Pi-Amp Rev. 6
PC Integrated Audio Amplifier
This log chronicles construction of Pi-Amp Revision 6.
January 14 - August 28, 2013
Log sections are listed chronologically in the navigation header.
Pi-Amp Revision 6 captured the following design objectives -
- Component Layout
- Reduce the size of the chassis to about 15"W x 7"H x 13"D by taking advantage of the reduced footprint of the Mini-ITX mainboard (6.7" x 6.7" vs. 9.6" x 9.6").
- Increase convective ventilation by using holes instead of slots. Since equivalent power is contained in a smaller chassis, convective ventilation must be improved. Drilling holes is less prone to mistakes than milling slots and can add an interesting look to the chassis.
- Eliminate the use of a salvaged mainboard tray and I/O shield by mounting the mainboard directly to the chassis. Four mounting screws and one expansion card is simple enough to layout using a template.
- Utilize tapped holes for machine screws instead of nuts wherever possible. This adds build time but reduces tedious handling of small parts. Simplifies removal of chassis cover.
- Eliminate counter sink machine screws where possible and use socket button head machine screws on exterior.
- Finish the chassis exterior by buffing with #0000 steel wool. Simplifies maintenance.
- Amplifier Power Supply
- Relocate the amplifier power switch from the face plate to the lower left corner of the rear panel. In my experience the amplifier is rarely turned off. Eliminates a length of high voltage wire running from the rear to front of the chassis.
- Eliminate the PSDU used on previous Pi-Amp versions by moving the bridge rectifier and mains fuse to the rear panel, as close as possible to the transformer, mounting the reservoir capacitors between mainboard and face plate, and positioning amplifier fuses and central ground lug on the chassis base adjacent to the transformer.
- Continue to utilize the face plate as the primary heat sink for the power transistors. This worked well on Pi-amp Rev. 5, reduces the cost, and improves the appearance of the face plate. Increase face plate thickness from 1/8" to 3/16" to offset reduced surface area.
- Provide three audio inputs to the amplifier using one switch to select between these line level audio sources: Front Panel 1/8" phono, internal PC audio card, and rear panel RCA.
- Incorporate the Intel Mini-ITX mainboard form factor. With the availability of the single CPU/GPU die and on-board wireless, the Mini-ITX form factor rivals the older Micro-ATX mainboard used in Pi-Amp Rev. 5.
- Eliminate the internal optical drive and rely on an external optical drive or other means to load new media and operating system. This will simplify construction and clean up the face plate appearance.
- Utilize the 2.5" hard disk drive (HDD) form factor. The 2.5" HDD drive is readily available in 1 TB capacity. Two 1 TB HDD's and one 2.5" solid state drive (SSD) will be used in this design. The SSD will contain the operating system and HDD's will contain media files.
- Provide one front panel USB 2.0 port.
- Eliminate PC LED's on amplifier face plate.
- Continue using the ATX12V power supply form factor. A smaller Mini-ITX power supply can be used, but the reduced size has no impact on the overall chassis dimensions. A full sized power supply will run cooler and last longer than a smaller, higher stressed, power supply.