Reference preamp Othello !

Reference preamp Othello

Hello everyone this article is about a new state of the art preamp , its easy to build not vey expensive and delivers splendid sound quality,

you can beat any commercial pre amp hands down ( at least the ones I have heard) its based on the idea that a tube works ideally when not loaded ,

so how to use a plate load resistor that's high enough so it bearly loads the plate , yet leaves enough DC drive to the tube , and how to keep low AC returnpath signal resistance low enough , well there are only 2 methods , battery bias and plate loaded chokes , and in the way you apply those there are several options ,

the good news batterys are cheap , the bad a good plate choke is not . Since the batteries , are in series they will be charged by the tube current so this is not a problem ,rechargable batteries should last a few years . the good thing about this design is also its good rejection of psupply noise and its good filtering of ripple (which is increased because it doesnt use a plate load resistor) hence a lot of advantages for such a small circuit ,furthermore it is DC coupled and this leaves

us with one capacitor in the outputstage ( which we will eliminate next year ) the output stage is just a CF to reduce output impedance , not to heavy loaded but biased in full class A as is the first triode . we advise to use one tube for the first triodes stereo and one tube for the outputstage so you can float the heaters to the appropriate DC levels, this offcourse means to filament supplys .
The power supply we use is choke regulated , carefully rectified ,filtered ,over and over until ripple drops too unsignifient levels.
I recommend the classic tubes 2C51WE ,6SN7,6SL7,6BL7 ect my heart goes out to the octal family with one exception the 2C51 WE is magic.
It uses just 1 capacitor in the direct signal path , a Jensen copperfoil , for the purists this can also be omitted by using an interstage in the cathode circuit of the outputtube , this is especially advantageous if you want to drive headphones .

Best rgds
Benny Glass