Tone for thought..

[tedstruk]

I Started a new guitar kit for xmas. It is listed as a Jazzmaster style kit.
I am building a rhythm jazz guitar. It has a strat style pickup configuration, and so I am really excited about my electronics options!
I got my hands on 3 single sized humbuckers, and the switches I need for complete control of the phasing. I also got a pair of 500k audio tapers and some caps.

Well the first thing I remembered about the Jazzmaster was the tone, I hope to at least mimic, all of the tones it made, and more- so I am employing a baxandall clone tone circuit that I built and tested on my cheapo USB scope.
Now the question sting I am so famous for!
The scope shapes are square on my little scope - and I am fairly worried about sinewaves burning things up! So ???
The bass to full on this circuit has a shark fin that changes to a nice square wave with jaggy tops and bottoms as you turn it down, And the treble circuit has this jaggy top and bottom square wave
on one end; and a front and rear spike about 5 volts in a heartbeat shaped wave.
Now, this is supposed to mean something!!! the pots are working! and I think the circuit is too--- cause of all the waving and forming and bs....
so I will post the circuit and my changes to it so you can see what it does in the simulator...
I really think it is going to make a great master tone circuit for the Rhythm Jazzmaster style tones I want.

I left the amp off for testing, I don't think I will need it with a 1.5v dc source as a driver.

 

[kellys_eye]

I seriously doubt your scope displays are telling you anything useful. You don't help your cause by stating:

The scope shapes are square on my little scope - and I am fairly worried about sinewaves burning things up! So ???

which only indicates that you have no clear understanding of how a scope works or what you should use it for.

A tone control circuit shouldn't 'distort' the signal - it should cut/boost the high/low frequencies and the only way you can test this is to sweep a signal across the audio spectrum and monitor the output of the tone control circuit.

This will give you a 'curve' representing the cut/boost effect and you can then monitor the effect of altering the potentiometers.

If your sine wave is being distorted (to a square wave) then you are suffering from 'clipping' - deliberately distorting the wave form is acceptable to some musicians and circuits are specifically designed to achieve this but a tone control isn't one of them.

 

[tedstruk]

The circuit I posted is a "Baxandall" tone circuit introduced by Peter Baxandall in the 50's, 1952 I think.
I think I said I am looking for tones that are similar to the original Fender Jazzmaster...??. anyone know where I can find some of the scope pics of this guitar?

Anyway I was wondering if there is a way to see the curves in the scope using the 2v calibration squarewave output from the scope....?

Do I need to use the X/Y ? how do I set it up so I can use it? do I need to use a seperate power source, like maybe the same one I want in the finished circuit?
Ive never used the X/Y set before....

 

[Audioguru]

The 2V calibration squarewave is used to setup a 'scope so that its voltage, frequency and frequency response are accurate then it is not used anymore when looking at signal waveforms.
Usually a fixed frequency is fed to the input of the 'scope and the horizontal is set for a linear sweep. The horizontal sweep must be sync'd with the input signal.

You can use XY to see a tangled ball of thread when stereo music is playing. Since a guitar is mono then only a diagonal line will be seen with the length of the line showing the level of the signal.

 

[kellys_eye]

The Baxandall tone control circuit is used in practically every electric guitar with tone controls fitted. It's not specifically associated with any guitar 'sound' as such afaik.

The 'tone' of any instrument is dependent on many variables, body material, solid/hollow, pickup style/number/position, string type etc etc so if you want a real Fender Jazzmaster sound, buy a Fender Jazzmaster.

Simulating it is, of course, the 'cheats' way (nothing wrong in that) and it's quite possible to do it in such a way as to be indistinguishable from the real thing but you need the reference as a starting point - as you mention, scope pics of the waveform would certainly help.

Try asking on guitar forums - I don't doubt for a moment that someone somewhere hasn't done this and got the data you need!

As for the X-Y function, that's used for phase comparison, not what you want to achieve.

 

[tedstruk]

Q. when using a series parallel tone circuit, should the rest of the components be connected in a similar fashion? ie. should the pickups be parallel and the feeds series, or the other way around?

The Baxandall is not used in many guitars, due to the number of components it takes to build the circuit. Usually the builder uses the existing components as 'parts' in the Baxandall circuit(the tone as a resistor, adding a cap to its line in, or just adding a cap where it parallels against the series volume...trying to build a tone circuit forgoing all the volume and phasing of the thing...
I am way passed this state(thanks alot!) of hacking and slaying!!!
The phase circuit in the custom I am building is a monster at the very least.
12 leads, 3 polarity switches, and a 5 way selector.
(Thanks Edd! think baxandall and polarize all the circuits in the same series parallel style)
ps.I will wire them together if it fails to act like a guitar.)

3 small size(they fit in the single pole hole)but have 4 leads, a grnd, a centertap signal, and two(2) coil connections - they are supposed to be hooked up as a "humbucker" which is---
an inphase, outphase switching- that helps to counter act EMF fluctuations in badly grounded amps and tightly circuited consoles. It helps combat the dreaded "flourescent light" spurting, and the current fluctuations caused by brownouts and device draw.

I just drew a failure diagram... you guys! I am trying to draw a wiring diagram, not a schematic!!!

 

[tedstruk]

just for thought....
I have discovered why my signal is square...
tscope only puts out a square wave....
so getting a sine wave out of it will require a special circuit???
Are there any genius' in here who built one of these to go on the calibration terminal so they didn't have to buy a function generator???

just drew a wiring diagram again but this one works...!!!!!
I found some RC circuits...(heh) that can change my squarewave to a sine wave, but I don't think that is a good idea with my calibration circuit in my scope!!!

 

[Audioguru]

Manufacturers of amplifiers for electric guitars use an input impedance of 1M minimum with a vacuum tube or Jfet. I hope your tone controls circuit does not have a lower impedance that will "smother and muffle" the output of your electric guitar.

 

[kellys_eye]

I have discovered why my signal is square...
tscope only puts out a square wave....
so getting a sine wave out of it will require a special circuit???
Are there any genius' in here who built one of these to go on the calibration terminal so they didn't have to buy a function generator???

Pointless.

For the tests you want/need to make the test signal has to be variable in frequency. The scope calibration output is fixed.