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Discussion Starter #1
i have heard so many ways to skin a an amplifier, yet I don't think I'm grasping it.

-On one hand I understand ohm's law completely, and how to use it to set gains.

-On the other hand, when it comes to matching the output of my dsp I am confused.

What I have been doing to "gain match" is measure my pre-amp voltage with a 1khz and 40hz tone and set the gain by the numbers listed on the amp.
So if my my dsp is outputting 1.7 volts @ 1khz and . 1.3 volts @ 40hz I will turn my gain knob to the nearest whole number (2v in this case and turn it to the right a bump.


I can feel deep down inside this is wrong and for some odd reason everytime I've done it I have no distortion, and everything sounds good. which makes me mad because sometimes I feel like I'm killing myself over gains and technicalities.
 

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The numbers on the amp are probably not even close to accurate. Search for a how to on this forum. Its been written a dozen times. If you find a guide and have questions than come back and ask...
 

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Discussion Starter #3
The numbers on the amp are probably not even close to accurate. Search for a how to on this forum. Its been written a dozen times. If you find a guide and have questions than come back and ask...
it's been written a dozen times and Yet I can't seem to find the questions I'm asking, being answered.

my gain knobs are in entirely different places when I set them by output voltage and Pre-amp voltage.

I don't understand what key part of this equation IM missing. i can set gain by ear, or with a dmm,
but I don't understand or know what it is that I'm overlooking or not understanding when it comes to gain matching.

From my standpoint, ohm's law doesn't take into consideration the amp input voltage, and you have to match the amp output with input,

but if you set gain by pre-amp, then you can allow the highest signal possible to your amp.

but as you said using the numbers on the knob is in accurate, so what exactly do I go by if not that? what is the phrase I need to be searching for? because I've searched over and over "setting gains by pre-amp voltage without gain knob numbers" or" gain matching with dmm".

everything I've read just stops at measure RCAs and match that.
or they only mention ohm's law.
 

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See if this helps:

 

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Discussion Starter #5
it's been written a dozen times and Yet I can't seem to find the questions I'm asking, being answered.

my gain knobs are in entirely different places when I set them by output voltage and Pre-amp voltage.

I don't understand what key part of this equation IM missing. i can set gain by ear, or with a dmm,
but I don't understand or know what it is that I'm overlooking or not understanding when it comes to gain matching.

From my standpoint, ohm's law doesn't take into consideration the amp input voltage, and you have to match the amp output with input,

but if you set gain by pre-amp, then you can allow the highest signal possible to your amp.

but as you said using the numbers on the knob is in accurate, so what exactly do I go by if not that? what is the phrase I need to be searching for? because I've searched over and over "setting gains by pre-amp voltage without gain knob numbers" or" gain matching with dmm".

everything I've read just stops at measure RCAs and match that.
or they only mention ohm's law.
See if this helps:

they don't mention gain matching, not once, and didn't meter a single rca.
This is exactly why I can't find any information on what has to be done to gain match point blank.
 

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It's an iterative process for me. Start with the multimeter and test tones to get a baseline and then use music with big bass peaks to set the gains. (Using the maximum non distorted output of the HU or digital input.) Then turn up settings in the DSP (watching the signal meter in the S/W) till it gets very close to peak or intermittently turns red every once in a while. Then turn up the sub amp gain to get what I want or to the clip light starts to flicker and then do the same for the mains till I get the level I want or need.
If I'm going to purely set the gains by voltage then I use an oscilloscope. There's too many variables if you're trying to truly max out the gain structure.

Sent from my SM-G965U using Tapatalk
 

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Discussion Starter #7
It's an iterative process for me. Start with the multimeter and test tones to get a baseline and then use music with big bass peaks to set the gains. (Using the maximum non distorted output of the HU or digital input.) Then turn up settings in the DSP (watching the signal meter in the S/W) till it gets very close to peak or intermittently turns red every once in a while. Then turn up the sub amp gain to get what I want or to the clip light starts to flicker and then do the same for the mains till I get the level I want or need.
If I'm going to purely set the gains by voltage then I use an oscilloscope. There's too many variables if you're trying to truly max out the gain structure.

Sent from my SM-G965U using Tapatalk
I'm just trying to figure out, if gain matching is different from, the typical method of using ohm's law, and what is the actual matching part.

Everytime I read a guide and it get to the point where it says to measure the Pre-amp voltage from my dsp. I don't know what I'm supposed to do with that information.


I' scoped my head unit , Meter it, and then perform unity gain at the dsp,and then I measure my RCA's and then I turn the knob to that number.... and then I scratch my head, at why that doesn't seem right and simply proceed to set gains with 0db tones and ohm's law at the amps, regardless of my dsp pre-outs voltage.
 

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Well your dsp has some gain just like an amp. If preamp output is rated at 6vrms that's what you should measure with a 0db sine wave. Just like if an amp is rated at X watts, you can do the math to measure the voltage output.

But absolutely maxing out your system for a 0 db sine wave isn't the goal for setting gains so dont bother. Use some common sense understanding of the material you listen to and find distortion free settings by working down your signal chain from HU to DSP to AMP.
 

