Is time ripe for emulations of emulations ?

[POTL]

...And Tech 21 had a huge success utilizing mere opamp clipping distortion* intogether with carefully tweaked filtering. In the end, clipping distortion is just a tiny ingredient in amp/effect tone so it's super important just for a specific tiny nuance. Besudes, opamps and diode clipping can mean a multitude of different types of circuits, just like saying "FETs" or "tubes". It's practically indicating nothing.

*(They employ diodes more frequently today but that's another story).

I agree, but they also used operational amplifiers not quite ordinary, at least in the character series.

[Vivek]

...And Tech 21 had a huge success utilizing mere opamp clipping distortion* intogether with carefully tweaked filtering.

I thank you for your analysis of the SansAmp GT2 in your eBook !!

I learnt a lot from reading that eBook.

which software had you used to generate the graphs of the SansAmp GT2 ?




Do you believe that using Diodes rather than Opamp rail clipping can lead to more consistent results, and with more graceful clipping ?



Do you believe that "tube like" Diode function generators are necessary ? or diodes in feedback loop / diodes shunt to ground are sufficient to achieve almost any sound ?

[Steben]

Where opamps and transistors tend to clip towards a flat rail, any diode clipper will not.
The difference may be small, but diode never get to zero resistance. This is of course different with each diode.
Tube amps do clip to the rail just as much. Sag, cathode shift nor graceful onset of clipping changes this.

So any opamp hitting its limits is in concept just like a tube (class AB power) amp. The type of onset of clipping (if no old school latch up) is of course different.
Full blown tube amp sounds are easiest done by opamps and EQ'ing, since they share the squasing against the ceiling. Low drives are not.
Power supply sag is possible with opamps, cathode shift not just like that.
But there is more. If opamps are used with diodes hitting fixed biased points, these points can shift along with the power supply. Diode ladders can be used for soft onset with the opmap itself as last clipping step. etc etc etc.


Ultimately one needs a certain amount of soft onset transition, a certain portion of linear transfer before and ultimately a flat transfer curve at full clipping.
This looks easier than it is. A linear portion is impossible with germanium clippers, the soft onset starts almost from zero. Germanium distortion sounds grainy dirty at low gain and simply not biting enough at full gain when compared to a high gain stack. Flat transfer curve at max gain needs a true hard clipper. etc etc.

This is somewhat achieved by cascading clipping. Any soft clipper combined with another results in satisfactory onsets while the total clipping image is harder than a single soft clipper.
This is a bit achieved in some way in the modded bluesbreaker circuits I looked into last summer.

[teemuk]

Quilter & company are awesome. But I think about them as their own thing, not an emulation of anything, even if they started like that.

Quilter amps do emulate some archetypal tube amp characteristics such as class-AB amp clipping, sag, and low damping. AFAIK, they do not try to emulate any specific amps. Same approach applies to e.g. H&K and Pritchard.

Peavey's also doing their own thing with several TransTube amps... sort of... because they emulate the company's own tube amp designs, such as Classic and Ultra series amps. 

[Steben]

Not all tube amps have power sag and/or cathode shift. Another thing to remember.
"The" emulation does not exist. It can be applied on emulations of emulations as well. 

Quilter & company are awesome. But I think about them as their own thing, not an emulation of anything, even if they started like that.

Quilter amps do emulate some archetypal tube amp characteristics such as class-AB amp clipping, sag, and low damping. AFAIK, they do not try to emulate any specific amps. Same approach applies to e.g. H&K and Pritchard.

Peavey's also doing their own thing with several TransTube amps... sort of... because they emulate the company's own tube amp designs, such as Classic and Ultra series amps. 

Peavey bandit 112 with T dynamics is such a nice SS amp. It is not a tube amp, but it does not need to be.

[teemuk]

which software had you used to generate the graphs of the SansAmp GT2 ?

A lot of the graphs in the book were generated with SPICE simulation (LTspice) and "cleaned up" with MS paint to suit B&W graphics and GIF format. Some are (evidently) photos of oscilloscope plots.

Do you believe that using Diodes rather than Opamp rail clipping can lead to more consistent results, and with more graceful clipping ?

Yes. AFAIK it is ourageously difficult (if not impossible) to get opamps to clip "soft" like diodes. All of them, even rail-to-rail ones employed by Tech 21, will "brickwall" clip because of the enormous amount of NFB opamps exploit. Rail-to-rail ones will - due to application they are designed for - be more consistent in providing symmetric clipping to rails and "graceful" clipping, if by
graceful we mean good clipping recovery and no side effects like spurious oscillations, rail latching or reversing polarity. Of course not even all generic opamps portray such side effects.

Do you believe that "tube like" Diode function generators are necessary ? or diodes in feedback loop / diodes shunt to ground are sufficient to achieve almost any sound ?

Neccessary for what? If you want to generate complex transfer curves (like mimicking triode IV characteristics) then "piecewise" diode circuits are great tools. AFAIK, nothing prevents from exploiting them in NFB or shunt circuits (and such architectures are often employed). But yes, one can generate clipping distortion with very simple NFB or shunt diode arrangements and in practice the audible differences between various types of clipping are only slight and somewhat subtle. Tech 21 is a good example how far in "tube like" tone one can get even by employing nothing but careful filtering intogether with very hard brickwall clipping of opamps and almost no dynamic effects whatsoever.
Is it a very realistic simulation? No. But it's good enough - even great - for rather great amount of people. There's lesser importance and lesser audible effect in nailing rest of the stuff correctly.

