Patrick Turner;976269 Wrote:
Look at my schematics at my website at http://www.turneraudio.com.au
Most have been done with MS paint. A large tube amp schematic typically
takes 12 hours+ of by-hand work to produce. I should be able to just
copy and paste one of my schematics into an LTSpice window, and nominate
part values and device type, enter B+ voltages, input, output, and then
go CLICK, and get a response, Rout etc, etc, etc. Too easy? NAH, Too
hard!
Just my 2c,
Patrick Turner.
Sorry to send you on a wide goose-chase on the Wolfram app, I forgot to
mention that you should just run the applet as it appears on the screen,
not actually download and install the code that the author provided,
which requires other softwares in order to run on your PC.
Anyway, as popular as LTSpice is, I too hate to use it myself, but if
you would like to convert some of the schematics on your site to be used
in LTSpice, let me know, I will be happy to draw up some for you
(hopefully not all, as there are just too many ;-)
Also a note on the tonestacks, most guitarists are already
trained/brainwashed on the Fender-Marshall-Vox type treble-mid-bass
tonestacks, it's too late to turn back the clock and design a "proper"
tone control for amps - they always revert back to the TMB it seems...
Cheers,
Jaz
Could you all forgive me for my unnecessary criticisms of the the tone stack program listed at Duncan's pages. It downloads fine, but gave strange results until *I woke up* about the use of the potentiometer slide positions.
When you try to adjust a pot between say 1 and 10, a little window follows the cursor arrow to tell you the % of the resistance between bottom of pot and wiper, which may or may not be connected to the top of the wiper.
So let us say you set a bass control on the amp at No5, ie, center of rotation, then you measure wiper to bottom on a real amp, ie, the re-issue Fender Deluxe now in my shed, you find R pot = 20k, and this is about 7.7% of the total pot resistance, and when you set the slider for 7.7%, then the shown response agrees with the experimental results one will measure.
Duncan or someone@somewhere could have made it more obvious about how to set the controls for the center of rotation, and extremes of rotation.
Usually there is a position for B, M and T pots which give the best looking square wave between say 400Hz and 2kHz and with amp set in for this position the sound is usually Dull&Boring because you'd find the sine wave response is then a fairly flat line. I guess the D&B sound is most likely if the strings on the guitar are old and gummed up with body oils and sweat and other rotting junk from players fingers. I played acoustic guitar a long time ago and noticed how fast a new set of strings became dull sounding. But not all guitarists have damp sweaty hands, I sure don't, but I knew one whose hands would ruin new strings in a couple of long sessions. All the gunk gets into the wound brass around the string. Now just how much this affects electric guitar strings is unknown to me, but maybe it does.
Solid bodied electric guitars are incabable of making their timber structure resonate to any high degree, and must rely on the magnetic pick ups. Its all very different to say an acoustic Maton or Guild or Yamaha folk guitar et all,
and then you have the 1/3 way betweens of jazz guitars.......But I digress.
So, in the sample amp I have in the shed for singing lessons, I'll add a CF buffer between input tube and tone stack which should reduce the IMD ( always sounds bad ) produced by change of gain of HF caused by high levels of LF.
THD is OK, and just adds or subtracts small % of harmonics already in the signal; it can be complex to contemplate because phase of amp H can be opposite of phase of string signal H.
The "proper tone stack" as you mention is in fact the *James* stack which has the exact configuration for a *passive* Baxandal bass and treble network..
It is a little tricky to get R&C values correct so that there is a centre F of say 700Hz and you get a flat response, and good square wave when both B & T are set at No5, ie, 50% rotation, on pure log pots, where the 50% rotation gives R below wiper and 9R above wiper.
Ampeg used the James, ie, Baxandal passive. There was no middle. So if you wanted the 500Hz suck out with an ampeg, you set B up a bit, and T up a bit, and gain down a bit. All a bit guessy, and imprecise, and musos could be confused.
The Baxandal with pure log pot can give lots of bass and treble boost, but there is higher insertion loss than other types of tone stacks which mainly just boost B & T without much cut, and with maybe +2dB and -6dB of middle adjustment centered around 450Hz.
Just a penny's worth,
Patrick Turner.