ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

MXR BLUE BOX DESIGN


 
7/2/2004 3:33 PM
Alvaro Salinas
email
MXR BLUE BOX DESIGN
I need some help with the blue box desing.. i'm doing an essay of applications of flip-flop circuits,, and instead of using the simple example of flip flops as dividers, i wanna explain in my essay how the MXR design works... I have the skills to debug and imagine how it works but i want the help of an specialist.  
 
ALso i have a problem with my tonepad design..  
 
An incredible lost of volume when i engage it.. also it sounds with so much gain and the octave down sound is not very similar to the original sounds.  
 
I asume that i have a bad component in the circuit b/c i've checked the layout and it's ok!.  
 
Some ideas?  
 
Thanks for your help!
 
7/5/2004 4:58 PM
Mark Hammer
email

My first instinct is to suggest that you have a transistor with different pinouts, or that you blew the 4013.  
 
I posted a scanned copy of the PAiA Rocktave construction article that appeared in Guitar Player (http://hammer.ampage.org). The Rocktave uses a 4013 the exact same way, and Craig Anderton goes into great length explaining how it works. You can read the article and maybe find some useful content.  
 
One of the interesting aspects of the Bluebox is that it uses an envelope-controlled gate. Looking at the Caja Azul layout at Tonepad, you will see that the output of IC1a not only goes to IC1b but also goes to a half-wave rectifier/envelope-detector formed by C7/8, D2/3, and R15. This envelope signal provides a voltage at the collectors of Q2/3. When no collector voltage is applied, they will not conduct. In this way, the BB gates the output of the fuzz and divider. Hopefully before it gets sputtery at the end of a note. In the PAiA Rocktave, a compander chip is used to kill the sub-octave before the decay of the dry signal. That also removes the sputtery quality at that point where the decaying note starts to produce intermittent triggering of the flip-flop, but by leaving in a naturally decaying straight signal it sounds better and less choppy.  
 
The Bluebox divides the input note twice, once to produce an octave down, and again to provide 2 octaves down. Only the divide-by-4 tone (2 octaves down) is available at the output. You can easily get one octave down by re-routing R11 from pin 1 of IC2a to pin 13 of IC2b.
 
   Page 1 of 1