Mark Levinson ML-9 Vintage Class AB₂ Amplifier

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General:
Very desirable ML-9 from the early days of Mark Levinson.

Very high current, capable of driving just about anything. 

"Designed to provide virtually the same sonic performance as the ML-3 in a component of about half the power, weight, size and price."

Fully tested and delivering 100W of pure Levinson Class AB₂ power. Super clean with little signs of use.

This ML-9 was also upgraded with standard RCA inputs instead of the difficult to find CAMAC connectors usually installed. 

More from Mark Levinson:
The ML-9 is a basic stereophonic amplifier with many of the features of the higher-powered ML-3. the ML-9 is rated at 100 Watts continuous sinewave power per channel into 8 ohms, with both channels driven, from 20 Hz to 20 kHz with no more than 0.2% Total Harmonic Distortion.

It will drive even the most inefficient loudspeakers to their full potential. In fact, the ML-9 will easily satisfy the power requirements of all but the most unorthodox applications. 

The design goal of the ML-9 was to provide the same overall performance of the Ml-3 in a component with about half the power, size and price. 

Thus, the audio circuitry of both models is similar. Push-pull operation is maintained from input to output. Full protection is provided for both the amplifier and the load. The power supply of the ML-9 consists of a 1,2 kVA toroidal transformer and a pair of 36 milli-Farad capacitors, allowing for energy storage in excess of 230 Joules.

The damping factor can be adjusted by means of a three-position toggle switch on each channel to meet the requirements of virtually all presently available loudspeakers.

The ML-9 has been designed to drive complex loads with complete stability. 

Circuit description 
The ML-9 is a high quality Class AB₂ stereophonic amplifier designed to provide virtually the same sonic performance as the ML-3 in a component of about half the power, weight, size and price.

Power Supply 
Consists of a 1,2 kVA toroidal transformer, a 30A bridge rectifer, and two 36,000 µF capacitors. Four 520 µF capacitors are used for added decoupling of the pre-driver stage. 

Pre-Driver Stage 
Consists of a differential amplifier with a cascode which drives a second differential amplifier with a cascode and a current inverter. The inverter converts from balanced to ground (differential) to unbalanced to ground while maintaining push-pull operation. 

Driver Stage 
Consists of a complimentary emitter follower, driving a second complimentary emitter follower. 

Output Stage 
Consists of four parallel complimentary push-pull emitter followers 

Protection 
The on/off switch doubles as an electromagnetic circuit breaker to protect the amplifier from excessive current. The power stages are protected by an energy limiting circuit which monitors power dissipation versus time. Independent energy limiting for positive and negative information minimizes distortion while in the overload condition. This circuit offers excellent protection without effecting the sonic quality. The loudspeaker is protected by a D.C. sensing circuit that monitors the output of the amplifier. The D.C. sensing circuit is connected to the circuit breaker. Several other techniques have been employed to protect the ML-9 from external sources of damage. 

Selectable damping Factor 
Loudspeakers, like all electrical devices, are not perfect. We have determined that certain loudspeaker characteristics can be effected by varying the damping factor of the amplifier. For the reason the ML-9 is equipped with selectable damping capability.

Brand Background:
After working in various recording studios and, as legend has it, creating the sound mixer for the Woodstock Music Festival, Mark Levinson began hand-crafting high-end stereo components. His first product, the LNP-1, was a rack-mounted system with two large VU meters and a high performance op-amp module. And with every subsequent product, the legend grew.

After working in various recording studios and, as legend has it, creating the sound mixer for the Woodstock Music Festival, Mark Levinson began hand-crafting high-end stereo components. His first product, the LNP-1, was a rack-mounted system with two large VU meters and a high performance op-amp module. And with every subsequent product, the legend grew.

Ownership:
Single Owner

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:
Just the unit and power cord.

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
Rated Power: 
100 watts continuous sine-wave power pre channel into 8 Ω with both channels driven from 20 Hz - 20 kHz, with no more than 2% T.H.D. 

Frequency Response: 
(-3 dB) 3 Hz, 44 kHz (ultra sonic filter is a modified bessel alignment) 

Input Impedance:
50 k Ω 

Voltage Gain: 
26 dB 

Power Consumption: 
400 W at rated output into 8 Ω, 50 Hz - 400 Hz (100 W at idle)

Dimensions:
(W x H x D): 482 x 216 x 339 mm (19" x 8-1/2" x 13-3/8")

Weight:
65 lbs.

Approximate Age:
1982

Link to Manual:
Click Here

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 Summit Series BiFocal XL Bi-Wire Speaker Cables (PAIR) - Best If Applicable 

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 1KHz 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 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.

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.