McIntosh C20 - Manuals

The C20 is the only Stereo Control Console that has enough flexibility to control all program sources. The C20 is the only Stereo Preamp with enough record compensation for the valuable Monophonic as well as the new Stereo records. The C20 has the most complete facilities for tape record- ing, playback, dubbing and monitoring. The C20 has by far the simplest yet complete control of tone balance. The C20 is by far the easiest to mount and still give pro- fessional appearance. Trie C20 is produced from three years of careful thorough research and development. C20 The The Greatest FLEXIBILITY The Finest PERFORMANCE The Highest QUALITY STEREO PRE AMPLIFIER LABORATORY, INC. 2 CHAMBERS STREET, BINGHAMTON. N. Y, Phone-Area Code 607-723-5491 2O-HP30-761 Printed In U.S.A. BE012003 In Canada: Manufactured under license by: McCurdy Radio Industries, Ltd., 22 Front Street West, Toronto, Canada Input Selector: Selects any one eight pro- gram sources including Tape, Tuner 1 and Tuner 2, Auxiliary, Phono 1 and Phono 2, Tape Head 1 and Tape Head 2. Each phono input has two switch positions, one for stereo the other paralles the stereo car- trige for Monophonic records. Mode Selector: Reverse: connects left channel to right speaker, right channel to left speaker, corrects for left-right reversal of program. Stereo: (normal Stereo mode selector posi- tion) left channel to left speaker, right channel to right speaker. Left: left channel to left speaker no pro- gram to right speaker. Right: right channel to right speaker, no program to left speaker. M Left: left channel only to both speakers. M Right: right channel only to both speakers. Record Compensator: Separate bass and treble compensator switches including " R I A A , " "LP," "Tape-Head," flat position for microphone and other positions for monophonic records. (Turning "TREBLE" control to "TAPE" gives flat response. Turning "BASS" to "O" gives flat response.) Tone Controls: Treble: boost 13 db at 20,000 cycles atten- uate 18 db at 20,000 cycles. Bass: boost 16 db at 20 cycles, attenuate. 20 db at 20 cycles. Balance Control: To balance for unequal pro- gram source: Turning control to left re- duces right channel to No Output Turning control to right reduces left channel to No Output. Phase Control: Reverses phase in the left channel to correct for speaker or program phasing. HF Cutoff Filter: Three positions providing (1) no filter action for normal use, (2) 9 KC cutoff, and (3) 6 KC cutoff to sucpress record noise and hiss. Loudness Control: Compensates for the Flet- cher-Munson hearing characteristics as program loudness is reduced. Rumble Filter: Suppress low frequency dis- turbences such as rumble. Tape: Front panel jacks, push button switch controlled to permit the addition of a port- able tape recorder without disrupting the equipment permanently installed. Tape Monitor: To permit instantaneous mon- itoring of tape before and alter recording. Low Frequency Trim Controls: On the back panel. Compensate for unequal response at low frequencies due to position of speak- ers or differences in speaker efficiency. Provides 6 db boost at 50 cycles starting from 500 cycles or 8 db cut at 20 cycles starting from 200 cycles. CONTROLS Main Output: 2.5V with rated input 2 output jacks in parallel for each channel Tape Output: 0.25V with rated input 1 output jack for each channel Left plus right output: 2.5 volts from source impedance of 23.000 ohms Voltage Amplification: Low level inputs to Main Output: 1,000 to 1 (60db) at 1000 cycles Low level inputs to Tape Output: 100 to 1 (40db) at 1000 cycles High level inputs to Main Output: 10 to 1 (20db) High level inputs to Tape Output: 1 to 1 (0db) Tape Monitor input to Main Output: 10 to 1 (20db) A.C. Aux. Outlets: 1 unswitched for