Tube power amp simulation

[Sheldon]

Hello,
I'm looking for some ideas to emulate the sound of a tube power amp.
I found here some schematics but they are quite old.
Thank you

[teemuk]

1. Phase split the signal
2. Asymmetrically clip both resulting signals
3. Sum the signals

Most clever embodiments integrate an envelope controlled clipping threshold to simulate clipping at plate (which's threshold is modulated by sag), grid conduction emulation with associated capacitive coupling circuits leading to DC bias shifts and crossover distortion under sustained overdrive plus an emulation of gain compression due to screen voltage modulation.

[Philippe]

*hmm...use a pignose amp?*

[Sheldon]

thank you
but for the pignose amp, the aim is to use it in front of a cab simulator!

[Sheldon]

@teemuk : thank you. Do you know if there are some examples of these?

[Johan]

Search my posts from Last summer
J

[sajy_ho]

Maybe some kind of FET differential amplifier, also you may take a look at Jon's "Snow Day OD". I've built it and IMO it sounds very close to a 20W Blackface at hi volumes.

[teemuk]

Something I've been cooking up lately. This simulates voltage sag, sag modulated soft clipping, and effects of grid conduction clipping such as crossover distortion. Low damping factor is also simulated.

Diodes after phase inverter stage simulate grid conduction, the other series diodes clipping at the plates. Reference voltage for this clipping threshold is derived from a differential amp that substracts output of an envelope follower from a steady DC reference. Last stage simulates response of an amplifier with low damping factor drioving a reactive speaker load. The circuit probably needs some tweaking, such as some pregain and some crude voltage limiting so that the input stages sans diode clipping won't get overdriven. Signal should never be allowed to swing above +/-13Vpeaks.

Something Peavey uses ("T-Dynamics"):

This is actually a complete power amp that simulates effects of grid clipping and associated bias shifts (crossover distortion) and the moderately soft clipping at plates. Sag is not simulated. Low damping factor is designed in but it requires that the final power amp section and a loudspeaker load is included. You could likely convert that to run at lower voltages and currents to a simulated high-impedance reactive load. This circuit does not use phase inversion but relies on bipolar reference voltages and polarities of the diodes.

Quilter:

Once again a complete power amp. This one simulates crossover distortion ("Zero crossing process") and sag modulated clipping at plates ("Soft clipping cell"). Low damping factor is again designed in to the final power amp stage with the aid of current feedback. Again no phase inversion per se but same goal achieved with bipolar reference voltages and diode polarities.

[sajy_ho]

Wow it's more complicated than I thought it would be, I've owned a Peavey Envoy 110 and I think Peavy really did a good job at analog simulations.
I thing adding some kind of speaker cab simulator would be nice too...

[Sheldon]

thanks a lot
I have to take a closer look at it cause I admit it's more complicated than I thought it would be too!

[Sheldon]

Maybe one solution for me is to start with the runoffgroove Thunderbird soft clipping stage :
http://www.runoffgroove.com/thunderbird.html
and try to implement a even harmonic generator and a zero crossing processor?
Which embodiment would have the more impact in the sound?

[Caferacernoc]

1. Phase split the signal
2. Asymmetrically clip both resulting signals
3. Sum the signals

Most clever embodiments integrate an envelope controlled clipping threshold to simulate clipping at plate (which's threshold is modulated by sag), grid conduction emulation with associated capacitive coupling circuits leading to DC bias shifts and crossover distortion under sustained overdrive plus an emulation of gain compression due to screen voltage modulation.

What would be the easiest way to sum the signals?

[J0K3RX]

Very interesting stuff there teemuk! - You are not by any chance The "Teemu Kyttälä" are you?

Once again I refer to KMG... Check out the micro power amp stuff. Click the "English" hyperlink if you can't read Russian.
http://milas.spb.ru/~kmg/index_en.html

More here
http://milas.spb.ru/~kmg/files/projects/fetpa/micro/xicon/sim/

[Johan]

 Or you could do as i suggested. ..Build a miniaturised hybrid amp with a push/pull tube output stage,  in a  stompbox format. One opamp, one transistor, one glas bottle... You might like a different "preamp" but the tubestage works and makes it sound and feel like a tubeamp instead of a fuzzbox... You could even start from the phase inverter(transistor) and use any stlmpbox as preamp...or place the tube stage alone in the loop of a solidstate amp to give it some tube character.
here is the thread

http://www.diystompboxes.com/smfforum/index.php?topic=107868.0
j

[Sheldon]

Modern amps have most of the distortion done with preamp.
My aim is to build the more compact as possible pedalboard to use instead of my amp head + cab for rehearsals or little gigs where I don't want to carry my amp+cab.
I'm building a tube stompbox preamp, I plan to buy a cab sim (ada gcs2?). I'm thinking of adding a compact "power amp sim" stompbox, not really for distortion, but only to sweeten/soften the preamp distortion (I don't know exactly which word to use, you know sometimes preamp distortion can be a little raw and harsh).

- A simple option can be the Runofgroove Thunderbird (only the last stage) with maybe adding teemuk embodiments (but as I'm a newbie I have to understand how all of these work!)
- KMG micropower seems another good option (and maybe if the embedded cab sim is good I can use it instead of buying an ada gcs)
- Johan project could be another good option but initially I didn't plan to use tube to make it as compact as possible. And I already have the "tube sound" from 2 12ax7 in the preamp. The only thing I'm looking to achieve is to add a little bit of the power amp stage feeling in the sound to sweeten the preamp distortion and make the preamp + amp sim + cab sim act more like a real amp.

[StarGeezers]

  While you're doing all that building , why not just build a Tube amp ...   They're really easy and not at all as expensive to construct as one might expect...   

[ggedamed]

  While you're doing all that building , why not just build a Tube amp ...   They're really easy and not at all as expensive to construct as one might expect...   

Try reading:

[...]
My aim is to build the more compact as possible pedalboard to use instead of my amp head + cab for rehearsals or little gigs where I don't want to carry my amp+cab.
[...]

[Sheldon]

I don't need to build an amp since I already have an amp!
I just want a compact pedalboard with preamp + power amp sim + cab sim to run direct in the PA when I don't want to carry my amp + cab!

[Sheldon]

@J0K3RX : are there some explanation somwhere on the KMG micro amp schematics?

[Sheldon]

I've always thought that depending how hard you drive it, the power amp section added a little bit of "warm distortion", less raw and more musical than the preamp one.
But I can't understand what is doing this.
As far as I can understand it, a push pull power tube section is attenuating most of the even harmonics, but I thought that it was those even harmonics that give the warm and musical tone?