# Which resistors should I use to generate a gain of 15 on an inverting amplifier?

1. Dec 7, 2012

### qablos

I have the set of values for resistors available:
10-12-15-18-22-27-33-39-47-56-68-82

And I need to get a gain of 15, which values should I use to get this?

Also, I have a non-inverting amplifier, and again, I need a gain of 15. I selected the values:
R2=12 and R1= 68+82+18=168
I assumed I was able to combine some resistors in series to solve this problem...

Is this correct?

2. Dec 7, 2012

### Staff: Mentor

Hi qablos. There are lots of "inverting amplifier" circuits, should we assume you are using an op-amp with just 2 resistors?

You list the resistor values available, as 10-12-15-18-22-27-33-39-47-56-68-82. Are you sure those are all you have? Are they all just Ohms? If so, they are not suitable, resistors of just a few Ohms are too low for most op-amps.

HOWEVER, I think it is probably intended you should understand that the resistances available to you are those values x10n where n is any integer 0..12 or so.

So you have 10Ω, also 100Ω, and 1000Ω, and 10kΩ, and 100kΩ, and 1MΩ, and 10MΩ, etc. Also, 12Ω, and 120Ω, and 1200Ω, and so on ...

3. Dec 7, 2012

### skeptic2

Quablos, why not use R2 = 10 and R1 = 68 and 82 in series?

4. Dec 8, 2012

### CWatters

Oops someone beat me to it.