McIntosh MA5100 Vintage Solid State Integrated Amplifier Serviced + New Glass and Great History

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General:
If you're looking for a vintage McIntosh integrated, there are only a few good choices. 

The premier piece is the MA230 which runs on tubes. If you don't want to fuss around with tubes or you have a space with limited airflow, this MA5100 might be a great alternative.

Same look, feel, and features, with the great McIntosh sound you expect. 

This unit lived its life at the music department at WLAC, a college in California. The MA5100 was a good choice for a music department mostly because of its reliability, robustness and ease of use.

There are WLAC markings scratched into various parts of the chassis which we thought was a cool sign of its history, and felt it would be best to keep in place thinking the new owner might appreciate. Sure we could have replaced the front panel and painted the chassis, but it would lose all its charm.

We did install new front faceplate glass to give a clean presentable look.

The chassis has some wear and the chrome shows marginal pitting typical of a piece from this era, but far better than most samples which often show actual rust. I'm guessing dry California weather had something to do it.

SkyFi Service Notes:
- This unit came to us in non-working condition.
- We located one damaged main filter capacitor underneath the chassis which we rebuilt.
- We also replaced some failed components in the output protection circuitry and driver cards that kept the amplifier section from operating properly.
- After restoring the functional condition of the unit we proceeded with some preventative maintenance.
- All small electrolytic capacitors in the unit were replaced.
- Select known troublemaker transistors have been replaced.
- We also swapped the original mica insulators on the TO-66 transistors to silicone pads.
- Lamps were all replaced.
- All controls cleaned and re-tested.
- Power cord replaced and re-tested.

Function Note:
- In order to achieve ideal frequency response the front portion of treble control needs to be offset slightly from the rear portion of the control. This is due to aging carbon tracks in 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.

Cosmetic Condition:
5/10 = Average - Multiple scratches, including some on the front faceplate. 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:
Power Output:
45 RMS watts continuous into 4 or 8 ohms both channels operating at 20 Hz to 20,000 Hz

Harmonic Distortion:
Does not exceed 0.25% at rated power output from 20 Hz to 20,000 Hz with both channels operating. Typical performance is less than 0.1% at rated power.

Output Impedance:
4, 8, 0r 16 ohms

Damping Factor:
50 with 4 ohms load
100 with 8 ohms load
200 with 16 ohms load

Frequency Response:
10 Hz to 20,000 Hz +0 -0.5dB at rated power
8 Hz to 20,000 Hz +0 -3.0dB at rated power

(Please see linked owner's manual below for complete specifications)

Dimensions:
Front Panel is 16" W x 5-7/16" H. Chassis is 16" W by 14-1/2" deep, including rear connectors. Clearance in front of mounting panel including knobs is 1-1/2".

Weight:
25 lbs.

Approximate Age:
1970

Link to Manual:
Click Here

Recommended Cables:

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Phono Interconnects - Better

Kimber Kable - Flagship Phono Interconnects - Best

Kimber Kable - Speaker Cables - Good

Kimber Kable - Speaker Cables - Better

Kimber Kable - Bi-Wire Speaker Cables - 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 device has the ability to decouple the preamplifier from the power amplifier, we remove the jumpers and independently test each section. If the device cannot be decoupled, we assess the electronic condition of the piece by analyzing the speaker level output only.

We start by connecting the “preout” jacks of the integrated 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 1KHz 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 1KHz 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 section 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.

Next, we test the power amplifier section by connecting the integrated’s speaker outputs to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1KHz test signal at the “main in” jacks 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.We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz 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.

If the preamp and power amp both pass these tests, we reconnect the sections and verify that the preamp section can drive the power amp to rated power with a 1KHz tone on one of the line level inputs.

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. 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.