Woohoo!! I actually got to help someone!

Hi all,
 
Rather than reading a bachelor-degree thesis in German, I highly recommend:
 
Merlin Blencowe.  Designing Tube Preamps for Guitar and Bass.  Second Edition, Wem Publishing, 2012.  ISBN 978-0-9561545-2-1.
 
It's pitched at the level of an electronics tech, but written by an MSc so readers would most definitely benefit from additional EE courses, some types of physics courses, etc. because these courses help in seeing beyond what is literally written in the text.  Reviews of this book, including those by EE's, often state that this is the best book on the market. 
 
I agree completely, and I do have Richard Khuenel's books which I would classify under Blencowe's description of "very technical books that are not really practical and seem rather to miss the point."  Op. cit. page vii.  Richard's books are very thorough, but IMO very few people are interested in looking over what could be regarded as an very extended homework assignment in circuit analysis --- homework problem after homework problem done in a very pedestrian manner: input impedance, output impedance, frequency response for low freqs, frequency response for middle freqs, etc.
 
Blencowe's work as a "soul" so to speak.  It's more a work of both art and engineering.
 
Regards,
Dave Clark
 

Hand made, Vacum Tube. 

Not exactly under the category software, but its:  Tube Preamp

I've yet to find a Software " Tube Preamp " that sounds like hardware

TL Audio 5051 seem to sound good of what i can hear 
with fat low's and bright pleasant open sound, with detailed tone
Together with RME Audio interface, that combo would be awesome.

To me a Tube Preamp, is more about sound and tone, ( it is an Amp )
compared to the " side effect " distortion, when driven hard

what TLAudio say:

Why Valves (Tubes)?

The science behind it all.
With the proliferation of digital audio and all it’s acknowledged advantages, the growth in demand for tube products has one very obvious justification... great sound.
Tubes offer a wide variety of sounds from completely ‘clean’ to ‘full-on overdrive’ which are invaluable when used in conjunction with digital audio, resulting in a less ‘sterile’ more ‘analogue’ sound. It would be difficult to describe every sound between these extremes but there are three quite distinctive sounds that occur below, on and above the signal clipping point.

• Clean Sound - where no perceptible overdrive is audible. But even when a tube operates well below its point of audible overdrive, it still exhibits an amount of sound compression, or sustain. Often described as ‘warmth’.
• Fuller, Creamier Sound - where the tube is pushed into subtle overdrive at the start of notes and chords, decaying into a cleaner sound.
• Overdriven Sound - delivering long sustain and smooth distortion.

i can agree on that
enjoy .....