First, exceptional-quality dual-layered PC boards are used throughout with through-hole connections between layers at what seemed like hundreds of places. This type of PC board does not lend itself to any kind of easy alterations and should therefore be left alone from typical surgical remedies except for those well trained in such high-tech connections (conventional soldering irons are too hot and will most likely damage or lift traces). So enough on this point.
Second, after taking 173 macro photographs of the headphone, surround sound, stereo output, and video circuit boards, I can tell you that this is a nicely engineered unit. The well-known reddish colored WIMA shunt capacitors are used in conjunction with JPCON electrolytic supply capacitors for primary filtering and secondary local supply-rail stabilization throughout. The combination of these two capacitors provides a more uniform (low) equivalent series resistance (ESR) throughout the entire audio bandwidth than using electrolytic capacitors alone.
Bus bars are also used at critical points to assure low-impedance supply rail stabilization and minimal ground looping. Between the low ESR capacitors and the use of the bus bars, local power at each device is nicely provided.
Co-located on the small Stereo Output Board is the first stage of a dedicated analog power supply with unusually large capacity (6,800uF per rail) to provide extremely low supply ripple and high stability under peak demands. To give you an idea how atypically large this supply capacity is for the low-power consuming devices used in the OPPO, most good-quality surround sound receivers typically use around 20,000uF per rail in the power supplies for the entire receiver (all electronic components for the preamp, amp, tuner, tone controls, DACs, and SS logic).
The OPPO's analog section power supply capacity is about 1/2 of that of a typical surround-sound receiver and the power demands are about 1,000 times less than such a receiver's. It is well understood that large capacity power supplies translate to higher-quality sound, especially when used in the analog section. The OPPO adheres to this common knowledge very well and the audible results are quite evident. There should be essentially zero power supply strain at any listening level or decoding peak meaning that music should sound uncompressed and it does. Inner detailing is revealed as are intricate nuances otherwise lost with smaller capacity power supplies.
Above are all of the pluses in this design, one that sounds and looks terrific. However, there is a noticeable trait used in some printed circuit board manufacturers that is also employed in this generation of the OPPO players and it has to do with the production process. Let's see how this process works.
Printed Circuit boards (PCBs) begin as a sheet of flame retardant substrate on which a conductive sheet (usually copper) is laminated. Single-layer PCBs have this sheet laminated to one side and dual-layer PCBs to both the top and bottom sides. This process can add many sandwiched layers (up to 42 have been achieved) so that complicated traces can be routed in three-dimensions and not intersect or require jumper wires.
So we start designing a circuit board with a computer program that lays out the engineer's design so the components can be optimally arranged. The program keeps track of point-to-point connections between all resistors, capacitors, connectors, and so on (called the "netlist") assuring that there are no mistakes (see the Nexlogic video). Once the physical layout is determined, now comes the task of transforming one single piece of laminated copper into individual circuit traces.
Once the physical layout is finalized and the computer program understands what needs to be connected to where, it develops a "map" routing these connections. This map is converted into paths (traces). To create these traces from a single piece of copper a section strip of this copper is precisely trimmed away. There are several ways to do this but once the material is removed from the outer edges of the point-to-point connection, it leaves the desired solid copper trace (see the Circuit Skills video to see one way).
While the method of removing this unwanted copper varies, all of these processes achieve the same thing: some material is removed and a lot of material is left over. This leftover material us usually all tied together in what engineers call a "ground plane" from the theory that ground planes improve noise immunity between adjacent components - which it does when properly designed. However, ground planes are also a source of ground loops when improperly designed, a destructive physical phenomenon well known to degrade audio signals.
OPPO uses this "ground plane" philosophy on its analog output stage PCB (I observed that the headphone board did not). As a result, the analog output stage PCB is full of ground loops. All one needs to do to improve the ground plane philosophy is to remove all possible ground loops by removing a small amount of copper in the trace at the appropriate points (see my previous posting on ground loops to understand more about what this issue is). The figure below shows how simple this is to implement but tracing down all of the ground loops created by the hundreds of component traces can be a daunting task.
Another issue related to the ground plane philosophy is to tie all available grounds to as many chassis points as possible, typically through the mounting screw connections of the PC board. OPPO does this also on most of the circuit boards thereby creating more ground loops between traces on the same board and between the other boards.
I highly suspect that a minor redesign to this ground plane philosophy to remove the built-in ground loops and use of single-point grounding will further improve the superb sound of this little player. I have emailed my suggestion to OPPO and it is one I hope that their engineers address in a future revision. But for now, sit back and be content with appreciating the fluid sound produced by this well designed and good sounding unit.
Yours for higher fidelity,
Copyright © 2015 by Philip Rastocny. All rights reserved.