Wish A 12AT7-like tube in preamp selection section

Larry Kehl

Inspired
Title says it all, looking for a LOWER gain preamp tube along the lines of a 12AT7. Yes less gain but more headroom. I'm looking to set up an amp that has an even longer time to get to breakup and when it gets there I want a little less of it.

Since the FX III preamp tube selection design is "all or nothing" (no I'm NOT criticizing the FX III) it's assumed that even if modeled preamp (Fender, Marshall, Mesa,,,) has 2-3 or more gain stages you can only select ALL 12AX7 's, or ALL 7025's, or all ECC83's, etc. I'd just like to see something slightly lower in gain.
 
yes and no (reduces front end gain but not the tonal "effect" of post tone stack gain) again it's just wish. Besides if it was just a matter of tweaking front end input gain (trim) then why model five or six brands of AX7's? Not to mention what is essentially a clone, the ECC83.
 
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...if it was just a matter of tweaking front end input gain (trim) then why model five-six brands of AX7's? Not to mention an essential clone the ECC83.
Good point. Though I still think that Input Trim would get you 90% of the way there.
 
I’m not trying to put Leon on the spot here, if I do then I'm truly sorry Leon, you a great resource here. But just stumbled onto this You tube so thought I ”bump” my own thread for two reasons.
  • I just saw a new wish list item for ”low’ish gain amps” and it just reminded me of my forgotten wish list item, and
  • Leon demonstrated (back in Jan of ’19 - but I didn’t see until this past weekend), what I already knew because I’ve done this in a few of my amps including my Lexicon Signature 284 (my main rack recording amp - well until FX III) that changing a preamp tube to a lower gain version is not the same as lowering the input gain, there is a different quality to the sound and dynamics.


I'm not worthy, I'm not worthy,...
 
+1. Changing V1 to a 12AT7 is something I’ve commonly done on my tube amps, and often with great results. I’m new to the FXIII, and was a bit surprised to see no 12AT7 listed, especially considering there are several brands of 12AX7 available.

It would be great if it could be possible to change V1 only. While it might be interesting to try 12AT7s for all the preamp tubes, I suspect the impact to the gain/tone may be too large. Would still be great to be able to try changing all tubes as well though.
 
12AY7 has a Gain factor of about half of a 12AX7. Set Input Trim in the Amp block to about 0.45 to simulate a the lower gain in the Input tube stage. The gain of a 12AT7 is about 60% of a 12AX7, so set Input Trim to about 0.6 for that. The gain of a 12AU7 is about 20% of a 12AX7, so set Input Trim to 0.2 for that.
 
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I second all motions here for more pre-amp tube options. That would go a long way into fine tuning amps.
 
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