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JFET Moving Coil (MC) Pre-Preamp Kit

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

Some History

I received the Boozhound Labs JFET Moving Coil (MC) Pre-Preamp Kit a while back and I promptly assembled the small circuit board. I'm a sucker for a simple kit and a hot iron. That is where it all stopped. The circuit board remained complete and laying about for a few years. Recently I required another MC stage because the tube moving-magnet (MM) preamp I had just completed did not work all that well with the Jean Hiraga MC stage I had been using for years. It appeared the Hiraga had too much output and was over-driving the tube stage. So I needed another MC stage.

I borrowed a friends Denon MC step-up-transformer (SUT) unit. The system sounded better with the SUT driving the tube MM stage but also sounded a bit dull. This finally pushed me to complete the Boozhound Labs MC Pre-Preamp kit.


Boozhound Laboratories JFET Moving Coil (MC) Pre-Preamp Kit

The $49 (Sept 2015) kit comes with the necessary components required to populate the small printed circuit board (PCB). The kit builder needs to supply their own power supply, enclosure and hardware (connectors, switches ...) The kit contents are shown below.

Boozhound Laboratories JFET Moving Coil (MC) Pre-Preamp Kit Parts

Photograph 1: Boozhound Laboratories JFET Moving Coil (MC) Pre-Preamp Kit Parts

The Boozhound Laboratories JFET Moving Coil Pre-preamp kit includes PCB and all passive components to populate the PCB. Four Stand-offs for mounting the PCB are included. You have to provide your own chassis, power supply (12-24VDC), and various connectors. The Boozhound Laboratories JFET Moving Coil Pre-preamp kit features:

  • Minimalist circuit using the 2SK170 JFET;
  • ~30dB gain;
  • Russian K40Y paper-in-oil coupling capacitors;
  • Nichicon Muse electrolytic filter capacitors;
  • nice quality PCB (made in USA);
  • circuit requires external 12-24VDC power supply (batteries work well);
  • Assembled dimensions (height with included standoffs): 4 x 2 x 1.625 (inches).

The MC PrePre kit only has a handful of components and for the practiced DIYer the whole soldering chore can be over in less than an hour. Some of the solder pads are quite small so a fine soldering tip and some soldering experience is required. Some solder points I found a challenge and I have been on the cooler end of a soldering iron for over forty years.

The schematic (shown in Figure 1 below) is from the kit assembly manual. If you take a look at the circuit you will see it is very simple. It is basically the Le Pacific MC PrePre designed with the usual Boozhound Lab tweaks. The tweaks I think have been quite smart and I believe have really advanced the basic Le Pacific designs.

JFET Moving Coil (MC) Pre-Preamp Kit Schematic

Figure 1: Boozhound Laboratories JFET MC Pre-Preamp Kit Schematic

Boozhound Labs is known for their designing and supplying audio kits around the Russian paper-in-oil (PIO) caps. Personally I have used these Russian PIO caps in many tube and solid state projects. In every case I have been pleased with the results. The Russian PIO caps are inexpensive and good sounding. A lot of other DIYers sing their praise also. The Boozhound Labs JFET RIAA Phono Preamp Kit is full of PIO caps and I liked the MM phono stage also.

Finished JFET Moving Coil (MC) Pre-Preamp Kit PCB

Photograph 2: Finished JFET MC Pre-Preamp Kit PCB


Building the JFET Moving Coil (MC) Pre-Preamp

As stated above, the circuit board had been assembled for quite some time, but now it is time to finish the project. I have been building Bruce Heran's Op-amp based MM and MC RIAA phono stage for a while and most of these builds ended up in small metal projects enclosures. These enclosure boxes I source from my local electronics store where I also work. They are light weight but with the addition of some bitumised heavy Aluminum foil, the enclosure can be considered reasonable.

Most of my MM and MC phono stages have been powered by batteries. I like batteries for a few reasons; the operation of the unit is usually very quiet and they are very portable. I arrive at others homes with phono stages and no mains power required. Generally battery changes are infrequent because power drain is very low with most devices using only a few jFETs.

