Building the Chopped OC2

[PereatMundus]

Did you include any of the mods ?? I'm hoping to build this next weekend with the 'variable filter mod' using a dual 1M pot.

Mods added, just replying to verify:

It all works well variable filter mod also.
everything works

Its really great to ad that extra bit of thickness to my general tone  
I'm thinking an octave pedal should be a requirement for nice thickness of tone!

just in case someone finds this thread and unsure how to make good use of the octave here's how to use it:
ToneKingTip

If you like to thicken up your tone with just a TINY! bit of Reverb+Delay+Chorus, adding a TINY bit of octaveing ontop of that. REALLY thickens up the tone.
[And if your me, you'll ad a tubescreamer, good amp distortion and a tiiiiny bit of fuzz+EQpedal to shape Fuzz ,  also ad the BBE Sonic Stomp youtube-video vid2  at the end of the FX chain, on top of that ad the Zvex Machine youtube-video video2 when needed.
KILLER! tone

[moosapotamus]

This is an awesome project. Great work, Taylor!
But I am having a problem with my build. Hopefully someone can help me figure out what I've done wrong.

It's not boxed up. I've got all the pots and jacks connected to the circuit through a breadboard.

When I first power up the pedal it sounds/plays great. But after about 10-15 minutes, the tracking gets all messed up.

Here's a clip of me playing on my Hamer Cruise Bass up around the 9th fret. This is the octave down output only.

http://moosapotamus.net/misc/ChopOC2-powerup.mp3

Now here is what it sounds like after playing through it for about 10-15 minutes without making any changes or adjustments.

http://moosapotamus.net/misc/ChopOC2-after15min.mp3

There is also a faint high pitch whine that goes along with the messed up tracking. There is virtually no background noise when it's playing well (ie. in the first clip).

If I unplug the power for 20-30 seconds, then plug the power back in, the tracking goes back to normal (like in the first clip).

I'm using a 300mA 9VDC wall wart that is actually putting out about 9.87VDC.

Nothing is getting hot, including the wall wart, and the wall wart's power output is consistent (previous build was madbean's aquaboy, and had no problems with power using the same wall wart).

If I plug in my active bass, the tracking seems to get messed up right away.

I've added the filter mod (nice one!) and attached wires for the additional outputs, but none of them are currently connected.

Originally, I had two TL074 chips and was getting the same result. So I found a LM324 and swapped it out for U2, but that didn't seem to make any difference at all.

I've also tried it with and without the tracking mod, and that doesn't seem to help either.

Not sure what else to try. Would appreciate any ideas, suggestions.

Thanks
~ Charlie

[Taylor]

That's really strange. I have never heard of something quite like that.

I can't think of anything that would cause this over time like that. My mind jumps to the breadboard - if this were my build, and it was working right, but then things got funky (in a bad way), I would be looking at the breadboard to see if something's getting shorted against something else, etc. Then when you unplug and replug the power, you might be jostling apart the things that were shorting.

The tracking part of the circuit (the lower half) involves another 2-pole lowpass just like the one we make variable with the filter mod. The cutoff there is fixed, but you can adjust this to make tracking better for your instrument. Active basses tend to be brighter, both because of the lack of loading and the EQ and the voicing of pickups that are paired with preamps. So the bad tracking could just be down to too much high freq content. Lowering the cutoff of the tracking circuit's lowpass will help with that, and it could even solve your problem altogether.

[bassesofdeath]

Did you include any of the mods ?? I'm hoping to build this next weekend with the 'variable filter mod' using a dual 1M pot.

Still waiting on a backordered dual 1M pot from http://www.banzaieffects.com/     so havent been able to try that mod yet.  but I will include that for sure just as soon as I can get my hands on that pot.
I have added the Tracking MOD thou fun

What type of 1M dual gang is used? 1M-A or 1M-B?

