Lafayette LA-224T

General Description

The LA-224T is an all-transistor integrated amplifier designed for high-quality stereophonic or monophonic reproduction. It combines a stereophonic control preamplifier and a 30-watt stereophonic power amplifier in one compact and handsomely designed unit. Its advanced all-transistor design offers instant warm-up, low current consumption, cool operation, low distortion and noise, good transient response, and wider frequency response at full power.

The amplifier features inputs for every type of stereo or monophonic program source, including record players, multiplex FM tuners, and tape recorders. A phonograph input is provided for record players equipped with a magnetic cartridge.

Tape recorder outputs allow recording of all stereo or monophonic programs reproduced through the amplifier. Speaker outputs consist of two terminals for each channel, accommodating speakers of 4, 8, or 16 ohm impedance.

A full range of controls provides complete flexibility of operation. A special protective circuit, employing a fuse in each channel, guards against the destruction of output transistors due to short-circuits in the speaker line. This circuit acts instantaneously to protect the output transistors.

For optimal performance, it is recommended to carefully read all instructions and keep the manual accessible for reference.

Installation

The amplifier can be placed in any convenient location such as an equipment cabinet, shelf, table, or bookcase. While the amplifier generates relatively little heat compared to vacuum-tube amplifiers, provision for some ventilation is recommended to disperse any generated heat.

Connecting Your Associated Equipment

Warning: Never insert or remove input cables while the volume control is at minimum or the amplifier is switched off.

Loudspeakers

The interconnecting diagram illustrates speaker connections. For indoor installations, use ordinary plastic-covered lamp cord (No. 18 gauge) to connect speakers to the amplifier. Transistorized amplifiers without output transformers require only one pair of speaker terminals per channel. All speakers, regardless of impedance (4, 8, or 16 ohms), connect to these terminals.

The absence of output transformers allows the amplifier to produce maximum power at low distortion levels and a wider frequency range, especially in the bass frequencies. Maximum output power and minimum distortion are achieved when connected to an 8 ohm speaker. Connecting to 4 or 16 ohm speakers will result in somewhat lower power output.

It is recommended that identical speakers be connected to each channel. Speakers of unequal impedance can cause an unbalance in speaker outputs, requiring adjustment of volume controls to compensate, which is not ideal.

Interconnecting Diagram Description

The interconnecting diagram shows the rear panel connections. On the left, inputs are labeled LEFT and RIGHT, with terminals for MAG (Magnetic Phono), TUNER, AUX, and TAPE REC. The right side shows OUTPUT terminals labeled R (Right) and L (Left) for speakers. There are also connections for FUSE (1A MTH, AC 117V, 50/60 CPS) and GND. A diagram shows a record player with a magnetic cartridge connected to MAG, a tuner to TUNER, and a tape recorder to TAPE REC. Right and Left speakers are connected to the respective speaker terminals.

Stereo Headphones

Stereo headphones (4, 8, or 16 ohms impedance) can be plugged into the PHONES jack on the front panel. The SPEAKERS switch can be set to OFF to silence the speakers during headphone listening.

Tape Recorders

All source material selected via the INPUT SELECTOR is internally connected to the TAPE REC jacks. Use shielded cables with phono plug connectors for connection to either the high or low level input of your tape recorder. The output level and frequency response at the TAPE REC jacks are unaffected by the VOLUME, BASS, or TREBLE controls. For playback, recorders with their own pre-amplifiers should be connected to the AUX jacks. Use the recorder's volume control for setting the output level to avoid overloading the amplifier.

Stereo Record Players

Use two shielded cables with phono type plugs, not exceeding 10 feet in length, to connect your stereo record player.

Phono

Connect magnetic or variable reluctance (constant velocity type) cartridges to the jacks designated MAG.

Tuners

The input jacks designated TUNER are for use with FM or AM tuners, FM multiplex adaptors, or TV receivers with at least 0.25 volt output. Use shielded cable with phono type plugs. For FM stereo multiplex tuners, connect the left channel output to the LEFT TUNER jack and the right channel output to the RIGHT TUNER jack. For monophonic tuners, use either the LEFT or RIGHT TUNER jacks.

