA230 presents two outstanding "FIRSTS" for your home stereo listening enjoyment.

. . . The MA230 is the FIRST stereo preamp-amplifier on one chassis that meets the traditional rigorous Mclntosh engineering performance standards.

. . . The MA230 is the FIRST stereo instru-

ment to combine a solid state preamplifier with a tube and transformer power amplifier on the same chassis.

The Mclntosh MA230 has eliminated all previous limitations of single chassis preamppower amplifiers. The compact design of the MA230 preamplifier allows adequate space on the same chassis for a cool running 30

watt per channel tube power amplifier. You can now enjoy Mclntosh performance and

reliability with the convenience of a complete

single chassis stereo instrument.

The dramatic difference in the quality of music reproduction through Mclntosh instruments is due directly to low distortion per-

formance. Mclntosh Laboratory is the only manufacturer in the entire industry to guarantee and deliver the lowest distortion at all audio frequencies.

Long life, flexibility, and highest quality construction are characteristic designs in every Mclntosh instrument. Wide electrical and thermal margins of safety for all components, transistors and tubes add to the long life built into every Mclntosh product. Advanced engineering and cool operating design insure reliability and low maintenance costs. A Mclntosh instrument is without doubt the most economical and worthwhile long term investment in the high fidelity industry.

Once you have enjoyed the outstanding performance of the MA230, you will understand why Mclntosh products have earned

their reputation as "THE BEST." Your Mc-

lntosh MA230 stereo preamp-amplifier will

give you years of the finest possible performance and will become a highly valued

part of your home music system.

TECHNICAL DESCRIPTION

The new Mclntosh MA230 combines, for the first time, a Mclntosh engineered stereo solid state preamplifier and tube power am-

plifier on the same chassis. Long months of

diligent research by the Mclntosh engineer-

ing staff have produced a compact solid state

preamplifier which meets all the traditional

Mclntosh performance standards. The MA-

230 solid state preamplifier eliminates the

drawbacks and limitations of all previous

solid state circuits. The compact design of this preamplifier has allowed sufficient space to properly position a 30 watt per channel

stereo tube power amplifier on the same

chassis.

The MA230 continues the Mclntosh reputation for cool and efficient operation. Careful chassis planning has permitted the output

tubes to be spaced well apart. This wide

spacing allows more air circulation around

the tubes. Better air circulation means cooler

operation. Cooler operation means longer trouble free life. The large Mclntosh output and power transformers are positioned across the center of the chassis for mechanical

stability and strength.

The MA230 preamplifier section is de-

signed around the latest type Silicon-Planar transistors. Silicon-Planar transistors were selected because of their high thermal sta-

bility, low leakage, low noise, and superior

high frequency response. A total of 12 tran-

sistors are used. Three transistors are used

in each channel of the phono preamplifier section. Three transistors are also used in

each channel of the tone control section. The entire preamplifier has low noise, low distortion, and is not affected by normal room temperature variations.

Typical Mclntosh care in design protects against input signal overload. Both the high level inputs (Tuner, Tape and Aux) and the low level phono and tape head inputs can accept much higher than average input signals without overload.

For example, at 2000 cycles the phono inputs can-accept 150 millivolts of signal before overload. No magnetic phono cartridge

now available is capable of even one half this

output voltage.

PREAMPLIFIER

Each channel of the Phono preamplifier section uses 3 transistors. The first input stage is a high gain amplifier. The output of

this transistor feeds a pair of transistors con-

nected in a Darlington configuration. A nega-

tive feedback loop connects from the output

of the Darlington pair back to the emitter of

the first stage transistor. This feedback loop

reduces noise and distortion and also provides accurate frequency compensation for phono records and tape head playback. Negative feedback remains in effect even at 20 cycles where gain is highest, to insure low distortion over the entire frequency range.

The phono input impedance is 47,000 ohms to match most magnetic phono cartridges. Other resistors may be added to

match the occasional cartridge which re-

quires a different input impedance.

The Tape Head input impedance is slightly over 1 megohm for uniform high frequency

response with typical tape playback heads.

The Tape Outputs come directly from the Selector Switch and provide signal level sufficient for feeding a tape recorder. For example, 10 millivolts of signal at the phono input results in 1.6 volts at the Tape Output.

The high level inputs feed through the

Balance and Volume controls into a transistor connected as an Emitter-Follower. This transistor is the first stage of the Tone Control section. The impedance of the high level inputs is 250,000 ohms. Any conventional

tuner or tape recorder may be connected to the MA230 without loss of low frequencies. The emitter-follower provides the required

high input impedance and low output im-

pedance for feeding the tone control negative feedback circuits. The last two stages of the tone control section are two transistors in a

Darlington configuration similar to the phono

preamplifier. The high gain of these stages is used to advantage for the tone control

negative feedback circuits. This type of circuit assures low distortion and the correct

shape for the tone control response curves. Negative feedback is maintained at all frequencies, even with the tone controls turned

to full boost. Distortion is, therefore, kept

very low, even at the frequencies where maximum boost occurs. The total distortion of the entire MA230 preamplifier circuit is actually only a few hundredths of 1 percent.

