Kenwood KA-7100 - User Manual

The Kenwood KA-7100 is a DC Stereo Integrated Amplifier designed to deliver high-quality audio reproduction with a focus on low distortion and stable performance. This amplifier incorporates several advanced features to enhance the listening experience and provide versatility in system integration.

Function Description

The KA-7100 functions as the central hub for an audio system, connecting various source components like turntables, tuners, and tape decks to loudspeakers and headphones. Its primary role is to amplify audio signals from these sources to a level suitable for driving speakers, while maintaining signal integrity and minimizing distortion.

At its core, the KA-7100 features a newly incorporated DC power amplifier. This design choice is significant as it aims to achieve extremely low distortion and excellent phase characteristics, particularly in the very low-frequency range. The DC amplifier ensures that output waveforms closely match the original input waveforms, preserving the nuances and dynamics of the sound. This results in a high quality of reproduced sound, offering a greater sense of power and accurately reproducing the high-energy sounds of live performances. A key benefit of the DC amplifier is the elimination of phase distortion, as there are no capacitors in the signal path to cause phase rotation, ensuring a faithful duplication of the input waveform.

The amplifier also boasts a dual mono construction with separate power supplies for the right and left channels. This independent power supply design effectively eliminates dynamic crosstalk distortion, contributing to excellent reproduction and a stable acoustic image.

For signal processing, the KA-7100 includes an equalizer circuit in the first stage, which utilizes an FET differential circuit. This design ensures a low distortion factor and a high signal-to-noise (S/N) ratio, crucial for clean audio from sources like turntables.

Tone control is handled by a BAX type low-distortion tone control, complemented by a tone defeat switch. This allows users to either fine-tune the bass and treble response or bypass the tone control circuit entirely for the purest possible sound, catering to different acoustic environments and personal preferences.

Volume control is managed by an ATT type master volume control with 32 contacts. This precise design minimizes interlock errors, ensuring accurate and balanced volume adjustments across both channels. Additionally, a multi-function attenuator switch is provided, which instantly cuts the audio level by 20 dB. This feature is practical for quick volume reduction, such as when answering the telephone or for making precise level adjustments without disturbing the main volume setting.

The amplifier supports two tape decks with a convenient tape switch and a through circuit. This allows for easy recording, playback, and tape-to-tape dubbing between two decks, offering flexibility for tape enthusiasts.

A 2-stage loudness control is included for low-frequency correction, which can be particularly useful at lower listening volumes to compensate for the human ear's reduced sensitivity to bass frequencies.

Usage Features

The KA-7100 is designed for user-friendly operation, with clearly labeled controls and versatile connectivity options.

Connectivity:

• Turntable Connection: Dedicated PHONO input jacks (left and right) are provided for connecting a stereo turntable. A grounding wire terminal is available to prevent hum.
• Tuner Connection: TUNER input jacks (left and right) allow for connection to an FM stereo or AM-FM stereo tuner.
• AUX Jacks: High-level INPUT AUX jacks accommodate miscellaneous sources such as additional tape decks, receivers, TV sound outputs, or other external components.
• Tape Deck Connections: The amplifier supports two tape decks (Tape A and Tape B) with separate REC (recording) and PLAY (playback) jacks for both left and right channels. A DIN connector is also available for Tape B, allowing recording and playback with a single cord for compatible tape decks.
• Speaker Systems: The KA-7100 can connect up to two pairs of speaker systems (A and B). Speaker terminals are clearly marked for left and right channels, and for positive and negative connections.
• Headphones: A PHONES jack on the front panel allows for private listening with stereo headphones.
• AC Outlets: The rear panel includes SWITCHED and UNSWITCHED AC outlets to supply power to other audio components. SWITCHED outlets are controlled by the amplifier's power switch, while UNSWITCHED outlets provide continuous power.

Controls and Switches:

