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Phono Preamp for the PR-101

Assembling the RCA Jacks

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.

Assembled Phono Preamp

We'll start at the beginning, and work our way toward the phono preamp output

Isolated Gold Plated Input Jacks

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.

Variable Cartridge Loading

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.

Electronic Termination for Lowest Noise

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

1% Resistors and Capacitors for 0.1 dB RIAA Equalization Accuracy

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.

Variable and Versatile High Pass Filtering

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 Best Capacitors and Opamps

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.

Just Enough Gain, and then up to 12 dB More

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.

Assembly Manual

Please have a look at the Assembly Manual.


Ordering the Phono Preamp Kit

We have phono preamp kits in stock for you to order. The cost, at $74 plus $6 shipping (lower 48 states) is so low you'll wonder how we can make it this great! Remember though, it's a kit. You supply the labor, I supply the parts, the great circuit and PCB design. The combination gets you an unbeatable combination of sound and value. Order yours now...You'll enjoy building it and you'll love the sound.

By the way, so long as you have a source of clean +/-12V to +/-15V DC, you can buy this kit and put it into any of your DIY audio projects. Yes, it fits perfectly into a PR101, but I'm sure you'll find a lot of other places to put this great sounding phono preamp!

Phono Preamp Kit for PR101 (PhonoZ, $74.00)

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