Pls help with a preamp

[kendt]

I have a pair of charlize-2 amp baords from diy paradise. They will be running my speakers bi-amped.I would like to build a simple tube preamp to drive the amps. I dont think i need much gain at all so i'm just trying to add a bit of tube goodness to the sound. I would like something fairly straight forward and not too hard on the wallet.

Thanks

 

[DF96]

Used properly, tubes don't add "goodness". If you want a subtle effects box, look for a badly designed 'tube buffer' - usually a poorly biased cathode follower.

 

[Eli Duttman]

Low gain and good sound sure seems like 12B4 territory to me. There are any number of decent designs available. Of course, I'm uploading the version I'm associated with.

Make the net I/P impedance presented by the "sand" amps 15 KOhms, to hold gain down.

 

[kendt]

That looks like a nice easy build, thank you. I'm toying with the possibility of doing a four channel pre so that each channel of the amp is driven by its own pre amp channel, but that will depend of course on cost.

 

[Eli Duttman]

IIRC, Allied sells directly in Canada. A Triad VPL24-400 (Allied stock # 70218209) takes care of providing 2X suitable "12" VAC heater windings. A Triad N-68X isolation trafo (Allied stock # 70218526) takes care of B+. Those 2 combined cost about 20 USD. Canada's own Hammond makes suitable filter chokes. A pair of Hammond 155Hs takes care of the 5 H. parts. A Hammond 193J will take care of the 1st inductor position. Use a 10 KOhm bleeder rated for at least 5 W.

A 2nd generation of high PIV SiC Schottky diodes has become available. The pricing of those parts is more favorable. Use 4X 2 A. rated 600 PIV parts in the bridge rectifier.

The rail voltage that pseudo choke I/P filter produces has to be set at the bench, with the bleeder installed. A 0.47 μF. cap. in the "fudge factor" position is a starting point. The capacitance in that position is adjusted until the voltage measured across the bleeder is > 125 V. and < 130 V.

The costly Mundorf O/P cap. can be quite comfortably replaced by a 4.7 μF. metalized polypropylene part, which is bypassed by a 0.47 μF. 716P "Orange Drop" film and foil part. The schematic was drawn, from a narrative I provided, by a fellow who uses the "moniker" Buzz and he LIKES "boutique" parts.

 

[roline]

Have you considered a SRPP stage with a follower?

 

[popilin]

Try this

http://www.diyaudio.com/forums/tubes-valves/207544-ecc82-12au7-line-preamp.html

If you consider 2K is much for output impedance try with an ECC99 reducing +B to 350V and cathode resistors to 1K5.
A cathode follower isn't necessary.