Building the Chopped OC2

[Taylor]

I thought it was time to start a thread for questions regarding the chopped OC2 aka "analog octave down". All questions, ideas, and build reports/photos can go here. I'll post my build when I get a chance.

but I can't seem to get it to work on anything but the bass E and A strings.

I've changed chips and transistors as well as tried just about every value of resistor in the filter section between 0 and 1M5. I've also swapped guitars.

Do you have octave happening on higher strings, but it's just too quiet, or it doesn't sound fat, or is it not there at all? Which mods if any have you done besides in the filter section?

[p_wats]

Do you have octave happening on higher strings, but it's just too quiet, or it doesn't sound fat, or is it not there at all? Which mods if any have you done besides in the filter section?

Thanks for starting the thread (I figured I'd stop poluting the original PCB thread).

I've restored my board to stock values all around to get it working properly first, so no mods at the moment.

Here's what I get from the effect:

With the clean level at 0 and the octave maxed out signal passes, but the fat octave only comes across on the E and A strings. On the rest there is a slight difference from the clean signal, but more like a dullness than an OC-2.

I should mention that in my initial build I did have a 1N4004 in place of the 1N4001 and my 4013 was hot enough to cook breakfast (switched it out and no more heat).

[Taylor]

Well, the diode won't really matter. That's just there for reverse polarity protection, and 1n4004 should do the same job. I think it might have higher current handling, but in this situation it won't really matter too much.

Do you have anything in front of the circuit? If everything's working properly on part of the instrument, but not up high, I wonder if the issue isn't the circuit but what you're putting into it. If the signal is too quiet, it won't track as well, and higher strings tend to be quieter than lower ones. Try putting some clean boost in front of it and see if/how that changes things. Or if you have anything in between the instrument and the octave circuit that could be attenuating it take that out.

[Rob Strand]

my 4013 was hot enough to cook breakfast (switched it out and no more heat).

Well that's not a good sign.

Check for shorts.

Also check for unconnected inputs pin on the 4013, CMOS chips misbehave with unconnected pins - possibly even getting hot.

[1878]

If built stock with PCB type pots, will this fit into a 1590b (112x60x27) type enclosure ?? I never use batteries so I don't have to worry about that.

[Taylor]

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

[p_wats]

Well, the diode won't really matter. That's just there for reverse polarity protection, and 1n4004 should do the same job. I think it might have higher current handling, but in this situation it won't really matter too much.

Do you have anything in front of the circuit? If everything's working properly on part of the instrument, but not up high, I wonder if the issue isn't the circuit but what you're putting into it. If the signal is too quiet, it won't track as well, and higher strings tend to be quieter than lower ones. Try putting some clean boost in front of it and see if/how that changes things. Or if you have anything in between the instrument and the octave circuit that could be attenuating it take that out.

Thanks. I figured the diode was just for protection, but thought I'd mention it just in case.

As for my signal chain, currently I've tried both a hollow body and a solid body electric straight in to the circuit (it's not boxed up, but gator clipped) and out to my amp.

For a volume issue I just tried putting a keyboard into it and cranking the volume. Seems to filter off about the same way (ie, no octave on the highs). Any chance of a sound sample going across all 6 strings so that I can compare acurately (I've got my friends OC-3, but it's got a couple more options, so I hope I'm not just on a wild goose chase...)?

In any case, I got the Gristleizer up and running last night instead...oooh boy! What a pedal. A few tweaks to go and it'll be ready.

[Taylor]

The OC3 is digital, so totally different circuit. But, I did check it out with guitar last night and I have octaving across the whole fretboard.

The next step might be to monitor the octave square wave signal. Check the PDF to see where that is and probe there, and see what you hear. That will help us locate where the issue is.

One other thing, there were some errors in the schematic in the first PDF I posted. I updated the PDF so go to the site and download the new version. But, if you built it from the PCB only, everything on the PCB is correct.

My guess is that something's up with the filter at the front end of the tracking circuit (U1D). If you have a wrong value in there it will filter out high notes and not track them.

[p_wats]

My guess is that something's up with the filter at the front end of the tracking circuit (U1D). If you have a wrong value in there it will filter out high notes and not track them.

That makes the most sense to me. I should have prefaced this by saying I'm very confident that it's something simple I've done wrong and NOT the design/parts/board in any way.   

I'll go through U1D when I've got some down time to see what's what.

[p_wats]

What do you know? When I was out buying parts I bought both 220pf and 220nf caps. Guess who mixed those up?

It's alive!

Now, to satisfy the part of me that no longer trusts myself one iota, I'll describe the effect I'm getting: nice and fat bass sound all across the fretboard, but there's a bit of a fuzz coming through even with both pots all the way off---is that normal (it sounds great, I'm just checking to make sure I didn't screw something else up)?

Thanks for all the help and patience!

[Taylor]

Yeah, that would be the logic signal coming through. Depending on your wiring it can couple into the audio path. If you can't hear it when the volumes are all the way up then you're in good shape.

[p_wats]

Yeah, that would be the logic signal coming through. Depending on your wiring it can couple into the audio path. If you can't hear it when the volumes are all the way up then you're in good shape.

Ok, just making sure. It doesn't bother me, as I'll never want a "clean only" signal from this (why have it on at all in that case?) and the octave buries it pretty well.

The only instance where it really affects things is with the extra signal mods---they seem the pick up and amplify that signal, so I may need to figure that out before implementing them (I quickly tested each of them and they sound great).

[Taylor]

Well, that's basically what the extra signals are. So amplifying the logic square wave isn't a by-product, it's what the mod does. So the best way to add the mods but minimize the buzz when you don't want it would just be to be careful with your wiring - keep them away from your input/out and bypass switch.

[chicago_mike]

I have the schematic of the Apeg Sub-Octave wich has a great filter section that works for bass guitar.

pm me and I can email it, its a pdf

[p_wats]

Well, that's basically what the extra signals are. So amplifying the logic square wave isn't a by-product, it's what the mod does. So the best way to add the mods but minimize the buzz when you don't want it would just be to be careful with your wiring - keep them away from your input/out and bypass switch.

Excellent advice. Thanks!

[PereatMundus]

I thought it was time to start a thread for questions regarding the chopped OC2 aka "analog octave down". All questions, ideas, and build reports/photos can go here. I'll post my build when I get a chance.

Got a few moments to fiddle with all the musicPCB projects this weekend.  and built this one.

Works great!   Lovely piece of kit as always from Taylor.
Finally got hold of a decent drill aswell.. so time to put 7 DIY effects into their boxes 
Still working on the design for waterslide decals to go on the boxes thou. will see if I post some pictures before or after I've done those.
[Not much space for decal's on 5pot Christine in a 1590A thou    guess I'll post pics of that atleast]

Not much to say really.  the Chopped OC2 works as intended. and does its Job just as its supposed to!

[1878]

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.

[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.

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

[Ben N]

If I were to want to kludge Tim Escobedo's Octup Blender in here, where would be the best place to grab signal from? And would the mixer of the OB fit right in at the junction of the two 100k resistors?

[Taylor]

If I were to want to kludge Tim Escobedo's Octup Blender in here, where would be the best place to grab signal from? And would the mixer of the OB fit right in at the junction of the two 100k resistors?

I'd try taking the signal from the output of u1a, and adding the output of the octave up at the base of the 2n3904.