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JFET RIAA Phono Preamplifier Kit

 Mark Houston  Australia Flag   To email Mark, type out the email address.

The Lure of Vinyl

There is no doubt that Long-playing (LP) record albums are not for everyone. Some just don't like the clicks and pops (more so with old vinyl records than new ones). Others don't like the fact that you have to get out of your seat to turn them over or that you need a turntable and cartridge. Luckily turntables and cartridges, even very good ones, are not expensive these days. Then there is the requirement of an RIAA phono preamplifier.

With the phonograph cartridges only delivering a few millivolts an additional high-gain preamplifier stage will be required. Also when LP record masters are produced the bass is removed from the music to make cutting the master easier and the grooves smaller. The phono preamp has two jobs then: to amplify the small voltages coming from the cartridge and to re-balance the bass against the other frequencies (RIAA equalization). Both tasks are not hard and a few dollars of simple electronic parts is all the required to build a good sounding phono preamp. Or you can take the consumer approach and purchase an inexpensive preamp or pay $10k for a top of the line model.

But all who regularly listen to LPs agree the sound quality rivals that of CDs. Music lovers and audiophiles alike who play LPs are passionate about the sound. Even with my humble gear (Rega/Grado) I have been able to impress many a hard core CD centric music lover. The sound of vinyl, beyond the pops and clicks, can be very moving and extremely enjoyable. And if you are a DIYer, like me, you get to build some more gear, this time a (or a number of) phono preamp(s).


Boozhound Labs JFET RIAA Phono Preamp Kit

Boozhound Laboratories (BHL) sell a partial JFET phono preamp kit that consists of a printed circuit board (PCB) and the passive parts. The kit builder needs to supply their own power supply, enclosure and hardware (connectors, switches ...) The kit contents are shown below.

JFET Phono Preamplifer Kit Package

Photograph 1: JFET Phono Preamplifer Kit Package

JFET Phono Preamplifer Kit Contents

Photograph 2: JFET Phono Preamplifier Kit Contents

The schematic (shown below) and included in the detailed assembly manual. The BHL kit uses the same topology as the "Le Pacific" circuit with some changes. Just two JFETs in each channel and a simple RIAA equalization network comprise the preamp. Regardless of that the design is very simple and open to a lot of tweaking. It is specifically designed for a MM cartridge. If you have a MC cartridge you will need a pre-preamp (see the DIY JFET Phono Preamp page for the schematic) or you can use a phono step-up transformer.

Boozhound Laboratories JFET Phono (RIAA) Preamplifier Kit Schematic

Figure 1: Boozhound Labs JFET Phono (RIAA) Preamp Kit Schematic

BHL has altered the schematic slightly by adding small source resistors, power supply (PS) decoupling resistors, additional smoothing capacitors and some refinements of the RIAA equalization network. But they took the whole concept of the kit a lot further than most by offering vintage new-old-stock (NOS) Russian military paper-in-oil (PIO) capacitors. Capacitors made in this way are very sought after and respected for their sonic qualities in the DIY community. Not only are these caps PIO but they are glass and metal encased.

The PCB is well thought out with the bottom of the circuit board acting as almost a solid copper plate that will offering excellent shielding. I found the pads a little small and difficult to solder. For best results use a fine soldering tip and some flux. The PCB is silk screened and solder masked so solder splashes and shorts should not occur. The PIO capacitors are large and look great. The metal-film resistors also appear to be of good quality.


Assembly - JFET Phono Preamp Kit

My method of PCB assembly is to leave the sensitive active devices to last unless it would be difficult to fit them. Because the JFET devices were easy to fit on a fully populated board I placed and soldered all the resistors then the capacitors and then the JFETs. It is easy to assemble the whole PCB in under an hour. Use a digital multimeter (DMM) to check resistors as some of the color bands were a little indistinctive to my eyes. I tick-off the components as I assemble the PCB. I like to use use solder with silver content . Quality solder will add to the final result. A photo of my finished board is shown below. The assembly manual includes detailed instructions and many photos to walk you through the build process.

