DUO MM/MC Phono Stage

Refined Performance! The Ultimate in Channel Separation and Spatial Listening! The Sutherland DUO MM/MC Phono Stage! 

Both 120volt 60Hz to 220volt 50Hz Operation! 

The short story is: The Sutherland DUO MM/MC Phono Stage is derived from the cost no object Sutherland Phono Block and the cost-optimized 20/20 Phono Stages. 

The long story is: No expense was spared in the design and construction of the Sutherland Phono Block Phono Stage. The Phono Block is at the pinnacle of phono preamp performance! It just doesn't get any better. The Sutherland 20/20 MM/MC Phono Stage was designed to get the most performance possible at its predetermined price point. To get there, extra was spent to get premium parts and circuitry into the signal path. Consequently, some expenses were squeezed out of less important areas. Those trade-offs have worked very well. The 20/20 has delivered an extremely high level of performance at a reasonable price and is an incredible performance value. 

What if all the price constraints in the Sutherland 20/20 MM/MC Phono Stage were lifted? The price goes up, the performance goes up. The 20/20 starts looking a lot like the Sutherland Phono Block. The actual signal path of the 20/20 is quite good. It uses a circuit very similar to the Phono Block. In critical positions, it also uses the same premium quality (and high cost) components. Very little was held back in that area. The opportunity for upgrade is focused on a more refined power supply, improved circuit board properties and dual chassis construction. 

Power Supply:

The Sutherland 20/20 uses external, bench-top power supplies. They are cost effective, reliable and offer good performance. Each supplies output is extensively filtered and regulated into one +/- 15 volt source for both of the gain stages. The Sutherland Phono Block has built in AC power supplies. There is an IEC power inlet on each chassis to accommodate the user's personal power cord choice. Two completely separate power sections (each providing isolated +/- 15 volts) are provided for each channel. One for each of the two gain stages. Each is independently filtered and regulated to provide the ultimate foundation for the gain stages. 

Each Sutherland DUO MM/MC Phono Stage has a built in AC power supply. There is an IEC power inlet on each chassis to accommodate the user's personal power cord choice. The shielded power supply module has one output. That output is split into two branches. One for each of the two gain stages. Each of those branches is independently filtered and regulated to provide a substantial foundation for the gain stages. 

Circuit board properties:

Circuit board dielectric properties can introduce detail damaging artifacts into the signal. The Sutherland DUO MM/MC Phono Stage mitigates circuit board dielectric properties using the same approach that has worked so well in the Phono Blocks. Circuit board thickness is doubled from the standard 1/16" thickness to 1/8" thickness. Not only is dielectric absorption addressed, but further advantages are realized with an extremity rigid platform for component mounting. It is the cost-no-object, preferred way to go. 

Discussion:

Anytime two conductors are at a different voltage potential, there is an electric field generated between them. The dielectric (the insulation between conductors) within that field become involved in charge storage. If not carefully considered, that extra charge storage can time smear details of a musical signal. Circuit board material is a dielectric. With normal double-sided construction, there are copper conductors on each side of the board. Unintentionally, a new capacitor is introduced into the circuit, formed by top surface copper, bottom surface copper and the circuit board dielectric sandwiched between the two. It is NOT the quality of capacitor we want to have in a high-end signal path. Some manufactures make the situation even worse by going to multi-layer boards in the analog audio sections. Instead of two layers of copper, there are four or more layers of copper. Even worse than that, the dielectric between layers is much thinner and the undesired capacitive effect is inversely proportional to thickness. At best, some manufactures make small, incremental improvements by using exotic board material. 

The Sutherland DUO MM/MC Phono Stage addresses the issue of circuit board dielectric by doubling the thickness of an FR4 fiberglass circuit board. Just that one choice reduces electric field strength by one-half. Additionally, the area of copper interacting with board dielectric is also reduced in critical regions. Signal lines are kept narrow. Power lines are extremely wide. Such choices get us refined performance. Good solid advantages based up the application of good solid physics. 

