Amp Emulation Pedals - Replication vs 'Stacking' EQs

[yxwvut]

Usually, 'Amp in a Box' pedals are conversions of the preamp section of a given amp from tubes to JFETs or the like. What I've always wondered is: why replicate the tone stack when the pedal is designed for the front of the amp? If you're not going to use the pedal direct into the effects loop, you're effectively stacking the replicated amp's tone stack, which I'll call G(x) on top of your own amp's, which I'll call F(x). Instead of replacing F(x) with G(x), you're just getting F(G(x)), where what you'd really want is a different tone shaping function H(x) so that F(H(x)) = G(x).

This is all not to mention the coloration of the sound via the speaker, which can be even more significant than the amp circuitry itself (go watch a video of a Bassman into a vintage Marshall cab - if that's not the plexi sound I don't know what is).

Has anyone experimented with these kind of 'stacked' tonal shifts in an intentional/scientific way? It'd be pretty cool to have a vox in a box with a 2-way selector for playing through fender/marshall voiced amps.

[Vivek]

You guessed it right that Amp in a box are best fed to return loop of Amp

Or clean Amp

Or PA with a Cab Sim


It's important to replicate the tone stack since that has major bearing on the sound


However there will always be people who feed to front of Amp, effectively land up with two sets of tone controls, and be very happy with the final sound !

[FiveseveN]

Yes, that's a very good observation. There are some caveats:

• I would not say preamp pedals are "designed for the front of the amp". Some, maybe many use it that way but that's independent of the designers' intent
• The "amp function" F(x) is ideally linear so in principle you can null it out with the inverse EQ. Since there are many amps with many functions it's not really practical.
• More recent development of "pedal platform" amps look to address some of this by leaning more towards linearity.

Like Vivek said, in the end it's more about what sounds good to the player than what looks right on paper.

[anotherjim]

Some sims have the tonestack last with a 1M vol control as per original. These have no chance of driving most power amp or mixer inputs properly, the best you can do is feed a clean channel or add another pedal.

I agree that cabs have a huge influence, especially at stage volume.

[niektb]

The pedals from Origin Effects have a switch that lets you flick between three types of EQ (going into a Blackface Fender-style, a Marshall-style or into a Power Amp) followed by a shelf eq to finetune for your particular amp settings

Too bad I can't find schematics of it on the internet

[yxwvut]

The pedals from Origin Effects have a switch that lets you flick between three types of EQ (going into a Blackface Fender-style, a Marshall-style or into a Power Amp) followed by a shelf eq to finetune for your particular amp settings

Too bad I can't find schematics of it on the internet

Wow, that's super cool. From the videos the effect of the EQ switch is quite dramatic - that's probably the only way to get a pedal that works well on both Voxes and Fenders without doubling the knob count.
They sound pretty great too, though I wouldn't say any of the amp emulations were as distinct as the real thing (always the problem with pedal emulations IMO). $700 is a pretty penny. Might as well just buy the dang amp at that point.

Also, re: 'pedal platform' amps and flat response, I think they still tend to have a fender-like scooped preamp EQ so that your clean tone doesn't sound like hot garbage. Plug into a power amp (eg: direct into the effects loop return) for a demo of a 'transparent' amp - it's quite a sad, lifeless sound.

[Fancy Lime]

+1 for "it's all about the cabs" (slight hyperbole).
Frequency shaping in a guitar-amp-cab-mic signal chain is a hot mess. Let's ignore the guitar for the time being because we only want to sim an amp into a miked cab and treat the guitar as a given. Cheap large speakers (the kind classic guitar cabs are made with) in a box of limited volume designed before the Thiele-Small parameters were developed, are essentially very bad (from a hifi standpoint) band pass filters with a lot of ripples in the pass band. And different cabs are wildly different in terms of response. The reason why guitar tone stacks are usually mid scooped is partly to compensate for the shitty cab response. The combined result is rather nice. Not flat or hifi or anything like that but pleasant for guitar use. The influence of the microphone is not as drastic as the other parameters, so we will ignore that as well. Mic placement has a huge impact on the treble, though.

What this boils down to is that in my opinion we need to differentiate between "amp sim into mixing console" and "amp sim into another amp and cab". For the latter case we again need to think about whether we are going into the input or effects return. The frequency shaping for these cases is, as has been pointed out by everyone before me in this thread, very different. When designing something to go straight into the mixer, I think it is worth considering to not try and emulate existing cabs and amps whose frequency responses fight each other but to just start from a clean slate and listen to what sounds good.

Andy