Zarcon Dee Grissom's Idea Page
Updated 16DEC2010
M.C.C. HPA17r16 History.
Necessity is the mother of invention. - Plato.
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M.C.C.HPA17r16 history

When I built my current workstation, I assumed I would be able to just plug in my headphones directly into the sound card like I did with the previous sound card in the old workstation. I discovered that the new sound card just didn't have the ability to drive the headphones beyond barely audible whispers from another room level. The temporary fix was a 150 watt per channel surround sound receiver with a headphone plug. A serious waste of electricity and source of sweltering heat during the summer of 2005. I immediately started looking for a more appropriate solution.

I built an op-amp-buffered C-moy amplifier on a breadboard, and it also didn't have the drive that the headphones needed. That and the 14pin DIP op-amps kept overheating. After that experience I knew I needed something a lot more serious then a op-amp directely driving headphones. I extracted some amplifiers circuits from some CDROM drives with the same results. My C-moy amplifier gave me the false impression that I needed more then +10dBV of gain, nudging me towards the +23dBV of gain in the original HPA17 design.

I discovered some antique 8-bit ISA sound cards with speaker plug outputs, so I started dicing up the cards to isolate there amplifier circuits. To my dismay, nothing seamed to improve the quality of the sound card amplifier chips. This in combination with my experience with the CDROM circuits reinforced my lacking impression of single chip amplifiers.

It was about the winter the of 2005 when I sat down and started making many different drafts of amplifier circuits, involving independent output drivers and voltage gain stages. The seventeenth combination was the dual op amp [midpoint reference buffer, and amplifier stage] driving a BUF634 as the finals. It was about this time I came across the PIMETA v1.0, and my gut was telling me to by one then. I held off to see if I could improve the HPA17 design, and build it cheaply.

The schematic went through fifteen revisions before I started laying out the circuit boards. The original HPA17 design had dedicated power rails for each channel, with a dedicated voltage regulator to drive each channels midpoint-reference. There was just no way to cram all that onto a single three by four inch circuit board, and I wanted a Solid ground plane. So a compromise was made, to drive both channels midpoint from a single voltage regulator, and the power rails were combined. Resulting in the "M.C.C. HPA17r15" back in 2009.

At this point, I had been using a diced up sound card for four years. This thing had a THD of 5.1%, a noise level of -40dB, and loved to AM demodulate every single PCI signal bleeding threw the sound card. I decided enough was enough as I dropped the HPA17 development and set out to buy myself a PIMETA. I discovered that the PIMETA V1.0 had been replaced with a newer one that required surface mount chips. I do not have the experience with surface mount hand soldering to trust myself with surface mount chips. Because I hesitated to buy a PIMETA, I now had no choice other then to finish the HPA17. Until this time the amplifier was something I was working on during my free-time. The name of the game from this point on was, "Failure is Not an Option".

Given the new drive to finish the HPA17, I set out to make sure the main amplifier board was good. I could adjust the input and output RFI filters cheaply at a later date, the HPA17r16mb had to be right the first time. After a year and a half of going over every single aspect of the main amplifier board layout, from via placement and size through signal and power trace proximity, the amplifier was ready for prototyping. The final "M.C.C. HPA17r16" design has NEPP listed MIL-PRF-55182 "Established Reliability" resistors, instead of the original 1% commercial grade parts. Every single electrolytic capacitor was replaced with 25 volt ESRL High Reliability electrolytic capacitors in the design, solder-dipped, and verified under 24/7 load for over a year to be tin whisker free. Every single part on the main board was burn-in tested for at least six months, to verify that it was good to go before being installed on the final circuit board.

<NULL< - ^HPA17r16 Intro^ - > NULL>

Home > Ideas > HPA17r16 Intro.
HPA17r16 Operating Environment.
HPA17r16 RFI filters.
The Main Amplifier Board.
HPA17r16 Vmon & Sources.
HPA17r16 Tests & Afterthoughts.
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