[Patrick Turner]

Hi all. At 66yo, I have automatically been granted the license to be a GRUMPY OLD MAN, acronym GOM, aka Experienced Curmudgeon or EC.

Why? because NERDS rule the world, and nerds only know how to "computerize" sensible processes of common sense. But Nerds comprise only 2% of the population.
All Nerds have no idea how common sense works, so that so many supposedly useful programs like LTSpice are never as easy to use as the older versions of say MS paint where it is very easy to draw excellent schematics.

One could hope in vain that a decent simple program like MSpaint, ( Not nerdized ), could be the basis of showing what's connected to what and allow the easy editing and changing of schematic, but no, its far too much to hope for.
So I have great difficulty getting a basic schematic established with LTSpice on the PC screen and with an Input, Output, place for a meter, and for basic aspects of network input and output impedences plus and a few other basic things that have always been wanted by engineers for about 90 years.

You see, if one can draw a schematic effortlessly with MSpaint, then one would think that a simulator program would understand just what is connected to what by reading what you have moused into position.

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!

Hmm, I have only got limited time on planet. Not sure I want torture my brain with LTSpice.

Thanks to Stephie for recommending LTSpice to me, but darned if I can proceed.

Anyway, long ago, extremely wise men were able to produce superb amplifiers without the existence of Nerds or any computer aided design, and armed only with slide rules and Book Of Rules written by the GOT ( God Of Triodes ).

I guess we see so little useful information about guitar amp tone controls that it is because so few blokes with IQs above 10 try to analyze it accurately.

At this point of time, aka Now, it seems to me that when all tone controls are set at 5, ie, 50% pot rotation, you get a slightly boosted bass 100Hz at +6dB, then sloping to 0Db at 400Hz, then sloping up to +6dB at 5kHz.
Not much bass or treble cut is ever needed. A very large boost of treble above 1k should be possible, say +15dB at 5kHz, and at least +10dB boost of bass at 100Hz, while 400Hz level remains little changed.
THEN, Mid control means reducing 400Hz by say 9dB max and boosting it by +dB, without affecting 200Hz and 3,200Hz levels very much.

Thus somehow there is way to co-relate the fact that human ears perceive loudness of bass F much less than mid F. And electric guitars don't seem to produce flat responses so you need the amp to boost the declining response
of upper harmonics of all strings. Plus, where you have the string fundamental F at say 0dB, then have 2H and 3H a bit suppressed, but then have 4,5,6,7,8,9H much boosted, then the sound becomes more attractive to many people than that of a well made acoustic guitar with no amp, or amplified with mike held at sound hole with no EQ applied.

So, by having a Mid tone control one is drawn to effectively making a 3 band graphic equalizer. It confuses many musos. Depends a bit on what kind of venue and audience they play to. Perceived loudness of different F varies with general average loudness and there's a famous graph which sums it up in Radiotron Designer's Handbook, 1955, written by wise old men.
The Q of the 3 wanted bands differ; one would seem to want a higher Q for mids. Well, to get that, perhaps the easier way for tone control is to do a simple bass & teble Baxandal, and then in a preceding or following gain tube connect a series resonant LC circuit and pot between cathode and 0V. Thus it is not too hard to get +/- 9dB at 400Hz, Q = 1 or 2, while having it non-interactive with the bass and treble controls. 100uF and 1.6mH become resonant at 400Hz, and
L can be air cored.

Just my 2c,
Patrick Turner.