Piezo Puppy - pickup preamp for ceramic phono catridge.

Yet another build of an OPAMP based piezo pickup preamp. The OPAMP again is an OPA2134 (socketed). The single cct. brd. holds both the differential PS, generated by a resistive network and capacitors and the preamp section itself. Control of treble is via a small pot and can be used to "tone-down" surface noise found on most 78 records. There is a battery test point at the front of the preamp to allow easy battery checks without opening the case.

A mustard cap is used on the input and a poly on the output. Internal wiring is solid core copper wire. The case is cast Al and again I have used the hammertone finish which I think is quite attractive. This completes my 78 setup with a new stylus in my Ronnette piezo cartridge. With some reasonable 78s I have managed to get some enjoyment out of the shellacks.

Piezo pickup preamp for musical instruments

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.

Chip based headphone amp

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.

SynergyII\Cu LM3875 compact chip amp

SynergyII\Cu started with 3.6kg of 100% very thick copper plate. The enclosure was selected, a 1U, 19” rack mount. The challenge was to build a pure Gainclone with its three resistors and simple 1500uf storage caps in a compact 1U enclosure. Everything had to fit in this tiny space including 48VAC of tranni, power filters and rectifier cct.

To achieve this two 24V ultra low profile toroid trannies were selected, the rec. cct. brd. was constructed on a tag strip with super fast, soft recovery diodes (snubbed with 0.01uf polies) and a compact EMI\RFI power filter installed across the mains. A pseudo smoothing cct. is provided with a couple of 4.7uf polies on the differential voltage rails. The 1500uf electrolytic are snubbed with 0.1uf polies at the chips.  A simple ferrite choke sat around the power cord inches from where it entered the amp.

Solid 0.4mm five-nines pure silver wire connects the earth point on the PS to the input RCAs and speaker binding post returns. Heavy multi stand copper wire connects the differential PS, individually, to each chip amp cct. Total weight is 9.6kg. Being a DC amplifier bass is extended and controlled. The sound is clean, clear and solid with plenty of power.

La Boca - MC phono preamp

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,

Boozhound Labs and Le Pacific phono stage

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.

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.

JFET phono preamp-in a chocolate box

I was never completely happy with my phono preamps weather tube or OPAMP base. I made the Boozhoundlabs two stage jFET "Le Pacific" style preamp. Once more I went for the vero-brd. Also, though I wanted to build it with the Russian PIO military caps I did not have some of the values I wanted. I opt for a build using high voltage (630V) brown polypropylene caps.

The cct. brd. above uses pure silver 1mm earth links, 2SK170 BL jFETs and silver based solder. Low ESR 220uf caps (snubbed) sit across a decoupled V+ rail and a single 10,000uf caps (snubbed) feed the V+ through a 1ohm resistor (a La Pass). Currently running under 27V of lithium batteries.

Ferrite beads sit across both the ground and hot wire to the cct. brd. from the input Also the PS input has ferrite beads also. No shielded wire is used (I don't like it) but the input wiring is heavily twisted, hot wire and ground. See previous post for chocolate box enclosure.

K295 Production Version

In an earlier blog I constructed a prototype K295 for a bass player. It proved to be a great success and produced richer harmonics making the bass sound fuller and a lot warmer. This build is the production version of the K295 and the kit can be purchased from Oatley Electronics in Australia In this version only a single tube is used. The PS, including a tiny mains power transformer, is mounted as part of the whole cct. brd. but can be snapped away.

As in the earlier preamp I used a plastic case lined with bitumanised Al foil. Single pots were used to allow separate channel control and large numbered knobs used so setting can be noted for future used. The central blue "on" led marks "0" for both pots. Guitar 6.5mm jacks are on the back to allow music instruments to be plugged in. All hook-up wire is twist single strand copper.

