Multi-capacitor tone control - Page 9

T-34 · #**161** 01-16-2013, 07:16 AM

I have this video made for an early version when it had 11 capacitors wired as boost-only.

(installed in a bass with PJ configuration, both pickups on)
http://player.vimeo.com/video/32754069

Another bass (jazz bass-like upgraded with Novak humbucker, more details in this thread: curtis-novak-pickups-has-anyone-tried-these )

I am skipping some notches here (the clicks are heard mostly because of microphonic effect of the pickups)

http://dolganov.free.fr/bass/chang-l...n+dm_boost.mp3

TJBass · #**162** 01-19-2013, 08:17 PM

So I did this mod but with three caps on a three position switch. As I posted a few months ago, the switch only affects the tone in the rolled off position, so can I just switch the leads going to the pot around or am I going to have to dig a little deeper? Don't have the bass with me, I only get home a few hours a week so I haven't had much time with it.

T-34 · #**163** 01-20-2013, 04:14 AM

Can you draw the schematics of your wiring? Or at least a good photo showing all the connections?

Cadfael · #**164** 01-20-2013, 05:42 AM

Hi T-34,

Your Megatone Duo looks great!
Sent you a PM ...

What I don't understand:
Why 6 resistors for the "Boost" positions?
One restistor, soldered between "A" (in the middle) and Ground should have the same parallel function as 6 resistors? The 6 resistors only make sense, when you make individual resistor values ...

Or am I wrong?

T-34 · #**165** 01-20-2013, 06:25 AM

You mean R1 to R6? Their only purpose is to discharge the caps from static voltage they can accumulate causing pops when switching between positions...

(Will respond to your PM soon)

Cadfael · #**166** 01-20-2013, 06:34 AM

Yes, I mean R1 to R6 ...
Isn't it possible to use one resistor instead?
Okay; in your scheme the switch lies in series with (R+C parallel).
In my scheme, the resistor lies parallel to (C+switch in series) ...

In the end the same - but it might not avoid the pops???

T-34 · #**167** 01-20-2013, 07:00 AM

The mobile contact of the rotary switch is only connected to one cap at a time, one resistor therefore won't be able to discharge all the caps...

TJBass · #**168** 01-24-2013, 07:13 PM

Quote:

Originally Posted by T-34

Can you draw the schematics of your wiring? Or at least a good photo showing all the connections?

I can a draw a schematic of how its wired as soon as I get home. I should be in this weekend and Ill post it up.

Doner Designs · #**169** 01-25-2013, 10:24 PM

Anyone here care to explain how the 6 position rotary below differs from a typical varitone? I know a "real" varitone also has an inductor, but do not really know what the inductor does or how it is wired in.

Stealth · #**170** 01-26-2013, 04:57 AM

The inductor basically works opposite a capacitor - in series it inhibits high frequencies, in parallel it inhibits low frequencies.
As you know, depending on the rest of the circuit, capacitors have a cut-off frequency that shows you which frequencies will get passed (for a standard tone control, below cut-off) and which get attenuated (above cut-off). The exact opposite works for inductors - if you had an inductor instead of a capacitor on your tone control, you'd have a variable high-pass filter, and that too would have a cut-off frequency.

If you have a capacitor and an inductor in a circuit together, they form a so-called resonant circuit. Normally, if those two components were in series, this'd mean any signal with a frequency close to their gets a slight boost. The closer their cutoff frequencies are, the more pronounced the effect is with a higher gain and narrower bandwidth (i.e. range of frequencies where the effect is noticeable). The resonant peak frequency, gain and Q-factor (a central-frequency versus bandwith ratio) can all be calculated from the inductance, capacity and resistances of the above two components, the pickups themselves and the rest of the circuit.

Now, since those components are in series with each other, but as a unit parallel to the signal going from the pickup to the output jack, what happens is that instead of getting boosted, those frequencies will get shunted to ground and thus attenuated. On an amplitude/frequency graph you'd see a dip at the frequency, which would be narrow and deep if the Q-factor was high or shallow and wide if the Q-factor was low.

In real life, what you'd hear is a change in the midrange with a slight hollowness to it - again, depending on the selected capacitor, the exact frequency that'd get "hollowed out" varies. Since you usually change only the cap and keep the inductor the same, the Q-factor would also change so you'd either lose a lot of high midrange or you'd have a wide dip throughout half the low mids.

TL;DR: inductors in varitones make dips and notches in the sound depending on which cap and inductor are selected.

T-34 · #**171** 01-26-2013, 07:42 AM

Just to add visuals to Stealth' explanations:

Here I've made simulations of frequency response for the two devices - first without a choke (schematics and graph at the left) and the second with a 1.5 Hn choke and 100K resistor (like an original Varitone) .

In order to make the comparison easier, I've entered the same cap values, corresponding to '61 varitone
Need help to identify Gibson bass

The difference is quite dramatic

TJBass · #**172** 01-26-2013, 01:20 PM

Quote:

Originally Posted by T-34

Can you draw the schematics of your wiring? Or at least a good photo showing all the connections?

Click image for larger version

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best I could do with a camera that wont focus on small objects!

T-34 · #**173** 01-26-2013, 01:41 PM

Its looking good, what is not working exactly? You'll have one of the three capacitors connected to your tone pot, depending on what position the switch is.
(assuming the switch is of on-on-on type).

tonebrulee · #**174** 01-26-2013, 01:45 PM

Quote:

Originally Posted by T-34

Can you draw the schematics of your wiring? Or at least a good photo showing all the connections?

The post has picked up a lot of other ideas, but three caps on a three-way switch is what my original post is all about - close-up photos here, and drawing here.

T-34 · #**175** 01-26-2013, 01:49 PM

Cool idea, for sure! The wiring as it is drawn is good and should work just fine.

T-34 · #**176** 01-26-2013, 01:50 PM

(and sorry for hi-jacking your post

)

tonebrulee · #**177** 01-26-2013, 01:56 PM

Quote:

Originally Posted by T-34

(and sorry for hi-jacking your post

)

Oh please, not to worry. It's cool that there's so much interest and other ideas - just wanted you to check back on the original stuff since that's the mod you were asking about.

T-34 · #**178** 01-26-2013, 02:09 PM

You're right, I didn't read it from the start, my bad!

Doner Designs · #**179** 01-26-2013, 02:09 PM

Thanks guys for the choke explanations!

I'm thinking about building an outboard varitone box with double or triple rotary switches and a pot for each rotary.

Conceptually it would be sort of a passive parametric equalizer. Thinking of calling it a Para-Tone.

Not sure when I'll get to it.

TJBass · #**180** 01-26-2013, 02:15 PM

Quote:

Originally Posted by tonebrulee

The post has picked up a lot of other ideas, but three caps on a three-way switch is what my original post is all about - close-up photos here, and drawing here.

This is a great mod, kudos for the original, but my issue is that it seems the switch doesn't effect the tone until I roll the treble all the way down. Should I swap the two connections at the tone pot?