tape machine or turntable. colored Red; 4 switched, colored Black Power Requirements: 117 volts 60 cycles A.C. 35 watts MECHANICAL SPECIFICATIONS Size: 155/8" wide by 51/8" high. Overall depth of chassis behind front panel is 1213/16".. The space required in front of cabinet panel for the thickness of the panel and knobs is 1¼". Weight: Chassis only 18 pounds. In ship- ping carton 28½ pounds. ELECTRICAL SPECIFICATIONS Frequency Response: ±0.5 db 20 to 20,000 cycles Distortion: Less than 0.2% at rated output, 20 to 20,000 cycles Hum and Noise: High level inputs: 85 db below rated output Low level inputs: less than 2 microvolts et input terminals Input Sensitivity and Input Impedance: Auxiliary; 0,25 volts 470.000 ohms Tape: 0.25 volts 470,000 ohms Tuner 1: 0.25 volts 470,000 ohms Tuner 2: 0,25 volts 470,000 ohms Phono 1: 2 to 10 millivolts 47,000 ohms for low output cartridge 10 to 70 millivolts 47,000 ohms for hi output cartridge 0.1 volt 220 mmf in series with 47,000 ohms for Xtal or Ceramic Phono 2: Same as phono 1 Tape Head 1: 2 to 10 millivolts 47,000 ohms for low output head Tape Head 2; Same as tape head 1 Tape Compare (Monitor): 0.25 volts, 115,000 ohms

C20 STEREO PREAMPLIFIER (Serial No. 6L700 & above) MAINTENANCE MANUAL DESCRIPTION COMPONENT NO. Switch, Input Selector Switch, Bass Compensator Switch, Treble Compensator Switch, High Frequency Cutoff Filter Switch, Rumble Filter Switch, Mode Selector Switch, Tape Compare Switch, Tape Jack Switch, Phase Silicon Rectifier, 50 PIV at 1.6A Transformer, Power S1 S2 S3 S4 S5 S6 S7 S8 S9 S1, S2 M199A DESCRIPTION COMPONENT NO. Filter Capacitor, 20/20/40 MF at 300/350/350V Filter Capacitor, 40/40 MF at 350/350V Filter Capacitor, 1000/1000 MF at 15/15V Control, Bass Control, Treble Control, Loudness (Aural Compensator) Control, Volume — 4 Section combined with power on-off switch Control, Balance Control, Bass Trim (Lo Bass) on rear panel C102 C103 C104 R1 R2 R 3 R4 R5 R7 (2 used) Special components used in the C20 are listed below. These compo- nents are designed and built specifically for the C20. They may be pur- chased directly from Customer Service, Mclntosh Laboratory Inc. When you Table 2. SPECIAL COMPONENTS (Schematic No. SC119-201) order parts be sure to give the SCHEMATIC NO. and DESCRIPTION from Table 2 below, and serial and model number for your amplifier. Table 1. C20 VOLTAGE AND RESISTANCE CHART (Schematic No. SC117-201) Tube 12AX7 (V1) 12AX7 (V2) 12AU7 (V3) 12AU7 (V4) 12AX7 (V5) 12AX7 (V6) 12AX7 (V7) 6X4 (V8) Pin No. 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 DC Volts No. Signal 146 0 1.0 5.6 -5.6 110 0 1.0 — 146 0 1.0 5.6 -5.6 110 0 1,0 64 0 2.4 5.6 -5.6 198 62 120 — 64 0 2.4 5,6 -5.6 198 62 120 —104 0 .7 5.6 -5.6 230 22 29 _ 104 0 .7 5.6 -5.6 200 22 29- 250 20 70 5.6 -5.6 250 20 70 0 315 AC —6.3 AC 0__ 315 AC 335 Resistance in Ohms Unit Off 130K* 1M 2.2K 5 5 360K* 56K 4K — 130K* 1M 2.2K 5 5 360K* 56K 4K _ 120K* <50 1.8K 5 5 14K* 1.1M 100K — 120K* <50 1.8K 5 5 14K* MM 100K —330K* 110K 1.8K 5 5 9K 222K 22K —330K* 110K 1.8K 5 5 31K* 222K 22K —7K* 1M 47K 5 5 7K* 1M 47K 0 580 _ .1 0 —560 * NOTES: 1. High impedance VTVM is used to measure operating voltages. 2. Resistance measured to grid, (chassis) 3. * Denotes pin 7 of V8 grounded for this test. 4. Control positions for tests are as follows; MODE SELECTOR BALANCE PHASE H.F. FILTER LOUDNESS INPUT SELECTOR BASS COMPENSATOR TREBLE COMPENSATOR BASS TREBLE RUMBLE FILTER, TAPE JACK, TAPE COMPARE VOLUME LOW FREQUENCY TRIM STEREO 0 0 FLAT FLAT TAPE HD 2 0 TAPE 0 0 OUT ON, CCW 0

