Envelope filter virtual ground with op-amp question

[mikeb]

Sometimes I feel a little dumb ... referring to the image (part of a schematic of a MutronIII clone called the EV1 drawn by Mike Burgundy), doesn't this arrangement of tying the mid 18-volt point to the circuit ground then mean that you need to use a separate power supply for a circuit utilising this design? Normally 0VDC is tied to ground, but here 9VDC is ground - to the opamps it looks like they are running from a bipolar 9VDC power supply. However, if you connect another effect (where 0VDC is ground), doesn't the cable connecting them then carry +9VDC?

I can't help but feel I'm missing something here. Enlightenment appreciated!

Mike

[ExpAnonColin]

Image doesnt work for me unless you copy paste it: http://prophecysound.com/images/filterps.jpg

(EDIT-listen to peter)

-Colin

[mikeb]

I struggle to get the hot-link protection thing disabled sometimes.  :oops:

But the output of the opamp is also connected to ground - which means the mid-point (9V) is connected to ground also.  :?

Mike

[Peter Snowberg]

...doesn't this arrangement of tying the mid 18-volt point to the circuit ground then mean that you need to use a separate power supply for a circuit utilising this design?

Yes it does. The key here is that the power supply negative must be different from "ground" which is the same ground that the guitar sees.

Take care,
-Peter

[mikeb]

As I thought .... thanks Peter!

Mike

[spongebob]

Yes, be careful with grounding in such a circuit, the opamp only provides a "virtual" ground, if you connect it to your DC ground you short out the power supply (the opamp will probably die first!). An isolated DC jack would do the trick...