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JFET Moving Coil (MC) Pre-Preamp Kit

Mark Houston

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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.

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.

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.

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.

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".

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!!

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

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.

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.

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.

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.

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.

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.

Last updated 6 December 2015. Created 19 September 2015. © Mark
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