PassDIY pearl 2 Phono Preamp
Completed 9-2021
The Pearl 2 phono preamp was designed by Wayne Colburn of Pass Labs, and published in 2010. Its a popular DIY project, and is well documented on the PassDIY website with the schematic, bill of materials, etc. here:
https://www.passdiy.com/project/preamplifiers/pearl-2
I suggest anyone interested start by reading the project write-up in the link above to get full details on the project and the design.
PassDIY.com also sells a pair of the PCBs and a matched sets of the JFETS needed for the project here:
Additionally, there is a lot of information on the DIYAudio website on the aPearl 2:
https://www.diyaudio.com/forums/pass-labs/204336-building-pearl-2-a.html
Note there are over 2700 posts indicating the popularity of this project.
Schematic of the Pearl 2. Note the 4 paralleled (matched) FETs at the input for lowered noise. On-board +/- 24 volt regulators supply power.
POWER SUPPLY:
For the power supply, I used an old PCB from Chipamp.com that includes a snubber circuit, otherwise very similar to that recommended by Wayne.
Here's the assembled power supply PCB. Nichicon 105 degree filter caps and MUR820 fast recovery diodes. The snubber resistors (R1 & R2) are missing in this photo - backordered.
Here's a closeup with partially completed wiring. IEC at the left with the fuse holder above it. the transformer at the right is a dual 22V 50VA Avel Lindberg.
For the IEC, I used a 10amp Qualtek EMI/RFI filter, p/n 858-10/015.
Here's a view of the completed unit. Power switch and LED at the left and IEC and cable out on the right.
I decided to hardwire the output cable at this end to avoid one extra connector.
Front view of the power supply before putting on the top cover.
And the back side.
You can also see the connector which goes to the preamp chassis. Its a 7amp GX16-3 aviation connector.
The supply provides about +/-31VDC to the preamp, which regulates it down to +/-24VDC.
Audio Section:
The populated audio PCB (one channel). PassDIY.com sells the PCBs and matched FETs needed for this project.
Power supply filter caps and regulators are on the top, audio inputs lower left, phono equalization at the lower center and audio output at the lower right.
Parts are are all as suggested by Wayne (including removal of C7), except I replaced C13 with a 4.7uf/50V Blackgate Type N non-polar coupling cap, and I added a 1K for R20 to match my cartridge. P1 is a 10 turn bourns pot to adjust DC offset. I also changed R14 from 1K to 332 ohm to increase gain from 55dB to 65dB for my moving coil cartridge.
For the preamp chassis I used an 8" by 12" by 3" Bud aluminum box I had on hand, and cut a top panel from aluminum stock. This shows the chassis after the holes were drilled and it was sanded before painting.
Top view of the PCBs mounted in the chassis. Wiring is simple: RCA's (at the top) to input and output, and power supply +/- and ground from the power supply jack (upper right in this photos) to the preamp boards.
I chose this layout to keep the audio leads as short as possible - especially the input.
The RCAs are Vampire PCB2F/S gold/teflon connectors.
The DC offset drifts quite bit as originally designed, so Wayne suggested adding a cap from R14 to ground, shown here. I used a 47/25V Silmic II with a 0.1 film bypass. DC drift was +/-200 to 300mv before this change, and stable at <1mv after.
Front view of the completed preamp and power supply. Pretty simple, some would say unattractive!
Note that in operation, Wayne suggests the power supply be located 3+ feet from the preamp chassis, not next to it as here.
And the rear view. Barely visible in this photo is the ground lug between the pairs of RCA jacks.