two circuits in one box - voltage regulators needed?

[therealfindo]

Hey guys..

So, I'm currently doing up a PCB for a Delay & Distortion pedal for a mate of mine, a Dist + on one side and a Sea Urchin (DBD) on the other.
The Delay has a 5V regulator, but the Dist+ uses a simple pair of 1M resistors for the Vref... my question is if I should put a 9V regulator before the Vref resistors so that the two circuits are both regulated?

Cheers.

[therealfindo]

come to think of it.. just a diode before the dist circuit would do the trick, right?

[anchovie]

Ideally you'd be using a decent regulated 9V power supply in the first place. If these were two seperate pedals, you'd just get a good 9V PSU and a daisy-chain lead to power both - no splicing extra components into the cable!

[therealfindo]

Ideally you'd be using a decent regulated 9V power supply in the first place. If these were two seperate pedals, you'd just get a good 9V PSU and a daisy-chain lead to power both - no splicing extra components into the cable!

Good point!!

[therealfindo]

For some reason I thought that because the pair of 1M resistors was halving the Voltage to the Dist+ IC, the Dely would only be getting that as well... 

[LaceSensor]

Some thing to consider would be some separation of the 9v supplies from the DC jack
a 47r resistor in series with the DC jack to your +9v on the PCB or similar works for this.

[anchovie]

For some reason I thought that because the pair of 1M resistors was halving the Voltage to the Dist+ IC, the Dely would only be getting that as well... 

Nah, the Dist+ is getting the 9V as its power supply. Vref is for biasing the audio signal into the middle of the power supply range.

Some thing to consider would be some separation of the 9v supplies from the DC jack
a 47r resistor in series with the DC jack to your +9v on the PCB or similar works for this.

The Sea Urchin already has a 33R on the board, so no need.

[R.G.]

It's a good question. The answer is - it depends.

My day job is designing and supporting pedals, most of which have the equivalent of two pedals in one box. Some of these need excruciating separation in power supplies, some don't. What makes a difference is the amount of current each section pulls from the power supply, how well the power supply is decoupled with capacitors from +V to ground (and -V to ground for some of them), how big the transients caused by switching are, and the care you take in routing the +V and ground lines.

And gain. The higher the gain of any part of the circuit, the more it amplifies any tiny disturbance into being noticeable.

So all the answers you got are all correct in one way or another. The bottom line is that there are few rock solid rules other than Ohm's Law, Maxwell's Equations, and the Three Laws of Thermodynamics. Beyond that, there is a forest of details of the applications of those laws for the Devil to hide in.

[therealfindo]

Thanks for the help! Glad to be learning stuff.. I've done the PCB and it's being fabbed, so I'll see how it turns out!