Jean Hiraga Bipolar MC preamp

Continuing the build of MC cartridge preamps I decided to tackle something different. In this build a Jean Hiraga MC preamp schematic was used. Jean uses low noise bipolar transistors instead of jFets.  He originally used discrete low noise transistors which are no longer available. But what is available is even better. In a single eight pin chip (SSM2220) two low noise, perfectly matched, transistors share a single substrate. The $AU11.00 chip, when used with a socket, makes construction and maintenance very easy. I use gold lined Mil-spec chip sockets. WBT 5% silver solder is used throughout.

Construction is on veroboard and the enclosure is a Hammond anodised Al type.  Where Mr Hiraga likes to run all devices from car batteries with huge capacitors I settle with a total of 1F (1000,000uf) of capacitance and 8 X AAA batteries all onboard. The batteries supply +/- 6V. To maintain even battery discharge and to guarantee all four 1F caps get equal voltage loads a resistive network is used. The capacitors are in series to meet voltage level requirements (4 X 1F @ 5.5V). Additional caps are added: 220uf low ESR and 0.1uf to ensure good midrange band pass and snubbing of noise.

Twenty five turn trim pots are adjusted to ensure zero volts at the input and Russian PIO caps are used on the output.  An exceptionally low current draw should ensure over 200 hours between battery replacements even with cheap batteries. On early listens this MC preamp sound natural and appears to be working well with my Audio-Technica  AT-F3/MKIII with an output of 0.35mV

Le Pacific pre-preamp for MC

To compliment a two stage tube phono preamp I added this Le Pacific jFet based Moving Coil pre-preamp. It uses only a single jFet and a few other components. This very simple pre will deliver good voltage levels to any phono preamp and being battery powered it does it quietly. The total construction was on a single piece of veroboard (proto strip board) no PCB.

The output capacitors are Russian PIO the same used in the retro-thermionic tube phono preamp. The loading is 100ohms and 1nF. Silver soldered and housed in a heavy cast Al enclosure sprayed in a delightful Sungold epoxy enamel paint. With a 0.35mV Audio-technica AT-F3/III cartridge this preamp produces good dynamics and a strong output.

Oatley/Mongrel Dog Audio - JFET phono preamp Red Case

See the earlier post for some more details about this new kit from Oatley, the K303. I decided to install the basic kit in a better case than the light weight "tin" box I used previously. I believe there has been an improvement in sound with the heavy weight enclosure. If nothing else it looks a lot better. An extremely good sounding phono preamp and a well presented and complete kit all for thirty dollars. It is a steal.

Oatley/Mongrel Dog Audio - JFET phono preamp cct.

Oatley Electronics of NSW Australia has released an all JFET two stage phono RIAA preamp. Previously their phono preamp was a JAN 6418/JFET hybrid type. I liked this kit immensely (see earlier post) and made two and sold two. It has a passive RIAA compensation network following a high gain front end (over 100X). The first JFET is a 2SK170 and the second a 2SK246.

Inexpensive MKP, MKT and green caps (polyester) capacitors are used as well as a lot of carbon resistors. The amp cct. is reasonable standard. The PS though employs a capacitor multiplier which filters the DC particularly well. Also the PS (which is part of the kit) uses an extremely small power transformer with dual voltages (110/240).

I found the gain stage excessive. By cutting away the bypass capacitor on the first JFET the gain fell slightly. A bypass capacitor for the second JFET is provided but not required unless you are using a MC cartridge. By having local feedback on both the active devices the sound stage is deep and detailed. See the earlier post for a description of the sound.

It is necessary to house the preamp in a metal enclosure to ensure AC and radio frequency shielding. The kit is easy to assemble and comes complete with PS. I would recommend the kit to novice and expert.

Oatley/Mongrel Dog Audio - JFET phono preamp

I originally housed this preamp in a timber enclosure but 50Hz hum invaded the signal. This enclosure is a lot more flimsy than I might normally use but, when connected to mains earth, did provide good shielding. See the earlier entry for more information about the cct.

I did ensure that I used isolating gold plated RCAs. The signal/power earth and the mains earth are separate. Usually I don't do this. With the gain of the front stage around 100 X good shielding and earthing is necessary. The sound from this AU$30 kit is quite astounding when you consider the common parts used. The PS having a capacitor multiplier does a very good job of DC filtering .

The bass is deep and very extended. It is also well articulated and not one noted or boomy. Mids are rich and detailed with treble well extended and well defined. But what really shines through with this "build-in-an-afternoon" kit is the sound stage. Both the active stages of this preamp have local negative feed back. This is achieved by neither of the JFETs having a bypassed source resistor. I have found on my single stage valve preamp this does appear to produce a very deep and highly detailed sound stage.

Piezo pickup preamp

This Mongrel Dog Audio piezo pickup preamp was built to preamp a piezo pickup in the bridge of a double bass. It has a 10M ohm input impedance and a single 2SK170 jFET. A PIO Russian military cap and two polypropylene caps add quality components to an excellent build.

The case is polished die-cast AL with a polyurethane coating and all is powered by a single 9V battery. I increased the storage cap to a 200uf low ESR variety. Tough , simple and good looking.

JFET phono preamp-in a chocolate box

The finished jFET boozhoundlabs-Mongrel Dog Audio incarnation is "Gold". I dropped the whole cct. brd. into a very nice gold embossed chocolate box. The box is lined with bitumanised Al foil. It also has a clear plastic cover which covers the inside. The preamp can be run from of batteries or external power source.

This is by far the best phono preamp I have ever built. It is far superior to any of the others. Not that they were bad just that is so good. So very good and not just my opinion. Current draw is 13.5mA. Wirewarp wire is used as hook-up wire. Heavily twisted WWW (earth/hot wire) is used to bring the inputs and power in.