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Old 7th March 2008, 05:32 PM   #1
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Location: Alps:Tube amp designs over 150W, SMPS guru.
Default preamp line ctt

Glancing through my 1960's dusty amp files, I came up with this preamp circuit and lashed it up using modern components.
The 2nd stage ECC83 bootstrap is a bonus upping the input Z and with gain control in cathode, the 3rd stage uses AC (36dB) nfb strapped back to cath 2nd stage. I have to tabulate the b/w performance and other issues.
For those who can't abide with true signal triodes, I used two EF86's as triodes an by golly it gave the b/w results I was after. Even with ECC83 it's good.
1V AC rms in and 18V rms at 3rd stage at only 0.15% thd 2nd harm. The THD drops proportionally with level. With such dynamic overhead performance, this would make a template for a line amp and with a Baxandall tone control stage + cathode follower o/p an excellent piece of kit..
Noise level using EF86's as triodes typ -90dB (pretty quiet).
The 2nd +3rd stage physics is pretty obvious, but I've only seen this config in one other preamp. Why not ?
The only other preamp I've seen anywhere near this is the Old Brimar/Thorn VP10 using obsolete ECC807's.

richj

Anyone else tried sim ?
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Old 7th March 2008, 05:34 PM   #2
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