[Steben]

Rail-to-rail ones will - due to application they are designed for - be more consistent in providing symmetric clipping to rails and "graceful" clipping, if by
graceful we mean good clipping recovery and no side effects like spurious oscillations, rail latching or reversing polarity. Of course not even all generic opamps portray such side effects.

The essence.
MOS rail to rail opamps?
Personally I still prefer the diode route.

[teemuk]

MOS rail to rail opamps?

Would be interesting to know why they were chosen over other solutions. Maybe just due to higher clipping threshold without any other circuit additions (regardless how simple)...

Interviews indicate that Barta at least wasn't concerned about producing soft clipping; his experience scoping tube amps had revealed it was a rare occurence to begin with. Interestingly Tech 21 designs later on DID start to feature clipping diodes in opamp feedback (back-to-back Zeners at about same clipping threshold as the overdriven opamps). PSA even uses both diodes and the encapsulated distortion module with overdriven opamps. Overall they still went with symmetric clipping route.

Interviews indicate that Tech 21 designers didn't pay much attention to asymmetric clipping and dynamic bias shifting until creation of the XXL effect. Barta states he didn't discover this characteristic before designing that, (but he had a previous career of fixing tube amps, building them, and had a very clear vision how they operated so I put some doubt to that claim). Again they chose to use opamps and simply make the DC offset user variable.

[Vivek]

Schematic of XXL


https://www.diystompboxes.com/smfforum/index.php?topic=29094.0

[Vivek]

Tech 21 is a good example how far in "tube like" tone one can get even by employing nothing but careful filtering intogether with very hard brickwall clipping of opamps and almost no dynamic effects whatsoever.
Is it a very realistic simulation? No. But it's good enough - even great - for rather great amount of people. There's lesser importance and lesser audible effect in nailing rest of the stuff correctly.

If there was one improvement we could make to the Tech21 stuff, what would you recommend ?

A) Softer clipping with more tube like curve ?
B) Asymmetry ?
C) Dynamic DC shift ?
D) Other

I mean given the existing circuit, which of these would add most value to it ?

[vigilante397]

If there was one improvement we could make to the Tech21 stuff, what would you recommend ?

Tubes. The answer is always tubes.

[Ripthorn]

In the early 80's Marshall designed opamp versions of their JCM800 line. I owned a Marshall 5210 combo for a couple decades and it's drive channel is a three opamp affair that is meant to mimic the drive channel of the Marshall 4210 JCM800 combo. Is it accurate? I don't know. Does it sound good? Yep. I took the drive channel and made it into a pedal after I sold the amp.

[dschwartz]

I went from opamps+diodes, to Jfets, then mosfets, then Cmos inverters, then real tubes.

And then, went back to diodes+opamps. As Teemuk always say, it's mostly about smart gain staging and filtering, and so little about the actual clipping device.

I designed the "simplifier" amps with only diodes and opamps, and has been quite successful despite competing with digital emulation and IRs. After selling about 5000 of them so far, absolutely NO ONE has asked how i emulate tube clipping or the power amp dynamics...no one cares...the only thing they care, and what really matters is "does it sound great?"

And that has to be the goal...good sound, good feel, low noise, build quality and simplicity.

[Vivek]

I designed the "simplifier" amps with only diodes and opamps

Daniel, it would be nice to hear your views on the new BOSS IR-200.

and your comments on Analog versus Digital for Amp and Cab modelling

[Vivek]

In the early 80's Marshall designed opamp versions of their JCM800 line. I owned a Marshall 5210 combo for a couple decades and it's drive channel is a three opamp affair that is meant to mimic the drive channel of the Marshall 4210 JCM800 combo. Is it accurate? I don't know. Does it sound good? Yep. I took the drive channel and made it into a pedal after I sold the amp.

I request you to post link to best schematic for the Marshall 5210. I would love to try and understand and analyze that schematic. Thanks

[marcelomd]

And we circle back again to "pre- and post-eq is king".

My unpopular opinion is we spend too much energy trying to sound like someone else.

[dschwartz]

I designed the "simplifier" amps with only diodes and opamps

Daniel, it would be nice to hear your views on the new BOSS IR-200.

and your comments on Analog versus Digital for Amp and Cab modelling

I just think it's a matter of taste. Both have their pro and cons.
I find digital simulations to sound really good in terms of frequency response, but usually they are too compressed. They sound more like "after post production mix"..too overly processed, compressed and EQd. If you want to sound like your guitar hero record, it's the way to go.

IRs are great but its a hassle to find one you really like (connecting usb cables, computers, etc) and most of them sound to me like a speaker thrown inside a oil can and listening through different diameters garden hoses. Some people assign magic properties to IRs, buth they are nothing but fixed EQs with maaaany bands.

Analog cabsims are of course, more basic, but just because we don't bother to make enough filtering peaks and notches. I think good IRs are superior to analog cabsims for recording, but for live playing, i like analog cabsims more.

[Steben]

https://www.angelfire.com/droid/burvenich/humbucker_100_.mp3

What do you think this is? besides imperfect playing

[FiveseveN]

Keep in mind that you can capture the impulse response of an analog cabsim just as well.
So if one can do all the things the other can, plus much more, where's the contest?

[marcelomd]

Keep in mind that you can capture the impulse response of an analog cabsim just as well.
So if one can do all the things the other can, plus much more, where's the contest?

In the mojo, obviously. More points if you use germanium and/or tubes in the cabsim. =)