Electric Mistress/Summing Amplifier Question

[blueduck577]

Schematic: http://www.generalguitargadgets.com/diagrams/dmistsc.gif

Lately I've been trying to tinker with the wet/dry mix of my deluxe electric mistress.  originally I thought that the one trimpot controlled the wet/dry mix, but after examining the schematic I noticed that it's actually just a wet signal level control.

Suppose I want to increase the level of the dry signal.  Correct me if I'm wrong, but IC2b in the schematic looks like it's configured like a summing amplifier, with both the dry signal and wet connected through 160k resistors.  If I were to decrease the value of the R40, the 160k resistor on the dry signal, would that increase my level of dry signal going into the mix, or is there something I'm overlooking?

I don't quite understand how the non-inverting input on this section is configured.  It's connected to the output of the bbd also, so I don't really know what I'm doing here.  Is it to cancel out the clock noise?

Any help is appreciated!

[blueduck577]

ps. i want to increase the level of the dry signal instead of the ratio dry:wet because with the gain adjust pot at the minimum (so there is no flange sound), the dry signal is less than unity with the bypassed signal.

[StephenGiles]

I think the components around the non inverting input of IC2b are to trick the 4558 into working off a single supply, and correct me if I'm wrong, to provide a DC path to ground.

To provide a balance control between dry and flanged signal, connect a 10k pot between the 160k resistors with the wiper connected to 0v. You may need to drop the 160k resistors to 150k or less in order to keep the output at the same level, as their relationship with the resistors around IC2B has surely been calculated

[Thomeeque]

Schematic: http://www.generalguitargadgets.com/diagrams/dmistsc.gif

Lately I've been trying to tinker with the wet/dry mix of my deluxe electric mistress.  originally I thought that the one trimpot controlled the wet/dry mix, but after examining the schematic I noticed that it's actually just a wet signal level control.

Suppose I want to increase the level of the dry signal.  Correct me if I'm wrong, but IC2b in the schematic looks like it's configured like a summing amplifier, with both the dry signal and wet connected through 160k resistors.  If I were to decrease the value of the R40, the 160k resistor on the dry signal, would that increase my level of dry signal going into the mix, or is there something I'm overlooking?

I don't quite understand how the non-inverting input on this section is configured.  It's connected to the output of the bbd also, so I don't really know what I'm doing here.  Is it to cancel out the clock noise?

Any help is appreciated!

You are right - after all IC2B circuitry makes normal inverting/summing amplifier, only uncommonness is that DC bias (for non-inverting input) is derived* from BBD output (by R15 + C7 working as an AC-canceling filter, like e.g. filters in power sources). You can linearly tune gain of each path by altering R40 (dry signal) / R14 (wet signal). Only in case you would go really low with R40, you should consider impact of C18's reactance (1.6kOhm at 1kHz).

* Integrated actually

[blueduck577]

\DC bias (for non-inverting input) is derived* from BBD output (by R15 + C7 working as an AC-canceling filter, like e.g. filters in power sources).

ah, i get it now. that's really clever!

thanks for the help

[Thomeeque]

thanks for the help

My pleasure