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Old 16th June 2009, 06:24 AM   #1
diyAudio Member
 
Join Date: Aug 2005
Default Building a 12B4 Line Stage

Hi all,

I think I've read most or all of the 12B4 linestage threads here. This brings me to ask some questions that I do not remember seeing there.

1. I get the impression that the output impedance of the preamp with the circuits shown is about 1K. Was thinking since the output gain of the 12B4 is about 5DB, was thinking about adding a 2nd stage and then getting the output to about 10DB or so. I want to get the output impedance below that 1K mark to then be able to drive long cables, and also to properly "match" my SS amp. Any ideas.

2. Is it possible to adapt or use the same PCB as the Grounded Grid and substitute parts. Now, I would think the tube pin out isn't the same, so you'd have to go to all the bother of rewiring the tube sockets with the correct pin out. I think I'd have to get some different transformers for the B+. Obviously, I also will have to get different parts too.

Otherwise, I thought I read somewhere that someone has a kit for the 12B4 preamp.

Also, in the various short reviews, between the GG preamp, and the 12B4 preamps, the 12B4 had an extended highend versus the GG. So this leads me to wonder if anyone had put this up on a scope to measure the freq response of both pieces. The GG is supposed to go out to 200K, down by 3DB. If I remember Mark's assetment of the 12B4 preamp was that you could hear every pop and click, seemingly to emphasize the upper mids and topend. So that would lead me to think that the preamp doesn't have a flat response curve.

I also think I got the impression that somewheres I got the impression about this 6J5, or the 5687 Linestage being better than the 12B4?

Ok, so here's a mind blower for the DIY community to ponder.

I am a blind person. Yeah, so? Ok, can't see any of the schems that are uploaded? So can anyone take one of the better circuits of the 12B4 linestage including the power supply and properly describe it. You will have to get granular. That's ok. I don't mind the extreme detail.

The last 12B4 thread was a few years back. If something els is better than the 12B4 linestage, I'll bite.In advance, thanks for your info, and help. Let's see where this goes.

Ray Bronk
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