From reading the TA3020 datasheet and the corresponding reference board datasheet, it would appear that certain capacitors and diodes should be soldered directly to MOSFET leads rather than mounted on the PCB in the normal manner. Apparently not doing so reduces the reliability and perhaps the sound quality of the reference board.
As I understand it, this situation applies identically to the Truepath because the Truepath schematic is component-for-component identical to the schematic of the reference board (apart from the inclusion of the mute auto recovery circuit in the Truepath which is not included in the reference board.)
The TA3020 reference board has the following notes on the schematic (refer to page 15 of www.tripath.com/downloads/RB-TA3020.pdf)
D106, D107, D206, D207 ARE MUR120 DIODES SOLDERED DIRECTLY TO FET LEADS ON BOTTOM OF BOARD
C113 AND C213 ARE SOLDERED DIRECTLY TO FET LEADS ON BOTTOM OF BOARD
The TA3020 datasheet (pages 7-8) refers to D106, D107, D206 and D207 as DO and says:
"These diodes absorb any high frequency over/ under shoots caused by the output inductor LO during high output current conditions. An ultra fast recovery diode that can sustain the entire VPP-VNN voltage should be used."
Likewise, the TA3020 datasheet refers to C113 and C213 as CHBR and says:
"These components must be located as close to the output MOSFETs as possible to minimize output ringing which causes power supply overshoot. By reducing overshoot, these capacitors maximize both the TA3020 and output MOSFET reliability."
Although the difference in inductance between PCB mounted components and FET mounted components would seem to be negligible, it is clear that Tripath considers this marginal minimization of the inductance of these capacitors and diodes to be very important, otherwise, why would they include this matter in their documentation knowing that it could result in significant increase in OEM product design and manufacture? I guess it could make the difference between amps used at high power lasting 2 years and 5 years before failing - something like that. I expect that this issue becomes even more important in cases where people have left MOSFET leads longer than necessary in order to accommodate particular heatsink arrangements. For example, I have seen photos where the leads are bent 90 degrees and the MOSFETs are mounted horizontally on the heatsinks, in which case the leads are perhaps double the length they would be if the MOSFETs were mounted vertically.
Im wondering has anyone followed Tripaths advice? Also I would be interested in whether there is any audible difference if the components are soldered directly to the MOSFET leads.