Using a Voltage Meter to set your amp gain?

Flyin11

Member
2007-09-26 1:29 pm
I've seen from a few sites that you can use a voltage meter to measure how much power is coming out of amp to set your gain to the right output. I uploaded a file on one I found to my site so you can download it and take a look. It's a Excel file. http://www.flyin11spage.com/Pictures/Audio-Calc.zip If you go into Gain Control Adjustment you will see what I'm referring to. You are suppose to set the voltage meter to read AC voltage and insert the leads into the channels you are using. When I insert them into the speaker channel inputs I get nothing on the voltage meter. However, if I touch the power and ground it reads around the voltage on the chart. I'm not sure if that's what they meant how to do it or am I doing something wrong? I mean, I get no read out from the channels on the amp but I get the reading from the power and ground, that doesn't make too much sense to me. Wondering if anyone has ever tried this using a voltage meter and what were your results? How did you do it? I might just have to wing it and go the regular route and turn it little bit by little bit everyday till I get the right mark but that could take forever. This would be a faster way for me and I really don't like having to stop the car every so often and turn the dial and so on, all day long to try and find a good setting. Any help would be appreciated...Thanks :cool:
 

Flyin11

Member
2007-09-26 1:29 pm
I don't what is going on...I did like it said to do once again during lunch and I'm getting nothing. Again, if I have it set to AC and touch the capacitor or the power and ground of a amp I get like 31.8 but that doesn't change when you change the volume. I'm still getting nothin in the speaker terminals which is weird cause I have sound full blast and all. I might try to use another one or something and see if another meter will work. I don't get it. It didn't work for the Alpine either and I touched the gold plated screw down terminals and all. I stuck the red lead into the + speaker terminal I use and the black in the - ...zippo...
 

Flyin11

Member
2007-09-26 1:29 pm
Okay...After checking out Luka's post about the Youtube thing and watching it, I figured out what I did wrong LOL I didn't have the RCAs hooked up :rolleyes: That might have helped. I didn't want it to play through the amp and have sound so I took them off and thought if I just touched the terminals it would show the output but I didn't think about the headunit volume and all that LOL

So, after going through the process, I have to say, I don't think I truly believe the readings on it. I mean, I checked and it said it was at like 40v coming out of it which according to that chart I had is equal to 800watts into a 2ohm load. Peak maybe but that is no way RMS. The amp was tested and is rated at 431rms max in a 2ohm load. Yep, that was with the bass boost off as well. My 2 JL's are rated at 50-150w RMS each and 300w max. I tried setting it according to the chart at 350w but it didn't sound and hit hard enough to me. So I ended up setting it to 400w and it sounds pretty clean and hard now. I think JL's are a little underrated anyways as I don't see any issues with it at 400w and 200 into each sub. Like I said though before, I don't think the numbers are exact as there is no way that it was pushing 800watts :confused: I might try and turn the bass boost down a little bit and that should clear it up a little but I think I have it where I want it now. :cool:
 
If you are matching gain on two amps, just set the meter to the lowest AC range and connect it between the two amps using the same speaker terminal on each amp. For example, use either the positive or negative of the bridge terminal on both amps. Run the same signal mono (better to use a "y" adapter splitting one signal into two from the deck to be more accurate) into both amps. Set one amp at a good point that matches the deck's volume control with good headroom and low distortion. Now play the set frequency coming from the deck (I used 40hz and then tried 80) with a constant volume level (use the repeat function to stay on the same track) and adjust the second amp until you find a point where there is the least difference in voltage between the two amps. I adjusted mine where there was about a 20mv average difference between the two and it sounds great. Amazing how much difference there can be in the gain controls between two of the same exact model.


I connected the negative meter lead to the positive bridge terminal on one amp and the positive meter lead to the positive bridge lead on the other. I might try to draw something...
 

Flyin11

Member
2007-09-26 1:29 pm
aznboi3644 said:
Using this method is not 100 percent spot on...it is better than the doing it by ear method...using a multimeter simply gets you in the ballpark range.

Speaker outputs are ac voltage...power and ground are dc voltage

Very true it's not 100 percent and I don't have a oscilloscope to measure soundwaves and stuff...I'm not rich enough for that so this is the best option for me and is better than like you said it's better than by ear as with just my ear I would have been adjusting it for months now and I got into the ballpark within 1-2 hours. All I really wanted anyways was to get me into the ballpark range as I shouldn't have tried to turn and mess with it before as I was enjoying it where I had it at but I did it thinking I could make it sound clearer but that wasn't the case. I now atleast have it back to where it sounded like it was before and I think I will now concentrate on the highs and getting them a little louder. I'm not worried about the clipping too much anymore and it sounds great right now so I can only do what I can with the tools I have. I tried listening to some clipping clips online on Perry's site but couldn't even tell the difference in it in the music one. I heard it in the frequency one where you only hear the frequency tone and I didn't hear it cutting out or anything after I set the voltage and turned the sound tone up so it's all good. I don't want to drown out the hard hitting sound of the lows either so I won't have the highs too high but I can always adjust them down on the headunit as well. I won't be using a voltage meter on the highs as that's going to be done by ear but I will get it to where I like it.
 

