Tuning line driver audio levels

akula169 · 08-18-2006, 03:09 PM

What is the best way to go about making sure that all the channel gains on an amp or line driver are set to about the same level? My paticular unit doesn't have any sort of markers to let me know the approximate settings.

There's gotta be a scientific way, as I'm pretty much a perfectionist and I know it'll bug me knowing that one channel might be 1 or 2 percentage points higher or lower than the other. My ear is pretty good, but not that good.

pancit175 · 08-18-2006, 06:10 PM

First question if you want to accomplish this in a "scientific way" is do you own or have access to a signal generator and oscilliscope.

akula169 · 08-18-2006, 06:38 PM

OK, maybe I mean a "low-tech" scientific way

Could I make my PC be a sort of signal generator? Although, that probably wouldn't do me much good as I don't have an oscilliscope...

pancit175 · 08-19-2006, 08:26 PM

I'd say its tough to get it within those tollerances without an osciliscope, because any other method would not give you a visual reading of distortion or clipping.

Anybody else have any other methods...

RedGTiVR6 · 08-19-2006, 08:52 PM

http://www.350z-tech.com/zwiki/Tutor...plifier_Tuning

It's not precise, but it's the generally accepted method.

akula169 · 08-21-2006, 02:23 AM

Quote: Originally Posted by Red GTi VR6

http://www.350z-tech.com/zwiki/Tutor...plifier_Tuning

It's not precise, but it's the generally accepted method.

Sweet - that looks like a great way to start.

Thanks

RedGTiVR6 · 08-21-2006, 07:26 AM

Good luck!

Damon · 08-21-2006, 10:50 AM

Just a thought, I have not tested it....yet.

You could do the excersise posted above to find max settings through the system. Then, if you have a line driver that will allow independent adjustment of left to right, and it is installed prior to any crossovers, you could disconnect the outputs of the line driver and play a 60hz test tone on your system. Then measure the voltage on the output of each channel with a DMM set to AC volts. (Household current runs at 60hz.) Then turn the high one down to match the low one. This would, in theory, match your right and left output levels without compromising the max setting found above.

When I get my system together I'll try it to see if it works.

JeffsGotMilk · 08-21-2006, 12:14 PM

The 350z site gives a good starting point, however, there is easier ways to do it that is far more precise. There are three things that you will need: a DMM (digital multi-meter), “Y” RCA connector, and a test tone CD. I would not use a downloaded mp3 file for tuning a system because the compression effects how it will be played back. The DMM is to show measure when you have distortion and also to match the gains. Here is what to do.

Start off with plugging in the “Y” connector in between the amp and rca. Set the DMM to AC and put the test leads on the unused rca connection to measure the voltage. Insert the test tone CD into your source unit and use 1khtz for the full range and something like 60 htz for the subwoofer(s). Put the volume at no more than ½ to check. Test tones are powerful. Once your setup, then match the voltage across the rca’s that you want to match. Try to get it within 0.1 volts of each other.

That is it.

If you want to take a bit of extra time to tune your system since you have the stuff out, then the process is similar but a few changes.

Set your source unit’s equalizer to flat and make sure that there is no boost or anything on. Take the gains on your amps and set them to zero. Using the test tone disc and your DMM set to DC voltage, keep turning up the volume on the source unit until you see a voltage reading on the meter. 0.05 is the max that I would go. What this is doing is measure the level of distortion. Once you know how far it took to turn up the volume to get distortion, then you know that that number or level is the max of your source unit. The reason that you leave the amps plugged in is because the amp puts resistance on the rca and that will throw things off if you did the test without the amp connected or no load.

Once you have the rca’s set, then move on to the amps. This time, instead of measuring the rca, put the test leads on the outputs to the speakers. Keep the source unit at just below the max that you just determined, start turning up the gain on the amp. Keep on turning it up until you see 0.05 volts DC or until the desired volume, which ever comes first. Then back off just a little bit on the gain. Rinse and repeat on the other channels.

Now your speakers may be distorting even though you are sending it a clean signal. Then you will need to adjust the crossover points to get rid of the distortion. I normally wear hearing protection during this because it is very easy to hear the distortion with them on.

Good Luck. If you have any questions, ask away.

akula169 · 08-21-2006, 07:34 PM

Ok, cool.

I don't think I have access (or the need) to tune the factory amp.

Here's what I propose to do:

run test tone (1khz) on factory head unit (half volume - flat EQ) and measure the output on the outs to a speaker - measure the voltage with a digital multimeter.

Then attach my PC/line driver to the factory amp and measure (again, half volume, flat EQ) and set levels of line driver to match the factory head unit.

Or at least something like that -- I suppose I could also measure the voltage coming off the factory head unit (before it hits the amp) and tune the outs on the line driver to match as well.

I guess I just didn't know about hooking a multimeter up to the output lines for taking measurements.

pancit175 · 08-21-2006, 07:56 PM

hopefully you get it as precise as you'd like to. I doubt that 1 or 2% differential would be noticeable. good luck

JeffsGotMilk · 08-21-2006, 08:47 PM

Why not just replace the factory head unit with an aftermarket one that has the RCA pre-outs like you need?

akula169 · 08-21-2006, 10:52 PM

Quote: Originally Posted by JeffsGotMilk

Why not just replace the factory head unit with an aftermarket one that has the RCA pre-outs like you need?

I am using the computer as the head unit.