McIntosh MC2300 Vintage Amplifier - Overhauled - 300 Watts!

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General:
"Most famously, the improvisational rock band the Grateful Dead employed 48 McIntosh MC2300 amps as the main power source for their enormous public-address system, the Wall of Sound." From Wikipedia's dedicated MC2300 page

The McIntosh MC2300 is one our favorite vintage McIntosh amplifiers, powerful and classic.

This particular example was extensively overhauled for long-term reliability.

From the official McIntosh Legacy Products page:
• Manufactured 1971 - 1980
• 300 Watts x 2 Channel, 600 Watts x 1 Channel
• Included Autoformers
• The amplifier that powered the Grateful Dead "Wall of Sound"

SkyFi Cosmetic Notes:
Cosmetic blemishes include light wear to all metal surfaces. There are some small spots within the meters, and a linear scratch running along the bottom of the faceplate under the controls.

This amplifier includes its original transit skid which is very uncommon. A small IEC power input adapter is also included to use a standard modern power cable. 

SkyFi Technical Notes:
This unit came to us in rough shape electronically. It was highly modified and had many blown output devices. It was, however, in very good cosmetic condition and warranted an extensive overhaul and reversal of all previous modifications.

All of the output devices and resistors on the output heat sinks were replaced with fresh thermal compound applied. Both driver boards were upgraded to new reproduction boards that faithfully mimic the original component layout.

The new boards incorporate all of the official McIntosh service bulletin modifications that were often approved and implemented at McIntosh clinics and service centers. The multi-section filter capacitor was replaced.

The input board received new caps and transistors. 

New gold plated RCA jacks and fresh output barrier strips, and new fan shock mount grommets were installed. We also replaced all of the input wiring with high-grade coaxial cabling as the original wiring was removed during a previous modification.

LED lighting was installed for both the power indicator and meter illumination. 

This amplifier is basically fully rebuilt with the exception of the (4) main filter caps which were pulled and verified for value, ESR, and leakage before being reinstalled.

This MC2300 tests to rated power, meeting the published distortion specification.

Shipping:
This MC2300 will ship inside an official McIntosh box securely strapped to a shipping pallet anywhere within the lower 48 US States for a flat $400. This figure also includes insurance. If you're outside of this area please contact us for a quote as we ship worldwide frequently.

Free local pickup is welcome, and local courier service is available within 25 miles of our Zip 07452 for an additional fee. 

Note these speakers are exempt from any free shipping promotions.

This amplifier is so significant that it has a dedicated Wikipedia page:
The MC2300 is a solid-state power amplifier which was built by the American high-end audio company McIntosh, and sold between the years 1971 and 1980. It can be utilized either as a 300-watt-per-channel stereo amp, or a 600-watt monoblock, and was rated by its manufacturer as being able to produce this amount of power continuously, with very little (less than 0.25%) distortion. McIntosh's ratings were conservative, however, because like many of their amplifiers, when bench-tested the MC-2300 has frequently been found to produce an even higher level of clean power.

As such, it was ideal for use in demanding, professional applications. Most famously, the improvisational rock band the Grateful Dead employed 48 McIntosh MC-2300 amps as the main power source for their enormous public-address system, the Wall of Sound. Designed by Owsley "Bear" Stanley and others, this system utilized more than 26,000 watts of continuous power fed into JBL and Electrovoice speakers, and was renowned for its natural, low-distortion stereo sound which carried for 600 feet without significant degradation. The Wall of Sound was only in use from March to October 1974.”

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, Speaker Binding Posts

Cosmetic Condition:
6/10 = Fair. Three to four minor scratches, or one major scratch. See our detailed rating description here.

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

Included:
Just the unit and power cord.

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
ELECTRICAL: 
300W Per Channel Stereo
600W Mono

Frequency Response: 
20 - 20 kHz (+0, -0.5dB)

Distortion:
0.25%

Noise and hum:
-90 dB. 

Output impedance:
Stereo: 0.5, 1, 2, 4, 8 and 16 ohms
Mono: 0.25, 0.5, 1, 2, 4 and 8 ohms

Damping factor:
14 or greater

Input impedance:
200k

Input sensitivity:
0.5v

Sentry Monitor

FRONT PANEL:
Anodized gold and black panel

Power level (meters read +3 at 300W)

Gain controls

Meter range switch
-20, -10, 0, and off

Power Switch:
On or off

Handles

BACK PANEL:
Output barrier strips

Audio inputs

Mode Switch: 
Stereo or mono

Circuit breaker

Dual temperature controlled activated cooling fans

Manual:
Click Here

Dimensions:
19" rack mounting Width, 10-1/2" Height and 17" Depth.

Weight:
128 lbs.

Approximate Age:
1975

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Speaker Cables - Better

Kimber Summit Series Monocle XL Speaker Cables (PAIR) - 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.

If the amplifier passes visual inspection, we move on to a controlled power on sequence using a Sencore safety analyzer to monitor current draw in real time. Once the amplifier is determined to be safe to operate, we connect it to full AC mains for function and power testing. We connect the speaker outputs of the amplifier to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1 KHz test signal at the amplifier's input and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping.

At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. If the device under test has both balanced and single ended inputs they are both tested at this time.

We finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz sine sweep to assess the amplifier's frequency response characteristics.

This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours minimum. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.