On a short listen through my system the preamp appeared to work very well providing gain and and good control over volume levels. The left channel has a slight buzz due to it being closer to the tiny transformer than the left. A larger case would solve this problem by allowing the input and output jacks to be mounted further from the power tranni and mains (110 or 240V). Or break the PS away from the amp cct. brd. and mount it separately. All in a good build and good result.

K295 - JAN6418 buffer/preamp

In this small plastic enclosure is the new Oatley K295 kit. But in this build an early dual tube prototype brd. has been used. The intended use for the build above is for preamping of a double bass for a player in a Rock-a-billy band. Red LEDs are mounted on the brd. to light the JAN6418 tubes.

From early reports Ray, the bassist, is very impressed with the sonic results so far from his electric bass.

BoZ on a Cap (BoZoaC)

BoZoaC (BoZ on a Cap) uses a recursive component-2-component construction method to build the whole of the preamp cct. on the output caps. See the posted images below of the BoZoaC engine.

In my system input caps are not required and an earlier BoZSE build (input capless) proved that removing these caps improved overall performance of the preamp. Anytime signal path can be reduced in length and component-2-component construction methods used, sound quality has to improve. If look at the BoZoaC engine below it is obvious the signal path on the cct. is reduced to component length.

Some very high-end preamp manufactures will not use metal cases to enclose the boutique components claiming magnetic and eddy current issues. I chose this plastic case for similar reasons and wanted a non-resonant slim case to enclose this unusual build.

Though only a few hours of play have pasted through this tiny little preamp cct. I am convinced the sound equals or betters that of BoZSE which is supported by 30,000uf of storage caps. There appears to be a greater immediacy of the music with equivalent bottom end. Only comparative listening will prove this but this whole build is very satisfying so far.

BoZoaC exposed

A ridged plaster instrument case was chosen to house the recursively constructed BoZoaC. Three 9V lithium batteries sit at the rear where two sets of gold plated RCAs are mounted. The output for the preamp can be found on the left of the case with the input selection switch.

On the right rear of the case the banana style low profile sockets are mount to allow battery checking. If the batteries are removed an external PS could power BozoaC. Silver solder and wirewrap wire are used throughout.

BoZ on a Cap - BoZoaC

Due to the low component count of the BoZ cct. it is quite possible to build the whole preamp on a the output caps. In my other BoZ constructs I employ 20,000uf of storage caps. To keep the whole build very compact I used 2 x 1000uf low ESR caps for storage caps.

There is no input caps or attenuator with this build. It is not required in my system but other systems may require those components. A big plus of a genuine component-2-component build is a very short signal path and a minimum number of solder joints. These two factors help to improve the over performance of the preamp. There is no additional wire used in the build, all components are directly silver soldered to each other components.

Pass capless BoZSE

My new Oppo BDP-83SE has input caps but my 6AS7 SET has no input caps. So make a preamp with no input caps but good output caps. In this capless SE version of BoZ I have no input caps but retained the 10uf polypropylene caps for the output. Also the output caps have been snubbed by 0.1uf polies.

Nelson suggests a total of 30,000uf for his B1 whose PS I stole a few ideas from. But only having 10,000uf caps I used three to get the filtering/storage up. Also I used a simple RCRCRC filter network. 1ohm/10,000uf/10ohm/10,000uf/1ohm/10,000uf. Each 10,000uf cap is snubbed. Silver plated wire wrap wire is used throughout. Input hookup wires and power wires were threaded through tiny bead chokes. Multiple earths (negative voltage) connections were made. Bitumanised Al foil laid in the top and bottom of the Hammond anodised Al case. Silver solder, Alps pot and 4oz brass added once more to a quality build.

The sound stage is massive, stage depth multi-dimensional. The mids are excellently rendered with transients laid bare. Treble smooth is silky-smooth. You almost feel there is no treble because it is just parts of the mix, part of the overall music. Bass is weighty and well extended.

Where I thought the B1 was the Bee's knees this capless SE BoZ may be much better on all fronts. And it has gain.