POWER AMPLIFIER

The output of the solid state preamplifier

feeds into one half of a 12AX7 dual triode

tube. The two triode sections of the 12AX7

are the first stage voltage amplifiers in each channel of the power amplifier. The output of each 12AX7 is direct-coupled to a 12AU7 tube used as a grounded-grid inverter-driver. The balanced output voltages of the groundedgrid inverter are precisely maintained in amplitude over the entire audio frequency

range. The inverter output balance is controlled by precise plate load resistors. An adjusting control is also included in the inverter plate circuit to insure exact signal balance and minimum low frequency distortion.

This control is factory set using a distortion

analyzer. Normally, the mid point setting of this control is adequate to keep overall distortion less than ½ of 1% at full output.

The outputs of the 12AU7 tubes are cou-

pled through mylar-insulated capacitors to the output tube grids. These capacitors are the only coupling capacitors used in the

power amplifier circuit, which keeps phase

shift very low at low frequencies.

The 7591 output tube plates are coupled

to the speaker through a special Mclntosh

engineered output transformer. A separate tertiary winding on the transformer also

couples the output tube cathodes into the transformer. Six db of negative feedback is

produced in the output stage with this circuit.

Twenty db of negative feedback around

the entire power amplifier circuit is achieved

by coupling a special secondary winding on

the output transformer back to the first stage

12AX7 cathode.

The fixed bias on the 7591 output tubes

is adjustable over a small range with individual controls. These adjustments are factory set to 0.7 volts DC at the test points. Convenient test point jacks are provided next to each output tube. The setting of these controls is not critical and need not be touched

in normal use. To assure best possible performance of the MA230 over long periods of operation, or whenever output tubes are changed, the bias can be checked and reset

if necessary.

A pair of stereo headphone jacks is pro-

vided on the front panel. The jacks are con-

nected to the amplifier outputs through 100 ohm resistors for low impedance head phones. The speaker switch turns off the speakers for headphone listening.

POWER SUPPLY

A silicon rectifier voltage doubler power supply assures stable voltages and cool operation. A zener diode holds the transistor preamplifier operating voltages at exact values and eliminates all traces of hum.

A thermistor is used in the primary AC circuit of the power transformer to protect against line voltage surges and extend tube and transistor life. The thermistor places slightly more than 25 ohms in the AC circuit when cold. As the amplifier warms up the thermistor also warms and its resistance then drops to less than 0.7 ohm. The amplifier then operates at normal line voltages but is protected during the initial warmup period. Again, Mclntosh care in engineering protects your investment in listening pleasure.

The combination of these features results in performance available only from a Mc-

lntosh amplifier. The MA230 delivers 30 watts RMS continuous power from both channels at the same time, 20 cycles through 20,000 cycles with harmonic distortion less than ½ of 1%. This superior level of performance is unequaled by any other preampamplifier. A listening test quickly proves the superiority of the Mclntosh MA230.

MECHANICAL SPECIFICATIONS

Size

Front panel, 16 inches wide by 57/16 inches high; chassis, 15 inches wide by 4½ inches

high by 14½ inches deep, including connectors. Clearance in front of mounting panel including knobs, 1½ inches.

ELECTRICAL SPECIFICATIONS

Power Output

30 watts continuous per channel with both channels operating simultaneously. 60 watts continuous, monophonic.

Harmonic Distortion

Less than 0.5% at 30 watts output, 20 cycles

through 20,000 cycles. Distortion decreases as power output is reduced.

Weight

43 pounds net, 57 pounds in shipping carton.

Finish

Anodized gold and black (Front Panel).

Intermodulation Distortion

Less than 0.5% for any combination of frequencies from 20 cycles through 20,000 cycles if instantaneous peak power is 60 watts per channel or less.

Phase Shift, Power Amplifier-

Less than ± 5° 20 to 20,000 cycles.

Frequency Range

At 30 watts output both channels.

+ 0, -0.5db 20 cycles through 20,000 cycles. +0, -3db 15 cycles through 70,000 cycles.

Output Impedance

4 ohms, 8 ohms, 16 ohms.

Internal Impedance/Damping

Less than 10% of rated load impedance;

damping factory of 10.

Tape Switch

Normal or Tape Monitor.

Phase Switch

Normal (0°) or reverse (180°).

Speaker Switch

Speakers ON, or OFF for headphone listening.

HF Filter

Flat, or 5,000 cycle cutoff, 12db per octave.

LF Filter

Flat, or 50 cycle cutoff, 12db per octave.

Input Sensitivity and Impedance

Auxiliary, Tape, Tuner, and Tape Monitor:

.25 volts, 250K ohms. Phono 1 and Phono 2: 1.5 millivolts, 47,000 ohms.

Tape Head: 1.5 millivolts, 1 Megohm.

Total Noise (including Power Amplifier)

High level inputs: 75db below rated output. Low level inputs: 60db below rated output;

less than 4.0 microvolts at input terminals.

