• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Balanced tube linestage???


2001-03-06 3:07 pm

have anybody built it or tested it? i cant read out all of the component values but i made i cleaner picture of it

can the ecc88 take higher voltages? i got some 0A2 tubes that could be fun to use. i thinkt they can handle about 30mA so i nead one for each channel right?...

or does anybody know of any other BALANCED tube linestage?....

(preferably something that could live from a dyaco Pas transforer and 12x4 rectification 2 x 10h and quite a lot of capacitance...



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2001-10-26 11:51 pm
Limiting the list to circuits with balanced outputs as well as inputs, there is Alan Kimmel's cross-coupled differential mu-follower at http://laplaza.taos.nm.us/~fvuotto/mustage.html and Allen Wright's designs at http://www.vacuumstate.com. As for complete articles, Glass Audio had at least two. One by Erno Borbely in Vol9 No 1 1997 and another more complex one in Vol9 No6 1997.
For the more adventurous how about something along the lines of the Sonic Frontiers SFL2? If you are up for a bit of reverse engineering or perhaps handy with Spice modelling, SF ran an ad a few years ago with what could well be the schematic for the SFL2. While it was not possible to read actual values, the fully balanced circuit topology was clearly visible.
And for a current example of a commercial balanced tube preamp there is the patent for the Atma-Sphere MP-1 and -3.


you should be tarred and feathered and chased through the streets for attaching a pix in BMP format :( .... :)

Looked at your pix, i don think paralleling high-G_m tubes is a brilliant idea. It may work, but it probably doesn't sing.
Paralleling eats up the detail.

Have one tube per side and maybe you manage to find tubes with system 1 matched to system 1 and 2 to 2. Then you could use them for left and right channel. Or simply waste them. use them for a tape output buffer or use them paralleled as tube current source which can handle the current.

Otherwise methinks this is a pretty decent circuit.

Other circuits:
Why not build a small power amplifier output stage using two E88CC see above and feed them with the center-tapped primary of a 15K to 600Ohm line-output transformer? Simon Shilton sells such a trannie, the pa102, world class, but it ain't cheap.
But better go with a 5687 than with a E88CC. Cheaper and better.


2001-11-09 6:35 am
another one...

... actually a fully balanced preamp (including RIAA stage) can be found on page 295 of the book 'Valve amplifiers' by Morgan Jones. Uses 2 6SN7's, 2 E88C's and 0.5 E182CC's per channel, and the voltages seem about right for a dynaco pas 211 power transformer.

i havent built this circuit, so cant say anything about the performance; i just spent an engrossing 4 hours reading the book in the library - so i thought i'd pass the info along. i can scan the schematic in if needed, (the book is heavily DIY oriented, so i don't think there'd be copyright trouble).

Re: 5687

kimarin said:
I have a pair of 5687 laying around and I want to build a line pre. does this schematic do if i use single coupling instead of double? Would be glad if someone had a suggestion to what I can use my 5687 valves for. Balanced or non balanced line pre would be intressting
have a look at http://home.t-online.de/home/MHuber/pre-5687.htm
or use the mentioned Shilton trannie for an AudionoteJapan level version of that.