Tuesday, August 28, 2018

"Grace" - 6SN7-SE preamp

The tubes are limited edition Psvane Treasure 6SN7-SE  globes or bulb shaped. They are strikingly beautiful with their gold metal and ceramic bases, quaint shape and gold markings. This build will not only be about a great performing preamp but an extremely beautiful build. 

Keeping as much gold as possible in parts selection the knob attached to a 24 step stepper (with gold contacts and only two resistors in circuit at any time) attenuator is 4oz of solid brass and gold plated. The six RCAs (two selectable inputs) also gold and the standard "retro-thermionic" name plate polished brass. The white sprayed chassis and wooden cheeks complete the lush look. The cheeks are rubbed with a finishing oil to lift grain and protect. A XLR connection on the back will bring in power required.

The external PS has double Pi filtering with a 5H Hammond choke. A total of 480uf of filtering and DC on the filaments insures quiet and stable operation. Expensive Jensen Copper foil, paper and oil are used as output caps, the only caps in the signal path. These large caps have silver leads. Silver solder was used and along with 4uf Russian military caps to hold the HT at the plate. 1W carbon resistors were used throughout though there is only three resistors per channel. These ensure a warm and balanced sound. No cathode bypass (Ck) capacitors are used to allow a little local NFB with no GNFB.

The circuit is designed to work to 100K and provide low output impedance. From a limited amount of serious listening I am extremely impressed with the overall sound which allows low level detail with hear with ease. Bas us rich and deep and mids flat throughout the whole range. A very balanced sounding preamp. 

"VoXUno - 12P" - with Markaudio drivers

These Markaudio - 12P driver based speakers relies on the one 8" driver handling from very low to very high frequencies. They may not have the super deep bass of a couple of 12" bass drivers or the airy highs of titanium tweeters but they do cover an extreme range and cover it well. What they do better than most multi-driver speaker is image perfectly. They produce a believable well scaled image and with the right amp will produce 40hZ. At 92db of efficiency they work well with low power amps. 

The boxes are about 90ltrs and are built to the design provided by Markaudio. The port is provided by a short front baffle board. Its dead quiet until 40hZ then comes into play. The boxes are braced and dampened with bitumanised heavy Al foil and Dacron.  There is no Xover but connect direct to the amplifier. Grills attach magnetically are best removed when speakers are in use. I'm extremely pleased with these simple and inexpensive drivers, so much from so little.

Saturday, August 4, 2018

Lagoon Take 2

The original Lagoon had a few noise issues and was not suitable for the intended user. When I got it back I wanted to take it back to a 4S single stage tube preamp. The second in the 4S series, the MKII or in my build "The Black", was the one I wanted to build. This series eventually lead to the 4SU (Universal) tube preamp. The MKII was a better tuned version of the rough original and more suited to the 12AU7, a tube I preferred in preamps. Not only that I had some Psvane "T" series MKII tubes which I have enjoyed in the past.

I had all parts on hand and was determined to only use parts on hand for the amp brd.  Metal film resistors and silver solder plus some MP caps. The rest of the preamp was complete so I only need to make the preamp section. The MP caps are metalized paper in oil. 

On some early listening the preamp sounds good. Unfortunately Lagoon can only drive into high impedance power amps. OK for me because that is what I intend to use it for. For an image of the back of Lagoon refer to an earlier Lagoon post. 

Saturday, July 21, 2018

"DC Duffer" - Black

These started life in a small metal enclosure but to increase safety I moved them into a light grey ABS enclosure. A request came for a black one and with black leads. Here it is, all in black.

Over the years I have modified components used and construct to the point where these are quicker and easier to build for me but still offer the high level of safety and performance. They still have a ferrite choke on the socket lead, are fused, a high current diode bridge is used and the usual RFI/EMI power filter included. Of those sold everyone has reported improvements in system performance and a couple have also used them on their TVs for better picture clarity. They really are simple and effective.

