McIntosh C42 Solid State Preamplifier - Serviced

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General:
If you like bit of EQ in your system, this might be your best option with just the right looks to match.

The C42 is a super quiet and feature loaded preamp featuring a "McIntosh Exclusive" 8-band EQ allowing you to get the most out of your speakers.

Plus the display is big and bright and easy to read from across the room.

We performed a light service on this particular C42 so it is ready for many more years of reliable service in your system. Included along with the preamp will be its double McIntosh box, manual, and remote. 

More from McIntosh:
Featured Technologies
EXCLUSIVE MCINTOSH 8-BAND EQUALIZER
The equalizer provides 12dB of boost or cut at center frequencies of 20, 35, 70, 150, 300, 600, 1200, and 4000Hz. Notice that the center frequencies are clustered at the lower end of the spectrum where room correction is most often needed. When an equalizer control is in the center or flat position, its circuit components are completely removed from the signal path.

SILENT ELECTROMAGNETIC SWITCHING
In a conventional preamp, an input signal travels to a switch, and then travels to the input circuitry. Unfortunately, the farther a signal must travel, the more distorted it becomes. And this says nothing of what detritus a dirty switch can add to the signal. McIntosh Silent Electromagnetic Switching literally brings the switch to the input. The distortion-free switch consists of a glass tube containing oxygen-free gas and two signal leads separated by mere thousandths of an inch. The tube sits in a multilayer copper coil and the entire assembly is encased in shock-absorbent plastic. When DC voltage is applied to the coil in response to a switching command, current flow creates a magnetic field that causes the leads to bend and contact one another, completing the circuit. The inert gas eliminates corrosion of the contacts, ensuring a low-resistance, distortion-free switch that never needs cleaning. Another benefit is that non-selected inputs are truly “off,” eliminating potential sources of interference.

PRECISION, OPTICALLY REGULATED VOLUME CONTROL
If McIntosh electromagnetic switching brings the switch to the input, then the C42’s volume control brings the attenuator to the input. The volume knob actually operates an optical rotary encoder with 128 steps; it sends instructions at the speed of light to the digitally controlled attenuator located near the inputs. Together they provide 0.5dB resolution with 0.05dB accuracy.

PROGRAMMABLE SOURCE TRIM
A traditional McIntosh feature that allows matching the output levels of different source components, source trim in the C42 establishes new standards for audio purity and operating convenience. Instead of adjusting individual potentiometers, the trim for each input is stored electronically as a volume offset, using the tuner level as the standard.

FEATURES
Extra-wide dynamic range
Ultra-low distortion
Exclusive McIntosh 8-band equalizer
Silent electromagnetic switching
Precision, optically regulated volume control with digital readout in decibels or percent
Programmable source trim
9 source selections including MM phono
Balanced input
3 balanced outputs (Main, Line 1, Line 2)
Independent listen and record selection
Dual processor loops
Control data output for source components
Remote power control (1 main, 1 accessory, 2 switched)
Separate electronic regulators for each preamplifier section
Polyester coupling capacitors
Low-noise 1% metal film resistors throughout
Ultra-precision (.5%) metal film resistors and 1% polypropylene capacitors for phono equalization
Gold-plated input and output jacks
Modular construction with steel chassis
Glass front panel with illuminated nomenclature Infrared remote control
Connector for external IR sensor
Headphone jack

SkyFi Cosmetic Notes:
The top cover of this preamp has some scratching. The top trim piece of the glass and the aluminum end caps show some scratching and wear as well. Overall presentable.

SkyFi Technical Notes:
This unit received a light servicing in-house here at SkyFi. We replaced both volume control ICs, replaced all the lamps, and cleaned the tone controls.

Brand Background:
McIntosh Laboratory is an American manufacturer of handcrafted high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh. The company designs and produces audio amplifiers, stereo tuners and other consumer electronics products.

Ownership:
Second Owner

Connections:
RCA, XLR, IEC Power

General Sound:
Accurate to the recording

Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Unit, remote, manual and power cord.

Packing:
Original Manufacturers Packing

Specs:
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.002%
Gain: 55dB (MM), 15dB (line)
Input sensitivity: 4.5mV (MM), 450mV (line)
Signal to noise ratio: 86dB (MM), 97dB (line)
Output: 2.5V (Pre out), 10V (Pre out Max)

Dimensions:
5.375 in. x 17.5 in. x 17.5 in.

Weight:
25.5 lbs.

Link to Manual:
Click Here

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Phono Interconnects

Kimber Kable - BALANCED XLR Connectors - Better

Kimber Kable - BALANCED XLR Connectors - Best

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

Testing Process:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface.

The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1 KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope.

We then switch to a 1 KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment.

Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.

We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected.

If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.