Green Ringer Mods

[ianmgull]

Hello again,

So I'm getting ready to build the GGG version of the green ringer. I plan on using it for bass. From what I've gathered the "stock" version of the LP filter is tuned for guitar. I know to lower the cutoff frequency I need to increase the three cap values in the filter section. I was just wondering if anyone has any good starting points for what cap values to use? I guess the cutoff frequency would ideally be somewhere under 1khz.

Also, do the values of the three resistors in series with the caps stay the same? I'm not sure I really understand their function.

And finally, I was wondering if anybody could explain the formula for how caps like this relate to frequency. I mean what value cap in this case will lead to what frequency cutoff? (I'm trying to be a good student and understand the math behind all this).

Thanks!!!!!

ian

[ianmgull]

Oh yea, schematic:

http://www.generalguitargadgets.com/pdf/ggg_gro_sc_filter.pdf

[mac]

When you have a resistor and a cap the roll of freq is ususally f=1/(2*pi*R*C)
In this case you have the input impedance of the trasistor plus the base resistors so things can be more complicated.

Maybe you should breadboard the GR before building it and increase the input cap to say 1uf. Also tweak the output cap and those 47nf beside the diodes.

mac

[soggybag]

I made one of these with both the Filter Mod and the Nulling mod. The Filter mod makes the octave very pronounced. The null mod helps dial in the octave.

[ianmgull]

So I'm correct in assuming the null mod just removes the "clean" signal leaving only the octave?

[mac]

Filter mod? I missed that. Schem?

mac

[ianmgull]

Regular schematic:

http://www.generalguitargadgets.com/pdf/ggg_gro_sc.pdf

Null carrier mod:

http://www.generalguitargadgets.com/pdf/ggg_gro_sc_null.pdf

Filter switch mod:

http://www.generalguitargadgets.com/pdf/ggg_gro_sc_filter.pdf


I'm in the process of putting both mods in a box myself. Does anybody know how critical the different values of R1, R2, R3, and R4 are for the Null mod?

[Processaurus]

hi, to shift an RC filter an octave lower (1/2 the frequency) for bass, double the cap values.  Makes sense because with the filter equation above the frequency is inversely proportional to the cap value (4 times as big a cap would lower the freq to 1/4) This has three rc filters in a row, so doubling all the caps should get you started, though sockets would be reasonable for the caps. I did that and just stuck in values til I found a cutoff frequency that would still barely let the highest notes on a guitar through.

This mod is an implementation of the idea in this article, if you're interested in the mechanics:

http://www.geocities.com/sunsetstrip/studio/2987/octave.html

[ianmgull]

Hey thanks for all the help. I got the thing fired up today and it sounds great. Kudos on the filter mod ben...  So I really wanted to impliment the null carrier mod but I was a bit hesitant because it called for a couple 2n5210 trannies...  Does anybody know if the regular old 2n5089's will work in there? Thanks!

[gigimarga]

hi!

a little help please...in the schematic of the switchable filter mod ( http://www.generalguitargadgets.com/pdf/ggg_gro_sc_filter.pdf) i have some doubts about how to wire the switch!

thx a lot

[Processaurus]

Hi, SW2a and SW2b are the two poles of a DPDT toggle switch, wire the common of one pole to the (-) of the 10uF cap, and one of the throws to ground.  On the other pole, wire the part of the circuit that has the 3 capacitors tied together to the common.  Wire one of the throws to ground (the same side as the other pole).

2n5089 will be fine for the null mod.  The null mod is to dial in the two halves of the full wave recified signal to be symetrical in amplitude.  mine, when I looked at it on the scope, was "null" ie: balanced with the stock green ringer values.  Oh, the filter sounded bad (muddy and unexciting) with the null out balance (with the sides of the wave asymetrical, and the fake octave less apparent)...

http://en.wikipedia.org/wiki/Rectifier#Full-wave_rectification

[gigimarga]

Thx a lot Processaurus!!