STEREO PREAMPLIFIER C20 TABLE OF CONTENTS GENERAL DESCRIPTION TECHNICAL DESCRIPTION Mechanical Specifications Electrical Specifications FRONT PANEL FACILITIES INSTALLATION CONNECTING A-C Connections Input Connections Output Connections Ground Connections (Program Sources) OPERATING INSTRUCTIONS Balancing a Stereo System To Adjust for Balance in the Treble Range To Adjust for Amplitude Balance in the Bass Range Adjusting Phase Listening to a Stereo Record To Adjust the Balance Control After the System has been Balanced Adjusting for Special Effects Using the C20 with a Stereo Tuner Using the C20 with a Stereo Tape Machine_ Using the C20 Front Panel Tape Jacks Using the C20 with Tape Decks Using the C20 with Microphones for Stereo. Monophonic Record Settings Operating Curves GUARANTEE 1 1 2 2 2 5 6 6 7 9 9 10 10 10 10 10 10 11 11 11 11 12 12 12 12 14 16 C20 C20 STEREOPHONIC PREAMPLIFIER GENERAL DESCRIPTION The Mclntosh C20 Stereophonic Pre-amplifier is a control center for any stereophonic sound system. This control center is necessary to accurately perform four specific functions to increase the enjoyment of stereo. First, the control center amplifies weak electrical impulses. As the record rotates on the turntable, un- dulations in the grooves move the pick-up stylus ap- proximately one-thousandth of an inch, in any direction, from the rest position. From this slight mechanical movement, the pick-up stylus generates a weak elec- trical impulse on the order of a few thousandths of a volt. To amplify and preserve the character of such an electrical impulse, the finest amplifier performance is required. Second, every sound system is used in a different acoustical environment. The tone balance of the music is affected by variations in environment. Also, people listening to the music have varying ideas of correct tone balance. To adequately compensate for these con- ditions, a high-quality control center is needed. Third, there is a great variety of stereophonic and monophonic records manufactured today, both domestic and foreign. The control center must provide record compensation for a great variety of recordings. Fourth, with programs originating from a variety of sources such as tuners, records, tape machines, micro- phones, etc., a control center is needed to select and switch these sources separately or in combination. All of these jobs are performed with excellence by the C20 and yet this instrument is easy to mount, simple to operate, and is the finest in appearance. TECHNICAL DESCRIPTION You now own the finest expression of stereo crafts- manship . . . designed and built to fulfill your needs. Through direct consumer contact, a unique Mclntosh marketing research program determines the application of electronic and mechanical engineering to fit your needs. Relentless research by Mclntosh engineers im- proves the selection of materials and the circuits in which they are used. It is this total concept of crafts- manship directed to consumer satisfaction that has maintained the Mclntosh reputation for excellence in performance, quality, and reliability. Perhaps you would like to know a few of the features developed through research based on con- sumer needs that place your C20 Pre-amplifier above all other pre-amplifiers. An example of the unique mechanical construction throughout is emphasized on the back panel where low- voltage program sources are connected to the C20. This portion of the panel is cut out and mounted on small electrical insulators. The ground circuit is connected to the main chassis at only one point. By breaking the path for circulating hum currents in this manner, the hum and unwanted noises induced in other stereo systems when used with various program sources and combinations of program sources are eliminated. Hum noises are also introduced into stereo sys- tems by the magnetic fields produced by the power transformer windings. The greatest care went into the design and construction of the power transformer in your C20. It is wound in such