Setting amp gain with multimeter - load or no load???

[momofx 10+ year member]

I searched and was unable to find a definate answer so I thought I would ask and hope someone who has done this and know for sure which method works, can chime in.

When setting the gain on the bass amp, does it make a difference if the subwoofers are still connected or not? I always thought that presenting a no-load condition to the amp would result in a false, high voltage reading on the dmm when setting the gain??

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[momofx 10+ year member]

LOL guess I will have to try for myself and find out and then come update this thread so it might help someone else later on //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[richericks 10+ year member]

I've never use a load with a DMM. O-scope on the other hand...

 

[goingdef 10+ year member]

LOL guess I will have to try for myself and find out and then come update this thread so it might help someone else later on //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

you do it with NO LOAD on the amp if you where to leave the sub/speaker hooked up impedance rise will play a role in how your setting it causing you to push a clipped signal to get past rise, so follow the directions unhook all speakers insert test leads into the speaker outputs and set the thing right the first time.

 

---------- Post added at 05:28 PM ---------- Previous post was at 05:27 PM ----------

 

I've never use a load with a DMM. O-scope on the other hand...

yep but with a scope you can visibly see the musical wave a DMM will not give you that option.

 

[momofx 10+ year member]

Thanks goingdef for resolving my dilemma - wish I did have a scope but then again my amp is about 400wrms more than what my subs can handle. So I am thinking as long as the input signal is clean, I can set the ac voltage for a bit less than what the amp max out at and not worry about clipping...

 

[maylar 10+ year member]

Set the output for what the subs are rated for, not what the amp is capable of. Since you have that much headroom the signal "should" be clean.

It's definitely better to have a load on the amp, but it should be a resistive load not subs. Having the subs connected with a continuous sine wave would destroy them. I use power resistors mounted to a heatsink and dunked in cold water.

 

[zako 10+ year member]

A sine wave should not destroy subs, not with wattage at equal or below their rated continuous power rating assuming the subwoofer is in a correct box, with subsonic filter enabled when necessary. If the sub is destroyed, it sub should be returned and you should ask for your money back. In any case, I don't connect load for DMM reading either ..

 

[momofx 10+ year member]

Ok let me do a test with and without the sub load and see what difference there is. I am using a Fluke true rms meter so its accurate I assume. I will be back later with results...

 

[maylar 10+ year member]

A sine wave should not destroy subs, not with wattage at equal or below their rated continuous power rating assuming the subwoofer is in a correct box, with subsonic filter enabled when necessary. If the sub is destroyed, it sub should be returned and you should ask for your money back. In any case, I don't connect load for DMM reading either ..

You have to consider cooling. The spec limit on subs is usually thermal. Prolonged operation at rated power and 100% duty cycle (sine wave) is a bad idea.

 

[AwesomeStranger 10+ year member]

Set the output for what the subs are rated for, not what the amp is capable of.

Why would you do this vs. setting what the amp is capable of?

 

[momofx 10+ year member]

Ok guys I did a small test with an old 12" 300wrms 4ohm Hifonics sub I have laying around together with a 50Hz 0dB sine wave from Bass Mekaniks CD, (head unit volume was well below half so no distortion / clipped input) and honestly there is BARELY any difference with and without the amp having a load. Here are the pics to prove the results //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

This is without the sub connected :

This is WITH the sub connected (0.04 AC drop - not even really worth worrying about!) :

Think I have found my answer //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Besides annoying the neighbors and risk of destroying the sub plus shaking stuff off the shelves in my garage lol, I think using the dmm method with no load, IS OK in my book!

 

[maylar 10+ year member]

Why would you do this vs. setting what the amp is capable of?

If I read correctly, he has 400 watts more than the subs can handle.

 

[maylar 10+ year member]

Think I have found my answer //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Besides annoying the neighbors and risk of destroying the sub, I think using the dmm method with no load, IS OK in my book!

In your case I would agree. Where it really matters is when you're trying to push every watt possible from the amp. You'll find that an amp will clip under load at a lower output than without. But you'd need a 'scope to see that, not a DMM.

 

[momofx 10+ year member]

Why would you do this vs. setting what the amp is capable of?

Because if you have a 3000w rms amp (real rating / cea) and your sub is rated at 2000w rms continuous then you probably want the gain lower than the amps max output unless you want to blow the sub OR if you are doing spl burps and know your sub can handle higher wattage burps.

 

[goingdef 10+ year member]

overpowering has never led me to damage a driver, atm I have two 12"s rated at 600rms each but there seeing 900+ and sound great, the only time I have ruined drivers is when I tried to run an amp that was matched as far as output and then tried to drive it harder causing the signal to clip and the voice coils to go thermal but this was my own fault obviously.