Pioneer M-22 Class A Amplifier - Unique and Classic Piece (1 of 2)

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This is a Full Class A Power Amplifier produced from 1977-1980 during a golden era of Pioneer and has a solid fan following.

As a Full Class A amplifier that idles hot - and rightfully so.

This unit was previously serviced by another shop before arriving at SkyFi. Their work included upgrading the power supply rectifiers, replacing some tired power supply capacitors, changing the power cords, and replacing all of the output transistors.

The original TO-3 package transistors have been changed to an alternate model with a different package shape. The new Sanken 2SC2921 / 2SA1215 are well regarded audio output transistors and have been confirmed authentic (Yes there are some nasty counterfeits out there). 

We performed some additional maintenance on the unit including replacement of a known troublemaker axial capacitor in the power on delay circuit. We also burnished all of the relay contacts, replaced the indicator lamps, and set the DC offset & Bias to service manual spec.

This is a beautifully designed piece of equipment that is also one of the easiest we've ever come across to work on. It incorporates a dual mono topology, with each channel receiving its own power transformer and power supply components.

The solid cast aluminum chassis sets it apart from other power amplifiers of the era giving it a timeless industrial look. It also features multi-function speaker binding posts that can accommodate spades, bananas, and bare wire.

Click here for a PDF copy of the Pioneer M-22 Owner's Manual

Click here for a PDF copy of the Pioneer M-22 Service Manual (13MB)

Our Testing Process for Amplifiers (Solid State) at SkyFi:

We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and transistors are checked for signs of stress or damage.

We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally, we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If everything reads clean, we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier then remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will be also be tested.

Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage Kef speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.

Please click here for detailed specifics regarding our specialized packing process that separates us from the rest.