Unstable voltage at speaker output terminals

[JoshuaKNelson]

I try to set the gain on my amplifier using a multimeter and a 40Hz tone only to have the voltage bounce all over the place. This has happened with 2 amplifiers in a row that were brand new and never hooked up to the subwoofers. I hooked up the power and ground wires, the remote wire and the rca cables. Then hooked up a multimeter to the speaker output on DC volts setting. Played a 40Hz tone off my usb at almost full volume with my bass knob all the way up. I'm using a 3000 watt amplifier that will be running at .5 ohms. So the target voltage when you take the square root of watts times ohms is about 37 volts. I start to slowly increase the gain and all it does is bounce from .2 to
.4 then back down to .1 then back up, etc. Not stable like it should be. The ac voltage on my rca cables going into the amp is stable at 2.5 volts. Not bouncing. My alternators voltage is 14.3. My batteries both hold a charge. All my grounds read 0 resistance to .1 on the ohms setting. Everything is normal. If I continue to increase the gain it will bounce from positive numbers and down into negative numbers then the amp will go into protect. I have no idea what is causing this problem. My setup has worked flawlessly for 2 years and now I can't set the gain or come anywhere near the voltage I need to set it too on any amplifier. This isn't my first install. Ive been doing it for over 20 years and have never encountered this issue. What could possibly be wrong? THANKS.

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[CarAudio.com - Hal AI Bots]

I try to set the gain on my amplifier using a multimeter and a 40Hz tone only to have the voltage bounce all over the place. This has happened with 2 amplifiers in a row that were brand new and never hooked up to the subwoofers. I hooked up the power and ground wires, the remote wire and the rca cables. Then hooked up a multimeter to the speaker output on DC volts setting. Played a 40Hz tone off my usb at almost full volume with my bass knob all the way up. I'm using a 3000 watt amplifier that will be running at .5 ohms. So the target voltage when you take the square root of watts times ohms is about 37 volts. I start to slowly increase the gain and all it does is bounce from .2 to
.4 then back down to .1 then back up, etc. Not stable like it should be. The ac voltage on my rca cables going into the amp is stable at 2.5 volts. Not bouncing. My alternators voltage is 14.3. My batteries both hold a charge. All my grounds read 0 resistance to .1 on the ohms setting. Everything is normal. If I continue to increase the gain it will bounce from positive numbers and down into negative numbers then the amp will go into protect. I have no idea what is causing this problem. My setup has worked flawlessly for 2 years and now I can't set the gain or come anywhere near the voltage I need to set it too on any amplifier. This isn't my first install. Ive been doing it for over 20 years and have never encountered this issue. What could possibly be wrong? THANKS.

It sounds like you're encountering a frustrating issue with your gain setting process. Let's go over some possible causes for the instability you’re experiencing when trying to adjust the gain on your amplifiers.

1. Incorrect Multimeter Setting: Make sure you are using the correct measurement mode on your multimeter. It should be set to measure AC voltage when you're checking the output from the amplifier, even if you’re using the DC voltage setting initially to measure speaker output. This can sometimes cause confusion.

2. Amplifier Configuration: Check the internal settings of your amplifiers, including the crossover settings. If the amplifier has a built-in low-pass filter that’s incorrectly set, it might be cutting the frequency range that's causing the bouncing measurement.

3. Subwoofer Load: Since you're running at .5 ohms, make sure that your subwoofers are properly wired. An incorrect configuration can cause the amplifier to go into protection mode, which might also lead to fluctuating voltages. Ensure that the impedance is what you expect when measured directly.

4. Faulty RCA Connections: While you mentioned that the RCA cables going into the amplifier are stable, double-check the connections at both ends for any damage or poor connections. Sometimes a loose or damaged RCA connector can cause instability.

5. Grounding Issues: You've tested the ground and it appears to be good, but sometimes grounding can be tricky. Make sure that the ground point is solid and clean. Also, recheck the connections where the amp is grounded — if you're using multiple amplifiers, ensure they share a common ground point to avoid ground loop issues.

6. Power Supply Issues: If you have two batteries, confirm that they are properly connected, and ensure that there are no loose connections or damaged cables. An inverter or any device that isn't delivering a stable voltage can also cause erratic readings.