Finished JFET Phono Preamplifier Kit PCB

Photograph 3: Finished JFET Phono Preamplifier Kit PCB


Battery Power on a 19" 1U Enclosure

Sutherland Engineering produces a number of very high-end and very respected phono preamps. Most are battery powered. Generally banks of D cells. Why D cells? Ron Sutherland believes you should only have to change your batteries once a year. Therefore the large cells. I have built a few JFET Phono Preamps and run both from batteries. With a draw of only about 15mA and a capacity of 2000mAh capacity for 1.5V AA alkaline batteries I would expect over 100 hours of play time between replacements (about four battery changes a year for me). The cells are inexpensive and can be purchased in bulk. I use two banks of 10 X AA cells. With 1.2V rechargeable batteries the supply will be 24V and with 1.5V alkaline batteries the supply is 30 Volts. The specified working voltage is 24Volts but I have found no problems running the preamp on the higher voltage. The assembly manual provided with the kit describes how to build the kit for use with a 24VDC wallwart power supply.

AA Battery Power Supply - JFET Phono Preamp

Photograph 4: AA Battery Power Supply - JFET Phono Preamp

I used wire wrap wire for all the hook-up wire. Wire wrap wire is very fine (30AWG), high grade copper with a silver plating and teflon insulation. The input wires leads are twisted to ensure no noise is induced into the input. This is done by putting the earth and hot wire in a hand drill and twisting the two wires tightly on each other. Small ferrite beads were added to the input wires to filter very high frequencies out. I do not like and do not use shielded wire. It is generally low quality and very capacitive.

Wire wrap wire and ferrite beads

Photograph 5: Signal Hookups - Wire wrap wire and ferrite beads

Computer sticky stand-offs were used to mount the PCB to the chassis. I use these types of stand-offs a lot because they stick extremely well, it is easy to remove the PCB if required and they provide some mechanical isolation from the enclosure. Bituminized Aluminum foil lines the bottom and top of the enclosure to provide additional RF shielding and to deaden the enclosure. The LED power indicator is powered from the battery supply through a large value resistor to limit the current through the LED.


The Finished RIAA Phono Preamp

The 19" 1U case has many screws which hold it tightly together and there is plenty of room to mount the battery holders. The empty space could be lightly packed with Dacron to keep resonance low and any echoing from external sounds to a minimum. The understated look of the preamp beguiles its inherent performance. Those who use rack-mounts for their audio gear will find this an easy enclosure to work with. The case is expensive and does require some assembly time.

Inside View JFET Phono Preamp

Photograph 6: Inside View - JFET Phono Preamp

Finished Boozhound Laboratories JFET Phono Preamp

Photograph 7: Finished Boozhound Laboratories JFET Phono Preamp


Hounds which can really howl

For the first three hours I was unconvinced that this build was any better than my other two versions using no PCB and very different parts. But after many hours of play I am now convinced that this is the very best phono preamp I have ever built. And ever heard. I am making comparisons with these DIY phono preamps:

Let's just compare the BHL kit to my two DIY versions of the preamp. Both of the DIY preamps are a little more forward in the upper mid to treble. They also both exhibit a very slight resonance in the upper mid region. Being a little more forward in the upper mids lets you feel you are getting more detail. Really it is the same detail as in the BHL kit but just dominating. Bass with my former two builds is slightly recessed compared to the BHL kit.

The BHL kit has more bass and a slightly dark mid to upper mid. The sound is laid back and easy listening. Bass is more dominant and well articulated. With this phono preamp in control you just want to keep digging out LP after LP. Classical, pop, jazz and rock all appear to play very well in a rich pool of alluring vinyl timbre. The howl of the hound is seductive, soft and comforting. It appears to gather you in and place you under the spell of Russian military caps, battery power and silver plated wire. Definitely my best build.

The kits can be purchased from Boozhound Laboratories for $79US (July 2011). The phono kit is worth every cent of it's $79 price tag. In fact, it's a steal. For additional information about this kit build or if you have any questions, feel free to ask them on the forum in the jFET phono preamp - boozhoundlabs thread.