Tuesday, February 19, 2013
I built a single jFET preamp for my mate's double bass which is fitted with a piezo pickup under the bridge. I couldn't make it work properly and therefore this OPAMP based attempt. Mustard caps are all the rage with pedal makers and I just happened to have about 6 from my early electronic days mostly 0.1uf. Mustard cap on the input and polypropylene on the output.
The paint job is a poor attempt at hammertone. Right colour no hammer?? The OPAMP is my fav. OPA2134 and is running at 18V. Input impedance is a ridiculous 10M. There appears to be good gain and the pot seems to enhance treble as it is turned up. I work both sides of the proto-board and even cut a track for compactness.
Wednesday, January 2, 2013
Based on the high performance OPA2134 OPamp chip this headphone amp\driver is good sounding and portable. The schematic is based on the CMoy design with some changes in passive parts values. I elected to run it on two 9V batteries for better battery life and greater dynamics.
There is only 4" total of hookup wire in the signal path and all component-2-component connections on the proto cct. brd. Low ESR 200uf caps and a resistive network provide the differential voltages required to operate the chip without an output cap. The brd. is silver soldered with Mil.spec machined chip socket and Russian PIO caps on the input. Power only comes on when both phone jacks have plugs in them and the power switch (at the back) is on.The enclosure is impact resistant and lined with heavy Al foil for shielding and enclosure resonance control. The sound is clean and bright with good volume and dynamics. The amp is dead quiet with no signal.
Monday, October 15, 2012
Sunday, August 26, 2012
I was asked to make a MC phono preamp for an audio club member. My experience with both my clone of a Boozhoundlab (BHL) phono stage and the Le Pacific MC preamp made it easy to put together a dedicated MC phono preamp. I used my previously made BHL Chocolate Box phono stage with RIAA equalization and a freshly built Le Pacific stage. Both of these modules are good performers.
The MC stage and BHL phono have there own battery supplies. The BHL phono stage has a large 10,000uf cap to allow bottomless drive and dead black back grounds. The cct. brds. are housed in a 1U 19" case and looks very purpose like. There is considerable RFI snubbing throughout and a light layer of Dacron is placed over the cct. brd. to control cct. and enclosure resonances. A battery test point is provided at the front. The synergy of the two cct. brd. and battery system makes for one extremely good sounding preamp. It will be missed in my system,
Saturday, June 2, 2012
After building the Boozhound Labs (BHL) MM phono stage, with RIAA compensation and finding it a fantastic preamp, I added to it a MC stage. The BHL phono is the best preamp I have built and I have built quite a few. Because I moved to an Ortofon Rondo Blue MC cartridge I required the addition boost of signal from the cartridge. The Le Pacific MC stage (also reviewed on my blog) is simple to build and works well.
Both the MM and MC stage run from their own battery sets and can be turned on individually. There are separate MM and MC RCAs on the back of the preamp to allow a MM and MC TT to be connected. A single switch allows you to chooses between either input. The preamp is housed in a 1U 19" metal case. Both the BHL stage and Le Pacific stage use only Russian PIO military caps which I have also used extensively on other projects always with excellent results.
Bitumanised heavy Al foil lines the base and lid of the case and when the lid goes on a layer of sound deadening Dacron is layered over the cct. brds and fills the enclosure. All hook-up wire is silver plated fine copper wire (wire wrap wire) and ferrite beads are used extensively on all RCA wire connections. The preamp is dead quiet using only 2SK170 JFETs and quality metal film resistors and electrolytics. If you have not tried the BHL kit for the money, they are excellent value and top performers.
Tuesday, January 24, 2012
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
Monday, December 26, 2011
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.