| Assembly Manual (original) | Schematics (original) | Specifications |
|---|---|---|
| Assembly Manual (current, Rev C2 PCB) |
Isolated RCA jacks avoid ground loops minimizing hum
The Phono Preamp for the PR-101 is nearly as quiet as the laws of physics allow. Only the noise of the record itself remains, and a bit of the unavoidable hum pickup exhibited by your RCA cables and phono cartridge. The distortion is vanishingly low, the equalization typically within plus or minus 0.1 dB of the RIAA ideal, and the low end is configurable to minimize rumble and stop your woofers from waffling in response to warped records.
We'll start at the beginning, and work our way toward the phono preamp output
Isolation minimizes the ground loops that cause hum. Gold Plated input jacks make the most reliable, lowest resistance signal and ground connections, critical to low hum and noise.
Your phono cartridge's frequency response depends upon selecting the correct capacitive loading. The PR101 lets you select among 8 load steps...0, 27, 47, 74, 100, 127, 147, or 174 pF. The selection is by a jumper field with wide contact area and gold plating for the most reliable contact with the lowest distortion.
For minimum noise, the preamp uses an electronic termination scheme. You'll recall that the standard loading resistance is 47 K Ohms. If you do this with a 47 K Ohm resistor, you get significant amounts of noise. Instead, you can terminate with a 1 Meg resistor in a controlled gain Miller loop that makes it look just like 47K Ohms, but it has (ideally) 13 dB less noise. This, along with the rest of the careful design choices makes this an extremely low noise preamplifier. You can read more about the technique here
You'll hear exactly what the recording and mastering engineers wanted you to hear owing to the extreme accuracy of the RIAA equalization. We do it with 1% resistors and multiple 1% capacitors in series and/or parallel. Using multiple capacitors increases the accuracy of the resulting capacitor.
Think about warped records and the low frequencies that they generate. There's no music in the warps, but they generate extreme low-frequency signals that wobble your woofers and muddy up your sound. With the PR101, you can selected between:
Mostly, I think the 3rd option is the best compromise between rejecting warp frequencies while saving the music, but you have the choice to try a number of variations.
The capacitors in the signal path are all either film or COG. These capacitors have tremendous linearity, and give the cleanest possible sound. There are a few DC blockers in the feedback path that are electrolytic, but they are so large that no signal voltage develops across them, so they create no distortion. The opamps are the classic 5532 and 5534, well known for their low distortion and noise.
The phono preamp has 30 dB of gain at 1 kHz. That means your cartridge won't overload the preamp. If your cartridge has low output, you can boost it up by 0, 3, 6, 9, or 12 dB to give you the most comfortable and optimum volume control settings for your system. Once again, the gain is set with gold plated jumpers for long term reliability and lowest distortion.
Please have a look at the schematic. Phono Preamp Schematics.
Please have a look at the original Assembly Manual.
Please have a look at the current assembly manual (anything shipped after 3/17/2023 and built on Rev C2 PCBs Current Assembly Manual
You can put this preamp into the PR-101, PR-102, or you can make your own stand-alone arrangement. One customer did just that. Here's a link to his review