This is from the music-dsp list, it seems relevant to what people were discussing with SPICE emualtion of tube circuits.
- Steve ----- Forwarded message from "Sergio R. Caprile" <[EMAIL PROTECTED]> ----- > Date: Thu, 07 Nov 2002 11:05:32 -0300 (ART) > From: "Sergio R. Caprile" <[EMAIL PROTECTED]> > Subject: RE: [music-dsp] Transformer emulation revisited > To: [EMAIL PROTECTED] > X-Mailer: XFMail 1.5.2 on Linux > > > On 06-Nov-2002 music-dsp-digest wrote: > > > I've been too lazy to sit down and calculate the typical Preamp hi-freq > > boosting from schematic component values, need to do that sometime. > > I did some Spice simulations some time ago, as far as I remember it was more a > sort of low-freq roll-off: single pole hi-pass between stages and poor resistor > decoupling. > > > Even if the preamp has hi-freq boost that emphasizes higher-frequency > > distortion, a downstream saturating transformer might "sound good" by > > selectively adding extra harmonics to the low notes? From one view, the > > transformer might be "undoing" the preamp's hi-freq emphasized distortion. > > But the two might work synergystically to make a more complex sound than a > > simple broadband fuzz? > > > > Since there is non-linear processing involved, the transformer is unable to > undo the preamp hi-freq distortion, but it adds a different color. The main > reason to hi-pass before distorting stages was to avoid that cutting rumbling > sound or excessive bass, well, that was before grunge and Metallica and... > > > There was no tone control setting that would completely straighten out the > > lines in the tri wave, even with the amp running clean. There were > > frequency-dependent effects in distorted tones which made the waves even > > more difficult to interpret. > > The Fender tone network (later adopted and modified by Marshall and almost > everyone, including Roland) is designed to color the signal, there is no "clean" > position as in a regular Baxandall network. There is an intentional notch at > 250/500 Hz that can be softened by the mid control and two bumps at 100Hz and > 5KHz. > I am not much into tubes, but most of the preamp stages where intentionally > biased so the tubes could easily be overdriven. Some Marshall have "feature" > capacitors running across different stages, I mean, the schems say: for model A > this capacitor, model B no capacitor, model C, change to this value. Pretty much > of the sound seems to have come out of sorcery ;^), or trial and error btw. > > James: > You said you simulated a simplified tone control > Did you simulate the Fender/Marshall network ? I tried to get the transfer > function but it gets a bit complicated and I always give up before bilinear > transform, and don't want to split the circuit as that might remove all the > interactions along the controls. > > Regards > > > > -- > -------------------------------------------------------------- > Sergio R. Caprile, Electronics Engineer, Bs.As., Argentina > http://www.geocities.com/scaprile > -------------------------------------------------------------- > > dupswapdrop -- the music-dsp mailing list and website: subscription info, > FAQ, source code archive, list archive, book reviews, dsp links > http://shoko.calarts.edu/musicdsp/ ----- End forwarded message -----
