possible tube amp simulation?

[rodriki]

Hi people.

I am new here.

The first - I am here to question about tube amps.

For years i have been reading on the web about
tube amps, and its comparation with SS amps.

It sounds like an endless discussion.

I am not a professional in audio.

But i know almost every guitarrist want to have
a good distortion of tube amps.

I do not have one tube amp.

All i know, after years of readings, maybe can be expressed
in a few lines.


- EVERY AMP GIVES SOME TYPE OF DISTORTION
AND TUBE AMP GIVES GOOD DISTORTION FOR GUITAR
- tube produces distortion with low harmonics
- tube produces distortion with EVEN harmonics
- tube gives large headroom (very good for audio)
- It is easier to implement tube amps compared to SS
- Good amps demands excelent electric source
- the output transformer affects the sound
- tubes are high impedance input
- tubes have capacitances that affect the sound
- output power tubes acopled with transformers give only odd harmonics
- With overload, EACH stages of tube amp give some amount of distortion. At the end the distortion
is very complex.
- When overloaded tube can have some sort of DC bias shifting
- Math associated with audio amps are complex and few people likes it
- Triode tube can exibit three halfes power law curve
- IMPORTANT: MID booster for guitar will do an amplifier distortion more assymetric.



Besides everything else, reading dimitri ideas about triode emulation
i got really interested.
I did contact to him. He is very gentle and intelligent and the idea is very interesting.
I would to thanks him and the other guys who share ideas here.
He has a lot of posts here.

I would say that i have tried a simple FET PREAMP with low source resistor and
a proper drain resistor in computer simulation (CIRCUITMAKER).

I got distortion of second harmonic followed by less third harmonic.

In practice, things sounded pretty nice for a simple fet preamp.

Some guys have made attempts to get one aproximation of tube amps with FET transistor.
The reviews say that they do not exibit the same tone and distortion. Even though they are
good in tone and distortion.


I must be very careful here........


FIRST QUESTION.

Somebody out there has tried FET emulation (sorry by this expression) for a tube amp ?
(this may sound crazy for some of you)


SECOND QUESTION.

Is it someway (technically) possible to simulate an entire tube amp in distortion ?
Without tubes of course.


If these question can be answered, I WILL GIVE UP searching for emulation of tubes.


I HAVE SOMETHINGS TO SAY ABOUT TUBES, JUST TO JUSTIFY MY QUESTIONS.


- TUBES AND GOOD OUTPUT TRANSFORMERS ARE REALLY HARD TO FIND HERE IN BRAZIL.
- TUBES WORK WITH HIGH VOLTAGES (that i dislike)
- TUBE AMP IS A BIG BOX WITH PARTICULAR TYPE OF SOUND (EVEN THOUGH IT IS GOOD)


I must warn that i know ideas from:

John Murphy duty cycle from CARVIN about SX100,SX200,SX300 amps.

Stephan Moeller with VOX ac30 sim.

Gabe Velez with fet buffering bipolar junction transistor.

Nad soft clipping schem.

Pritchard and his patents.

Lots of related patents.

((((((Thanks to all these guys.)))))))


GOOD LUCKY FOR ALL (KEEP STUDYING)

rmfidelis@gmail.com

http://geocities.yahoo.com.br/rmfidelis/TubeSimulator.html

 

[Brion55]

It's really not necessary to have a complete tube amp to get the tube distortion sound. For years I have used a tube preamp which I can drive into distortion with a solid state power amp. The combination works as well as any of the tube amps I've ever owned.

The key is to never drive the solid-state power amp to clipping (distortion).

If you think about it, all big bands run their sound into a large sound system, which invariably use solid-state mixers and power amps for presentation to the audience. Having a tube preamp for the "tube" sound feeding a solid-state amp for the power is basically the same thing.

I've also heard some digital "amp simulation" processors that sound pretty convincing.

As far as FETs, several amplifier and effects companies have built distortion devices using them, with varying results. Many schematics for FET distortion devices can be found on the Internet. Here are some places to look:
http://www.fortunecity.com/tinpan/humperdinck/223/effect.htm
http://www.muzique.com/schem/
http://www.harmony-central.com/Effects/

 

[rodriki]

Tube sim

Thanks a lot for answer.

I was almost giving up this thread.

I agree with that.

But sometimes we are discussing a matter of taste.

I have heard a lot of critics of preamp tube distortion.
Guitar men use to tell the advantages of output tube power
amp distortion (pentode and transformer).

The so called SAG effect is very well aclaimed.

I do not know SAG effect from a live experience.

I am thinking if sag could be "emulated".

Other thing is that tubes exibits non linearities
like CHILD LAW (even though some say its is not apliable to tubes).

Inspired by Dimitri ideas (one of the most clever
article on the subject) i would say Fets are my hope to be
one way to get tube type "distortion" and "clipping".

My knowledge is not so good yet.
The math of tubes is a hard stuff.

The guys in www.runoffgrove.com has started one important
work about tube simulation.It is not perfect yet.

But i think that is the way.

Thanks again. If somebody want to help stay at will.

Rodrigo

 

[darkfenriz]

Hi

- tube produces distortion with low harmonics
- tube produces distortion with EVEN harmonics

This is rather a matter of topology and class of operation.
This would be true for SS no feedback single ended amplifier and false for tube class B relatively high feedback amp.

- the output transformer affects the sound

Yes, it is designed to distort

- tubes are high impedance input

So are JFETs for example.

- output power tubes acopled with transformers give only odd harmonics

Yes. push-pull output stages behave like this. But I saw once a schematic of Marshall, where there was intential asymetry applied to phase splitter to create even too.

- Math associated with audio amps are complex and few people likes it

Harmonic distortion is based on theory of Fourier series. Not so heavy stuff.

 

[darkfenriz]

You can try this:http://www.diyaudio.com/forums/showthread.php?postid=719709#post719709

 

[rodriki]

tube distortion

Thanks a lot for new ideas.

- tube produces distortion with low harmonics
- tube produces distortion with EVEN harmonics
- the output transformer affects the sound
- tubes are high impedance input
- output power tubes acopled with transformers give only odd harmonics
- Math associated with audio amps are complex and few people likes it

To make things easier:
All i mentioned before was a compilation of various possibilities
and desirable caracteristics for GUITAR TUBE AMP.

When i told about heavy math, i got impressed with calculus to prove
the laws behind tube curves. Example: CHILD LAW or three halfes power law.
Like Dimitri exposed in this forum.
It is too much advanced (diferencial equations and calculus - I could remember
my time when in science computing school and have some base at math)

Dimitri has done the work to prove that triode type of curve can be
reproduced with FET.

I would really like to know if it is possible to get the same tone caracter
or the same distortion from some TUBE amp with FET.
Maybe some unusual technic must be created, maybe that is totally foolish.


By the way i like the other post...


Thanks again.