It really is a simple procedure.

The best place for tones and test audio is without a doubt the Autosound 2000 series of test discs...

I have a Minerator MR1....but you could find a "basic" tone generator from Radio Scrap....you are looking for a 1k tone to set with....and you can do this via the head unit also.....just make sure you are on a "full-range" output

Use the output of the tone generator to the left or right input of ANY of you amps with the head unit (radio) disconnected(if using a generator)....and the speakers....be it low/mid/high also disconnected.

Purchase a CHEAP piezo-electric tweeter, and wire it to the output of the same channel you are inputting....be it from the head with a tone disc or with your purchased tone generator.

Now, turn the gain up until the piezo makes "noise"....the back down until it stops. You have now maximized the output of the amp WITHOUT potential for distortion.

If you are using a test disc, you would put the piezo with an rca end from the head unit and note the volume level at which the piezo makes noise. Just beloew that point is where your head unit is delivering non-clipped signal...

Here is how it works.....the piezo has no ability to play 1k. By putting a lower than possible tone to it, you hear it trying to replay the 1/3 octave distortion.....created on both sides of the 1k tone by OVER adjusting the gain.....or volume from the head..

The procedure is the same with a test tone disc in the head unit.

Now, here is the down side. The guarantee here is that your gains are set at a point of maximum output without distortion. Unfortunately, you will find that your system sounds good....just not loud enough. Safe....forever....but...

Here is another thing to think of...

You said "Sherwood"....so kind of an oxy moron trying to get "good" sound. I'm not trashing it, but it is what it is. Fine for bass....but thats really the end. I know it has a thd of about 5%.....not .01% to .08% like most modern pieces.

The other thing is the input rating. Take care if you have a 5v head unit!! None of this will matter if you smoke the inputs of the amp!!!

 

thats all the sherwood is connected to, the subwoofers. in fact the subwoofers are 8" roadmaster, you got to laugh at that, but after 12 years there still sounding good. and how about two dr.crankenstein amps, one to power the pioneer door speakers and one to power two 15 year old sony xplod 6" X 9"s i mounted the same box as the subs. might be hard to believe but it sound great., and the setup as been working for 15 years. also have a dr.crankenstein amps in my wifes car fro the same length of time without any problems at all. and no its not that i have a hearing problem, my home unit is a yamaha receiver with two cannon 10" speakers, yamaha center channel and yamaha 150 watt powered subwoofer, granted my home stereo sounds better, should hope so, but the hosh posh ive got put together in my truck doesnt do to bad. by the way i downloaded the test tones but seeing as ive been setting it by ear for 40 + years and havent fried anything yet ill leave it at that. im looking at better subs, kicker i think, DVC seems to be the way to go with them be able to be wired for 2 ohm, doubling my amps output. learning about this as i go. but im sure the old roadmaster 8" subs wont be lasting long, then again maybe they will. guess it depends on who assembled them at the time.