a way that the magnetic fields produced by the windings tend to cancel. This is accomplished by splitting the windings into two seg- ments. Further reduction of the magnetic field intensity is achieved through the use of additional magnetic and electrical shielding. With these construction improve- ments the hum noises introduced by ordinary pre- amplifiers are eliminated by the C20. Nearly all of the small resistor and capacitor com- ponent parts in the C20 are mounted on military-type terminal boards. This specialized construction prevents damaging mechanical strains. In addition it makes servicing, if ever required, much easier and more effective. The mechanical layout of the C20 allows maximum separation of the left and right channels. The terminal board at the rear of the C20 is associated with the right channel and the terminal board at the front with the left channel. C20 terminal boards are constructed of natural bakelite because of its low-volume resistivity. This prevents the gradual increase of electrical noise common to other terminal board materials after con- tinued use of the control center. The C20 is the only control center that has an illuminated front panel to provide convenient reading under low-level lighting conditions. This feature is of particular importance when a closet is adapted to house stereo equipment. Front panel tape input jacks are another exclu- sive feature provided by the C20. With the start of stereo FM broadcasting it will be important to tape and preserve those special programs that will other- wise never be heard again. This feature will be greatly appreciated by you and your friends when recording on portable tape machines. Only extensive research and planning combined with skilled engineering and manufacturing knowhow, directed toward consumer needs, can produce such a fine electronic instrument. 1 MECHANICAL SPECIFICATIONS DIMENSIONS Chassis: 14-1/2 inches wide; 4-1/2 inches high; 12 inches deep Front Panel: 15-5/8 inches wide; 4-7/8 inches high Front Panel Mounting Space Required: 16-3/8 inches wide; 5 inches high ELECTRICAL SPECIFICATIONS WEIGHT Chassis: 18 pounds Shipping Weight: 28.5 pounds FINISH Anodized gold and black (front panel) POWER REQUIREMENTS 117 volts, 50/60 cycles, ac, 35 watts INPUT SENSITIVITY AND INPUT IMPEDANCE Auxiliary: 0.25 volt; 470,000 ohms Tape: 0.25 volt; 470,000 ohms Tuner 1: 0.25 volt; 470,000 ohms Tuner 2: 0.25 volt; 470,000 ohms Phono 1: 2 to 10 millivolts; 47,000 ohms for low-output cartridge 10 to 70 millivolts; 47,000 ohms for high-output cartridge 0.1 volt; 220 mmf in series with 47,000 ohms for Xtal or ceramic cartridge Phono 2: Same as phono 1 Tape Head 1: 2 to 10 millivolts; 47,000 ohms for low- output head 10 to 70 millivolts; 267,000 ohms for high-output head Tape Head 2: Same as tape head 1 Tape Compare (Monitor): 0.25 volt; 115,000 ohms FREQUENCY RESPONSE ±0.5db; 20 to 20,000 cycles DISTORTION Less than 0.2% at rated output, 20 to 20,000 cycles HUM AND NOISE High-level inputs: 85 db below rated output Low-level inputs: less than 2 microvolts at input ter- minals MAIN OUTPUT 2.5 volts with rated input 2 output jacks in parallel for each channel TAPE OUTPUT 0.25 volt with rated input 1 output jack for each channel LEFT PLUS RIGHT OUTPUT 2.5 volts from generator impedance of 23,000 ohms VOLTAGE AMPLIFICATION Low-level inputs to Main Output: 1,000 to 1 (60 db) at 1000 cycles Low-level inputs to Tape Output: 100 to 1 (40 db) at 1000 cycles High-level inputs to Main Output: 10 to 1 (20 db) High-level inputs to Tape Output: 1 to 1 (0 db) Tape Compare (Monitor) input to Main Output: 10 to 1 (20 db) A-C AUXILIARY OUTLETS 1 unswitched for tape machine or turntable, colored Red 4 switched, colored Black FRONT PANEL FACILITIES Figure 1. C20 Front Panel 2