Power Supply question

[Vlad123]

I don't understand what IC is doing at the biased voltage in power supply. Examples are Suhr Riot and MXR line driver. Can anybody explain me why it is important, and why are they using that? I guess it's a buffer

[Kipper4]

Without a schematic its hard to say but here goes I'll dive in foot in mouth first.
I guess so.
If ever i have a spare op amp rather than ground the inputs and waste it I buffer the power supplys Vb biasing voltage AKA      1/2V   most times for pedal building 4.5v call it what you will.
i digress....
It stabalises the Vb cant remember who told me that or if I read it somewhere.
Hope this helps
Hope I got this right too...

[Groovenut]

I don't understand what IC is doing at the biased voltage in power supply. Examples are Suhr Riot and MXR line driver. Can anybody explain me why it is important, and why are they using that? I guess it's a buffer

Yes it is a buffer for the bias voltage. In this particular circuit, IMO it's not "important" as much as it's something benificial to do with the extra opamp stage. In order to leave it "unused" you would still have to use almost the same parts count, so may as well have it be useful as a bias buffer.

[Vlad123]

Now i understand  thank you very much

[Guitar Poppa]

I don't understand what IC is doing at the biased voltage in power supply. Examples are Suhr Riot and MXR line driver. Can anybody explain me why it is important, and why are they using that? I guess it's a buffer

Hello Vlad

You're right when you guess that in the Suhr Riot disto, one OpAmp is a buffer.
It receives the half supply voltage created by the 20K + 20k divider, decoupled by 47μF. Its output gives a replica of this half voltage, but in low impedance: it works as a current amplifier. (that's why the inverting input is connected to the output). This voltage is used to bias the non-inverting inputs of the second and the output preamps without risk of interference. A common and classical system. You can remember it for future realisations.

However, it is something else in the MXR line driver, I barely looked at the schematics, and I did not know much about this pedal ... It seems rather to be an envelope amplifier which controls the compression system.

Guitar Poppa

[Groovenut]

In the MXR Line Driver schematic,this is the correct way to connect an unused opamp half. You can see it is essentially the same as the bias buffer but there is nothing connected to the output. So IMO it just makes more sense to use it as a buffer for the bias network. Unless you are looking for a specific higher impedance to your bias network.

That is if this is the correct schematic

[Vlad123]

And what about this

[Groovenut]

And what about this

That's the same as the Suhr Riot. Bias buffer.