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they don't mention gain matching, not once, and didn't meter a single rca.
This is exactly why I can't find any information on what has to be done to gain match point blank.
The use 75% volume as an assumption the source unit will be clean... also measuring 1khz with a multimeter won’t be accurate, even the decent fluke meter he’s using only has good certified accuracy between 10hz and 100hz, lots of meters only specify ac voltage between 40-70hz for mains measurements

In short that jl guide is poor at best as it makes a lot of assumptions

I tend to use 0db tones for scoping upto and including a processor with a scope to establish clean signal from front to rear, then set amplifiers with -5db tones

making sure that crossovers in dsp are turned off as they will reduce output levels in various regions of signal depending where the crossover is set at... so if you have a 60hz low pass on a sub don’t then use 50hz as it will be attenuated a little by the crossover, scope it with no crossover on and find max output

Set your gains with -5db tones as that gives you some scope as most music is recorded at no more than -6db, this keeps your signal path clean all the way to the drivers

Then turn down your system and reduce gains in the dsp from where they were and set the system up, you will find one driver (normally midbass (or mids if cut a lot) depending on eq) that then has its level set full and the rest are all turned down to match

Ideally you want the gains on amps on minimum before you turn your gains on the dsp output down to get the most signal to noise ratio

Put simply you have to remember maximum points and juggle the amp gains if not down fully to find a nice happy tuning point
 

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I'm just trying to figure out, if gain matching is different from, the typical method of using ohm's law, and what is the actual matching part.

Everytime I read a guide and it get to the point where it says to measure the Pre-amp voltage from my dsp. I don't know what I'm supposed to do with that information.
Scope the HU for undistorted output.
Use that HU setting to scope the dsp for the same - what the voltage is does not matter cause every amp input is different and at this point all you want is undistorted max output to maximize your noise floor.
Set amp gains just loud enough to do your initial tune. Unless your the "eq is only for cuts and no boost" you'll probably have to reset the maximum gain after your initial tune. Once you have your tune at a happy starting place then start cranking up the amps while scoping them if you want maximum gain structure. If you change your eq after that point then you'll have to adjust gain by the same in order to stay at maximum. That's why it's better to be over amped and have lots of headroom with the amp gains set lower than it is to have the amps maxed out.
Once you've gone back and forth a few times and found a happy medium where you're not clipping anything with small changes in tuning then you'll know you've got it right.

Sent from my SM-G965U using Tapatalk
 

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Discussion Starter #11
Scope the HU for undistorted output.
Use that HU setting to scope the dsp for the same - what the voltage is does not matter cause every amp input is different and at this point all you want is undistorted max output to maximize your noise floor.
Set amp gains just loud enough to do your initial tune. Unless your the "eq is only for cuts and no boost" you'll probably have to reset the maximum gain after your initial tune. Once you have your tune at a happy starting place then start cranking up the amps while scoping them if you want maximum gain structure. If you change your eq after that point then you'll have to adjust gain by the same in order to stay at maximum. That's why it's better to be over amped and have lots of headroom with the amp gains set lower than it is to have the amps maxed out.
Once you've gone back and forth a few times and found a happy medium where you're not clipping anything with small changes in tuning then you'll know you've got it right.

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yeah I scoped my HU, and I have a c-dsp so I was able to set the gains on my dsp from in the software. I don't know about anyone else, but I went the unity gain route as they explained to do. and then I set my gains with 0db tones no filters of any kind on the amp and went to eq.

then I open up my dsp software and play the 0db tones based on the lowest 0db frequency for each crossovers and if that point is cut in the Peq, I'll change the tone to the next highest frequency in the Peq. unless it has a really high Q, then I'll move up once more, and after I find the frequency point I'll read the output meters on my dsp. If the highest/prominent/most demanding frequency is reading -6 db I'll set the gain with -10db. and continue on.

if -4db is the largest gap, I'll count the clicks from max volume on my dsp until I'm at -4db and, then I'll carelessly turn the volume up to max for every single song anyways, because I wasn't fooling anybody, I have no self control... or hearing.

I back off 1.5 volts for everything, I was told not to use a scope, unless I have a load applied, and my scope just can't read the amps with a load applied.
 

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BTW Ohms Law has nothing to do with setting gain structure till you get to the load on the amp. HU and DSP have such high impedance that it doesn't affect the amount of current enough to be of any concern.

An oscilloscope is a high impedance connection as well; with no effect on the signal. The current flowing out of the amp has no bearing on what the oscilloscope can or can't read. It only looks at voltage and frequency. Keeping turning up the voltage selector dial on the oscilloscope till the frequency you could see coming out of the HU is visible coming from the amp. Start with the gain low and ramp up the gain and the voltage range on the scope at the same time. When you see the waveform distort you'll know you've turned the gain up too far.

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Discussion Starter #13
BTW Ohms Law has nothing to do with setting gain structure till you get to the load on the amp. HU and DSP have such high impedance that it doesn't affect the amount of current enough to be of any concern.

An oscilloscope is a high impedance connection as well; with no effect on the signal. The current flowing out of the amp has no bearing on what the oscilloscope can or can't read. It only looks at voltage and frequency. Keeping turning up the voltage selector dial on the oscilloscope till the frequency you could see coming out of the HU is visible coming from the amp. Start with the gain low and ramp up the gain and the voltage range on the scope at the same time. When you see the waveform distort you'll know you've turned the gain up too far.

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i may have worded that wrong, but scoping
without speakers connected is not accurate,
 
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