What kind of problems should I expect with the Zombie Chorus

[scottosan]

What kind of problems should I expect with the Zombie Chorus?  Are ther some suggestions that are not part of the build instructions.  Any suggestions?


Thanks,
Scott

[Connoisseur of Distortion]

Do you mean issues in the nature of the circuit? or issues with building the circuit?

The circuit DOES tend to click, and it will have a slightly uneven sweep range. Another thing i am noticing is that the depth seems more pronounced at higher speeds. But that just might be me. And, the circuit has a fast LFO (hehe), so i piled some more resistance in.

For building problems, STATIC SENSITIVE DEVICES! use sockets on your ICs. Fire up the shower on full tilt hot water, and stand in the bathroom while socketing the ICs (moisture in the air helps protect from static discharge... and you don't want to have to buy another 3007).

Other than this, the thing fired up as soon as i put the chips in place. You may have to modify some parts to taste, but it's a good sounding circuit.

[Mark Hammer]

Like ANY BBD-based project, it is important to keep things away from, or protected from, the clock circuit.  So, if there is any chance your controls or your wires carrying audio might come near the clock section, you will likely want to shield those leads or move them somehow.

I suspect your query was prompted by a variety of caveats mentioned in different threads.  One of them likely refers to clicking.  The Zombie uses a single bias circuit to cut down on parts and size, and provide a Vref for the audio portion and LFO, as well as a bias voltage for the BBD.  It works, but not as well as hoped.

The "cure" is to provide separate bias voltages for the BBD and the rest of the circuit.    Where you see R12 and R13 on RG Keen's layout, replace these with a pair of 10k or even 12k resistors to divide +9V in half and provide a +4.5V Vref.

Since the Vref in U1a wouldnormally provide the appropriate bias to the BBD (but now it doesn't), you need to provide that bias.  Instead of a direct link between U1a and U2 input, cut the trace and replace it with a NP capacitor between .1 and 1uf.  To the input pin of the BBD, you will now want to connect a fixed resistor of, say, 47k-100k.  Next, wire up a 22k-25k trimpot such that one outside lug goes to V+, the other outside lug goes to Gnd and the wiper goes to the free end of the fixed resistor you've just added.  Finally, connect a 10uf cap between the wiper and Gnd with the + end tied to the wiper.

Voila.  You now have your separate bias voltage source.  Rotating the trimpot, you will pass from no chorus to fuzzy chorus to clear, then through fuzzy to no chorus again.  Tweak until clarity emerges.

[scottosan]

Like ANY BBD-based project, it is important to keep things away from, or protected from, the clock circuit.  So, if there is any chance your controls or your wires carrying audio might come near the clock section, you will likely want to shield those leads or move them somehow.

I suspect your query was prompted by a variety of caveats mentioned in different threads.  One of them likely refers to clicking.  The Zombie uses a single bias circuit to cut down on parts and size, and provide a Vref for the audio portion and LFO, as well as a bias voltage for the BBD.  It works, but not as well as hoped.

The "cure" is to provide separate bias voltages for the BBD and the rest of the circuit.    Where you see R12 and R13 on RG Keen's layout, replace these with a pair of 10k or even 12k resistors to divide +9V in half and provide a +4.5V Vref.

Since the Vref in U1a wouldnormally provide the appropriate bias to the BBD (but now it doesn't), you need to provide that bias.  Instead of a direct link between U1a and U2 input, cut the trace and replace it with a NP capacitor between .1 and 1uf.  To the input pin of the BBD, you will now want to connect a fixed resistor of, say, 47k-100k.  Next, wire up a 22k-25k trimpot such that one outside lug goes to V+, the other outside lug goes to Gnd and the wiper goes to the free end of the fixed resistor you've just added.  Finally, connect a 10uf cap between the wiper and Gnd with the + end tied to the wiper.

Voila.  You now have your separate bias voltage source.  Rotating the trimpot, you will pass from no chorus to fuzzy chorus to clear, then through fuzzy to no chorus again.  Tweak until clarity emerges.

:? Thank you some much for your knowledge.  I will definately try your suggestions.

[Connoisseur of Distortion]

Like ANY BBD-based project, it is important to keep things away from, or protected from, the clock circuit.  So, if there is any chance your controls or your wires carrying audio might come near the clock section, you will likely want to shield those leads or move them somehow.

I suspect your query was prompted by a variety of caveats mentioned in different threads.  One of them likely refers to clicking.  The Zombie uses a single bias circuit to cut down on parts and size, and provide a Vref for the audio portion and LFO, as well as a bias voltage for the BBD.  It works, but not as well as hoped.

The "cure" is to provide separate bias voltages for the BBD and the rest of the circuit.    Where you see R12 and R13 on RG Keen's layout, replace these with a pair of 10k or even 12k resistors to divide +9V in half and provide a +4.5V Vref.

Since the Vref in U1a wouldnormally provide the appropriate bias to the BBD (but now it doesn't), you need to provide that bias.  Instead of a direct link between U1a and U2 input, cut the trace and replace it with a NP capacitor between .1 and 1uf.  To the input pin of the BBD, you will now want to connect a fixed resistor of, say, 47k-100k.  Next, wire up a 22k-25k trimpot such that one outside lug goes to V+, the other outside lug goes to Gnd and the wiper goes to the free end of the fixed resistor you've just added.  Finally, connect a 10uf cap between the wiper and Gnd with the + end tied to the wiper.

Voila.  You now have your separate bias voltage source.  Rotating the trimpot, you will pass from no chorus to fuzzy chorus to clear, then through fuzzy to no chorus again.  Tweak until clarity emerges.

Woops... forgot about the BBD clock issue  

and thanks for the click cure!

[Mark Hammer]

Cripes, it's been so long I almost forgot....

The Zombie will have improved reduction of audible ticks if you decouple the bias for the LFO from the audio bias.

Yup, that's right.  Make yourself a THIRD bias/Vref circuit with a 10k/10k pair and 10uf polarized cap for the LFO.  Those points on the schematic in the LFO where it says Vref (pins 2 and 5) now go to the junction of the two 10k resistors and cap.  This addition will separate and sudden draws on the battery by the LFO from the audio path.

[gorohon]

http://diystompboxes.com/sboxforum/viewtopic.php?p=129017#129017

This thread goes over how I went about doing an off-board trimpot device for the zombie.