MXR Blue Box help

[Danny G]

Cool, it's been awhile since I've needed build help.  Guess I'm either getting better or have been lucky, heh.

I'm building a Blue Box from the Tonepad layout.  It fired right up and sounds really cool, however, I don't think it's supposed to sound like this...  A wall of neato feedback when I don't play, and the octaves are jumbled and confused.  Both of the pots work, but nothing gets rid of that roaring feedback--it's way over saturated.

Suggestions?  I've re-checked the layout many times, making sure I got all the right parts in the right places.  Printed the layout backwards and quadruple-checked all the circuit connections.  I can't figger out what's wrong with this thing.  I'm building it for somebody, and it's the only project I've got built that ISN'T quite working right.  Go figure.

I'll audio-probe it and mebbe check the voltages, maybe that will shed some light.

[vdm]

well sorry i can't add any help.... but i can tell you the octaves *are* meant to jump around like crazy.... if you add a feedback pot on it, you can get this great spot where it starts tricking the 4013 into doing 5ths..... or maybe im crazy (can't remember whether this is possible with the set up or not)...... but it gives some crazy noise.

hope you get it working to your satisfaction...... you can't really say when you've got it working 'right' :wink:

trent... (18 today !!! :twisted: )

[DDD]

Danny,
first try to "block" the fundamental frequency and leave only octaves. Also check if "detector" circuit works properly, particularily the filtering cap.
Octaves are jumping because... please read reviews on B*ss OC-2 and OC-3 suboctavers at Harmony Central.

[Danny G]

DDD--thanks for the advice, but unfortunately I have no idea what you just said...  :oops:  

As soon as the effect is on, SCREOOOOOOOOOOOOOOOOOOOOO!  Nothing but feedback, like when you have 2-3 distortion pedals all on at the same time.  I did some voltage readings and they all came out ok, voltage divider is just dividing away.  I audio-probed it and found the horrendous feedback occurs when the signal hits the 4558 chip.  

I am building this for someone!  What can I do to get rid of the distortion?  I can't find anything wrong on the circuit board.  

Any of you guys build the Blue Box before?  Did it (mis)behave like this?

[vdm]

if the feedback and things occur when it goes through the first gain stage (4558), then i'd suggest the problem is with R8, C5, or R5. other than this i'd say there is a short somewhere causing the gain in the opamp to be maximised.

trent

[DDD]

As I remember the MXR BB has only distorted output (square wave) and  a high gain. So it's not surprising you've got distorted sound. Octaves are square waves waves, too.
Maybe it's OK with your BB and you have just what you've built?

[StephenGiles]

DDD how are you doing today? - when you say BLOCK the fundamental, could you please explain what you mean - do you mean extract it, which is my understanding.
Stephen

[Tychobrahe1979]

Hi Danny G that is really frustrating having that kind of problem where you look and look but can find nothing wrong. I've built the Blue Box from the info on Tonepad and I can't give you and any help on the feedback but as far as the jumbled octaves, for my guitar (  Double Humbucker ) I get those confused octaves at anything above the 12th fret. Anything below sounds awesome to me though. I have not experienced any strange feedback using this effect alone or with any distortion types. So I hope this kind of helps.

[Danny G]

I'll keep poking around with it.  In its present state it is COMPLETELY UNUSABLE as an effect, unless I want to annoy people!  

So the Blue Box is supposed to be a Octave/Distortion pedal...  Is there any way to wire a pot in to control the distortion level?

Are there any other DIY Octave down pedals that aren't also distortion pedals?  The person I'm building it for doesn't need any more distortion, just octave down.

[cd]

Are there any other DIY Octave down pedals that aren't also distortion pedals?  The person I'm building it for doesn't need any more distortion, just octave down.

You could try DIYing a BOSS OC-2, but it's so complex that you'd be better off spending the $50-75 to buy a used one.

The Anderton Rocktave Divider is not horrible for an octave divider, but it has a lot of fuzz to it as well.  It basically spits out a square wave below the guitar fundamental.  THat's the problem with a DIY octaver - most work on using another chip to generate a square wave (no real sampling/pitch shifting, which would require digital).

