I recently installed a component set and a old school kenwood amplifier. The sound from the speakers fades in and out, and produces static from any little bump. So I tried installing another amp and the power and protection light would blink with the same sound effects. Is this a bad ground?
Replies (8)
MrBrownstone on 03/7/2006 13:51:32
You probably have a couple of loose wires or something. Tell us a little more about your installation, and the rest of the system.
It is possible that the amp has a problem with it, but usually amps either work, or they don't...and if there's a problem, they usually quit working fairly quickly.
swez on 03/7/2006 22:16:04
Agreed! Check all wiring connections and make sure you have a solid ground to bare metalk for the amp.
Swez
JAYSQ on 03/8/2006 12:25:50
96 HONDA PRELUDE . RIGHT NOW ITS A BASIC INSTALLATION. hEAD UNIT , ONE TWO CHANNEL AMP, COMPONENT SET IN THE DOORS , AND COAXIALS IN THE REAR DECK. I CHANGED OUT THE RCA PLUGS AND THE SOUND IMPROVED , BUT IT STILL GETS A LITTLE STATIC HERE AND THERE. I THINK THE RCA INPUTS ON THE AMP ARE GOING BAD. I RE-DID THE GROUND WIRE AND BOLTED IT DOWN TO BARE METAL. I ALSO AM GETTING ENGINE NOISE AT LOW VOLUMES.
swez on 03/8/2006 13:02:37
CAPS = shouting... No need to shout.
Have you also tried grounding the HU to bare metal on either the floor pan or firewall?
Amp may have "loose RCA's" (Are they tightly secured, or wiggle a bit?) as inputs and losing the needed ground to amp chassis. If this is an older amp, rather common and if you are handy with a soldering pencil, 60/40 solder and get brite, shiney joints when finished, that would be the likely fix.
Also, clean the RCA input outer sleeves with a clean pencil erasure. This is a mild abrasive and is good enough to remove any oxides (rust) that may be on them. (We may not always see the oxides, but they do develope normally with age and use)
Finally, be sure the amp gains are matched to HU output voltage. (Ie: If the HU is rated at 2.0 volts output, set amp gains at 2.0 volts too)
Swez
JAYSQ on 03/8/2006 14:07:26
thanks Swez, sorry about the caps. The HU is grounded to metal. The amp's RCA's do wiggle a bit, and seem loose. All of the connections at the HU are ok and, it has 4.0 volt preouts. The amp gain is set at 3.5 volts. I also noticed that when a turn the gain knob it produces static also. The amp in question is a Kenwood KAC-921 which power wise matches up perfectly with the rms wattage of the component set at 100x2 at 4ohms.
swez on 03/8/2006 17:58:48
Noisy pots can be cleaned and de-gunked with a small shot of WD-40. Do this on a workbench with no power connected to the amp.
To get to the gain pot, you'll need to remove the amps outer cover, to get a good shot into the pot internal wiper and resistive pathway. Just a little shot will do, then work the pot back and forth a few passes in both directions for about 30 seconds. That should clean things nice. (WD-40 will not damage the pot, surrounding board or localized components)
Now, while you have the covers off, have a close look at the RCA jacks and how they are mounted on the PC board. If they wiggle at the board, (where the feet go into the PC board) the solder joint has been compromised. Here, the board may need to be removed from the casing enough to get a soldering tip in there to re-solder the joints.
The board is usually fastened to the lower casing with a number of small screws. Most of the main wiring harnesses have disconnect sockets if they need to be removed. (Make a sketch of what wires go where on the board, if they need to be removed before soldering)
Now, lift the board out of the lower casing enough to gain access to the location where the RCA's are soldered into it. You see at least 4 pins coming through the board, that attach to eyelits and copper tracings. If the pins are loose, (Like a wobbly tooth) they need to be re-soldered back into the board. A 25 watt soldering pencil should give enough heat to get the job done.