Dual chassis construction:

A sense of space and dimensionality is conveyed by the difference in the left and right channel information. To preserve those auditory clues, each channel must be isolated from the other and not spill over. Both the Sutherland DUO MM/MC Phono Stage and the Sutherland Phono Block use a stack of two mono phono preamps for stereo. Absolutely nothing is shared between the left and right channels. Each channel is a completely free standing mono phono preamp. That is the ultimate in channel separation. The ultimate in spatial listening involvement. 

Quality Parts: 

• FR-4 fiberglass circuit boards, Double-sided with plated thru holes. 1/8" thick for extra rigidity and minimal dielectric influence.

• Dale/Vishay 1% metal film resistors

• Wima Polypropylene capacitors for power supply bypass and DC servo

• Custom wound, 1% polystyrene film capacitors for equalization

• 14 gage cold rolled steel base

• Baked epoxy powder coat finish

• 1/2 " thick anodized aluminum panel

• Anodized in front panel artwork

• Gold plated, Teflon insulated RCA connectors

• Gold plated configuration headers and shunts

Specifications: 

Gain Options: 40 dB, 46 dB, 52 dB, 58 dB, 64 dB

Loading Options: 47.5 k Ohm, 1 k Ohms, 475 Ohms, 200 Ohms, 100 Ohms

Power Requirements: Power: 20 watts (10 watts per channel)

Operating Voltage: 100 to 240 volts (universal, no adjustments)

Size: 17" x 2 ½" x 12, total

Weight: 11lbs

Initial Set Up: 

Release the top cover by removing the four knurled screws. Audio boards are located on the right side of the enclosure. On the left side of each circuit board you will find headers for receiving the plug-in configuration shunts. Legends printed on the circuit board clearly indicate position and function.

Linear Power Supply Option

For many years now, switching power supplies have been used at many price points by many manufacturers of high-performance audio.   For adequate performance,  special attention must be focused on two aspects of mitigating the noise they inherently generate.   High frequency switching devices leave a high frequency ripple component in the DC output voltage.   It must be effectively removed.   Also of concern is keeping current spikes on the primary side from injecting noise into the AC power line.  If that is not dealt with, the switching power supply will pollute the quality of AC power available to all the audio system components.

Sutherland has been using switching power supplies on several models. In our designs, they have worked well.

There is always that urge to make refinements.   When designing the PHONO LOCO, there was an opportunity to try a new linear power supply design.   With no cost constraints or attachment to convention, it was the perfect place to explore.   It delivered an advancement in AC power line isolation, filtering and regulation.  Which, ultimately,  gave the audio circuits the best ever DC power foundation.  With that foundation, music flowed with purity and authority. 

That same power supply approach is used in the little LOCO. Again, performance was advanced.

Turns out the same power supply designed for the little LOCO could also be installed in the INSIGHT and the DUO.  Over the years, there have been inquires about using linear power supplies with those models.  It has taken a while to develop and refine this new circuit.   That option is now available.

Technical Overview:

The power transformer is toroidal for minimal radiated magnetic field.  The already low magnetic field is further reduced by connecting the primary windings in series rather than parallel.  The transformer flux density is reduced to half of normal.   There is still plenty of power for the job at hand.   

The transformer's AC output  is full wave rectified, current limited and applied to a first stage shunt regulator.   That not only gives the first stage of voltage regulation, it also smooths the current waveform drawn thru the transformer.   The usual current spikes become much more sinusoidal in shape.   Thus current spikes are not injected back into the power line or project a radiated noise field. 

That first cut at regulation is followed by several stages of R-C pi filtering.   A passive approach that has been well proven in other Sutherland designs.   There is another DC shunt regulator applied near the audio circuitry.    

This combination is new and incredibly effective.   It is also straight forward in it's simplicity.  Rock solid in performance, stability and reliability.   Nothing fussy about it.  No active voltage series regulators to add their colorations.  No switching regulator noise to deal with.