The McIntosh C24 was the company's first solid-state stereo preamplifier, built between 1960 and 1969, with specifications including a frequency response of 20Hz-20kHz (+0 -0.5dB), 0.1% total harmonic distortion, 2mV input sensitivity for MM phono, and a maximum output of 10V. Key features include a six-position input selector, dual concentric tone controls with ±18dB range, separate bass and treble adjustments, a loudness contour control, and both low and high-frequency filters. The unit measures 16 inches wide by 5-7/16 inches high and weighs 17 pounds.  

Key Specifications 

Frequency Response: 20Hz - 20kHz (+0, -0.5dB)
Total Harmonic Distortion (THD): 0.1%
Input Sensitivity: 2mV (MM Phono), 0.20V (Line/Aux)
Input Impedance: 47k ohms (Phono), 250k ohms (Line/Aux)
Maximum Output: 10V
Power Output (Rated): 2.5V
Noise and Hum: -75dB (Aux), -60dB (Phono)

Features & Controls
Tone Controls: Dual concentric Bass and Treble controls with ±18dB range for each channel 
Filters: Low-Frequency (LF) filter at 50Hz and High-Frequency (HF) filter at 5kHz, both with a 12dB/octave slope 
Loudness Control: Continuously variable bass and treble compensation 
Phase Switch: For normal (0°) or reverse (180°) phase 
Input Selector: Six positions: AUX, TAPE, TUNER, PHONO 1, PHONO 2, Tape Head 
Mode Selector: Multiple options including L to L+R, R to L+R, STEREO REVERSE, STEREO, MONO (L+R), L+R to L, and L+R to R 
Left Plus Right (L+R) Output: Dedicated output with level control adjustable from -6dB to +6dB relative to the main stereo output 

Physical Characteristics 
Dimensions: 16 inches (W) x 5-7/16 inches (H)
Weight: 17 pounds
Finish: Chrome/Black