smcrosby
Power User
Thanks for taking the time to share these notes!Some notes:
1. This firmware will update various parameters to default values when loading presets. This includes Power Tube Bias, Bias Excursion, Negative Feedback, etc., etc.
2. I have adjusted the Power Tube Bias vs. the previous beta. In the previous beta the Fender (et. al.) default bias values were based on the original factory values. After much consideration I have decided to use "best practice" bias points.
The reason for this is that Fender amps were biased very cold from the factory to ensure the tubes lasted beyond the warranty period and cut down on warranty claims on tubes. However when replacing the tubes in ANY amp the best practice is to bias the tubes at 60-70% of max plate dissipation (for Class-AB amps).
I have some old Fender amps here with the original tubes in them and they are biased around 50% which is extremely cold. If I were to replace the tubes I would adjust the bias to around 66% (my personal preference).
So the bias point for all models is now commensurate with the typical bias point a technician would set the amp at rather than the factory value as the factory value almost always errs on the cold side for tube reliability reasons.
Therefore you will now see bias points of around 0.5 to 0.6 for 6L6 amps and 0.45 to 0.5 for EL34 amps and so forth. Feel free to experiment with colder or hotter bias points. Setting the bias colder (lower) results in a more dynamic response but harsher breakup and more crossover distortion. Setting the bias higher results in a warmer but less dynamic tone. For a Fender model the factory bias equivalent may be as low as 0.45.
For "Class-A" amps the bias point is adjusted using the Cathode Bias Resistance parameter. For those amps that parameter now appears on the Power Amp tab of the amp block. Increasing the value results in a COLDER bias point and vice-versa (opposite of the bias parameter behavior).
3. This firmware is more aggressive in the very high frequencies than the previous beta. There was a mistake in the power amp algorithm that reduced the drive into the virtual power tube grids by about 30% typically. So the grids weren't clipping as soon as they should resulting in reduced high frequency overtones. This typically will only be noticeable on non-MV amps. On non-MV amps you should hear a bit extra "sizzle" in the top end.
4. If you complain you'll be sent to the back of the room and will have to sit in the corner with a funny hat on for the rest of the day.