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-   -   Tuning amp gains with DMM? (http://www.wakeworld.com/forum/showthread.php?t=793488)

corerider 05-21-2012 4:27 PM

Tuning amp gains with DMM?
So after trying to tune in my Rev410's this weekend I figured out really quick I need another way. hey are so loud I don't feel as if I can accurately tell when they are distorting. I've been doing some research on tuning using different frequency sine waves and reading the voltage of the amp output with a digital multi-meter. I think I understand everything, but have a few questions...

For reference the equation is Voltage = square root of watts * ohms.

1) All the reading and videos I've watched talk about doing this method on 2 ohm loads. The Rev410 runs on a 4 ohm load so I'm assuming I need to multiply the amp RMS by 4 instead of 2.

2) I also read that if the amp has 2 gain controls to treat it as 2 separate amps. EX. If the amp is 100W RMS by 4-channels for a total of 400 watts, divide the total RMS by 2 to get your voltage calculations. 400RMS / 2 = 200RMS * 2ohms = gain voltage.

3) So given these scenarios, the Syn4 running a 4 ohm load should calculate as:
400W RMS * 4 = 1600/2 = 800
Square root of 800 = 28.284 VAC at the amp outputs.

4) Another way to think about it is the Syn4 when bridged only uses one gain knob. So do I calculate it like a 2 channel amp then?
400W RMS * 4 = 1600
Square root of 1600 = 40 VAC at the amp outputs.

Is this correct?

tx_foilhead 05-21-2012 4:50 PM

My JL iPhone calc says 14.5, I think your 1st attempt is right but you have 2 channels not 1. Bridged each channel outputs 400 watts. I too tried to set my Rev 10's by ear and realized that was not going to work.

corerider 05-21-2012 7:39 PM

I'm not real sure how you got 14.5? I downloaded the JL app and it gave me 40 VAC with the 400W RMS (like when I calculated on paper) and 56.5685 at 800W RMS.

CobraRob 05-21-2012 8:53 PM

I think to really maximize this type of method you really need an O-scope to see when the sound is clipping. I think that is the method I am going to try this time when I get the new 410s in

tx_foilhead 05-21-2012 9:00 PM

Oops, I forgot to clear it out first, that just assures that your amp won't send a signal that it clips if it is making the stated power, if it underrated then your leaving something on the table or if its overrated you could be doing damage, O-scope is best, but kinda spendy if you don't need it but once every few years.

corerider 05-22-2012 5:26 AM

From what I've read, yes the o-scope is the best method, but they are hard to find and expensive. Using the DMM is the "DIT" way to do things. I think if the math is correct it will work just as well. I also plan on listening to the different tones once I have set the gains with a DMM just to make sure they are safe. Just want to make sure the math is right.

cowwboy 05-22-2012 6:04 AM

A volt meter won't tell you when your clipping. You need a o-scope for that and they have dropped in price quite a bit lately.
But looking at the electronic signal will never tell you when your pushing the driver to it's mechanical limits.
A volt meter is good if you're running multiple identical amps and have tuned one and are looking at matching the other.
Steve mead makes a device that can tell when the audio being played starts clipping. I personally have never used it but beyond a Real Time analyzer thats the only way you can electronically tell when you are pushing the driver to hard.

BradM07SS 05-22-2012 11:24 AM

I set all my amps with the SMD DD1 meter. Here is link to check it out.


hunter660 05-22-2012 11:35 AM

$150? I may buy one and rent it out. Any one interested in that?

tuneman 05-22-2012 11:39 AM

A volt meter won't help you when setting gains. Just get a $10 pair of earmuffs and a flat blade screwdriver and you're set. Earplugs work too.

ryanbush11 05-22-2012 3:06 PM


Originally Posted by tuneman (Post 1753608)
A volt meter won't help you when setting gains. Just get a $10 pair of earmuffs and a flat blade screwdriver and you're set. Earplugs work too.

can you go in-depth a little more?

shawndoggy 05-22-2012 3:34 PM

I'm pretty sure the ear plugs are for your neighbors and the screwdriver is for turning the gain up and down...

corerider 05-22-2012 6:08 PM


Originally Posted by BradM07SS (Post 1753601)
I set all my amps with the SMD DD1 meter. Here is link to check it out.


Well I borrowed Brad's DD-1 and it was very easy (and quiet) to setup the gains. Needless to say I was no where close to the right settings. I did have to call their tech support because I could not get the tower and in-boat amps to clip on the HU. Turns out some HU's will send a good signal all the way to the top volume range at 1kHz. My aux. input was at probably 96-98% before clipping. I feel much better at what the settings are now and hope to get a chance to get on the water to hear it again. I did notice that my subs are not nearly as loud now, but I'm hoping it's just because I didn't want to bother the neighbors.

This did lead me to another question though... When setting up the in-boat and tower speaker amps the instructions on the DD-1 say to set the cross-overs at "full range". The setup on the Syn4 when bridging a pair of Rev410's sets the cross-over at "high range". If the 410 was run on "full range" will that cause damage to the HLCD Is this why WS says to run "high range"?

CobraRob 05-22-2012 9:02 PM

What is everyone using for test tones? I have 2 o-scopes sitting in the closet so I am going to use it this time for tuning and see how that work.. Going to add a 420 so I can find max HU volume without clipping.. then WS420 gain then the amp gain that should allow for the maximum volume of clean audio.

corerider 05-23-2012 5:20 AM

The DD-1 I was using senses 40Hz for subwoofers and 1kHz for full range speakers. In some of the research I did some people were using tones as high as 8kHz.

The DD-1 tones for finding the HU clipping point were at 0dB, but the CD also had tones at -5dB, -10dB, and -15dB to set the amp gains by depending on weather you wanted sound quality, loudest possible, or a compromise.

cowwboy 05-23-2012 5:44 AM

I use a function generator app on my iphone but have used test tones in the past.

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