RTFRN
"Fixed wrong Input Drive taper [...] in 5153 Red amp model."
I have a few 5153 Red presets with a Drive setting of approx. 2 in FW14.02. With 15.00b I have to raise the Drive to approx. 4 to get the same result. Could this be due to the new taper?
Yes. I had the taper set as a Log10A but it's actually a Log5A. This means you have to increase the Drive to get the same response. It's simply a taper change though. Going from 2 to 4 sounds about right.
The values mean this in a log taper pot:
Log10A = logarithmic response, 10% at midpoint, audio taper. What this means is that the pot is not linear in its response. At midpoint (50% rotation) the value between the wiper and the ground terminal will be 10% of the pot value. So a 1 Megohm pot set to noon will have 100K between the wiper and ground.
I incorrectly had the taper set to Log10A which meant that at noon there was 20 dB of attenuation. The correct taper is Log5A which means at noon there is 26 dB of attenuation. So you need to turn the knob up to get the same gain.
This amp model has a bright cap so as you turn the gain down (which is effectively what happened by changing the taper) you get less gain and more highs. So "jingle, jangle, indy sound" is a likely result if you don't turn the gain up to compensate.
Note that taper only affects the response of the knob vs. position. It doesn't affect anything else. It just means that to get the same response you need to put the knob in a different position. Amp designers use tapers to voice their amps. It's not that it actually voices the amp though. It's because people dial in amps with their eyes. Human nature is to put the knobs near noon. We are reticent to deviate much from noon. Amp designers exploit this and use different tapers to change the sound of their amps WITH THE KNOBS AT NOON. A prime example are Bogner amps. Everyone says "Bogner amps are dark". No they aren't. But he uses a Log10A taper for the treble pot. It's a standard Marshall tone stack. Usually a linear taper pot is used for the treble. The treble knob at 5.0 (noon) on a Bogner is equivalent to the treble knob at 1.0 on a Marshall. People put the knob at 5.0 and go "wow, this amp is dark". No it isn't. If you turned the treble up to 8 or 9 it would sound a lot like a Plexi but humans are reticent to turn the knobs to extremes. Amp designers know this and exploit it to give their amps a "signature sound".
The more you know...