[Taylor]

Linear (which would be 1M-B by the common naming convention, but some people use the opposite so I like to be clear) is probably ideal. It will work either way, but the frequency taper will probably feel more right with linear.

[moosapotamus]

Thanks, Taylor. That's at least a couple of things that I hadn't looked at yet.

What about the 4013? Might I have a bad chip? I don't happen to have another on hand, but suppose I could get one.

Thanks
~ Charlie

[Skrogh]

Since the problem happens some time after power-up, then disappears after some time powered-off, it might be related to a capacitor. Have you checked that all electrolytic caps are orientated the right way around? And of the right size?

[moosapotamus]

Thanks for the tip, Skrogh. I'll check it out again tonight.

~ Charlie

[MonkeyWrench32]

I'm planning on building this with all of the mods. Right now I'm drawing up drilling plans for the enclosure.

Question: Wouldn't the unison square wave be sent to vref on the clean pot instead of the octave pot since it's affecting the clean signal?

[Taylor]

Hmm... I'm having a little trouble understanding your question. The square wave unison signal is totally separate from both the clean signal and the octave signal. The doc shows it being mixed with them at the output buffer, but you could just as well give it its own output or whatever you want to do with it - it doesn't and should connect to the clean pot or the octave pot.

[MonkeyWrench32]

OK, I was mixed up. This is my first build so forgive me. Vref = voltage reference, thanks to Google. I thought that was the signal path.  I have it straightened out now.

[Taylor]

No need for embarrassment - we're all beginners at some point.  This is bit complex for a first build, though. I really recommend that you build it without the mods first, get it working, and then add the mods. Good luck with it!

[MonkeyWrench32]

Thanks.

I do have experience putting together PCB kits. It's been a while though. First time I've ever run across vref.

I'm definitely going to wire it up without the mods first but I'm still drawing the drilling plans with all of the mods because I'm going to get it work no matter what.

[MonkeyWrench32]

Taylor, I have one question before I order everything. As far a mixer circuit, will this work? http://english.cxem.net/amplifier/amplifier24.php

Would I just replace the 10K pots and 22K resistors with the 100K pots and 100K resistors in the plans for the extra signals?

Thanks.

[Morocotopo]

Guys, I want to share with you some info:

I`m making my own layout for the chopped OC2, just out of curiosity and for the challenge, I want to fit it into a B box (small!). When looking at the PDF that is posted here, I noticed a couple of errors in the schem. First, the FET, diode and 1M resistor that connect to U1A and B should be connected to Vref. Second, the 10n cap connected to leg 5 of U2B lacks a 68K R before the ground connection.
I suppose those are correct in the PCB you had made...

[Taylor]

Thanks for bringing those to my attention. Yes, the PCB is correct, since it was designed from Processaurus's schematic, and my schem drawn afterwards. I'll make the corrections to the PDF

[phector2004]

No, but it will fit in a 125b, just slightly larger.

Uhhh...

Are you sure?? 

I just ordered a 1590B this morning...   

[MonkeyWrench32]

No, but it will fit in a 125b, just slightly larger.

Uhhh...

Are you sure?? 

I just ordered a 1590B this morning...   

I'm putting mine in a 1790NS because with all the mods it's SEVEN pots (plus I'm adding an extra footswitch to turn the synth mods on/off).

[Taylor]

No, but it will fit in a 125b, just slightly larger.

Uhhh...

Are you sure?? 

I just ordered a 1590B this morning...   

Am I sure about what? That it will fit in a 125b? Yes, I have my prototype one sitting right here in a 125b.

Or do you mean, am I sure it won't fit in a 1590b? The board itself will fit, but I can't guarantee it will fit with jacks and the stomp switch in a 1590b. If you measured it all out and it fits, then it fits.

[karter2000]

I just finished mine yesterday.  It's working but not in a box yet.  As far as I can tell, it works absolutely great!  I'm batting 2-0 with Taylor's projects so far.  On to my way to the Tap Tempo Tremolo...