MXR Blue Box Issues

[Alkali2010]

Hey guys - Haven't posted except for once or twice, but I've been reading these forums a lot, and they've provided a TON of help - so thanks

But I'm building my second pedal, but first working (sort of) pedal. I'm making the MXR Blue Box (http://tonepad.com/project.asp?id=33) and I'm having some issues. The pedal gives me exactly the same distortion that any real blue box has. The fuzzy tone is dead on. But two things:

1. There's no octave down. There's no octave modulation at all actually, its like my build is just another fuzz pedal.
2. The Blend and Volume knobs aren't different in any way. I basically have 2 volume knobs and no blend knob.

Here's what I've done to try to fix:

1. Replaced and reversed all transistors. No change.
2. Triple checked the board for bad joints
3. Triple checked the board for correct orientation of parts.
4. Replaced both ICs.

Is there something I'm doing wrong? The schematic says to use a "4558" and a "CD4013" I couldn't find simply those exact models on Mouser, so the exact ICs that I'm using are a CD4013BCN and a something1458, but the bag also says MC4558.

Could I be using the wrong ICs? What do the letters after the numbers represent? I'm so new to this that I feel way above my head, but I've never let that stop me before... Is, for instance, a CD4013 the same as a CD4013BCN or a CD4013CN?

Thanks guys!

[R.G.]

There's a stickie message posted at the top of the forum. It's called "Debugging Thread; what to do when it doesn't work".

You might want to read that. It will help us help you. A lot.

[Alkali2010]

Hah, I'll get on that for sure. Thanks for posting that thread, that's great While I'm typing all this up though, is there a significant difference between the aforementioned ICs? Do letters at the end produce varying effects?

[anchovie]

Type a part number into Google along with the word datasheet. The datasheets should explain which part of the code is the 'core' part number and what any suffixes indicate.

[Mark Hammer]

The flip-flop chip you have is a suitable one to use.  However, were you aware that such chips can be destroyed by static electricity?  They should be kept on conductive foam when not in use, and it is preferred (though not absolutely essential) that they be installed in a socket once everything else is soldered in place, rather than soldered directly.

So, it is possible (though not a certainty) that you hear no octave because the flip-flop that divides the signal to produce the octave has been damaged.

Other thigs to consider:
- is the chip inserted correctly?  Are the pins where theyare supposed to be and making contact?
- is the blend pot doing what it should?

[oldrocker]

Mark M.  has already sort of hit on this but I thought I would mention my experience.  If the 4013 isn't damaged you might check the grounding on pins 4, 6, 7, 8 and 10.  Although mine was a perf build I had a cold solder joint where these pins were grounded.  I had fuzz but no octave down.  Just something to double check again.  I know you said you checked for cold solder joints but there's more than one way to do that.  1. Visual (magnifying glass - good lighting) 2. Resoldering all suspected joints.  3. Use a meter to make sure the continuity is actually there.  That's why when builders say “I already checked for cold solder joints”  I wonder which or how many ways they've used to check that. 

[Kinetic]

I recently did a Blue Box clone from that tonepad layout and had some issues with the blend pot as well.  In the end, I think I moved both pots.

Try taking both pots out of the circuit.  Replace R20 with a fixed resistor or a jumper.  Then put one end of the pot to pin 1 of the 4558, and the other end to the junction of C9 and C10.  The middle lug goes to one end of the output pot.  The other end of the output pot goes to ground, and the middle to the output jack.

With the octave effect, try fiddling with the tone control on your guitar, and try switching pickups too.  I have found the effect more prominent with the tone control rolled back and using the neck pickup.  I also tried it with a few guitars and I found that the effect was again most obvious with lower output pickups.

[oldrocker]

Not to undermine Kinetics advice but moving the blend pot imo is a drastic measure to solvable issue.  I didn't use tonepads PCB but this is the first I've heard that about the Blue Box.  I agree with rolling back the guitars tone and the using neck pickup.  My suggestion would be post pin voltages and all other postings recommend by the (what to do when it doesn't work).  I have been over the Blue Box circuit and have bread boarded it, perf built it, and modified it and I can tell you if you do all things right it will work.  I even posted a schem on my website of the Blue Box with the 1 octave and 2 octave down mod and the tone cap bypass mod.