Le Pacific JFET Phono Preamp for MM and MC Cartridges

Description: This document describes a DIY build of the Boozhound Laboratories JFET Phono Preamplifier constructed on a stripboard. The BHL preamp is primarily based on the Le Pacific RIAA phono preamplifier circuit. The construction utilizes brown polypropylene capacitors sourced from a local electronics store, and a large electrolytic capacitor rated at 10,000 µF, fed by a 1-ohm resistor. Wire wrap wire is employed as hookup wire, and silver-based solder along with gold RCA connectors are used, all housed in an embossed gold chocolate box. Multiple builds of this simple JFET phono preamplifier have been completed. Another DIY JFET RIAA Phono Preamp build is also mentioned. The equalization circuit is constructed on a stripboard and fitted into a Hammond extruded aluminum chassis with a black anodized finish. The use of Moving Coil (MC) cartridges with turntables is preferred, as they typically have a lower output than Moving Magnet (MM) cartridges, necessitating additional gain for compatibility with the Le Pacific Boozhound Labs phono preamp kit. This gain can be achieved through passive phono step-up transformers or an active circuit like the Le Pacific PrePre for MC cartridges. The MC PrePre circuit is designed to be placed directly before the phono preamplifier. The JFETs used are matched 2SK170BL, and the output capacitors are NOS Russian military paper-in-oil (PIO) types. The MC pre-preamplifier is powered by eight "AA" batteries, providing a clean supply voltage of 12VDC. Modifications include the addition of a 220 µF low ESR capacitor across the 12V battery supply and a 0.1 µF snubber capacitor. A small switch allows for the use of the phono preamp with both MM and MC cartridges.

The Boozhound Laboratories JFET Phono Preamplifier is a well-regarded circuit that provides high-quality audio signal amplification, particularly for vinyl playback. The design emphasizes low noise and high fidelity, making it suitable for audiophiles. The use of stripboard for construction allows for flexibility in layout and easy modifications.

The circuit's foundation is based on the RIAA equalization curve, which is essential for proper playback of vinyl records. The inclusion of brown polypropylene capacitors indicates a choice for high-quality components that contribute to the overall sound quality. The large electrolytic capacitor serves to smooth out power supply fluctuations, ensuring stable operation.

The choice of wire wrap wire for connections helps in maintaining signal integrity while minimizing parasitic capacitance, which is crucial in high-frequency audio applications. The use of silver-based solder enhances the electrical connection quality, further improving signal transmission.

For users employing Moving Coil cartridges, the additional gain provided by the Le Pacific PrePre circuit is vital. This circuit is designed to amplify the low output of MC cartridges, which typically output less than 1 mV. The PrePre circuit can be easily constructed on a protoboard, making it accessible for DIY enthusiasts. The use of matched JFETs, specifically the 2SK170BL, ensures consistent performance across different builds.

Powering the MC pre-preamplifier with eight "AA" batteries provides a clean and stable DC voltage, which is essential for maintaining audio fidelity. The addition of capacitors across the power supply aids in noise reduction, contributing to the overall performance of the preamp.

The design's versatility is enhanced by the inclusion of a switch that allows for the seamless transition between MM and MC cartridges, making it a flexible solution for various audio setups. This comprehensive approach to phono preamplification ensures that users can enjoy high-quality audio playback from their vinyl collections.This is my DIY build of the Boozhound Laboratories JFET Phono Preampifier, but on a stripboard. The BHL preamp is based heavily on the Le Pacific RIAA phono preamplifier circuit shown below for reference. This is a strip board construction using brown polypropylene caps from the local electronics store. The large electrolytic capacitor is 10, 000u F fed by a 1 ohm resistor. Wire wrap wire is used as hook-up wire. Silver based solder, gold RCAs and all installed in an embossed gold chocolates box. Photographs 1 through 3. I`ve now built a number of these simple JFET phono preamplifiers. Photograph 4 below shows another of my DIY JFET RIAA Phono Preamp builds. The equalization circuit is also built on a stripboard and fit into a nice looking Hammond extruded aluminum chassis with a black anodized finish (Photograph 5). I also like to use Moving Coil (MC) cartridges with my turntable. MC cartridges have a much lower output compared to Moving Magnet (MM) cartridges. MC cartridges typically have an output of less than 1 mV, while the output level of MM cartridges is typically between 2.

5 and 7 mV. Therefore you will need some additional gain if you would like to use an MC cartridge with the Le Pacific Boozhound Labs phono preamp kit. The additional gain can be achieved by using passive phono step-up transformers or you can use an active circuit like the Le Pacific PrePre for MC Cartridges shown below in Figure 2.

The Le Pacific MC PrePre circuit is placed immediately before your phono preamplifier. The MC preamp circuit is ultra simple to construct and like the Le Pacific can be easily built onto a protoboard. I`ve built a number of the LePacific MC PrePre circuits and have used them in front of both the Le Pacific preamp and the Boozhound Labs phono preamp kit.

The PrePre builds have been tested with a two different MC cartridges with an output of 0. 35mV and the PrePre circuit works extremely well. The J-FETs are matched 2SK170BL and the output capacitors are NOS Russian military paper-in-oil (PIO) types. The Hammond cast aluminum enclosure case is painted using Sungold color paint. The MC pre-preamplifier is powered using 8 "AA" batteries to give a clean supply voltage of 12VDC. I made a slight modification to the circuit by adding a 220uF low ESR cap to sit across the 12V battery supply along with a 0.

1uF snubber capacitor. Photograph 8 below shows a Le Pacific MC PrePre circuit which I put in front of the Boozhound Laboratories JFET Phono Preampifier kit. With the addition of a small switch I can now use the phono preamp with both MM and MC cartridges. See my review of the Boozhound Laboratories JFET Phono Preampifier kit for additional information. If you have any questions about these phono preamps, feel free to ask them on the forum in the Le Pacific J-FET Phono Preamp- the original.