bipolar ps for zombie chorus...Mark?

[swt]

Hi: i'm just wondering if the lfo and 4046 ic will run ok with those values in a bipolar situation. I love bipolar choruses. But i also like the features of the zombie, with Mark's mods, and ring mod, etc. The fact of being able to change delay time it's good. So i'll mix something like a ce1 and the zombie lfo and driver clock to th mn3007. Is this possible?. Also, i remeber a thread of htose 68k and 100k resistors at 4046, and it's function. What do they do?. I've found that it's a little bit rigid, with respect to other units, and i think it comes from the delay time generated around there. Thanks a lot for any help!!

[Mark Hammer]

I'm not so sure there is anything special about choruses with bipolar supplies.  Whether the ground is between 2 batteries or a derived reference voltage midway between V+ and negative ground makes no difference to the chips involved.

On the other hand, it is often the case thart bipolar supplies are used when more than +9v is used or required for powering the circuit, and perhaps what it is you like about "bipolar" choruses is the potentially cleaner sound you can get with a bigger supply voltage, and the extra headroom that provides.

The Zombie CAN be used with a bigger unipolar supply voltage, but you would need to play by the following rules:

1) The MN3007 does not want to see more than 15v, and neither does the 4046, so whatever you use, make sure that these two chips receive a regulated 15v or else you will be shopping for new chips.  Good for Steve Daniels, but not so good for you.

2) The MN3007 wants to see the input signal sitting on top of a DC voltage.  The 10k/15k Vref divider that John Hollis has provided gives that bias voltage, but feeding the bias/Vref circuit with 15v may not give the MN3007 the right bias voltage.  This won't destroy the chip, but you probably won't hear any chorus effect unless the bias is correct and the Zombie circuit/board provides no way to adjust it.  If you look at a number of other BBD-based effects, you will almost always see a 10k-100k trimpot connected to the input of the BBD through a 10k-100k resistor  One end of the trimpot goes to V+ and the other goes to ground.  This voltage divider is adjusted to provide a proportion of the supply voltage as the DC bias at the BBD input.  Copy one of the bias circuits you see used with a MN3007 with the supply voltage you plan on using and use that, instead of using the 10k/15k divider/Vref/bias circuit that the schematic shows.

Let me emphasize that the schematic is NOT incorrect.  John did a pretty good job of providing the lowest parts-count working chorus these eyes have ever seen.  The problem is that it is designed around one specific scenario and is not as good at adapting to other scenarios (such as a higher supply voltage) without changes.  Incidentally, adding the bias circuit will also let you use other op-amps, includiung many with lower noise than a TL062.

These rules apply to the MN3007 and CD4046.  The opamps can use a much wider variety of supply voltages, but quite frankly I don't think you will see tremendous advantage to using more than a 15v supply within the context of this design.