Sutherland 20/20 phono preamplifier
It starts with separate external AC power modules for each channel, followed by 10 sections of passive RC filtering and finalized with local constant voltage shunt regulation.
It is AC powered, and it is quiet!
“I like design challenges. That is how all new products begin.” — Ron Sutherland
This time the challenge was to offer an AC line powered phono preamp that would fit comfortably in with the Sutherland series of battery powered phono preamps. An extremely low noise floor and precise resolution was a must.
Not only was this an opportunity to creatively address AC power line isolation but to also
take dual mono to a new level.
And the other design challenges: do this with extremely high performance, extremely high quality and extremely high value
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Another path to the same destination.
It is a pleasure to announce a new phono preamplifier from Sutherland Engineering. It is derived from the best elements of the PH3D and the Hubble. The signal path is almost the same as the Hubble; the construction is as simple as the PH3D. It has an elegant esthetic of performance, value, craftsmanship and minimalism.
That heritage, however, does not keep the 20/20 design from taking on its own unique character.
Everyone wants the advantages of AC power line isolation offered by battery operation. The 20/20 is for the person who wants those advantages, but does not want to mess with batteries. The 20/20 comes as close as possible to offering an equivalence of battery isolation from AC line power.
Two-Mono (definition: bumping it up from dual-mono) construction. The 20/20 is literally two
identical mono phono preamplifiers. Each channel is on its own circuit board, has its own shielded
compartment, power indicator, its own AC power supply and its own power cord. It is the ultimate in
In the quest for the ultimate in stereo separation, the 20/20 goes beyond dual mono, offering instead what Sutherland likes to call “two-mono.” Many audiophiles prefer using mono-block amplification for the benefits of eliminating crosstalk and other noise contaminants associated with shared power supplies. They also prefer the benefit of each amp having its own reservoir of power, increasing dynamic capabilities, and giving the amp a sense of ease.
The exact advantage can be had in a phono-preamplifier, where noise is the worst of enemies. The 20/20 may look like a conventional stereo phono stage, but take off the cover. You will discover two identical mono phono circuit boards, sharing only the same front and back panels. Power supplies, power cords, and all circuitry are separate. Even the power indicator lights are independent.
We don’t know of any audiophile who likes power supplies that even remotely resemble ‘walwarts’. The 20/20 uses not one, but two of the wallwarts’ more sophisticated relatives – politely called a regulated tabletop power supply.
To understand this choice, let’s look at AC to DC power supply elements required for no-compromise high-end performance:
- Rectify the AC to DC
- Filter that DC
- Use that raw DC to power a regulating DC to DC switching inverter (this stage also provides galvanic isolation between the AC power line and the DC load)
- Provide additional levels of filtering to remove the high-frequency ripple from the switching inverter.
- Provide additional levels of noise isolation from the switching inverter to the load
- Provide local voltage regulation right at the audio circuitry.
From an engineering viewpoint, items 1, 2 and 3 can be accomplished with a well chosen, off-the-shelf table top power supply. It does those tasks well, reliably and at a very reasonable cost. The supplies included with the 20/20 are rated at a MTF (Mean Time between Failure) of over 100,000 hours. They are used at less than 10% of their rated capacity, so reliably should be even further increased. If one were to fail, replacement is simple and inexpensive. In addition to that functionality, they are already safety tested and approved for use all over the world. A great deal more time, effort and money could be spent on custom circuitry – but to no performance advantage.
From an audiophile viewpoint, it is items 4, 5 and 6 that determine the quality of DC available for the sensitive audio circuitry. That function is so important it takes up over 2/3 of each amplifier’s circuit board area. Ten cascaded stages of passive RC filtering, provide an enormous distance from the preamp area to the incoming DC power connector. There are over 35,000 microfarads of capacitanceon each board. The electrical ‘distance’ is so great, when power is first applied, it takes over 10 seconds for the power to travel thru these ten sections of filtering and reach the preamp stage. Voltage slowly ramps up until the zener diodes clamp it to the correct value. Until that voltage is reached, the audio output is muted. It is this section of circuitry that provides the extreme isolation from AC power line affects.
DC CONNECTOR LOCATION
Don’t be looking for power connections on the back panel. Instead, you will fi nd them located at the front and under the cover. That is one of those form follows function decisions. The front of the circuit board IS where the power enters the circuit, there fore that is where the connector went. On your car, the gas cap is very near the gas tank. It is not located at the opposite end of the car.
Putting the entry point at the front permits power supply wires (low voltage DC) to be routed well away from all the sensitive part of the circuit. Contrast that with the AC IEC power connector (high voltage AC) conventionally located on the back panel very near the preamp circuitry and all the input/output jacks.
BEAUTIFUL ON THE INSIDE
- FR-4 fi berglass circuit boards, Double-sided with plated thru holes
- Dale/Vishay 1% metal fi lm resistors
- Wima Polypropylene capacitors for power supply by passing
- Custom wound, 1% polystyrene fi lm capacitors for equalization
- 14 gauge cold rolled steel chassis
- baked epoxy powdercoat finish
- 1/2″ thick anodized aluminum panel
- front panel artwork anodized in
- gold plated, Tefl on insulated RCA connectors
- gold plated configuration headers and sockets
- output muted during power up and power down
- 40 dB
- 46 dB
- 52 dB
- 58 dB
- 64 dB
- 100 ohms
- 200 ohms
- 475 ohms
- 1k ohms
- 47k ohms
- 17” wide
- 2 ¼” high
- 12” deep
EXTERNAL POWER SUPPLIES (each):
- 5” deep
- 1 ½” high
- 2” wide
- 11 lbs. net
- 19 lbs. shipping
- Power: 20 watts (10 watts per channel)
- Operating Voltage: 100 to 240 volts (universal, no adjustments)