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Hi Guys,

Been looking at this schematic and wondering why they have biased the opamp this way using the non-inverting configuration. Could someone please explain this for me ?

The normal bias for the inverting stages comes the op amp + inputs connecting to VB. The fact R4 is DC coupled to IC1A doesn't change the bias because IC1A's output is also at VB. R17 has no effect on the bias because C14 AC couplings that arm of the circuit.

If you look at a non-inverting amplifier the bias is set by connecting the op amp +input to VB, usually via a resistor.

So in both case it's the opamp + input that sets the bias point. (Minor caveats suppressed to keep things simple.)

Hi thanks for your reply., Normally the input signal, like in tube screamers the signal enters the non inverting input, With the mad bean the non inverting input is biased (normal) but the actual input is sent to the inverting input doesn't make sense.

Oh I understand, it's the signal path that doesn't make sense to you. Using either input is perfectly OK, provided the surrounding circuit is configured correctly as well. That's why the signal is inverted in one circuit and not the other.

You can read-up on the details,
https://eng.libretexts.org/Bookshelves/ ... Amplifiers

It might seem complicated at first but at least you can see there is sense behind using either input.

Hi, thankyou for the reply I think I'm starting to understand, but if I apply my signal to the inverting side of the opamp. Won't that invert my signal (sine wave) 180 degrees? From the input signal?

drocelot wrote: ↑15 Mar 2023, 06:18 Won't that invert my signal (sine wave) 180 degrees?

Yes but 180° from IC1A + 180° from IC1B gets you back where you started.
Also phase is only an issue when you want to mix two signals (e.g. for a clean blend).

ahhh now that makes sense thanks!