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Old 05-03-2016, 08:40 AM   #1
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For You Car Audio Gurus

Hey everyone. I'm using the ohms law to use a multimeter to tune my amplifier. I know you have to set all bass boosting and gain adjustments to zero, but I have an external gain control knob built into my line out converter for my stock HU. My question is, when tuning, should that knob be all the way up so when I turn it there, it hits the voltage I calculated? Or should it be somewhere in the middle? Here is my math to prove that I did it lol.


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Old 05-03-2016, 09:45 AM   #2
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That knob is going to change voltage INTO the amplifier. So the position of the gain knob on the amplifier will have a linear relationship with it. You can change the knob on the LOC or the gain on the amp to alter the voltage OUT of the amplifier to get to the 24.49VAC you're looking for. Rule of thumb is generally to provide the amplifier with the strongest signal possible so you can then leave the gain on the amp as low as possible. This reduces the amplification of any induced noises in the signal chain.

When setting the gain this way, please realize increasing the bass boost, bass EQ, etc will all then add distortion. So hands off.

When I set this way for a customer, I turn ON the loudness setting and turn up the bass boost some before setting the gain. Because we all know that's the first damn thing the customer is going to do anyway. And I'm not about to replace a blown subwoofer for free a week later.
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Old 05-03-2016, 09:49 AM   #3
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Quote:
Originally Posted by firebirdude View Post
That knob is going to change voltage INTO the amplifier. So the position of the gain knob on the amplifier will have a linear relationship with it. You can change the knob on the LOC or the gain on the amp to alter the voltage OUT of the amplifier to get to the 24.49VAC you're looking for. Rule of thumb is generally to provide the amplifier with the strongest signal possible so you can then leave the gain on the amp as low as possible. This reduces the amplification of any induced noises in the signal chain.

When setting the gain this way, please realize increasing the bass boost, bass EQ, etc will all then add distortion. So hands off.

When I set this way for a customer, I turn ON the loudness setting and turn up the bass boost some before setting the gain. Because we all know that's the first damn thing the customer is going to do anyway. And I'm not about to replace a blown subwoofer for free a week later.
So I should leave the standalone gain knob set to max while I adjust the amp knob? My reasoning with it is that when the bass knob is turned all the way up (aka very rare for me) I'd get the full 24.5ish volts, so I don't crank the knob over half for example and clip it out. Am I correct or wrong?
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Old 05-03-2016, 09:52 AM   #4
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What line output converter are you using?

Also realize that you'll NEVER get the full same voltage out of the amp while playing music as you did with a sine wave. And that's why people often use sine waves recorded at -3db to give them a bit of gain overlap.
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Old 05-03-2016, 09:55 AM   #5
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What line output converter are you using?
Here it is: Link The knob does not connect into the amp any way, it adjusts the signal outputted by the converter.
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Old 05-03-2016, 09:59 AM   #6
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Huh. I've never seen that LOC before.

It would really depend if that knob controls the full signal out, or if it limits/boosts the bass frequencies only. It would be pretty easy to tell once installed, but my guess is that it affects all frequencies. So yes, leave the knob cranked to max while setting your amp gain. Then you can back it off after you're done. That would mean you'd never clip the outputs on the amplifier, unless you were to turn on bass boost, loudness, etc on the head unit.

Remember what I said above about gain overlap.
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Old 05-03-2016, 10:01 AM   #7
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Quote:
Originally Posted by firebirdude View Post
Huh. I've never seen that LOC before.

It would really depend if that knob controls the full signal out, or if it limits/boosts the bass frequencies only. It would be pretty easy to tell once installed, but my guess is that it affects all frequencies. So yes, leave the knob cranked to max while setting your amp gain. Then you can back it off after you're done. That would mean you'd never clip the outputs on the amplifier, unless you were to turn on bass boost, loudness, etc on the head unit.
It does control all of the frequencies. I just have my low pass filter on my amplifier for the bridged sub. If I turn the low pass off, I can hear mids and highs trying to play on the sub like it was a normal speaker. One weird thing about that knob is around half it doesn't change anything. What I mean by that is from half to full gain on the knob, it doesn't make it any louder. Probably because the amplifier was tuned by ear and not a multimeter, so it could be maxing out the amp at only half of the knob's adjustment.
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Old 05-04-2016, 09:40 PM   #8
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If you started maxing out the amp you would instead start hearing clipping or your amp going into protect. I would bet that it is just due to the quality of the LOC. Keep it maxed regardless when you set the gain. If possible I would try to find out which volume the radio starts to send a clipped signal as well. Then when you set your gains, set the radio level 1-tick below the measured clipping for max volume.
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Old 05-04-2016, 09:49 PM   #9
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You're not going to be able to see any clipping from the head unit without a scope or DD1. And you're not going to hear clipping until you're well into it. Through a subwoofer, 10+% THD. The amp will only go into protection if the heavily clipped signal causes your electrical system to drop voltage or the amplifier overheats. If neither of those happen, it'll let the dirty dirt fly all day long.
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Old 05-05-2016, 10:21 PM   #10
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Quote:
Originally Posted by Tundrafoci View Post
If you started maxing out the amp you would instead start hearing clipping or your amp going into protect. I would bet that it is just due to the quality of the LOC. Keep it maxed regardless when you set the gain. If possible I would try to find out which volume the radio starts to send a clipped signal as well. Then when you set your gains, set the radio level 1-tick below the measured clipping for max volume.
Well, I did set it according to my calculations. Made my sub super quiet. So, no clipping. But I know it will play much louder without any distortion. Almost sounded like stock with the voltage set to where I calculated. I have it set to 30 volts now, which is what number I got from using the maximum amp power (400 watts). Still no clipping.
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