Tedious question about my SE/30 reloaded

[Steve Rieck]

My R1 and R2 resistors are reading .5K yet they are 1K on the schematic redraw...is it possible the schematic is incorrect? is this because they are in circuit? If anybody happens to have a meter and a board in front of them would you mind checking yours and let me know the results? Having sound issues. Also, what are the jumper pads for?

 

[dougg3]

I just measured them on my stock SE/30 board that happens to be sitting out right now, and it's the same. They're marked as 1k but they each measure 519 ohms. It's definitely because they are in circuit. I think I can explain why that is in more detail:

The top end of each resistor is tied together, and then if you trace further from the bottom end, one side of each resistor ends up going through the headphone jack (as long as there's nothing plugged into it), then through L2, to R3 or R4 (both 47 ohm resistors) which then both go to ground.

Doing the math, this means when you're probing one of these resistors in circuit, you're basically probing a 1k resistor in parallel with a 1000 + 47 + 47 = 1094 ohm resistor, which comes out to: (1000 * 1094 / (1000 + 1094)) = 522.445 ohms.

If you plug something into the headphone jack, that will break the circuit and then you can measure them individually as about 1K.

 

[Steve Rieck]

I just measured them on my stock SE/30 board that happens to be sitting out right now, and it's the same. They're marked as 1k but they each measure 519 ohms. It's definitely because they are in circuit. I think I can explain why that is in more detail:

The top end of each resistor is tied together, and then if you trace further from the bottom end, one side of each resistor ends up going through the headphone jack (as long as there's nothing plugged into it), then through L2, to R3 or R4 (both 47 ohm resistors) which then both go to ground.

Doing the math, this means when you're probing one of these resistors in circuit, you're basically probing a 1k resistor in parallel with a 1000 + 47 + 47 = 1094 ohm resistor, which comes out to: (1000 * 1094 / (1000 + 1094)) = 522.445 ohms.

If you plug something into the headphone jack, that will break the circuit and then you can measure them individually as about 1K.

thanks! That is an outstanding answer to the question. I appreciate it.