Cello Duet 350 Amplifier - 350WPC Beast - Serviced

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General:
The Cello Duet 350 is an incredible amplifier rated at 350 watts per channel into 8 ohms stereo, and then 1200 WPC bridged! It represents some of the very best amplification money could buy at the time. 

Designed by renowned engineer Mark Levinson, the Cello line of products exemplify the absolute top of the class. Coveted by audiophiles and collectors, Cello products don't trade very often.

This particular unit was service in house and is working beautifully. 

I'm listening to it right now with a gorgeous set of vintage B&W Model 801 Series 80 that we'll be listing for sale soon. It is an incredible combination!

The Duet 350 Amplifier
Real music fills a room. Even the softest instruments are more present in life than most music systems can reproduce from recordings. Part of the problem has been the limitations in power amplifiers.

The Duet 350 Power Amplifier is a stereo power amplifier that has achieved affordable excellence in sonic quality, power capability and reliability.

In its normal stereo mode it has more than enough power to drive most speakers to their limits with the kind of open, clear, effortless sound which are the hallmark of Cello. When used in a bridged configuration, the Duet 350 becomes a monoblock power station capable of high speed and powerful dynamics under any condition.

The Duet 350 Amplifier has been specifically designed by Cello engineers to be compatible with a wide variety of available equipment.

SkyFi Cosmetic Notes:
This amplifier has misc. light blemishes throughout including some mottling on the left side of the faceplate and left handle. But overall it presents well.

SkyFi Technical Notes:
This amplifier has a handful of known to fail sprague capacitors throughout. We have identified and replaced the troublemakers.

Ownership:
Single Owner

Connections:
Mini XLR inputs, Speaker screw down connections

General Sound:
Smooth, uncolored, undistorted natural and clean

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

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
Class of operation:
Class AB2

Power Output (single amp):
@8 Ohms Rated: 350 Watts
@4 Ohms Rated: 600 Watts

Power Output (bridged amps):
@8 Ohms Rated: 1,200 Watts

IMD (SMPTE):
0.3% (60 Hz / 8 Ohms / 52.92 V Output)

IMD (CCIF):
<0.2%

THD (20 - 20000Hz):
<0.3% (8 Ohms / 52.92 Volt Output)
<0.6% (4 Ohms / 49 Volt Output)

Frequency Response:
+0/-0.8 dB @ 10 - 20000 Hz

Dynamic Headroom:
1.8 dB

Channel Separation:
90 dB

Signal to Noise:
< -100 dB (10 - 22000 Hz / Rated Output)

Input Sensitivity:
1.491 V (8 Ohms / 350 Watts / 52.92 Volt Output)

Input Impedance:
1 mOhm (Non-Inverting)
5000 Ohm (Inverting)
1 mOhm (Unbalanced)

Gain:
31 dB (Unbalanced)
37 dB (Balanced)

Dimensions:
19" x 12.62" x 23.25"

Weight:
90 lbs.

Link to Manual:
Click Here

Recommended Cables:

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.