How to set Gains with a dmm

cargodz · Post by **cargodz** » Sat Apr 28, 2007 3:21 am

How to Set Amp Gains with a DMM (digital Multi-meter)

I’ve realized lately that although we recommend to many that they should set the gain on their amp with a digital multi-meter (dmm), most may not know how. And although there is a lot of information out there on “how to”, most of it is jumbled with mathematical equations that some may not be able to understand and then they just give up.

Here’s what you’ll need:
1) Digital Multi-meter that reads AC voltage (this does not have to be an expensive model, in fact most $15 models have this feature)
2) Calculator that has a square root button (looks like a little check mark with a tail, this also can be a cheap dollar store item as long as it has that button)

Use this equation to figure out voltage power output:
- Take the RMS wattage per channel and multiply by speaker(s) ohm load
- Now take that number and push the square root button on the calculator
Example: 50 Watts RMS x 4ohm load = 200, square root = 14.142135
So the voltage reading for our example on the digital multi-meter should be 14.1

Remove positive wire speaker wire from the amp (while some say this is not necessary, I recommend so as not to accidentally cross the positive and negative wires)

Next with your system turned “OFF”, turn the gain all the way down (counter clockwise)
Side note: Although Bass Boost is something that most do not recommend using, if intend to use this feature, turn Bass Boost “ON” after turning your gain down.

Now turn your head unit (stereo) “ON”, make sure that all equalization features (bass, treble, etc.) are set to Zero (0)

Set your head units volume to 85-90% - while some prefer to suggest 75%, I recommend 85-90% since most listen to music at no higher than 75% and this gives plenty of room to use equalization features later (remember that every adjustment on the head unit will adjust the voltage value and even though you thought you had it set correctly, the speaker(s) may receive a clipped signal once you increase any equalizing features (bass, treble, etc.)

Play a test tone 50-60hz (if you do not have a cd, tape, etc with a test track, then play your favorite song with similar features)

While playing the test track, use the dmm (set to AC voltage) on the positive output of the amp and slowly adjust your gain until it displays the voltage that you figured out earlier.

Now turn your head unit down and then shut “OFF”, re-install positive speaker wire to amp

You have successfully set the gain on your amp with a digital multi-meter and you may now turn your system up to a comfortable listening level (50-75%) and adjust equalization features to your liking.

cargodz · Post by **cargodz** » Sat Apr 28, 2007 3:29 am

Hey Ryan, wanna throw that up in the FAQ section since I can't post in there, thought ya already did when I pm'd ya about it, but I'm sure you got busy and forgot.

smoker · Post by **smoker** » Sat Apr 28, 2007 6:16 am

i hate to admit it but most of the time i still do it old school, 3/4 volume, gain all the way down, play my decades old bass mekanic disc and start to increase until it sounds the way it should, notice i said "sounds" the way it should, not "until its as loud as it i want it", its been said on here a million times the gain is not a volume knob and though everyone will think im nuttier than a squirrel turd, im so used to using that disc to set gains and have been using it for easily 10 years, i can listen to a few of the songs while tuning and tell you when its there by listening to the subs, of course i have to use normal music to bring the full range amps in but i AM NOT recomendding this just pointing out my own flaws and reminiscing about a time when everyone used their ears or mike may remember the days when amps werent always compatable with other manufactuerrs products so if you wanted to run a kenwood amp you had to have a kenwood head unit, there were adaptors available but everyone had their own din plug and you couldnt plug a kenwood din into an orion amp

cargodz · Post by **cargodz** » Sat Apr 28, 2007 6:41 am

Don't get me wrong... there is nothing wrong with setting an amp by ear, but ONLY if you are experienced enough to do so (as in Terry's "smoker" example).... Please do not attempt setting by ear if you are a novice at amplifier installs... Just cuz you've put in a couple of your buddies head units, speakers, subs, and amps... This does NOT qualify you as an expert, since you thought it sounded good, so please use the above "How To" and you'll be dead on every time... besides, if you start breaking out the dmm and calculator the next time you do one of your friends amps, they'll think you're being much more precise and professional once you start showing them the figures and how it works

breakjunki · Post by **breakjunki** » Sat Apr 28, 2007 7:07 am

wow.. damn smoker, you made me feel old with that post..I don't think half of these people were around even when orion was good.. let alone the old din plugs.. I almost forgot about that.. I used to love my old sherwood 240!

smoker · Post by **smoker** » Sat Apr 28, 2007 7:57 am

do you remember what a mess it used to be to use an orion eq in a setup with anyone elses amps?

brownbob06 · Post by **brownbob06** » Sat Apr 28, 2007 7:19 pm

breakjunki wrote:wow.. damn smoker, you made me feel old with that post..I don't think half of these people were around even when orion was good.. let alone the old din plugs.. I almost forgot about that.. I used to love my old sherwood 240!

I had an old Orion 10 in an Orion ported box , it POUNDED. Got it for free cuz my uncle had it about his garage. Sucks, I burnt the box and gave the sub away...after a while I realized how nice that setup was, and I'm currently working on getting the sub back. (it was a pretty heavy sub too)

I swear I didn't know what I was doing!

cargodz · Post by **cargodz** » Sun Apr 29, 2007 5:14 am

Okay wanna show some age... I remember having one of these in an Impala I had... and although the car was used, it was only a few years old... check this out: http://cgi.ebay.com/ebaymotors/Chevy-68-68-70-71-72-73-gm-radio-am-8-track_W0QQcmdZViewItemQQcategoryZ80741QQihZ002QQitemZ120114367642QQrdZ1QQsspagenameZWDVW
so yeah, I remember the plug ins

But I believe that especially with the wide variety of amps on the market today with their different power ratings, the above tutorial will is must for anyone looking to do their own install