Anyone done the Blue Box -1/2 Octave mod ??

[Derringer]

does it make a very noticeable difference?

I just built one following oldrocker's advice here:
http://www.diystompboxes.com/smfforum/index.php?topic=79181.0

When I throw the switch the only difference I really hear is that the 2-Oct side has a bit more sustain.
Should it be this underwhelming or did I make a boo-boo ?

[Mark Hammer]

Done it.  It works.  Makes a difference.  One octave down sounds like an octave.  Two down sounds like something very different.

[Derringer]

when I first wired it up today (tonepad layout) I omitted the dreaded HF-reduction/volume loss cap.
I decided that maybe the absence of that filter was making it difficult to hear what was going on.
So I popped in a 0.0082 cap and voila ... I could hear the difference between the two settings.


But now on to other things with this circuit. It tracks horribly. Twelfth fret and above stuff was ok, but then playing below the 12th .... yech. My shocktave did a way better job.
I did find though that with my tone control rolled all-the-way down (I always play on the neck pickup) it tracked much better.
So I checked out the first stage of the circuit and what-do-you-know ... there're two low pass filters that start attenuating at about 1Khz.
So I first upped the 300pf cap in the loop with a 560pf cap. That definitely made a difference but i decided I should go further. So next I upped the 1000pf cap to ground right before the gain-stage's input to 2200 pf.

So now it tracked much better but the balancing act was off. That 0.0082 cap on the output was removing too many of the highs. So I removed that guy and now I think I'm closer to making this thing sound the way it should sound

I might go back in and filter more from the front end ... we'll see.

[Mark Hammer]

The Blue Box is a rather bare-bones circuit for what it does.  Almost a miracle that it tracks at all, really.

The reason why it, and so many other units track so poorly on lower frets is that the strings are just too damn loose down there.  That has two aspects to it.  On is that the pitch will waver more.  The other is that it will have enough harmonic content that the triggering will be "confused".  As you play higher up, the shortened string length at that point on the neck makes the string stiffer, and cuts out a lot of the harmonics.  Use the neck pickup with the tone rolled back, and you're in an even more advantageous position.

If a person wanted one of these babies to perform flawlessly, they'd be playing a long scale guitar (put the Fender Mustang down!) with heavy-gauge flatwound strings (and an unwound G).