Assembled JFET Moving Coil (MC) Pre-Preamp Kit in Metal Enclosure

Photograph 3: Assembled JFET MC Pre-Preamp Kit in Metal Enclosure

For this build I decided to use better RCAs. I have always used gold plated RCAs but in this instance I used a premium grade gold plated connectors. The kit was designed to run on 12 to 24V. Using two 9V batteries put the supply voltage right in the sweet spot at 18V. Using quality batteries is not essential but generally means few battery replacements. I'm currently using Panasonic batteries. To further assist in battery monitoring I include a battery test point at the front of the units. Thus battery testing does not require the enclosure be opened.

As always I used wire-wrap wire (fine high grade copper with a silver plate) for hook-up and WBT silver (4%) solder . Bitumanised heavy Aluminum foil lines the inner lid and bottom of the enclosure to help control vibration and resonance. Battery clips hold the 9V batteries and a low-glow yellow led indicates "ON".

Assembled JFET Moving Coil (MC) Pre-Preamp Kit in Metal Enclosure

Photograph 4: Assembled JFET MC Pre-Preamp Kit in Metal Enclosure


Some possible improvements

If you want to use different components, the PCB is available for US$24 (Sept 2015) plus postage to your country. The kit is so simple that any possible improvements means different resistors and caps. Vishay Dale resistors could be used though I think the provided metal film types are sufficient. The only capacitor to change (Russian PIO) could be replaced by quite a variety of very fine caps; Jensen, M-Caps, V-Caps, Jupiter etc. A more solid enclosure and perhaps a regulated DC supply are other improvements that could be had. Even better quality RCA connectors again, for example silver RCAs, is another area improvements can be made. Will you hear a difference, not really sure? For this build I changed the load resistor to 50-ohms which better suits my MC cartridge, but outside of this simple change I would probably not change a thing.


The best MC Stage I have ever made!

I have made and sold quite few MC stages over the years. A number of the original Le Pacific MC stages and the Jean Hiraga bipolar MC pre-preamp. Lately I have even tried a step-up transformer. BUT I know I have never heard any MC stage which has allowed my Ortofon MC Rondo Blue to speak so clearly and with as much authority. The Ortofon Rondo Blue is noted for its extended dynamics and its balanced reproduction of deep bass to extended treble. From the very moment I heard the music being delivered I knew I was onto something really special.

The Boozhound Laboratories JFET MC Pre-Preamp kit is very good. It has opened a new world of clear, detailed and open analogue sound to me. It has shown me (combined with my Radi0kit-RK318 - MM tube phono preamp) what my Ortofon MC Rhondo Blue cartridge can really sound like, and for that alone I am truly grateful. I thoroughly recommend the kit and would be surprised if it is not liked well. Highly recommended!!

Assembled JFET MC Pre-Preamp Kit in Metal Enclosure

Photograph 5: Assembled JFET MC Pre-Preamp Kit in Metal Enclosure

Completed JFET MC Pre-Preamp Project - Bourbon

Photograph 6: Completed JFET MC Pre-Preamp Project - "Bourbon"

The kits can be purchased from Boozhound Laboratories for $49US (Sept 2015) and that includes shipping within the USA..


Tengu - Extreme Version with Audio Note Silver Foil Capacitors

 UPDATE  - 11 November 2015
After building the Boozhound Labs MM preamp and dedicated MC pre-preamp featuring the Russian PIO capacitors, I was inspired to build an extreme version of this MC prestage as I was very impressed with the performance of the MC stage built from a kit. Having on hand some ultra expensive Audio Note (AN) capacitors, I thought what better to use.

