Monday, June 2, 2014

"Black Lace" all Ozzie valve 6V6 power amp.





























Ozzie, Ozzie, Ozzie. All Australian made Miniwatt tubes (at least 50 years old) on a Murbue base. "Black Lace" was always going to be a very Ozzie build. All tubes: 6V6, 6SN7 and 5U4 are Ozzie Miniwatt made. The 6V6s are black glass and spent 40 years under a house nearby uncovered. To keep with the old school feel carbon film resistors are use throughout except for the cathode Rk which are 5W wire wounds.

The PS is split at a Russian 4uf PIO first cap. The power tranni is rubber mounted to stop vibration reaching the tubes also on the top plate. Domed chromed nuts, securing the power tranni, sit on copper and brass washers purely for looks. The bottom plate has a heavy strip of bitumanised Al foil for dampening.

Two 5H Hammond chokes split the PS to pass through C-R-C filters. 100uf-6.8ohms (carbon film)-100uf. Even at the driver tube the PS remains split in two for two drop down resistors each with a 47uf snubbed electros for storage and further filtering. As you can see a dual PS stream right from the first cap all the way through. Most filter electros are snubbed with 0.1uf high voltage polies. Russian Military PIO caps are used for the inter-stage. The amp is exceedingly quiet.

All hook-up wire was off-cuts from the power tranni and OPTs. The solder was from the 60s or 70s - lead, tin and copper and Ozzie made. The sockets are a resin style, no ceramics around here! OPTs - Edcors - strayed black. The bypass caps on the 6SN7 are bypolar and the bypass caps (Ck) on the 6V6s are low ESR electros. The black lace with the amp (Black Lace) has been photographed on will be cut to for a dust cover when the amp is not in use and will be weighted down with clear and emerald glass beads. All tubes should be run in but all other components are new. The sound for now playing laid-back jazz is crisp, fast and un-coloured.

Sunday, April 27, 2014

"Parley" - valve preamp with jFet buffer





























This build is to replace a single stage valve preamp with a jFet buffer\driver stage. This allows a  simple valve preamp to drive low impedance loads. The frontend is a 12AU7 plate follower with moderate gain and the back-end a Pass inspired B1 buffer. The buffer stage uses two jFet with one acting as a constant current source. Either stage could be used by itself but together you get the better of two worlds. I called this preamp "Parley".

The enclosure is a 2U 19”, black stippled rackable. Four modules: 250VHT\12VDC reg, 18VDC for buffer stage and the valve preamp section. There are three selectable inputs on the rear and with Alps Blue Velvet pot and 4oz solid brass knob the build is stylish and good sounding. It also compliments my tube and chip amp, “Number 9” which is in a similar enclosure and from both the front and back look the same.

Wednesday, February 12, 2014

"VoXDeuX65" - 2-Way with 6.5" woofer\mid and Isodynamic ribbon tweeter















Building on the success of VoXDeuX, my first inexpensive 2-ways, comes VoXDeuX65 and goes to the next level of sonic delivery. These new 2-ways still pertain to the original idea of being inexpensive speakers but always with the ideal of excellent sound. And they have. 20ltr, 18mm MDF boxes with once more the well worked vertical bracing. There is a bass trap chamber formed to one side of the box designed to hold rear reflection and make the box look bigger and better dampened but not to dull the sound. Box weight is 11.2kg. Xover is at 2,350Hz and is a 12db slope. Speaker effciency is about 87db.

The brighter, zingier. treble crystallizes the sound stage and puts a fine, bright edge on the overall sound. Music has better weight with the bigger driver and added with the brighter treble demands to be listened to. I like the sound of these new boxes. I really like it.





Wednesday, December 25, 2013

6AS7 headphone amp with Sophia Mesh Plate 274B rec. tube



















The power supply and amp section are on two die-cast Al bases. A Sophia Mesh Plate Princess 274B rec. tube does the rectification. The PS has its own power filter to reduce EMI\RFI and the mains cable is choked. The power tranni is Hammond and the 20H choke is Hammond also and these are both isolated from the chassis by rubber grommets to control vibration. The 6AS7 power tube is NOS Winged "C" Svetlana and a NOS Tesla E88CC gold pin for the driver and is directly coupled. XLRs connect the HT and AC filament current to the amp section. A single 6.5mm input upfront with dual headphone output. Attenuation is provided by an Alps Blue Velvet pot. Both enclosures are dampened with bitumanised Al foil and the paint is Epoxy Enamel. The attenuator knob is 4 ounces of solid brass.

The Sophia Mesh Plate 274B rec. tube and a 4uf PIO Russian  filter cap start the filtering network with seven stages of filtering and storage in all. I believe the great sound of this amp is due to the Sophia tube and the PIO cap. There is no PCBs or shielded wire used in this amp to dull the sound. Wiring is all point-2-point and component-2-componet. Fine silver plated wire warp wire carries all the audio. The only caps in the amp are the output caps. All PS caps are snubbed with polypropylene caps and the output caps with Russian PIO caps.WBT silver solder is used throughout.

The amp is is absolutely dead quiet. Through my Audio-Technica ATH700 Air headphones music is like I have never heard before. Harmonics are rich and deep, detail is fine grained and dynamics unlimited.This may well be the greatest piece of audio gear I have ever made.





Saturday, December 7, 2013

Inexpensine MM\MC phono preamp MKII



For a 1000th the price of some SS phono preamps on the market these days I'm very happy with the second Bruce (of Oddwatt's fame) deisgn named "Mimic" This can be built in an afternoon and even with batteries cost about $40. Mine runs on 3 X 9V batteries wich should give 50 to 100 hours play with no change. The sound stage is detailed and expansive and instruments have there own place. Over-all tone is flat and natural.

Some better caps were used in this build over the earlier one. WBT silver solder, a dampened enclosure (bitumanised with Al foil)  and wire wrap wire hookup used throughout. A simple off-the-shelf enclosure keeps this preamp cheap. But sound is rich.

Saturday, November 23, 2013

Mains DC blocker and RFI\EMI power filter



















In Australia our mains supply has gone from clean power to not so clean power. For a number of years now I have built power filters into my power amps but not in media players or preamps.  DC on the mains can cause many problems with audio gear and particularly audio gear using a toroid transformer a DC mains blocker may improve sonic performance. This simple DC blocker also incorporates an RFI\EMI power filter. A choke on the input lead and 10A slow blow fuse round out a simple and neat solution to "dirty" mains power.

OPAMP phono preamp with high RIAA EQ accuracy









































The creator of the oddawtt series of tube amps and kits has developed an OPAMP based, highly accurate, phono preamp. In my build you can switch between, MM and MC and in MC mode switch between 50 and 100ohms load. This MC loading suites my Ortofon Rondo Blue and I can switch between the two loadings on the fly to gauge the effect. I run my build on 4 X 9V batteries and on a 1.75" square single prototype cct. brd. I have a simple resistive network to provide +/- 18V. A couple of low ESR 220uf caps ensure smooth power to the chip an OPA2134. A battery test point is at the front.

The cap compliment is polies and MKT with a NP electro on the output. Better caps could have been used but a wanted a neat tight build. The preamp came out looking attractive and most of all sounds glorious. For an inexpensive build with great flexibility (two switchable TT inputs for my Rega (MC) and AT (MM) TTs)this would be hard to beat. Tested RIAA EQ tracking is better than 0.25db!