dc voltage regulater for metal detector

i have a minelab metal detector that runs on 6 volts dc...they are finding out that these detectors run better and go deeper with a little higher voltage...around 7.2-8.5 volts...what i want to use is a 12 volt battery and build a little adjustable voltage regulater to drop the voltage to 7.2-8.5 volts...also these metal detectors dont have a volume control and arent very loud....can anyone tell me how to bulid an adjustable regulater and an audio booster with volume control ?....i'm not an electronics expert but i can solder and read simple curcuits...so the simpler the better..thank you

If your detector use less than 100mA of current you can use a LM317L regulator as shown. If it draws more current use the LM317

https://www.electro-tech-online.com/custompdfs/2005/01/LM317L.pdf
https://www.electro-tech-online.com/custompdfs/2005/01/LM317.pdf

The resistor values give about the range you want. Diagram shows voltages with pot set at max and min.

For an easy amplifier with volume control use the LM386. Look at the examples.
https://www.electro-tech-online.com/custompdfs/2005/01/LM386.pdf

regulator

thanks for the reply....but i made a mistake in my first post....my input voltage is 8.4 volts..not 12volts...will this make a difference?...thank you

Yes it wil make a difference. The regulator needs a input 1.5 to 2V higher than the output otherwise it can't regulate. What is your current consumption at 6V?

current draw

i had to do some checking..but i found the detector pulls 700-800 milliamps