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SoftAmp PSA

Guitar Amp and FX Modeling Plugin by AXP
SoftAmp PSA
SoftAmp PSA by AXP is a Virtual Effect Audio Plugin for Windows. It functions as a VST Plugin.
Windows XP SP3 and higher
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SoftAmp PSA is a virtual-analog guitar pre-amp supplemented with noise gate and compressor, all modeled after famous guitar gear that needs no introduction.

At its core there are 5 distortion stages. First three are based on op-amps with zener diodes in the feedback chain, while the last two are just op-amps being overdriven into saturation. They are followed by tonestack, speaker simulator and an output level control. Each overdrive stage has a distinct frequency shaping quality according to their names. See the EQ plot in the bottom right corner for details.

All stages are modeled as nonlinear filters with their outputs depending on both the frequency and the amplitude of the input signal. It gives the most accurate digital representation, compared to cascaded filter/static waveshaper approach.

In addition to the basic controls, there are two more knobs that control the speaker simulator parameters - Shape and Rolloff. With both knobs at 0, the speaker simulator is completely bypassed (for example, to be used with external impulse loader).

Giving even finer control over the gain structure, there are two more buttons - Asymmetric and Soft-Clip. The former applies to the zener diode stages and replaces the default 4.7v/4.7v zener pair with intentionally unbalanced 3.3v/4.7v pair to saturate the signal with even harmonics. The more the first three stages are overdriven, the more pronounced is the effect. See the clipping LED indicators to have a feel of which stage gets the most saturation from the signal. The Soft-Clip function applies to the two overdriven op-amps and changes their open-loop gain from 1 million to just 200. This effectively makes the transition from linear to saturated region much more softer, making the distortion less harsh and also helping the fading notes sound smoother.

The PSI Denoiser noise gate has a handy "Learn" function. Don't play anything on your guitar and hit the Learn button. As soon as the LED goes off, the gate threshold would be automatically set to your noise level. The noise gate is applied directly to the input signal.

The Squeezo Range compressor is applied to the signal right before entering the PSA pre-amp. It's a very nonlinear, but musical sounding device. It acts as both upward and downward compressor depending on the gain and bias setting. In the original device those controls were not available for user adjustment.

For further details please see the included manual.

Latest User Reviews

Average user rating of 4.67 from 3 reviews
SoftAmp PSA

Reviewed By tr00_kvlt [all]
August 25th, 2021
Version reviewed: on Windows

Such a flexible plugin for shaping both guitar and bass tones! Also great for boosting other amp sims. Endless possibilities.

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SoftAmp PSA

Reviewed By Faydit [all]
November 23rd, 2020
Version reviewed: 1 on Windows

Sounds and behaves even better than the real gear! Much more flexible too, due to a lot of additional features.

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SoftAmp PSA

Reviewed By free4theworld [all]
December 4th, 2016
Version reviewed: 1.0.00 on Windows

i really like it .. sounds good and has a lot of features ... nice work !.

is there a manual ?


Read Review

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Comments & Discussion for AXP SoftAmp PSA

Discussion: Active
1 December 2016 at 6:31pm

Works great for me. Excited to see AXP's submission to DC16. :)

5 December 2016 at 11:35pm

Thank you Vospi :)

2 December 2016 at 8:52pm

Very nice emulation of a PSA-1, with some additional parameters to tweak ... the speaker emulation is better than on the hardware unit. Good job AXP !.

5 December 2016 at 11:37pm

Thank you Catchaway. Funny thing is, I never heard the hardware unit.

6 December 2016 at 8:56am

I wonder what should this BIAS knob do with stereo signal? For now it really destroys stereo image. Beside that the knob makes trrrrrr while moving. v 1.0.01 x32.

8 December 2016 at 1:13am

I didn't have time to do a proper stereo link, so gain for both channels is derived from the left channel signal (when the stereo mode is turned on). It should not destroy the stereo image, since gain is same for both channels. I'm looking into this.

Yep, changing bias produces crackling noises, because all capacitors need to charge to new values (this control was an internal trim pot on the original unit). I will fix this in future versions.

7 December 2016 at 8:30pm

Well, you did it again. This is very nice. Probably the best chimey fenderish tones yet. Not being familiar with the hardware, I youtubed it. Wow, that is an impressive unit. I spent a few hours with it using gtr. There are so many great things about this vst. First off you really have total control with out being limited to any particular voicing (fender, marshall etc.). All the parameter adjustments are sensitive and make a differencs.. The speaker sim is a true thing of beauty. After all they are just eq curves anyway. These two controls allow you to dial in what works in the mix without being distracted by loading impulses. Tonight ill try it out on bass. I can definitley see where it can be used on anything really. Great job.

If I could add anything to it. It would be the spring reverb from Flextron.

8 December 2016 at 1:08am

Rcl, thanks a lot!
A post-processing FX was planned but I couldn't finish it before the deadline.

By the way the manual is ready now, included in the same .zip file.

10 December 2016 at 1:24pm

Very well done! Sounds great.

Buuut...can we get the Noise Gate separately? :D It works so convenietly smooth. Excellent addition.

10 December 2016 at 1:41pm

Thank you.

Yes, all three units are planned to be released as separate plugins with additional features. I got a ton of requests for that.

10 December 2016 at 7:07pm

That's great news - thanks for your amazing work.

17 December 2016 at 3:14pm

Updated to 1.0.02, fixing the stereo mode issue in Squeezo Range.

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