Celestra RA475x Mod
This page documents the modifications I did to a couple early versions of Celestra RA475x amplifiers that I made a mini review a few months ago.
I ended up replacing all power supply capacitors to United Chemi-con KY series low impedance caps and capacitors in the driver boards to Panasonic FC's. I also changed the op amps to Burr Brown OPA2132 in DIP8.
The mods are discussed in more detail in the pictures and descriptions below. Enjoy!
Mod was started by cutting the silly soldered fan wires. Leaving just enough left to reach the board when it's time to put it back together.
Since this amp was an early production model (Serial #59) It appears that it is a hand soldered unit (not machine wave soldered) and there are some bodge wires and parts underneath. Another difference is that the bottom plate is chrome plated while in the newer models, it is matte aluminum.
Driver boards are removed to make room while removing power supply caps.
Bags of goodies from Digikey.
The original 47uF 63V caps in the driver boards are removed and replaced with Panasonic FC's.
1/2 of the power supply caps are removed but left the other half in the opposite board as reference for the cap polarity as there are no markings on the PCB.
Once all new caps and connectors for the fans are installed then the driver cards reinstalled into their places.
Driver cards reinstalled at a slight angle to clear the sides of the top cover during reassembly.
Original TL082 op amps are then replaced with Burr Brown OPA2132 op amps.
After all parts are installed, the entire board is washed and cleaned with IPA to remove solder flux.
The fan wires are prepared to add connectors to.
Fan wires with connectors added for easy removal of top plate during servicing.
Serial #'s of the two units I modded. It appears they are both early production units.
Leftover parts from the modification.
Here's one of the caps 'squished' so it would fit in the tight misdesigned PCB layout.
Turns out the resistors used to drop the 40+volts to the 15volts needed by the op amps are insufficient and could not push enough current to supply the new op amps with enough voltage. Also they are too small power rating wise and I didn't have the appropriate resistors in stock so I had to go to the store to buy replacements.
Old resistors removed and PCB cleaned.
I bought 1kOhm 1watt resistors for more supply current and higher power dissipation.
Loose parts are then glued and now the amps are now ready for use.
Parts that I had ordered from Digikey that I used in this amp. Links go to Digikey parts page.
470uF 50V caps for the power supply secondary side
1000uF 25V caps for the power supply 12V side
47uF 63V caps for the driver cards
and Burr Brown op amps for the preamp/crossover circuit
Page updated and copyright R.Quan © 31 Mar 2012.