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.