by sevenasterisks » Tue Apr 25, 2006 2:34 am
okay, setting the gains with a DMM is really quite a simple proceadure (once you know how to do it). The only supplies necessary are a DMM that measures AC voltage (I would guess that all of them do), and a test tone recorded at 0db (very important that it not be -10db, or whatever). One caution about this test tone: make sure it is in a frequency range that will be passes at full strength to the amp output lead (not beyond crossover frequencies currently set), and also don't use one too high in frequency, as some multimeters start to lose accuracy beyond 1Khz or so. Here are the approximate steps (or just follow the tutorial linked to above).
1. determine the target voltage for your amp, found using the formula voltage=sqrt(resistance*power(rms)). This can be easily derived from ohms law (V=I*R) and the fact that power=I*V.
2. disconnect speaker from amp, and set gain to minimum setting.
3. play the 0db source to the amplifier (gain/eq in headunit should generally be at 0), with the volume set at the maximum unclipped level. Three quarters is usually considered pretty safe, unless you know it clips at a higher or lower level.
4. measure the voltage accross the speaker terminals, and slowly adjust the gain upward until the target voltage (from step 1) is reached.
5. recconect everything up (after stopping the test tone and turning down the volume of course)
this sets the maximum gain position, from here it may be necessary to adjust the gain downward (either in the headunit or on the amp), in order to achieve the desired system balance. If possible, it would be ideal to reduce the gain at the amplifier, since this will allow the signal to be tranfered at a higher voltage, thus improving the signal to noise ratio.
Some people reccomend setting the gains by ear intead of by DMM, since a small amount of clipping during peaks of songs is unlikely to be noticed. I am, however, rather picky, and I don't want ANY unneccesary distortion in my system, so I prefer this method for setting gains, until I get an oscilloscope :)
okay, setting the gains with a DMM is really quite a simple proceadure (once you know how to do it). The only supplies necessary are a DMM that measures AC voltage (I would guess that all of them do), and a test tone recorded at 0db (very important that it not be -10db, or whatever). One caution about this test tone: make sure it is in a frequency range that will be passes at full strength to the amp output lead (not beyond crossover frequencies currently set), and also don't use one too high in frequency, as some multimeters start to lose accuracy beyond 1Khz or so. Here are the approximate steps (or just follow the tutorial linked to above).
1. determine the target voltage for your amp, found using the formula voltage=sqrt(resistance*power(rms)). This can be easily derived from ohms law (V=I*R) and the fact that power=I*V.
2. disconnect speaker from amp, and set gain to minimum setting.
3. play the 0db source to the amplifier (gain/eq in headunit should generally be at 0), with the volume set at the maximum unclipped level. Three quarters is usually considered pretty safe, unless you know it clips at a higher or lower level.
4. measure the voltage accross the speaker terminals, and slowly adjust the gain upward until the target voltage (from step 1) is reached.
5. recconect everything up (after stopping the test tone and turning down the volume of course)
this sets the maximum gain position, from here it may be necessary to adjust the gain downward (either in the headunit or on the amp), in order to achieve the desired system balance. If possible, it would be ideal to reduce the gain at the amplifier, since this will allow the signal to be tranfered at a higher voltage, thus improving the signal to noise ratio.
Some people reccomend setting the gains by ear intead of by DMM, since a small amount of clipping during peaks of songs is unlikely to be noticed. I am, however, rather picky, and I don't want ANY unneccesary distortion in my system, so I prefer this method for setting gains, until I get an oscilloscope :)