Flyin11

Member
2007-09-26 1:29 pm
I'm still working with the gains a little bit using this method but I'm still confused on something...I'll turn everything down and off like I'm suppose to, the gain, crossovers, bass, treble, bass boost, everything...Unhook the speaker wires and turn it up to around 80% of the volume. When I read the meter and turn the gain up it starts to reach the 425watt point on the chart. I can turn it up higher than that which I don't understand. How can it be showing over like 450watts with everything turned off and the amp has the certificate rating it at 431watts rms at 14.4 volts? Is the meter reading max wattage instead of rms? I mean, the max wattage rating is at 1200watts max. I'm just reluctant to really trust this type of setting for the gain like this now, that doesn't sound right....
 
Unless the amplifier has a fully regulated supply, the maximum no-load voltage is going to be significantly more than the maximum voltage when loaded.

Your meter is reading RMS or average voltage. If you're using a test tone near 60Hz, most meters will give readings very close to the actual RMS voltage. Frequencies well above or below 60Hz will be less accurate for many meters due to the limited bandwidth of the meters.

Although you need to understand how the gain settings affect the system, you shouldn't spend too much time on it. There's virtually no fool-proof way to set the gains. If you set them so the amps never clip, there will be lots of music that will not be able to reach full power. When the gains are set so the amps can never clip, the owner is VERY rarely satisfied.
 

Flyin11

Member
2007-09-26 1:29 pm
One other thing I always have to keep in mind is that music is produced differently and it all also depends on how it is formatted and all...especially when it comes to mp3's. Like if I listen to some Breaking Benjamin, of course it's going to sound harder and hit better than if I'm listening to Lifehouse cause of the bass lines. I find the same thing with a band like Three Days Grace. Each band is different sounding and some will sound better than others. I'm just trying to find a pretty neutral point to judge them from.

I tried 80hz yesterday and the bass is a lot harder hitting for rock music but the kick drums aren't as clear. I went back to 60hz and kick drums are kicking but the bass isn't always nice and deep and hard hitting. Maybe I need a mutual point there and need to try a 70 or 75hz tone? I'm also gonna try some HU tuning and tuning the Bass Q Factor, Bass Extend, Middle Center Frequency, and Middle Q Factor...Some little adjustments could help as well..

So, are you saying clipping isn't a bad thing? I know judging from previous conversations around the baords that it's almost like a kiss of death but then again everyone tries to run their amps into it. So, is that a good or bad thing?
 
The amp shouldn't have to clip to get it to sound the way you want. Having the gain adjustment just allows you to have the correct level of "headroom" so you don't have to max the volume out on your deck to have the subs peak out every now and then. (the same way you'd adjust your highs amp) You are correct about the music having different recording levels and if you don't have the amp gain adjusted properly/high enough, you won't be able to tweak it with the eq/bass settings on your deck. There are several factors to take into account such as the actual frequency the deck adjusts and the "Q" of that frequency range.
 
So, are you saying clipping isn't a bad thing?

Clipping isn't good but most people don't have the resources to buy the equipment they need to reach the volume levels they want so they generally have to drive their amps into clipping to be satisfied.

Some CDs have significant dynamic range. Let's say you have only 100 watts/channel. If you were listening to a disc with significant dynamic range (like some of the Sheffield Lab CDs), and you never wanted to drive your amp to clipping, the majority of the music may be at a relatively low level (10 watts) so that it wouldn't clip on the peaks. Most people would want to have the majority of the music near the maximum power and would allow it to clip on the peaks.
 

Flyin11

Member
2007-09-26 1:29 pm
Was wondering....I know you turn off all your filters and crossovers and all that stuff...but what do you do with the sub level control? I have been setting that to 0 but saw someone post on another forum that you are suppose to max it out. Wondering if you are suppose to max it out, set it at 0, or set it at -15 at it's lowest point?

Well, I didn't turn off my LP crossover on my amp and still had my frequency set at 60 so I kind of screwed that up last time I tried to set the gain. I put the crossover on AP (All Pass - that's the only way to turn off the crossover on the amp) and put the frequency all the way up to 500hz on the amp per some advice on another board cause they said that you don't want to have the crossover point too close to the tone crossover you are using, that it would defeat it if you tried to use like a 60hz tone and set the crossover at 60hz. Tried a 50hz tone and that sounded good with one band but when I went to some others it was way too much low bass. 1 certain song wouldn't even play good as it made the speakers distorted but was ok with other songs. So, I stopped at a parking lot and reset the amp for 70hz....and now it sounds really loud on some songs and a little distorted as well. I might need to back down the wattage a bit, maybe try like 65hz, or turn the bass eq down which is quite surprising as it's at halfway so it's not turned up too much...Hmmm..Some thinking to do...