The original Pearl2 was designed by Wayne Colburn and is still offered as a partial kit from PassDIY.

The Pearl2+ is a culmination of several hot-rod modifications to the Pearl2 kit. I chose to name it 2+ and not 3 out of respect to Wayne, which may one day release the next version and obviously would want to name it version 3. Since it was offered to resourceful experimenters, why not polish up that gem with a few simple modifications that are well within the grasp and budget of the average vinyl lover.

I believe this is a worthwhile upgrade project, but I will not argue with those who prefer to keep their original unit unmodified, for whatever reason. The original Pearl2 is a fine phono preamp in its own right.

Capacitors:

                                                                                                                              


The typical builder uses tiny capacitors in the signal path and the PCB is marked for those. Small is cute but generally for caps that compromises the sound quality. In fact, if you check under the cover of many fancy phono stages you will find the same WIMA or other metalized caps, that were chosen mainly to meet budget constraints. That is false economy in my book.

The first order of business for the Pearl2 and many commercial units is to install decent film/foil caps in the RIAA circuit and in the supply bypass positions. Even inexpensive Dayton caps from Parts Express yielded a major improvement. I've used them successfully in other projects so that was no major surprise.
You can install silver Mundorf or Duelund (maybe, if you find the space) caps but you are very much playing with diminishing returns and unreachable rainbows...

Speaking of caps, especially bothersome is the 22uF electrolytic output capacitor that blocks the DC from reaching the line-stage preamp. That capacitor is too big to replace with a high-quality film/foil capacitor. An attempt to replace it with a reasonable quality metalized cap was not sonically transparent enough.
More about that later.

                                                                                                                                  

On-board Power Supply Regulators:

The original design utilized monolythic 7824 and 7924 regulators to supply the +24V and -24V rails with minimal ripple.
A lot was written regarding the AC and transient response of series regulators, and while the current in this design is nearly constant, those seem to have a slight sonic signature.
The second modification replaces these circuits with shunt regulators. It is very economical to buy a kit from ebay instead of building one from scratch. These are usually based on a TL431 with TO-220 current sink devices, sort of a classic approach that yields very satisfactory results.
At such a low cost, it's tempting to use a separate regulator per channel, but that's not necessary. The cross-talk of this preamp is negligible compared to that of the best cartridge.

The shunt regulators have to be set for specific voltage and current. The positive supply consumes around 35mA per channel and the negative supply consumes only 12mA per channel. If you add additional circuitry (see later) then you should account for the increase in current consumption.
The shunt device requires some minimal operating current, so you should add some current margin when adjusting the regulators. While you are at it, why not check the input stage current by measuring the voltages on R21-R24. This will help you verify that Q6-Q9 are somewhat matched.
Listening tests to the preamp powered by the shunt regulators showed a good improvement in transparency and speed (transient response). Skip the installation of the original on-board regulators when you build the Pearl2 kit to save yourself time and money.

The Holy Grail: Adding a DC Servo:

As mentioned earlier, the 22uF electrolytic capacitor at the output has to go.
This requires a circuit that would remove the average DC at the output of the phono stage and bring it to the Ground terminal potential.
The final schematics is shown below.

                                                                       

Reviewing the schematics of the Pearl2, it is obvious that the circuit after the RIAA network forms a discrete DC-coupled opamp. A simplified circuit of this topology is analyzed in the opamp tutorial by Nelson Pass.
Transistors Q4 and Q5 form a differential input stage, which drives the class-A output amplifier Q2. Transistors Q10 and Q11 are current sources for the two stages of the opamp. The gain of the opamp stage is dictated by the negative feedback (R15+R16)/R14. The positive input of the opamp is the gate of Q4, which is driven by the voltage developed on resistor R13.
The DC servo is implemented by a low-offset OPA627 opamp or equivalent, which integrates (averages) the output voltage of the preamp and returns the correction voltage to the positive input of the discrete opamp. The OPA627 requires a lower voltage supply than the discrete circutry. Since it's operating at a very low frequency cutoff we can utilize monolythic regulators without adverse effects on the sound in the main audio path. While the concept sounds complicated compared to a capacitor on the output, the whole servo circuit consists of only 9 parts, which can be easily built on a small PCB.
Listening tests to the fully modified phono stage showed not only improved treble response and transparency but also a tighter bass response with a more natural reverb on percussion tones.

                                                                                                                   

...And Beyond

A battery supply is the natural next step.
However, if we want a unit that is easy to use, the battery will require an automatic charger that disconnects from the AC outlet (mains) when music is playing.
This method avoids any digital noise from the charger's on-board microcontroller leaking into the rest of the audio system and system noise from reaching the phono preamp.
The smart battery charger is another small project that will take some time to implement. Until that happens, the present state of this phono stage is not far back sonically.

Final Words

First I would like to thank Nelson and Wayne for being so generous with the DIY community.
This project started for me when a friend demonstrated a Pearl2 that he built in a dual-chassis with custom engraving and great attention to detail. It sounded very good, but was not transparent enough to my liking. As it turned out, the luke warm sound was due to a mistake in the cartridge loading but that mistake started me on this journey. Happy mistakes do happen...
I was aware of the original Pearl and the following Pearl2 schematics and always liked the concept of a JFET input stage for low noise and the sonic transparency of a passive RIAA. I also could see that the Pearl2 can be easily upgraded beyond the scope of the original kit. So I scribbled some circuits and my friend followed up with a clean implementation. He was in fact a fine lab technician!

It takes an extra effort to implement all the changes outlined, but it should not be too hard for the average DIYer with basic prototyping skills. Implementing the design in a dual-chassis takes an extra effort, both in ordering and assembling parts and in extra work to eliminate hum when connecting the two units.
There is an extra cost in doing all that, but the final result is a ridiculously good phono stage at an even more ridiculous (in high-end standards...) price!

                                                                                                                        

Have fun discovering a whole new sound out of your old vinyl!!!