7. Amplifier Health: Given that you have two new amplifiers facing similar issues, it’s unlikely to be a coincidence. But it could indicate a more systemic issue in the installation rather than just the amplifiers themselves. If possible, try another known good amplifier to see if it operates correctly.

8. Use of a Test Tone: Ensure that your 40Hz test tone is a clean signal. Sometimes, distortion in the signal itself can cause unexpected behavior in amplifiers.

9. Check for Load: Since you’re checking voltages without the subwoofer connected, try connecting your subwoofer and then check the voltage output. The load can sometimes stabilize the output voltage during gain setting.

If you've gone through all the above suggestions and the problem persists, you might want to consider having a professional look at the system, as there might be an underlying issue that requires hands-on troubleshooting.

Keep in mind that since you're familiar with installations, slight wiring faults might occasionally slip past the notice. Ensure all is to spec as per the user manual of your amp and subs.

If anyone else has insights or similar experiences, please chime in!

 

[Jimi77 Premium Member]

Is the meter set to the correct range? Do you have dummy loads? If not use the subs as a load and see if voltage stabilizes.

 

[JoshuaKNelson]

Is the meter set to the correct range? Do you have dummy loads? If not use the subs as a load and see if voltage stabilizes.

Thank you for the reply. I did have the multimeter on the incorrect setting. It works much better that way. Have a good one

 

[JoshuaKNelson]

It sounds like you're encountering a frustrating issue with your gain setting process. Let's go over some possible causes for the instability you’re experiencing when trying to adjust the gain on your amplifiers.

1. Incorrect Multimeter Setting: Make sure you are using the correct measurement mode on your multimeter. It should be set to measure AC voltage when you're checking the output from the amplifier, even if you’re using the DC voltage setting initially to measure speaker output. This can sometimes cause confusion.

2. Amplifier Configuration: Check the internal settings of your amplifiers, including the crossover settings. If the amplifier has a built-in low-pass filter that’s incorrectly set, it might be cutting the frequency range that's causing the bouncing measurement.

3. Subwoofer Load: Since you're running at .5 ohms, make sure that your subwoofers are properly wired. An incorrect configuration can cause the amplifier to go into protection mode, which might also lead to fluctuating voltages. Ensure that the impedance is what you expect when measured directly.

4. Faulty RCA Connections: While you mentioned that the RCA cables going into the amplifier are stable, double-check the connections at both ends for any damage or poor connections. Sometimes a loose or damaged RCA connector can cause instability.

5. Grounding Issues: You've tested the ground and it appears to be good, but sometimes grounding can be tricky. Make sure that the ground point is solid and clean. Also, recheck the connections where the amp is grounded — if you're using multiple amplifiers, ensure they share a common ground point to avoid ground loop issues.

6. Power Supply Issues: If you have two batteries, confirm that they are properly connected, and ensure that there are no loose connections or damaged cables. An inverter or any device that isn't delivering a stable voltage can also cause erratic readings.

7. Amplifier Health: Given that you have two new amplifiers facing similar issues, it’s unlikely to be a coincidence. But it could indicate a more systemic issue in the installation rather than just the amplifiers themselves. If possible, try another known good amplifier to see if it operates correctly.

8. Use of a Test Tone: Ensure that your 40Hz test tone is a clean signal. Sometimes, distortion in the signal itself can cause unexpected behavior in amplifiers.

9. Check for Load: Since you’re checking voltages without the subwoofer connected, try connecting your subwoofer and then check the voltage output. The load can sometimes stabilize the output voltage during gain setting.

If you've gone through all the above suggestions and the problem persists, you might want to consider having a professional look at the system, as there might be an underlying issue that requires hands-on troubleshooting.

Keep in mind that since you're familiar with installations, slight wiring faults might occasionally slip past the notice. Ensure all is to spec as per the user manual of your amp and subs.

If anyone else has insights or similar experiences, please chime in!

Thanks for the reply. I did have the multimeter on the wrong setting. I appreciate the response.

 

[Jimi77 Premium Member]

Thank you for the reply. I did have the multimeter on the incorrect setting. It works much better that way. Have a good one

Ask me why I suspected that???