Phase Linear 2000 Pre-Amp Rebuild

Gepetto

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#41
Hi everyone it’s been a while. This project has been on the backburner for some time. I’ve been following the DChristie's PL 2000 thread and will use the knowledge gained to make my final assembly better. I was also wondering why there was the break in the ground plane back near the RCA’s. I will also join the planes in the middle and isolate the screw on the transformer side.

I got my +/- 12volt power supply made and mounted. I tested it w/o the pcb attached by attaching resisters across the voltage and ground, I found it craps out at about a max of 120mA. I’m guessing that’s all that the small transformer can give. Hopefully that will be enough power to run thing properly. Initially I tested with the pcb attached but w/o the Brown Dog 4739 and eBay 4136 adapter boards installed. Once I saw that the correct voltage was on the right pins, I installed the adapters. Everything was good except that the adapter for the phono input didn’t have the +/- 12 volts I expected. I found that the voltage drops across two 680ohm resistors R7 & R14. The resulting voltages going to the NE5532 opamp is +7.49 and -7.38. Any ideas on why PL did this? Are those resisters and the capacitors hanging off of pins 7 and 14 some sort of filter or were they just going for a lower voltage? Assuming they were just going for a lower voltage what would the sweet spot be for the NE5532? The recommended voltage is +/-5 – 15 volts. On the clip the voltages are before and after the 680 ohm resister.

View attachment 47158
They wanted extra power supply filtering for the low level signal processing associated with a phono stage. The 7.5V+/- is quite adequate.
 
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