Saturday, June 30, 2018

"Retro-TubePhono" - MM tube phono preamp

Yet another Radi0Kit K318. The kit comes from Greece and has some good quality parts; Wima, Dale, ceramic sockets. polyprolene caps and some JJ 12AX7. I swapped the JJs out for some Psvane 12AU7 "T" series MKII. If there is any PS noise the A7s will bring it up. The Psvanes are matched and more expensive and provide a much smoother sweeter sound. The JJs can be a touch edgy. 

External PS from an earlier build in a Hammond extruded Al anodised enclosure. A 24V 1A wall wart provides the AC. Quality gold plated RCAs and fine silver plated wire-wrap wire is used for audio internal hookup plus silver solder make this another "nice" build. 

The larger enclosure is a Jaycar steel and Al project box. From the AC wall wart a step down tranni is used backward to regenerate 280V for the HT. Double Pi filtering is used with nearly 400uf of filter caps. The 12V filament voltage is rectified and filtered for DC on the filaments.

At the users house (on a very nice VPI TT and Denon Karat cartridge) an earlier Le Pacific MC step-up is used before the MM tube pre. The sound was "club". Smooth flowing, solid and with great image. Bass and treble sounded, once more; "club". Most enjoyable and highly believable. 

Tuesday, June 12, 2018

Lagoon - Two stage tube preamp with cathode follower

On request from an owner of one of my Parley preamps I build this cathode follower. Parley had been used as a tube preamp to drive some large SS amps. Parley had a tube frontend with SS backend to drive into lower impedances. This new build has a 4SU (Single stage universal tube preamplifier) frontend with a cathode follower backend. Now an all tube preamp capable of driving low impedance SS amps. You still have the ability to swap any 12A?7 tube at the frontend. A 12AU7 has been selected as the logical driver tube.

The 2U enclosure is steel with Al front and back plates. The finish is a fine black stipple. Six selectable RCAs are on the back with two small power switches to select your input. Power switch is also on the rear. The enclosure is fused and earthed. The power cord has a ferrite choke and a RFI\EMI internal dedicated power filter helps provide clean mains AC. A 3A over-size EI power tranni supplies 24V for rectification and breakdown for filaments and to drive a stepdown tranni backward for HT. 

The PS uses 1A diode bridges for HT and DC filament voltage. The bridges are snubbed. HT filtration is a double Pi the first with two 100uf caps and a 5H Hammond choke the second Pi with a small limiting resistor and a further 200uf of smoothing. DC for filament is single Pi and limiting with 10W resistors. The preamp is dead quiet. Mains earth, filament and HT negative are all connected. 

An Alps Blue Velvet 250K audio pot and 4oz solid brass gold plated knob provide attenuation. The tube compliment is Genalex Gold Lion gold pin 12AX7 preamp tube and Psvane's top of the range 12AU7 "T" series MKII gold pin. Sockets are on a turret board and are ceramic with gold pin sockets. Russian PIO military metal-over-glass caps are used in the inter-stage and the output. Metal film resistors use on the amp board. All signal path wiring is silver plated unshielded fine copper wire wrap wire. All soldering is WBT 4% silver solder. A low glow 3mm retro-yellow led indicates on. 

On only a brief listen the sound was bright and clear and sounded very balanced with good drive. This preamp will require about 50hours burn in so how it sounds in the end I will never know. I would imagine the preamp to mellow a little. With easy tube changes with the preamp tube the final sound is quite tailorable. Looks smart and sounds very smart.

Tuesday, April 10, 2018

retro-Oatley 6J6 Headphone amp (take 2)

Yet another Oatley 6J6 tube headphone amp. See an earlier posting for more details. A different chopping board for this mount and different beige boxes for connection points. The big improvement is the toroid power transformer. Where the earlier prototype hand an EI tranni which induced hum into the OPTs this toroid version is dead quiet.

An excellent HP amp to listen to. A pretty cct. brd. to show off. Good sounding and good looks make this a winner.