• POWER Switch: Turns the amplifier on or off, with a pilot lamp indicating power status.
• SPEAKERS Switch: Selects which speaker systems (A, B, A+B) are active or mutes all speakers for headphone listening (OFF position).
• PHONES Jack: For connecting stereo headphones.
• TONE Switch: Engages or bypasses the bass and treble controls (ON/DEFEAT).
• FILTER Switches (SUBSONIC, HIGH):
  • SUBSONIC: Attenuates frequencies below 20 Hz (6 dB/octave) to prevent intermodulation distortion and loudspeaker damage from inaudible low frequencies.
  • HIGH: Attenuates high-frequency noise above 8 kHz (6 dB/octave), such as tape hiss or record scratch.
• ATTENUATOR Switch: Reduces audio output by 20 dB for quick volume reduction.
• VOLUME Control: Adjusts the overall output level for speakers and headphones.
• LOUDNESS Switch: Boosts bass response at low volume levels with two settings (+3 dB at 100 Hz, +6 dB at 100 Hz) to compensate for human ear characteristics.
• MODE SELECTOR Switch: Selects between STEREO, REVERSE (stereo with reversed channels), and MONO (mixed left and right channels) reproduction.
• INPUT SELECTOR Switch: Selects the audio source (PHONO, TUNER, AUX).
• TAPE Switch: Manages tape deck operations for playback, recording, and dubbing.
  • SOURCE: Plays the selected input source.
  • TAPE A/TAPE B: Monitors a recording or plays back from the respective tape deck.
  • B MON (A→B): For dubbing from Tape A to Tape B, allowing monitoring of the recording on Tape B.
  • SOURCE MON (A→B): For dubbing from Tape A to Tape B while simultaneously reproducing another program source (e.g., FM broadcast or phono disc) through the loudspeakers.
• BALANCE Control: Adjusts the relative volume between the left and right channels.
• TONE Controls (BASS, TREBLE): Click-step controls for adjusting bass and treble response.

Operational Flow:

• Initial Setup: Before operation, users are guided to set all selectors, switches, and controls to their default or desired positions (e.g., SPEAKERS to OFF, TONE to ON, FILTER to OFF, ATTENUATOR to 0, VOLUME to minimum, TAPE to SOURCE, LOUDNESS to OFF, MODE SELECTOR to STEREO).
• Source Playback: Simple steps are provided for playing FM/AM radio (select TUNER, operate tuner, adjust volume/tonality), turntables (select PHONO, operate turntable, adjust volume/tonality), and AUX sources (select AUX, operate component, adjust volume/tonality).
• Tape Deck Operation: Detailed instructions cover playback from Tape A or B, monitoring recordings with 3-head tape decks (comparing recorded sound with source sound), and recording with one or two tape decks. Recording levels are adjusted via the tape deck's volume control, and the amplifier's controls (BASS, TREBLE, BALANCE, TONE, FILTER, ATTENUATOR, VOLUME, LOUDNESS) do not affect the recording signal.
• Tape-to-Tape Dubbing: Clear procedures are outlined for duplicating tape recordings from Tape A to Tape B, including options for monitoring the dubbing process or listening to a different source simultaneously.

Maintenance Features

While the manual primarily focuses on operation, it includes important precautions and checks that contribute to the longevity and safe use of the device, which can be considered aspects of maintenance.

Safety Precautions:

• Power Disconnection: Users are advised to switch off the unit and disconnect the power plug immediately if any abnormality (smell, smoke, etc.) occurs.
• Wet Hands: Never connect or disconnect the power plug with wet hands to avoid electric shock. Always hold the power plug itself, not the cord.
• Thunderstorms: Disconnect the power plug and any outdoor antenna cables during thunderstorms.
• Long Absence: Disconnect the power plug from the AC outlet if leaving the house for a long time.
• Internal Access: Never dismantle the case or touch internal parts, nor modify the unit, to prevent electric shock.
• Power Cord Care: Avoid pulling, bending forcibly, scratching, or extending the power cord with an extra cord, as this can cause electric shock or fire. Do not place heavy objects on the power cord.
• Liquid Contact: Do not place items containing water (e.g., vases, pitchers) on or near the unit.
• Foreign Objects: Do not insert inflammable materials (paper, celluloid) or metal objects (needle, hairpin, coin) into the unit.
• Ventilation: Do not block the ventilation holes on the case top with cloths or curtains, especially during prolonged use.

Troubleshooting (Prior to Servicing):

The manual provides a comprehensive "Points to Be Checked Prior to Servicing" section, which acts as a first-line maintenance guide for common issues. This empowers users to diagnose and potentially resolve minor problems before seeking professional service.

• No Pilot Lamp/Sound: Check AC plug connection.
• No Sound (Left/Right): Verify speaker cord connections, SPEAKERS switch position (should not be OFF unless using headphones), VOLUME control setting, and TAPE switch position (should be SOURCE unless using tape decks).
• Sound from One Side Only: Check speaker cord connections and BALANCE control setting.
• Volume Level Difference: Adjust BALANCE control.
• Turntable Issues (No Sound, Hum): Ensure turntable output cord is firmly plugged into the amplifier input. For hum, check for proper grounding, keep turntable output cord away from AC cords, and try reversing turntable AC plug connections.
• Continuous Background Buzz: Route the turntable cord to minimize interference, especially if near a TV transmitting antenna.
• Howling Noise: Increase distance between turntable and speakers, choose speaker locations carefully, and ensure loose flooring does not induce howling, as speaker vibrations can cause feedback in the pickup.

These detailed instructions and troubleshooting tips aim to ensure safe, optimal, and long-lasting performance of the Kenwood KA-7100 amplifier.