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Makes

Phono preamp

A friend of mine designed a simple phono preamp for me to use with my newly purchased turntable. Once he was done with the design, I used EAGLE to design PCB layouts for both the power supply and amplifier boards. They were fabricated by OSH Park.

The power supply outputs 27V and uses a LM317LZ regulator. The amp section uses 2N5088 transistors.

The build was relatively unremarkable. I used an aluminum Hammond chassis, and point-to-point wired everything before, between, and after the PCBs.

It sounds great and has been trouble-free for years!

Categories
Makes

Fisher CA-272 rechassis

I bought a Fisher CA-272 100w/ch amplifier that had very noisy controls. Specifically, the amplifier had a built-in EQ and the sliders were deteriorated to the point of being unrepairable. Instead of ditching the amp, which sounded relatively good, I decided to transplant it into a new chassis.

The cool thing about this amplifier was the beautiful pair of heatsinks for the output transistors. I decided to show those off a bit in the new chassis. Since I was ditching the front panel, I had some power to play with as well.

Upgrades

I replaced any capacitors in the audio path with Nichicon KL series as these are known in audiophile circles to have the best performance in these applications.

For the volume potentiometer, I used an ALPS “Blue Velvet” RK27112A00CC.

Chassis

For the chassis I decided on a steel Hammond 1441. The power transformer of this amp was pretty hefty, so I needed a relatively stout panel to mount it. Also, working with steel is a bit easier than aluminum when it comes to machining.

Construction

After drilling holes for the board mounts, transformer, RCA jacks, and power cord, I mounted everything in place.

To show off the heatsinks, I cut rectangular slots in the top removable panel using a dremel.

LEDs

The front panel of the original amplifier was fed using +17.2VDC, so I used this source for LED lighting. I decided to illuminate the heatsinks that would be protruding through the top panel. Eight amber LEDs were connected in series along with a 470 Ω current-limiting resistor. The array draws about 30mA.

I used a combination of Bivar LED holders and Panduit adhesive cord clips to secure the LEDs around the perimeter of the heatsink cutouts.

To position the board and heatsinks at the correct level, I used Keystone standoffs to offset the board from the bottom of the chassis.

Putting it all together

I was pleased with the end result, but I wish the lighting was a bit more diffuse. At some point I plan on addressing this. I’d also like to clean up the edges of the heatsink cutouts using grommet edging.