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Passive Tone Circuit

Started by phatt, May 24, 2009, 10:18:18 AM

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Hi Zappacat,
No I can't afford all that kind of $teck test gear$.  :(

This is the cheats way,, It's called *Computer Aided Simulation*.
I use Circuitmaker, the student version (Free up to 50 components)
Like all modelling don't rely on it as perfect but It gives one the ability to grasp what kind of Tone response you are likely to get from a schematic you wish to use,,, makes short work of stomp box circuits.

Say you're breadboarding a circuit and your not sure where your loosing the bass?
well Sims can help ,, Draw up the schematic on screen then just click on different parts of the circuit and it gives you the AC plot *at every point* in the circuit.

Quite frankly it's put me light years ahead and I highly recommend it,,,
Even if your understanding of electronics is limited (which of course includes Me)
it won't take you long to catch onto how it works, and how to use it.
If you are good at software/computers and you know how to find the signal path through a circuit,,
then you qualify.
Test whatever you want,, even if it's way wrong,,,heck you can't blow anything up with sims!  There will be some setup paremeters that need to be tweaked to get the AC Analiysis happening.

Being able to *SEE* just how much the tone shape is altered and Which part is actually doing the distorting as it passes through each component opened up a whole new world,, hence my grasp of how amps work (TONE) is vastly different than the early days of just thowing money away on every new gizmo.
Cheers, Phil.

J M Fahey

Hi Phatt, thanks, I´ll give it a try.
So far I´ve been using the "old method", you know, with soldering irons that burn you deep if you grab them the wrong way, components that burn, smoke, crack, etc.
I think it will be a way of saving some $$$ and also uttering wild expeletives such as: "!@#º$%&/()=?¿\|"  >:( :( ::) :-[ :-\ :duh :trouble :grr .
J M Fahey


Quote from: J M Fahey on June 10, 2009, 11:28:09 AM
Hi Phatt, thanks, I´ll give it a try.
So far I´ve been using the "old method", you know, with soldering irons that burn you deep if you grab them the wrong way, components that burn, smoke, crack, etc.
I think it will be a way of saving some $$$ and also uttering wild expeletives such as: "!@#º$%&/()=?¿\|"  >:( :( ::) :-[ :-\ :duh :trouble :grr .
J M Fahey

Oh Yes all of that is what I wanted to avoid,, so I'm in love.<3)
From reading some of your posts I doubt you will trouble finding your way around.
I used the word *cheat* because I do realise that to do this in the good old days required a lot of maths and geometry skill.
So I feel somewhat privelidged to be able to press a button and Bingo, have it all done in the blink of an eye.
You can't help but respect those folks who burnt out pincils and brains to plot a curve.

The thing that really struck me about plotting amplifiers in general was the very different way SS and Valves work. SS is kinda a dead flat response whereas tubes are very specific in there response curves.
Though you can make tube gear HiFi flat but they don't sound good then.

In the end I had one of those enlightening moments and kinda realised that the whole game is about the tone curves ,, one response running into another,, to my limited mind this makes sense and from that any guitar player like *ME* can at least start to grasp the idea of tonal manipulation. The marshall simulation trick found on JTM 30/60 Marshall Amps is a classic example of how to go about reproducing specific tones.
From what I've read Teck21 use similar circuit tricks to capture the tonal signiture of certain amps.
Have fun,, Phil.


  I was wondering if you've ever messed with any of the 18watt related stuff?  I just got the parts for most of my 18watt build which consists of an old Hammond AO-43 amplifier chassis with components and a universal 18watt turret board.  My goal is to build an 18 watt variant of the 1974X but I'd like to use your tone stack in lieu of the standard 18 watt TMB tone stack found on most 18watt schematics.  Have you ever integrated one of your passive tone circuits into a classic tube amp?  My ultimate goal would be a 1974X tremolo with VVR and your tone stack.  Is this a realistic goal to pursue or am I missing some problematic issue here when  it comes to combining those elements together in the same amp?

Thanks in advance!
I put my pants on just like the rest of you - one leg at a time. Except, once my pants are on, I make gold records.


Oh dear,, the tube amp Bug has bitten you ay?,,, have fun.

1st answer;
YES,, absolutly any of those tree type tone stacks can be used in just about any tube amp.
I have no doubt that HiWatt will give a bigger mid cut than the others.
with the mid *full off* there might be a smidge less gain in the amp.

I opted to chuck tone stacks in tube amps because they just waste triode voltage gain,,, that's why I built the PhAbb Tone box, it just simplifiys a whole lot of hassels.  ie, I can use any amp and get the same tonal signiture happening,,,, whereas if you wack a tone stack in a tube amp you can only get that tone with That particular Amp.

I only have 4 Valves in my rig,, it's very much like a Fender Pro Junior.
Volume and tone cut knobs only.

ALL the rest is done via SSate gear.
Read 4th post on this page for a more complete coverage of how my ReAmp System works.

The VVR thing works but I've found this to be more rewarding as you can do some Very slick post power amp tweaks.
Any tone within reason I spose,, at any SPL I wish to dial in.
Cheers,, Phil.


Ei, i want to save some money, can i use 500k pots instead of 250k pots in your design?


Hi Tom,  Only the Bass control can make use of 500k :'(

And even that comes with a  BUT,,,,, and it's a big one.

The 500k **LOG** pot you can buy off the shelf at electronics warehouse stores is likely to be the modern ***Fake Log*** pot And these will be very disappointing in use as all the bass is between 1 and 3 and nothing will happen after that.

On the other hand if you *Do* happen to have some genuine log taper pots (i.e. 10% of total resistance @ 50% rotation) then yes use them.
***Remember the Mid and Treble are Linear,,, only the bass is Log***

You can use 250k for both Treb and Mid and even 100k Log for bass.
It just changes the interaction between controls. I wanted the mid to have more control than the treble otherwise you end up back at good old fender where the treble overides everything. :grr

Truth is 500k won't do much for guitar as the larger value only boosts freq below 100 Hz and as the lowest freq on guitar is about 80Hz you won't even notice it.
Bass Amp tone stack with big Amp driving a couple of bins,, then it will then be heard.

If you are breadboarding it all then heck try anything out and see how it sounds before you build.
Have fun,,Phil.