Veroboard build using Audio Note Silver Foil Capacitors

Photograph 7: Veroboard build using Audio Note Silver Foil Capacitors

The AN capacitors are silver foil, paper and oil clad in a pure copper outer. The leads are made using fine silver wire and these caps currently sell for AU$427 each! To further ensure that this was going to be a "killer" build I used Vishay resistors, Nichicon electrolytic caps, solid copper high-end RCA connectors and a Hammond extruded enclosure. The sliding plate of the enclosure is lined with heavy bituminized aluminum foil to help dampen resonance and vibration. All hook-ups are made with silver plated fine copper wire and the solder is WBT silver (4%) . Construction is on Veroboard, there is a battery test point at the front and a soft blue "ON" LED to indicate power. On an initial listen the bottom end appears a little richer and the sound stage more defined compared to the kit. But early days. The cost of parts is over AU$1000! "Tengu" are Japanese mystical creatures let's hope this has a mystical sound to compliment the price.

2sk170 JFET MC PrePreamp with AudioNote Silver Foil Capacitors

Photograph 8: Tengu-2sk170-JFET-MC-PrePreamp.jpg

Tengu is an improvement in my home system over the Boozhound Labs kit, but at the cost of parts it should be. I could not AB the two builds as the the original Boozhound is off in a new home. I particularly noticed that on solo piano music there was a lot more piano from LPs I know quite well. Definitely greater depth to each instrument. I have been very pleased with the sound right off the bat and was particularly impressed with the dynamics and detail of sound. I was not prepared for how well this stage would sound 12 hours later. I believe in component burn it and especially with caps and even more especially when they are big expensive and exotic audio caps. The whole sound of my system, with this new MC stage in place, has lifted the my system to a level I have never heard before. I should have known something great was coming when I heard how good the original Boozhound MC kit was and with the addition of a high-end caps, as the only caps in the audio path, it had to improve. I'm not going to talk of bass and depth of field etc. but just to say the overall dynamics of my vinyl setup, which includes the new tube MM stage, is off the planet. Yes a $AU1k+ MC stage which runs on batteries should sound good and thankfully it is a lot better than good. I'm going to build another one of these stages using copper or tin AN caps wich are lower cost than the AU$427 silver puppies.

2sk170 JFET MC PrePreamp with Audio Note Silver Foil Capacitors

Photograph 9: 2sk170 JFET MC PrePreamp with Audio Note Silver Foil Capacitors - "Tengu"


Salix - DIY Version with Audio Note Tin Foil Signal Capacitors

 UPDATE  - 6 December 2015
Having built the Boozhound Labs JFET Moving Coil Pre-Preamp kit and then building the super expensive Audio Note Silver Foil capped version, I was wondering "WHAT NEXT?" The standard Boozhound Labs JFET Moving Coil Pre-Preamp kit is excellent and the Audio Note Silver Foil capped version, "Tengu", was ridiculously good to say the least. But I had to try something else. I had used the very best and most expensive caps that Audio Note sells so I decided to try their line of Tin Foil signal capacitors. I have never built anything using tin foil audio caps. In fact I didn't even know you that tin foil capacitors were available. So I just had to try them out.

Veroboard build using Audio Note Tin Foil Signal Capacitors

Photograph 10: Veroboard build using Audio Note Tin Foil Signal Capacitors

Building the exact same MC stage, only using the Audio Note Tin foil caps in place of the Silver foil caps I was surprised at the result. Firstly these caps are better priced at about AU$30 each landed and secondly the leads are solid silver. Nice touch. I called this build "Salix" and was pleased just how good it sounded. But which version is better? Remember these two DIY MC stages are 100% identical except for the output caps.

2sk170 JFET MC PrePreamp with Audio Note Tin Foil Capacitors

Photograph 11: 2sk170 JFET MC PrePreamp with Audio Note Tin Foil Capacitors - "Salix"

Now here's what it comes down to; If your vinyl is in pristine condition, little to no surface noise, no pops or clicks and the recording has no hiss, tape hiss or otherwise, Tengu (Audio Note Silver Foil caps) is for you. But should your LPs be a little on the noisier side then Salix (Audio Note Tin Foil caps) is for you. The reason is Tengu is hyper-detailed and not only does it allow the full music to be presented in the finest detail possible, all the noise on the record is also presented in perfect detail. Salix still gives you a genuine and detailed musical presentation of the recorded music but tends to hold pops and clicks and all other unwanted noise at bay. It is much easier to listen to vinyl through Salix than Tengu.