mxr bluebox 1 octave mod

[dist]

A while ago i made an MXR BB Clone from Tonepad. I did the One oct switch mod, but. Tonight i tried the same thing with a new MXR made bluebox and the onlything that happens when i flip the toggle is a large volume drop and total absence of octave effect.

Annyone got any idea what might be wrong?

[SonicVI]

The PCb's are different.  As I recall the tonepad board happened to not need any modification for the switch to work, but the MXR might.

[dist]

But the circuit should be the same right.  The mod is only to connect pin 1 &3 on the 4013. Although the Factory new ic is  an mc14013cp the datasheet says its pin equivalent to the 4013. So in theory et should work right?

[SonicVI]

No, you don't want to connect pins 1 and 3.  I think if you did that you'd be feeding IC2a (as it's ;abelled in the tonepad project) back into itself, essentially dividing the frequency down to nothing.  What you're doing with the switch is selecting the output of the IC1b (pin 13, one octave down) or the output from IC1a (pin 1, two octaves down).   In the tonepad project you make that selection before R11, a 1Meg resistor connected to Pin 1.

The switch is an SPDT wired so that the pole is connected between pin 1 and the 4013 side of that 1 Meg resistor, and the throws are connected to Pin 1 and Pin 13.

[dist]

Correct me if I'm wrong.

But wont that be the same thing.

If i connect the pole between r11 an pin1 it would be the same thing as connecting it to pin 1.
Throw 1 connected to pin 1. That would be just like connecting a vire from pin 1 to pin 1 so in that position the toggle wont do much good.
And pin 3 and pin13 is according to tonepad already is connected so connecting the throw to any of these pins would result in the same ting?

Ore do you mean that I'm going to have to cut the trace connecting 1 and 3.

In the MXR box the a and b parts  of the IC actually has swapped places, but lets use the tonepad layout as reference and I'll "transelate" it.

[SonicVI]

When pin one is connected to R11 (toggle position one) you have the normal two octave down operation, it not doing anything different from stock, but it is doing something. Then if you connect Pin 13 to R11 you have one octave down.  The switch switches between pin 1 or pin 13.     The 4013 has 2 flip-flops in it (IC1a and IC1b in the schematic).  The first one drops the frequency in half (-1 oct), then the output of the first one goes to the second where it is halved again (-2 oct).  The MXR may have the actual flip-flops in the 4013 reversed, but it's dong the same thing.  To get the one octave down you have to tap into the signal between the flip-flops, before it's divided for the second time.   

How did you wire the switch in your Tonepad build?

[dist]

On the tonepad build i just connected pin 1 and 3, Inn and out of ICb. Ant assuming bypassing it.

But i got the mxr to work.
Connecting the outputs to 1M resistors -> toggle throws toggle pole ->R11 on the buffer side.

It does what i want now. You certainly gave me the idea Sonic

[sevenisthenumber]

Maybe my brain is dying but "dist", can you explain how to get the one octave mod in an easy to understand way?
Thanks!

[oldrocker]

You can see the mod over on the right.

[sevenisthenumber]

Does this mean when you disconnect one leg of r11 it does the mod?

[oldrocker]

Nope actually it connects R11 to pins 13 and 3 which are connected together already and pin 1 is not attached via the SPDT switch to acheive a 1 octave down effect.  When the switch is toggled back the other way to pin 1 it brings the 2 octave effect back.