PPA-How to wire pot for bass boost?

[bingalls]

I'm planning to wire in an Alps RK27 as a variable resistor in place of R7. This is for a v 1.1 board. I went and checked out the PCB layout at Tangent's site for the v 2.0 revision, since it has provisions for the pot to be directly mounted to the board. If I'm correctly following the circuit, the pot wiper pin is tied to the pot input pin for each channel. These then become common and are connected to one end of R7. The other end of R7 is connected to what is normally the ground pin on the pot. So , I wouldn't need to connect anything on this pot to virtual ground like the volume pot is?

 

[tangent]

Your pin connections are correct. You might need to connect the pot's chassis to virtual ground if you experience noise, but I'm not sure that's ever been a problem due to the way the pot's being used in this instance.

 

[bingalls]

Thanks for the response Tangent.

The thing is, I had already wired up the pot before I checked your site. The way I actually wired it up is the the wiper pin goes to one end of R7. What is normally the ground pin goes to the other end of R7. The remaining input pin, I wired to one of the spare virtual ground pads next to the volume pot. I've tested the bass control out in this configuration, and it seems to work. I've studied the circuit diagram and I think that the way I've wired it up basically accomplishes the same thing, I just made it hard on myself by running extra wires to the PCB when I could have just shorted the input and wiper pins right at the pot.

Are my assumptions incorrect? I will gladly rewire the pot the other way if the current configuration raises the possibility of degrading the sound quality or worse. As I say, my test session seemed to result in normal ramping up and down of the low frequencies when turning the pot.

 

[Pars]

No, that isn't the same if I understand what you did correctly. You have one end of the pot connected to one side of R7, the wiper to the other side of R7, and the other end of the pot connected to VG. You are connecting a portion of the feedback loop to VG thru half of the pot, at a value determined by the rotation position. Depends on whether you have the pot wiper connected to the R4 side of R7 or the output side as to exactly what you are doing, but irregardless, it would be better to disconnect that side of the pot and connect it to the wiper (i will work without connecting it to the wiper as well.)

The v2 PPA connects each end of the pot to one end of R7, with the wiper tied to one end of the pot.

 

[bingalls]

Pars,
Yes, you understood my wiring description correctly. Thanks for correcting me. After looking over the schematic again, I see what you mean about shorting the feedback loop to virtual ground.

I went ahead and severed the two wires and all seems well. I guess I won't bother with soldering jumpers between the wiper and these pins, since you indicated that it will work the way it is just as well?

 

[tangent]

There may be some small benefit from shorting this extra circuit path in the pot, but again, it would only be something to try if it were noisy. If you can't hear it, it don't matter.