MXR Blue Box replica, tracking?

[gbkd80]

I know historically the Blue Box has always had a weird tracking thing going on.  i just built a clone/replica of the script version with 2 single op amps, and functionally, it works.  Sounds mostly like i remember when I owned one back in the day.  My question is basically how bad the tracking really was?  I want to make sure none of my parts are bad.  it seems fine at higher registers but mid-to-lower notes tend to bleep and bloop all over the place at random.  I'm pretty sure I recall this being the "charm" of the BB but can someone confirm for me that this is normal?

[Elijah-Baley]

Hello.
I'm studying this effect, indeed I opened this topic: http://www.diystompboxes.com/smfforum/index.php?topic=114812.0 (could be useful to you).

If yours it's a "vintage" replica I think you don't have a resistor 470-330R between 9+ and pin 14 of the IC. I still don't know the real effects of this resistor, but someone without it had called it "glitchy".

Another thing I can say is about the pots. Using a 100k pots you gets «slightly less flip-flop trigger noise», it refers more than else about the blend control, I guess.

What transistors are you using? What is the value of the pots? The schematics I found have a dual IC, anyway, what ICs are you using?

I still have no much familiar with this effect nor with words like flip-flop or bleep and bloop, but if you meant this I hope my advices will be useful.

[thermionix]

I have zero experience with the Blue Box, but that is a cool looking build!  Somebody at MXR sure liked 56K, huh?

[Mark Hammer]

The Blue Box has two "threshold issues" to grapple with.  One is that the signal hitting the flip-flop has to be above threshold to trigger it.  It can be the case that the "on" threshold is a little lower or a little higher for some brands or individual chips.  That can be addressed by changing the gain applied to the input signal.  The first op-amp applies a gain of 471, but I suppose one could increase or decrease it with a trimmer, as required.

The other threshold issue pertains to the two transistors that serve as "gates" for the fuzz and divided outputs.  The envelope is rectified and extracted, via those two diodes, and the result turns the transistors on and off.  Glitchiness can result from the forward voltage of the series diode (not the one going to ground) being too high, or perhaps the transistor properties for the pair selected require something other than the 56k at their respective collectors.  I've never explored it or experimented, but all gates can be quirky and require fine-tuning.  I imagine these are no exception.

[gbkd80]

Interesting stuff, Mark.  Thanks!  As Vincent Gambini would say, "Well, I guess the f*ckin' thing is broken!"   

It's still pretty much what I remembered, back when I had 2 or 3 of those script Blue Boxes in the mid-90s when you could still find them for 50 bucks

[gbkd80]

I used vintage 2N3904 in this circuit that I stole from an old scope; I should just put in new ones and see if there's any difference to start. 

The trimmer on the input IC is actually a pretty slick idea. 

[Spoutnique2]

Hi, i hope i can can the layout and schematic of the vintage Blue Box, can you share it with me please?
I am not new to mods or building and i and searching for an OG circuit version.
Thank you