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!

Monday, November 4, 2013

"Abstinence" - 6EM7 power amplifier

Yet another 6EM7 power amplifier. This time some expensive and different parts were use in construction and a different internal layout was employed. The power transformer and choke are isolated top and bottom by rubber grommets. This ensures no AC vibration reaches the tubes.The initial PS filtering is preceded with a on-board power filter, a 4uf\400V Russian PIO cap and 20H\100mA Hammond choke. The HT is supplied by a Hammond power transformer and a very expensive Sophia Electric mesh plate rectifier tube. The second stage of filtering is 47uf and 100uf electros. with a large limiting resistor ensure the amp is totally free from of hum and noise. All PS caps and cathode bypass caps are snubbed.

This amp sounds better than the last and I think it may be the Sylvania NOS 6EM7 tubes. Russian Teflon caps are used in the inter-stage coupling  and once more large NP caps for the bypass on the power tubes. For the first time I have used Chinese made H&K 15W OPTs, can't fault them. The look of the amp is almost under-stated "sexy" and the sound the same - sexy and natural.

Thursday, September 26, 2013

"Number 9" - Tube and Chip 80W Integrated

From a $48 printed cct. brd. and a bag of parts I fashioned this very functional looking 80W amplifier. The parts include a 6N3 valve (preamp), two TDA7294 high performance power chips and all the parts required to complete the cct. brd. You have to source the rest and that's where the expense starts.

The amp has been constructed in attractive charcoal grey 2U 19" rack enclosure. Three sets of switchable RCAs on the back and 4oz volume knob and Alps pot to control loudness. Speaker protection is included on the PCB and there is a delay complete with flashing led before the amp is ready for use. Very clean sound, holographic presentation.