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# DIYAMP-EVM: Is the gain adjustable

Part Number: DIYAMP-EVM

Hi Team,

The gain of the evaluation board is determined by the resistor R1 and R2. Is the gain adjustable?
When I bought this evaluation board, were R1 and R2 soldered, or were they adjustable resistors? I didn't find the values of R1 and R2 in the user guide.

Beat Regards,
Tom Liu

• Hi Tom,

Which circuit would you like to change the gain?

For instance, in the following circuit in Figure 18 and its transfer function is shown below. It will be a good idea to simulate the same circuit in Tina. You can change the resistor value by removing it with solder iron. If a desired resistor values can be obtained by parallel another resistor on top of R2 or R1, you may first simulate it in Tina, then try it out in the real circuit.

Use DMM and measure the current resistor values in EVM (check your schematic with your EVM).  If you are not sure, use the transfer equation to calculate your resistor values. If you are still not certain, start with resistor values with 10 kOhm and calculate your Vout transfer function.

If you want to use potentiometer to replace R2, you may do it as well, but it won't be pretty. Simply select a potentiometer value about 10 to 20X above and below R2 value from the EVM, and it will help you to get started.

Enclosed is the Precision Op Amp video training series from our group, and it may help you to under these topic better.

Best,

Raymond

• Hi Raymond,

However I think my description was not clear.
I also want to know if there are resistors soldered on R1 and R2 at the factory and what are their values?

Beat Regards,
Tom

• Hi Tom,

Are you referring to this DIYAMP-EVM board? if not, what are markings on the resistors?

All resistors' markings on this board are 2742, which means 27400 Ohm or 27.4 kOhm. If you are not sure, use DMM, to measure these.

Best,

Raymond