#65167 - 06/21/06 06:33 PM
How to Set Your Amplifier's Gain Correctly
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Bastard Kid Kris
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We have edited this thread, updated it with new info and links. Enjoy.
Edited by keep_hope_alive (03/20/10 08:56 AM)
Edit Reason: 2010
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#65168 - 11/05/06 10:55 PM
Re: How to Set Your Amplifier's Gain Correctly
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92oldsTrefeo
currently "Civic96Lx"
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How to set gain video
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#1294233 - 01/16/08 06:11 AM
Re: How to Set Your Amplifier's Gain Correctly
[Re: kkrkeith7]
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keep_hope_alive
Acoustics Engineer
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Registered: 04/24/07
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Loc: Quad Cities, IL
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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)
Example:
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
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You need to determine what the maximum volume level you SHOULD use on the head unit - not the actual maximum volume level possible. If your HU goes to VOL 40 but you never go past VOL 25, the set the gains at VOL 25 - and don't go past that level. It may not be that easy for you to determine, so here are a few tips.
Determine the maximum head unit voltage you want to use as follows:
1. if you have a factory head unit and factory speakers and are using a LOC for your sub amp, use the highest volume level you do for music (without distortion to the speakers).
2. if you have an aftermarket head unit powering factory or aftermarket speakers and are using the HU preouts for your sub amp, use the highest volume level you do for music (without distortion to the speakers).
3. if you have a factory or aftermarket head unit feeding a signal to amplifiers for speakers and subs, you need to verify the maximum unclipped, non-distorted output - or just use a 75% volume setting if you are unsure if your headunit is capable of 100% unclipped volume. You can verify this with an oscilloscope.
With the invention of the SMD DD-1 (distortion detector) the steps above can be done with more accuracy and without an oscilloscope.
When setting a subwoofer amp - if your head unit is powering speakers, you really want to disconnect them or use a high pass crossover on them. however, this may not be realistic for you. if not, then your max volume setting may not be possible without distorting your speakers. don't distort your speakers for this exercise. use whatever volume you can that doesn't distort your speakers. This is not the ideal situation, to do it right you should put high-pass crossovers on speakers when you have a sub.
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Once you have the head unit max volume determined, and the test tone CD playing on repeat. Set the EQ to flat, turn off processing. Make sure the fader is centered, balance is centered, sub level controls are maximum (sub level is just attenuation anyway).
You can go back to your amplifier. Your system is on and your car can be on or off - but for this work I recommend the car is on and the battery voltage is close to 14VDC.
You can disconnect any speakers/subs not associated with the channels being adjusted. The speakers/subs connected to the channels you are adjusting will be connected. I work on channel (or channel pairs) at at a time.
Set the gain to minimum. Turn off any bass boost. With the DMM set to VAC (Volts AC), touch the DMM positive leads on the speaker outputs. Slowly increase the gain until the DMM reads the voltage determined by equations above.
While you're increasing the gain - LISTEN TO YOUR SPEAKERS/SUBS!!! Listen for any distortion - popping, scratching, noises that go away when you turn the volume back down. When playing test tones it is pretty easy to hear distortion.
If you cannot achieve the voltage you calculated then turn the gain back down - avoid leaving any gain setting on MAX. it is possible that your HU output isn't strong enough at your determined volume setting. It is also possible your amplifier isn't capable of that output without a higher battery voltage.
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You can use resistors to load the amplifier so you get a more accurate reading (like in the eD video), but the resistor load bank must have a power rating greater than the output power expected. Most of you reading this won't have a load bank on hand, especially for loads over 500W. Don't worry. You should be able to leave the speakers/subs connected - you're listening for clipping and distortion anyway.
Once you have set the gain on all of the channels separately, all of the amps separately. Hook up everything as it should be - all speakers and subs (if anything was disconnected).
Now listen to your system with music. Listen for balance between all of the speakers and subs. If you desire a more balanced sound (i.e. subs overpower speakers) you TURN DOWN GAIN on the loudest speaker/sub. DO NOT INCREASE GAIN past your set points determined above. Most head units have sub level controls, fader, etc. that allow you to attenuate the signal from your HU.
Now you can start introducing EQ, boosts, etc. Note that any bass boost more than 3dB can result in clipping or damage. I prefer a mix-minus EQ process, where i use the EQ to reduce the response peaks, not add response peaks. You've already set the amp gain as high as it should be. Once you get your EQ and boosts set, you should check your gain setting once again. Excessive bass boost settings will cause clipping with the gain steps taken above. If you require bass boost to "sound good" then repeat the gain steps above with bass boost engaged - i.e. you will turn your gain down to compensate for the extra signal level.
If you hear noises then reduce the gain at the point where there are no noises or popping as it may be an indication of amplifier clipping, or speaker/sub distortion. Some systems will develop a background hiss with improper gain structure.
If it's not loud enough - buy better or larger speakers/subs, more or larger amps, and start over.  Don't force your equipment to be louder than it can, or you'll destroy it. Understand that every system has limitations.
Edited by keep_hope_alive (01/29/12 08:22 AM)
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#1320931 - 02/17/08 04:07 PM
Re: How to Set Your Amplifier's Gain Correctly
[Re: jandk3400]
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dbaxronin
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Registered: 02/25/06
Posts: 6
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Hey all. In my quest to figure out the required voltage of my system, I found the adventure arduous and even frustrating with my limited experience in this field. So many variables come into play, and I spent quite a bit of time ensuring I was doing everything right. So, I got inspired and as a result, I made a pretty fool proof web-based utility to take the guess work out of all this under most circumstances.
Here is a link, please give it a try.
http://trussinme.com/Apps/audio/voltagecalc/default.asp
What this tool does is ask for a number of specifics from you. Including the wattage of your amp, the number of subs it is pushing, the number of voice coils per sub, and the impedance of each sub/voice coil.
It then prompts for the type of wiring configuration you have. If you have multi-voice coil drivers, it asks if they are parallel/parallel or series/parallel, as well as give a small reference diagram of what the difference between the two is.
The primary and biggest advantage of this utility, at least in my book, is that it will calculate the load on your amp FOR YOU based on your inputs. No more guess work in what your load is if you have multi-sub/voice coils wired this way or that. It takes it all into consideration.
Its pretty straight forward and you should find it easy to use. I also provide a link to a downloadable 50Hz test tone in the event you need one, as well as precise instructions on how to measure the voltage.
There is a link to email me from if you have any questions or comments, or you can post them in here but I check my email a lot more than this board so that would be your best bet.
Now my disclaimer. Please, if you find a quirk in the calculations, don't bash me for it, rather, provide some details on what the problem is. I spent a good deal of time working on the formulas and am pretty sure they are accurate, but I am by no means an expert on the subject so I wouldn't be at all suprised if someone found something a-miss.
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#1718617 - 10/13/09 10:10 PM
Re: How to Set Your Amplifier's Gain Correctly
[Re: keep_hope_alive]
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keep_hope_alive
Acoustics Engineer
SD Sith Lord
Registered: 04/24/07
Posts: 18650
Loc: Quad Cities, IL
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the Autosound2000 cd has test tone tracks that intentionally clip the signal for 4 seconds at a known location. that way the user can hear clipping, and knows that it only exists at that specific time frame (in the recording). it's a neat trick.
If anyone has a question about this process, create a thread and ask. A description of how to use an oscilloscope to set gains will follow.
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