Tape Output

.25 volts into 25,000 ohms with rated input;

1.6 volts with 10 millivolts at Phono input.

Left Plus Right Output

10 volts from generator impedance of 5,000

ohms.

Bass Controls

±18db at 20 cycles, with friction clutch for independent adjustment of each channel.

Treble Controls

± 18db at 20,000 cycles, with friction clutch

for independent adjustment of each channel.

Loudness Switch

Normal or compensated bass and treble.

Headphone Jacks

Two, for two pairs of headphones.

Input Selector

6 positions: AUX, TAPE, TUNER, PHONO 1,

PHONO 2, TAPE HD.

Mode Selector

7 positions: L to L and R, R to L and R, STEREO REVERSE, STEREO, MONO (L+R),

L+R to L, L+R to R.

Transistor Complement (Preamplifier)

8-2N2926 Silicon Planar 4-11BQ101 Silicon Planar

Tube Complement (Power Amplifier)

4-7591 Power Output 2-12AU7 Driver/Phase Inverter

1-12AX7 1st Audio Voltage Amplifier

Power Requirements

120-125 volts AC, 60 cycles. 150 watts at

zero signal output; 210 watts at rated output.

Comp (Compensator) Switch

RIAA or LP phono equalization.

FRONT PANEL INFORMATION

Figure 1. MA230 Front Panel.

INPUT SELECTOR

Figure 2. INPUT SELECTOR Switch.

Select any of six program sources with the

MA230 INPUT SELECTOR switch.

1. AUX: Use the AUX position for any auxiliary program source requiring flat amplification, such as a tuner or television sound,

connected to the back panel AUX input jacks.

2. TAPE: Use the TAPE position for a selfcontained tape recorder (tape recorder having its own playback preamplifier), connected to the back panel TAPE input jacks.

3. TUNER: Use the TUNER position for

any AM, FM, or FM stereo tuner connected to

the back panel TUNER input jacks.

4. PHONO 1: Use the PHONO 1 position for any magnetic phono cartridge connected to the back panel PHONO 1 input jacks.

5. PHONO 2: Same as PHONO 1. (For example, PHONO 1 can be connected to a

record changer while PHONO 2 is connected

to a manual turntable.)

6. TAPE HD: Use the TAPE HD (Tape

Head) position for a tape deck that does not have its own playback preamplifier. The Tape Head leads are connected to the back panel

TAPE HD input jacks.

MODE SELECTOR

Figure 3. MODE SELECTOR Switch.

Use the MODE SELECTOR to:

Listen to normal stereo (see 4 following

and page 15);

Reverse the left and right arrangement of musical instruments (see 3 following and page 15).

Balance the amplifiers and loudspeakers

in a stereo system (see 6 and 7 following and page 15).

Listen to monophonic sound (see 1 and 2

following and page 15).

Listen through both loudspeakers to either channel of a stereo program source (see 1 and 2 following and page 15).

Turn the MODE SELECTOR to:

1. L TO L & R: connects the "left" input to

both loudspeakers.

2. R TO L & R: connects the "right" input

to both loudspeakers.

3. STEREO REV: connects the "left" input

to the "right" loudspeaker and the "right"

input to the "left" loudspeaker.

4. STEREO: connects the "left" input to the "left" loudspeaker and the "right" input to the "right" loudspeaker.

5. MONO (L+R): adds the "left" input

and the "right" input and then connects the L + R program to both amplifiers and loudspeakers.

6. L + R TO L: connects both left and right

inputs to the "left" loudspeaker only.

7. L+ R TO R: connects both left and right

inputs to the "right" loudspeaker only.

VOLUME

Use the MA230 BALANCE control to balance unequal volume in the left and right channels of a program source. The volume of each speaker system relative to the other

can be varied, at the same time the combined

room volume level is not changed.

LEFT . . . turning the control to the left

accents the left channel by reducing the right channel output.

RIGHT . . . turning the control to the right

accents the right channel by reducing the

left channel output.

BASS

Figure 4. VOLUME Control.

Use the MA230 VOLUME control to regulate the volume level of both channels. Turning the VOLUME control clockwise increases

volume level.

BALANCE

Figure 5. BALANCE Control.

Figure 6. BASS Control.

The BASS control is a dual-concentric control. The two are friction coupled. The center knob controls the left channel. The outer ring controls the right channel. With the

BASS control it is possible to vary the bass loudness relationship existing between the left and right speakers. Both controls can be,

turned together as a single adjustment or one

may be held as the other is turned. Clockwise rotation increases bass loudness; counterclockwise rotation decreases bass loudness.

TREBLE

The TREBLE control is dual-concentric control. The two are friction-coupled. The center knob controls the left channel. The outer ring controls the right channel. With this control it is possible to vary the treble relationship existing between left and right speakers. Both controls can be turned together as a single adjustment or one may be held as the other is turned. Clockwise rotation increases treble loudness; counterclockwise rotation decreases treble loudness.

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