THANKS GUYS!Posted on FSB:

A few things:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point. I'm sure there is a good reason for it, but I don't understand the purpose of the parallel resistors (circled in red). The volume control is fairly un-orthodox (circled in green)Not sure of the value of the mystery pot{ (circled in blue).I'm going to throw this on the breadboard tonight or tomorrow to see what I can figure out. ...And here is an unverified vero layout from the schematic.

Evanc521 wrote:Nate Dort wrote:tarandfeathers wrote:Nate Dort wrote:Evanc521 wrote:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point.Ground (technically the zero-volt reference) is connected to the "half point." This effectively creates a +-4.5VDC bipolar supply for the 4558. Fairly common in pedal designs. The alternative is to bias the signal to +4.5VDC at the input of each opamp with a high-value resistor and run the opamp at 9VNo idea what a real one is like but that schematic is drawn with two batteries, so the supply is +/-9VDC.You're right. Double the numbers I wrote up there.I'm pretty sure they're wired in series, so it'd be 18V.The batteries are drawn in series, but I'm pretty sure that just like most of the other EHX pedals that use two batteries, it's +/- 9V also the center of the power supply is earth which also says bipolar. The rest of the power supply is drawn for bipolar and it shows pin 4 of the 4558 connected to the negative side of the power supply, which would be earth if it were a single 18v supply. It's confusing because it's drawn wrong.

The blue circled portion is a trimmer, as seen in pics of the original.

Evanc521 wrote:Okay that makes a lot more sense... I'll try and draw up a corrected schemI don't have the knowledge or experience to get in the middle of this, but before you draw up a corrected schematic you may also want to read Nate's comment that followed the one you quoted.Nate Dort wrote:No, it's drawn just fine. 9VDC below "ground" to pin 4, 9VDC above "ground" to pin 8. +/-9VDC bipolar, or 18VDC between pins 4 and 8. It will work as drawn.The alternative is to connect the series junction of the two batteries directly to ground rather than using a voltage divider. The problem with that is if one battery has much lower voltage than the other, then you don't get a matched bipolar supply. The voltage divider always divides the total voltage by two (since the resistor values are the same), so the +/- swing will be equal above/below "ground".My mistake was missing that there were two batteries in the drawing, not one. Therefore, the voltages I originally stated need to be doubled.

tarandfeathers wrote:Nate Dort wrote:Evanc521 wrote:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point.Ground (technically the zero-volt reference) is connected to the "half point." This effectively creates a +-4.5VDC bipolar supply for the 4558. Fairly common in pedal designs. The alternative is to bias the signal to +4.5VDC at the input of each opamp with a high-value resistor and run the opamp at 9VNo idea what a real one is like but that schematic is drawn with two batteries, so the supply is +/-9VDC.You're right. Double the numbers I wrote up there.

No, it's drawn just fine. 9VDC below "ground" to pin 4, 9VDC above "ground" to pin 8. +/-9VDC bipolar, or 18VDC between pins 4 and 8. It will work as drawn.The alternative is to connect the series junction of the two batteries directly to ground rather than using a voltage divider. The problem with that is if one battery has much lower voltage than the other, then you don't get a matched bipolar supply. The voltage divider always divides the total voltage by two (since the resistor values are the same), so the +/- swing will be equal above/below "ground".My mistake was missing that there were two batteries in the drawing, not one. Therefore, the voltages I originally stated need to be doubled.

Nate Dort wrote:Evanc521 wrote:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point.Ground (technically the zero-volt reference) is connected to the "half point." This effectively creates a +-4.5VDC bipolar supply for the 4558. Fairly common in pedal designs. The alternative is to bias the signal to +4.5VDC at the input of each opamp with a high-value resistor and run the opamp at 9VNo idea what a real one is like but that schematic is drawn with two batteries, so the supply is +/-9VDC.

Okay that all makes sense, thanks!

Nate Dort wrote:tarandfeathers wrote:Nate Dort wrote:Evanc521 wrote:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point.Ground (technically the zero-volt reference) is connected to the half point. This effectively creates a +-4.5VDC bipolar supply for the 4558. Fairly common in pedal designs. The alternative is to bias the signal to +4.5VDC at the input of each opamp with a high-value resistor and run the opamp at 9VNo idea what a real one is like but that schematic is drawn with two batteries, so the supply is +/-9VDC.You're right. Double the numbers I wrote up there.I'm pretty sure they're wired in series, so it'd be 18V.