[vdm]

the reason the square wave is used (which cd touched on) is because the wave out of a guitar is not simple like a sine wave, and as such when you send something into the chip that divides the pitch down (4013), it is very hard to track the signal. because a squarewave is so simple in comparison it tracks MUCH better and is useable to move the sound down the octave.

the blue box is known to have very bad tracking, so it's not overly useable to turn your guitar into a bass, because it also doesnt perform very well on notes in the lowest octave on the guitar. most people use it as a noisey - special effect type pedal to create some strange unpredictable, but still musical segments.

and again, if the feedback is occuring after the first gain stage, then you have only a small amount of the effect where the problem is occuring. have you tried using a different 4558??

trent

[DDD]

Hi Danny G,
Hi Stephen, thanks for your interest to my person â€" I’m all right and feel fine. Hope you’re OK, too.
About blocking the fundamental frequency in the Blue Box:
-   BB has a mixture of two frequencies on its output â€" fundamental and 2 octaves down, both square waves
-   If there is an acoustic feedback, the simple way to eliminate screaming is to have only 2-octave down frequency on the output â€" this will stop feedback. It’s a common idea. It may give an initial possibility to find what’s wrong. Maybe you didn’t understand my idea properly (sorry for my English, once again)
Danny G, could you please explain us what sort of feedback do you experience â€" acoustic feedback or feedback inside your effect box? It’s easy to find â€" please try headphones instead of loudspeakers.
If the feedback remains the same â€" you have a problem inside your box. Please check with oscilloscope if supply voltage is clean and there are no peaks on it. Since there are high gain preamp and comparator on the board as well as logic ICs, the feedback is possible.
What about suboctavers in general â€" they are very complicated devices if you want to have a good one. As far as I know all of the existing analog suboctavers are not perfect. They work in a limited frequency range or the range is to be adjusted to the desired frequencies every time. They performance heavily depends on too many critical factors and even subtle changes of one factor can cause suboctave jumble.
Also, I venture to strongly recommend having a mixture of original (dry) sound and suboctaves on the output, maybe just a touch of lower octaves. Otherwise the sound is unpleasant and/or distorted.

[Samuel]

I'll keep poking around with it.  In its present state it is COMPLETELY UNUSABLE as an effect, unless I want to annoy people!  

So the Blue Box is supposed to be a Octave/Distortion pedal...  Is there any way to wire a pot in to control the distortion level?

Are there any other DIY Octave down pedals that aren't also distortion pedals?  The person I'm building it for doesn't need any more distortion, just octave down.

From your previous thread on octave pedals:

"Also, keep in mind that none of the DIY octave down solutions will work in a similar manner to the Boss. The DIY octave pedals out there typically make for a great deal of signal distortion apart from the octaving, don't track well on pitches below the 12th fret of the guitar, and are very affected by the pickup used and the position of the tone knob. "

[Bill_F]

So the Blue Box is supposed to be a Octave/Distortion pedal...

Here's a link that might help you understand this box a little more. Hope it helps.

Bill
http://guitargeek.com/gearview/180/

[Bill_F]

Here's a nice simple set up so you can get the most out of it.  :shock:

http://guitargeek.com/rigview/223/

[StephenGiles]

DDD - your English is very good, better than a lot of English people!
Stephen

[cd]

Anyone here have a sound sample (or know where one exists) of the Blue Box?  A long one that demos various settings, from nice to extreme, since notes & chords (i.e. not the 3 second clip on the Dunlop web site)?

[Mark Hammer]

From the sounds of it, the circuit is highly unstable.  This is not likely to be a problem resulting from the need to tinker with the circuit itself.  Rather, my money is on one of the following:

a) a solder bridge jumpering some pads that need to be separate
b) an open circuit somewhere, either because of a cracked trace or a missing trace
c) something installed backwards (though this is much less likely)

Stuff like this happens.....all the time.  If you're lucky, you only have parents or a room-mate to irritate when it squeals, and not a wife or partner who will question your sanity in pursuing your hobby and remind you about all the things you made that don't work....all the time.

[DDD]

Thanks StephenGiles, I'm trying hard.
cd,
There are only few suboctaver sound samples on the Net. Also it seems there are absolutely no any BB samples there. But they say the sound is the same as you can hear in the simple TV computer games, especially if you play on higher frets.