Biasing to Vref VS Ground which is better?

[panterafanatic]

I've been reading a lot since I've joined (mainly lurking  ) and I've noticed one particular thing. A lot of commercial pedals and DIYs are biased towards ground with caps and such. But one of my favorite pedals , Sansamp GT-2, is biased almost entirely to Vref rather than ground on its opamps. What are the advantages of biasing towards Vref rather than ground? I've read that it "looks" the same to AC signals, so what's the purpose of biasing it towards a positive voltage rather than 0 (ground)?

[R.G.]

I've been reading a lot since I've joined (mainly lurking  ) and I've noticed one particular thing. A lot of commercial pedals and DIYs are biased towards ground with caps and such. But one of my favorite pedals , Sansamp GT-2, is biased almost entirely to Vref rather than ground on its opamps. What are the advantages of biasing towards Vref rather than ground? I've read that it "looks" the same to AC signals, so what's the purpose of biasing it towards a positive voltage rather than 0 (ground)?

This issue has been discussed many times.

The purpose is to bias with Vref where you need a source of zero volts AC, but non-zero volts DC.

As in, you're using an opamp which needs its output in the middle between 0V and +9V. You make and use a Vref of +4.5V and tie the + input to that. The output follows. "Bias" inherently means "non-neutral". And a bias voltage is a non-zero source of DC.

You cannot "bias to ground with a cap". A point in a circuit connected to ground through a cap has its AC signals shunted to ground according to the capacitor and resistor values, but it is not biased at all - the cap blocks the DC.

If your question is why choose to connect the gain-setting resistor's cap to Vref instead of ground, the answer is - it doesn't matter. At least it does not matter to the extent that the Vref is properly decoupled to ground by the method which generates the Vref. Anything which is capacitor connected largely does not care what the DC levels on each side of the cap are - that's what the cap is FOR - to block DC. But it cares a lot about what the AC impedance is. A good Vref has a neglibly small impedance to ground. A poor one has a non-insignificant impedance and causes problems.

At the bottom line, since it does not matter much, connected capacitor-blocked points to Vref is often a matter of convenience, habit, or making the layout easier.