Is my assumption correct on this circuit aspect?

[Guitarfreak]

The circuit is an SD-1, and the components that I am looking at are C7 and R10 as well as the volume trimmer.  Do the first two act as a "volume mod" i.e. an RC filter like one would apply to their guitar from input lug to wiper of their volume pot in order to retain tone as you roll down the pot?  Or is it simply a static High Pass filter acting on the output of the clean boost section?

http://cdn.tonegeek.com/wp-content/uploads/51.jpeg

[CynicalMan]

The cap is just there to filter out DC. I'm not sure why they included either part as they don't seem to be doing much, but they don't affect the sound in any significant way.

[Guitarfreak]

Ok.  So if I were to apply an RC volume mod to the volume pot those components shouldn't interfere with it?  I just ask because I did apply such volume mod and things didn't seem quite as expected.

[CynicalMan]

Why did you do that mod on the volume pot? There should be no treble loss at all when it's turned down. If there is then your pedal is likely broken.

[ashcat_lt]

C7 blocks the DC bias voltage.  If nothing else it keeps DC off the pot, which otherwise might cause scratchy noises when it's turned.  Probably also helps keep that transistor acting the way it should.

The resistor is basically best practice.  It defines a minimum load impedance to limit the current demanded from the opamp and (I think?) might help set the rolloff of that cap.

The "volume mod" normally placed on a guitar's volume pot actually turns the thing into a bass cut (highpass) filter which also happens to silence the guitar when turned all the way down.  It does not even come close to maintaining a flat frequency response through the sweep of the pot.  The sound will get thinner and thinner down to that point.  As mentioned above, it should be unnecessary in this situation.

[CynicalMan]

The resistor is basically best practice.  It defines a minimum load impedance to limit the current demanded from the opamp and (I think?) might help set the rolloff of that cap.

The cap's rolloff is fine at 10k, so the minimum load sounds more plausible. Still, R14 should limit the output current, so R10 would only be needed if the volume pot was shorted. Maybe that's more common than I think, but it seems unnecessary to me.

[Earthscum]

Imagine the 4.7k and the 10k pot as a single resistor... that's what it's acting as, right? So, at volume all the way up, it's limiting the output to a maximum of 2/3 the total output. That's all it's doing. As well, it makes sure that there, as said before, a minimum load impedance if the next stage wasn't buffered. I think, in this case, it's to limit the amount of current going to the jfet switch, which would probably distort the signal if you went the true full output of the op amp.

So, your rolloff is 14.7k and 1u, rolling off lows at 10hZ, and your volume is between 0-2/3 of the signal at the junction of the cap and 4.7k.

[PRR]

> C7 blocks the DC bias voltage.  If nothing else it keeps DC off the pot, which otherwise might cause scratchy noises when it's turned.

Since everything returns to Vref, ideally there is "no" voltage. In fact there will be some small stray DC. A minimalist would ignore it. A hi-class manufacturer would add the blocking cap so no customer complains about a small scratchy.

Bass-cut with 1uFd and 14.7K is below 12Hz, no effect on guitar.

The R10 VR2 3:2 loss is because the opamp can swing more than the JFET can block. The opamp can swing to within a volt of the 9V rail. The JFET gate is held near 9V, but needs a couple volts difference to stay "off". Since the opamp will often be slammed, the "bypass" mode would be corrupted by positive peaks breaking-through the JFET. Reducing the signal just a bit keeps it below JFET breakthrough.

> RC filter like one would apply to their guitar from input lug to wiper of their volume pot in order to retain tone as you roll down the pot?

That is "needed" when high-impedance volume pots drive long cables or hi-gain tube grids. However that's 250K-1Meg pots and 100pFd-1,000pFd loads. This is a 10K pot and a buffer Q6 offering hardly-any load. No "tone compensation" should be needed. If you must try to brighten-up the mid-zone, 22nFd would be a good trial value (not the ~~250pFd often seen on hi-Z pots).

[Guitarfreak]

I agree, it wasn't really a necessary change, but it may have been desired.  I removed the mod because I think the volume knob performs better without it.  I am co-developing this overdrive along with a close friend who owns a recording studio, so really I am just looking under every stone for things to improve even if they don't necessarily need improving.  I believe that is the definition of obsession?