Operating Controls

• INPUT SELECTOR: Selects the program source connected to the amplifier's inputs.
• MODE: Determines reproduction manner. STEREO provides normal stereo reproduction. MONO combines L and R channel signals for identical output on both channels.
• VOLUME: Concentric controls allow individual adjustment of volume for each channel, enabling "balance" between speakers. The knob closest to the front panel controls the right channel; the other controls the left channel.
• BASS: Acts as a master tone control for both channels, increasing or decreasing bass (low) tones. Vertical position (12 o'clock) is normal response. Clockwise rotation increases bass; counter-clockwise rotation decreases it.
• TREBLE: Operates similarly to the BASS control but adjusts treble (high) tones for both channels.
• SPEAKER: Set to ON for speaker operation. Set to OFF to silence speakers during headphone listening.
• POWER: Switches the unit ON or OFF. The pilot light illuminates when the unit is ON.

Operating Procedure

Before operating, ensure program sources and loudspeakers are correctly connected. Verify the power source is 105-125 volts, 50/60 cycles AC, and the power switch is OFF.

1. Set the INPUT SELECTOR to the desired input, the MODE switch for desired operation, and the SPEAKER switch to ON. Set the VOLUME control to minimum. BASS and TREBLE controls should be set to their mid-position.
2. Set the Power Switch to ON. Operate associated equipment and increase the amplifier VOLUME control for the desired sound level. If using a single monophonic source, set MODE to MONO. For stereophonic or separate monaural sources, set MODE to STEREO.
3. Adjust BASS and TREBLE controls to your preference.

Speaker Phasing and Balancing

Correct phasing and balancing is crucial for stereophonic systems. Out-of-phase speakers work in opposition, causing a loss in low frequencies (bass). Unequal speaker output levels result in an unnatural distribution of the musical program and loss of stereo effect.

Procedure:

1. Set INPUT SELECTOR to PHONO and MODE switch to STEREO.
2. Play a monophonic record with heavy bass tones. Set VOLUME to a desired listening level.
3. Position speakers about 6 to 8 feet apart, facing inward slightly. Position yourself equidistant between the speakers.
4. Adjust VOLUME controls so sound output is approximately the same from both speakers. Listen carefully.
5. To check phasing, reverse the speaker leads (+ and -) of one channel. When speakers are in phase, there will be a slight increase in bass response, and the sound source will appear to come from a point between the two speakers.
6. Repeat lead reversal if necessary until the "in-phase" condition is achieved. Speaker leads should remain in these positions.

Apparent Sound Source Diagram Description: This diagram visually represents the optimal listening position, showing a listener positioned centrally between two speakers, equidistant from each, to achieve the correct stereo imaging.

Service

If trouble is encountered, follow these steps:

1. Verify the amplifier is plugged into the correct power source (105-125 volts, 50/60 cycles AC). If the pilot light is not lit, switch the unit OFF and check the 1A MTH screw-in fuse at the rear. Replace with a fuse of the same rating. If the fuse blows again, a fault in the amplifier is likely. DO NOT USE A FUSE OF A HIGHER RATING.
2. Check L and R output protective fuses, as described in "Operating Procedure" regarding output circuit failures. External speaker selector switches can sometimes cause momentary short circuits.
3. Check for incorrect control settings. Never insert or remove interconnecting cables while the amplifier is switched ON.
4. Check all connecting cables between equipment.
5. If trouble occurred during initial operation, re-check all interconnections for accuracy, ensuring proper inputs and outputs are used.
6. Ensure your program source (record player, tuner, etc.) is not at fault.

If trouble is confirmed within the amplifier, DO NOT ATTEMPT TO SERVICE IT YOURSELF. Return the amplifier to the store of purchase or to the LAFAYETTE Service Division for professional checking and repair.

Shipping Instructions

Tag the amplifier with your name, complete address, and a brief description of the difficulties. Wrap the unit in heavy paper and place it in a carton large enough to allow at least three inches of shredded paper or excelsior cushioning on all sides. Mark the carton "FRAGILE-ELECTRONIC EQUIPMENT" and address it to:

SERVICE DIVISION
LAFAYETTE RADIO ELECTRONICS CORP.
111 JERICHO TURNPIKE
SYOSSET, L.I., NEW YORK

Include your name and address on the carton and ship by prepaid express. The unit will be returned via express collect.

Schematic Diagram Description

The schematic diagram (Figure 7) provides a detailed technical layout of the LA-224T amplifier's internal circuitry. It illustrates the arrangement of components such as transistors (e.g., 2SB54, 2SB56A, 2SC734, 2SD143, 2SD150), resistors, capacitors, diodes (e.g., 1N60, IS1212), fuses (1A FAST BLOW), and switches. The diagram maps out the electrical connections between these components, including input stages, tone controls, volume controls, mode selection, power supply, and output stages connecting to left and right speakers and headphones. Voltage levels at various points are indicated, providing essential information for understanding the circuit's operation and for advanced troubleshooting.