Pork Barrel Blend Control

[Bio77]

Can anyone give me a quick run down of how the blend control on the PB is working?  It seems like it is setting the wet and dry signals at different bias voltages depending on where the pot is set.  But how that creates the mix of the two is a mystery to me. 

[madbean]

Can anyone give me a quick run down of how the blend control on the PB is working?  It seems like it is setting the wet and dry signals at different bias voltages depending on where the pot is set.  But how that creates the mix of the two is a mystery to me.

When the blend is all the way up, all the dry signal goes to virtual ground (which here acts the as if sending it to signal ground). When all the way down, all the dry signal comes through and all the wet goes to virtual ground. So the mix happens when each of those signals has some amount of resistance between each other and also virtual ground. That creates the blend.

It helps to visualize the blend pot as two fixed resistors connected to VB in the middle. The pot just changes their values in a reciprocating fashion.

[Bio77]

Thanks Brian!  Now I see it, I missed the virtual ground part. 

Kind of has my wheels spinning how the bias voltage on the BBD input is the virtual ground. Pretty cool.

[madbean]

Thanks Brian!  Now I see it, I missed the virtual ground part. 

Kind of has my wheels spinning how the bias voltage on the BBD input is the virtual ground. Pretty cool.

Sure thing. I thought of a more straight forward explanation - both dry and wet signal levels are pre-mixed at fixed levels and the blend pot simply determines how much of each signal is sent to ground via the wiper.

[Bio77]

Thanks Brian!  I need to do some more reading about the virtual ground idea.  I'm guessing the set up wouldn't work the same if pin 2 of the pot were tied to true ground versus the virtual ground?

[madbean]

Thanks Brian!  I need to do some more reading about the virtual ground idea.  I'm guessing the set up wouldn't work the same if pin 2 of the pot were tied to true ground versus the virtual ground?

It would, but you would need two or three coupling caps to block the DC going across the pot (otherwise you might get some scratchies when turning it). Tying it to VB instead allows you reduce the part count.

[Bio77]

Thanks Bean, you rock! 

[Bio77]

I was hoping to get confirmation that I set up the PB blend correctly in this circuit?  I guessed that 4.5V is the virtual ground, but I'd love to get a second opinion. 

[madbean]

Yeah the looks right. The correct value for the pot may take some experimentation. Depends on how fast you want the modulation to come on with the blend pot.

[Bio77]

Thanks Brian!  Is the taper something that should be experimented with as well?