Tuesday-evening April 12th

Special Line 6 User Group Meeting; Vetta

 

Go to page 3; Page 4 from several pages.

 

The modeling proces, a different approach

We take a different approach. Over the years that we've been doing this now, we've discovered that the interactions of these components as well as the natural aging process plus any modifications or even part tolerances all contribute to the tone and feel of an amp. The story goes that Jim Marshall, back in the day would often vary the values of parts depending on what was available in the local electronics store. So if there wasn't a 660 Ohm resistor available , he was happy to put in an 680 Ohm. Also many of the parts in the old Fenders and Marshall's that we all love had 20% tolerances, that means that no two amps are going to sound exactly a like.

We know that the schematic is not a sufficient guide to great tone. Our process is this: we start by finding a great sounding amp, then we check out the schematic, open it up and probe around. Jeff will then break the schematic down into it's major blocks …

We’ll identify the pre amp clipping stages, pre and post filtering, control interactions, etc, them move onto the tone stack..

Most tone circuits are based on the original Fender design. Leo was very interested in saving every possible penny. So he took a tone circuit out of a 'hifi cook book' and literally started removing parts until it still worked but with as few parts as possible. That's why tone circuits are so interactive.

You know, some Fenders have a midrange, and that midrange almost acts as a volume, there's not even so much a tone control anymore, it's sort a like level. We measure: presence, the tone stack, the drive in every possible combination. i.e., with bass full, treble, mid and all the combinations to understand how that tone stack is interacting and reproduce that on our amplifiers. So that not only we get the range of each control but completely capture how each control interacts with each other. And that's all cooked in to each amp model.

 

 

Power to Tone...

We then look into the power-amp section, understand the tonality, clipping, things like voltage sagging like when you really dig into an old Marshall, well the power amp steals power from the pre amp pre-amp and gives you this sort of squishy compressed sound. We're able to capture it, measure it and re-produce that.

We also model power modulation, like with an old Vox AC30 - you sort of dig in around the seventh fret on the D or G strings you kind of hear this ghost note thing going on (this is in because there where questions about the gostnotes). Back to power modulation, that's power from the AC mains leaking into the signal path and it kind of sounds a bit like a ring modulation. So that's also really important to reproducing tone and feel of many of these amps.

Now we've got all these blocks, put them all together and then we'll set the original head (or amp or whatever it is) down next to the Vetta (or another product the we are running / using) and we'll spend hours, days listening to it, tweaking it by hand until it's doing what it needs to do.