How to tune amp correctly? Without an oscope

Discussion in 'Car Stereo Amplifiers' started by SoloX531, Jul 17, 2011.

  1. SoloX531

    SoloX531 Full Member

    I just set up my system and I had my buddy whose pretty knowledgable about car audio tune it, a lil while later after he left I turned it up there was def a good amount of distortion. Could someone please assist me in dialing it in correctly. It has your level, sub sonic 15hz-50hz, LPF 50hz-150hz and bass boost 0-12db. Help me out please.
  2. shriver187

    shriver187 Full Member

    turn gain all the way down. and then turn the cd player to the volume u listen to it at.. then start turning the gain up slowly until u hear distortion and then back it back off a little.. lpf is more to however u like listening to ur music.. for me id have it all the way down if it only went down to 50... and subsonic filter just turn it up to about 25 or so.. it helps protect ur subs from hitting to low and ruining them..
  3. Fbmowner

    Fbmowner Full Member

    as far as bassboost and your other settings, id set them by ear and try to get as flat a sound as possible. Pulled from . this is what i used to set my gains with test tones.. How to set your amplifier gain with a DMM:

    There are a lot of tutorials on the internet talking about setting your amplifier gain using a DMM (Digital Multi-Meter). Here I will clean up the process as simply (but accurate) as possible.

    Necessary Tools/Skills

    1. A volt-meter or DMM with standard test leads.
    2. Ability to do 6th grade math.
    3. Screwdrivers and/or Allen Wrenches (to make amplifier connections).
    4. A CD with test tones - 50Hz for subs, 1000Hz for speakers.

    Start by making a quick list of your equipment and their output voltage (head unit, LOC, processor, crossover, eq, etc.) and input sensitivity (amplifier(s)).

    Next, list your power output ratings (actual RMS power)

    Then, list your speaker/subwoofer impedance(s).

    You need to know how your speakers/subs are wired - what the final impedance is going to be at the speaker terminals. If you can't figure out these numbers, you shouldn't be installing amplifiers. Pay someone who does and save yourself the damaged equipment.

    Those numbers are VERY important as it is needed for the calculations below:

    We are going to use the equation solving for Voltage using Power and Resistance.

    Voltage = SQRT(Power x Resistance)


    I have a single subwoofer with 4 ohm DVC coils. I'll wire the coils in parallel for a 2 ohm load. The sub is rated for 500W RMS.
    I have a single amplifier rated 500W x1 at 2 ohms. I want all of that power available (knowing that power will only happen for small durations).

    Volts = SQRT (500W x 2 ohms)
    Volts = SQRT (1000)
    Volts = 31.6VAC..

    Edit - What you want to do, is get the final voltage rating from your equation on your amp. So if you get 31.6VAC from your equation you need to put your meter on your speaker terminals and get it as close to 31.6VAC as possible, and your set!
  4. Bluliner

    Bluliner New Member

    All you need are test tones (1000hz/50hz), a really crappy speaker or headphones you don't want, and a larger speaker that will not blow up in 10s.

    What you do is run the test tones through your headunit on repeat. Hook up a crap-tacular speaker or hack up some equally poor headphones and connect it to the RCA outputs BEFORE the amp. Turn the radio up and listen for the low-level output to distort...that's your max clean volume. Do this with both test tone frequencies.

    Next, hook up the RCA's to your amp. Use a bookshelf speaker or whatever will not blow up and hook that up to your amp. It's difficult to hear distortion through your front speakers if you're in the trunk turning use something you can easily hear.

    With the gains down all the way on your 4ch/high freq amp and your radio set to its MAX clean volume - play the 1Khz tone on repeat. Slowly turn the gain up until you hear distortion through the speaker you now have in your trunk. Back off the gain slightly and you're done with that channel.

    For the remaining channels on the amp for your 'highs' you can use the same method or use a multimeter to set the gains so the voltages are equal for each channel.

    For subwoofer duty, you're going to need a robust speaker/sub because sine waves/test tones are rough on drivers. You basically do the same thing you did for your highs except use a 50hz test tone when you listen for distortion. After that, you're done.

    The key is really finding out if your headunit and whatever processors are sending a clean signal because if they're distorting, your amplifier will amplify that along with the music. Most people look over this step and instead go with the usual radio at 3/4 and play music until you hear it clip.


    I don't like using strictly using a voltage meter & math b/c amplifiers from different manufacturers will react differently when they see a given load. A tightly regulated amp, such as a JL Slash, can be set with a DMM. But an unregulated amp, like a vintage Fosgate, will have 2 different voltage readings when a speaker is hooked up and when it's not. Lastly, many head units that advertise 4v outputs do not live up to those claims...especially at the end of a 16' foot run of small gauge RCA. And even then some clip at higher volumes.

    If you'd like an o-scope; keep checking eBay & Craigslist as deals come up every now and then. I picked up a Phillips scope for $35 from a university selling of lab deals are out there.