Correct way to set gain with DMM?

[retrojordans 10+ year member]

Do not use a DMM and voltage + that useless formula to set anything..

An amp's gains adjust where the amp reaches it's full power on the head unit's volume scale. If the head unit clips @ 40 don't turn it above 38? Set your amp to reach it's full power @ 38 using the gain knob.

To do this you will need an oscilloscope. Turn the radio to volume 40 (forbidden zone) and run a tone. Put the scope on the amp and adjust the gain until the amp just starts to clip (At volume 40) Then don't turn it up past 40 because at 40 it clips at that tone.

Now repeat that on every frequency to avoid clipping on any frequency.

That formula is total garbage because a sub can ricochet back and forth from .5 ohm to 100 ohms in seconds..And a DMM doesn't show anything but voltage..

To use a *true RMS DMM* and that formula to test an amp's wattage you'd need to attach a "x ohm" resistor to the amp and run a series of tones. A resistor's ohm load doesn't fluctuate like a speaker does for example by: coil temperature, box rise, humidity, vehicle dimensions, etc.. But if the speaker is going to fluctuate why would you use that number? lol..the whole situation is useless.

Oscilloscope.

Amazon.com: Hand Held Digital Oscilloscope-40MHz: Electronics

 

[VWBobby 10+ year member]

I agree that the sub/speaker changes ohm load constantly, but its not as extreme as you say. People in SPL and SQ competitions set their amps with a DMM on a daily basis.... Its the only sure way to set your gains or final power to your subs (if overpowering).

Otherwise an oscilloscope is still the best way.

 

[Heeltoeclutch 10+ year member]

If I could begin to afford a scope... I'd be all over one. I'd sleep with it under my pillow every night and it would have a name.

thanks for your help retro.

I didn't think this thread was going to return - I was at a presentation when it was deleted. thanks for the undelete mike. though I still don't know what was said. //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif whatever.

 

[JuicyJeff 10+ year member]

I set my lpf ~100 hz, but this is just to set what frequencies to send to your subs. You wouldnt want to have it down though and set your gain bc your amp wouldnt be sending out that 50 hz tone that you're using to set it with so it would be quite pointless.

I tuned like that and my subs barely move. The amp is rated for 1500 Watts and I hacmve two sa8s. I can't get these baby's to move unless I Jack the gain up

 

[Chriszle 10+ year member]

I agree that the sub/speaker changes ohm load constantly, but its not as extreme as you say. People in SPL and SQ competitions set their amps with a DMM on a daily basis.... Its the only sure way to set your gains or final power to your subs (if overpowering). Otherwise an oscilloscope is still the best way.

People in SPL competitions use a clamp to measure current along with a dmm for the voltage in order to compete within certain classes. Without the clamp, the DMM is useless.

 

[Heeltoeclutch 10+ year member]

I actually have a clamp in Cali //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif perhaps ill look into getting one here.

This is a pretty surefire way to measure power, eh? this seems to be the best option considering money.