Here's what ya need for tools:
1. 25 watt soldering pencil
2. 60/40, rosin core solder (1/8" dia or smaller is great for this job)
3. Solder wick braiding (a small spool of flat, fine braided copper wire, will wick up the old solder when heated on the joints)
4. A wet paper towel (cleans the solder tip when it gums up)
5. A bright work light and a 10X magnifying glass (now you can see what old and fresh joints look like)
6. A small pair of needle nose pliers, forecepts or tweezers (may be helpful to keep things from getting to hot on the fingers)
7. An old toothbrush and some IPA (rubbing alcohol) to clean the yellowish residue (old fluxing agent) off the board as needed
That's the skinny on what is needed, how to do it and make effective repairs on your own. If you wish a soldering primer before tackling this one, have a look at this link:
http://www.bcae1.com/solder.htm
NOTE: We are shooting for bright, shiney joints after soldering is done. If grainy or grayish, it's a cold solder joint and needs to be re-heated.
Tips:
a. When soldering, we allow the pencil to heat up to operating temperature, apply fresh solder to the tip and wipe off excess with the wet paper towel. This is called "tinning" the solder tip. A soldering pencil works best with a pre-tinned tip as the tinning provides excellent heat transferto the board and components to be soldered.
b. For best results, we apply heat to the the component until the old solder is molten, then add fresh solder until it melts and flows a bit. Then, remove heat and allow the joint to cool to a nice shiney silvery look. (the whole process takes less than 30 seconds between contact of pencil to board) Much more then that and we risk overheating the joint and get a poor job)
Finally, inspect the joints after soldering so there are no soldering bridges (shorts) between each connecting pad. That's where the bright lamp and magnifying glass come in handy. If you see clean, round humps of fresh solder on each pad, you have done very well.
Ready to try it?
Swez
PS Radio Shack or WalMart should have everything needed for this little repair job. Under $15.00 for all materials noted.
Victor on 03/8/2006 18:10:10
That is a very explanatory and useful procedure swez suggested...
But before opening up the amp, can u just set the gain at 4 volts or even 4.5 volts and see the difference..It should ideally reduce a lot of unwanted noise.
Victor..
P.s . You have set the gains at 3.5v where as the Hu gives out 4v.
This higher sensitivity setting on the amp also works a lot on picking up static, alternator whine and a lot of unwanted noise.
Ideally the gains on an amp should be set at exactly the same volgate as the Output of the HU.
Most people mistake the gain setting as the volume setting, and in the process to make it louder they add loads of distortion to the sound. It could be that u have tried doing it, but whats the harm in trying it out again.
swez on 03/8/2006 20:21:07
If the amp gain was set on 2.0 volts and the HU output reaches ~2.25 volts or higher, (when you dial up the volume) the HU will drive the amp into much distortion and clipping mode. This level of sensitivity settings can also pick up engine and electrical noise as mentioned by Victor.
However, since your amp gain setting is very close to 4.0 volts and the HU is able to supply 4 volts, (at ~80% full volume) amp distortion should be minimal here.
I think your biggest problem may be the loose RCA's. If the grounds are loose or not well connected to the amp circuit board, humming and other strange noises are likely. That means a repair job, inside the amp as noted earlier.
Swez
Replies (8)
MrBrownstone on 03/7/2006 13:51:32
You probably have a couple of loose wires or something. Tell us a little more about your installation, and the rest of the system.
It is possible that the amp has a problem with it, but usually amps either work, or they don't...and if there's a problem, they usually quit working fairly quickly.
swez on 03/7/2006 22:16:04
Agreed! Check all wiring connections and make sure you have a solid ground to bare metalk for the amp.
Swez
JAYSQ on 03/8/2006 12:25:50
96 HONDA PRELUDE . RIGHT NOW ITS A BASIC INSTALLATION. hEAD UNIT , ONE TWO CHANNEL AMP, COMPONENT SET IN THE DOORS , AND COAXIALS IN THE REAR DECK. I CHANGED OUT THE RCA PLUGS AND THE SOUND IMPROVED , BUT IT STILL GETS A LITTLE STATIC HERE AND THERE. I THINK THE RCA INPUTS ON THE AMP ARE GOING BAD. I RE-DID THE GROUND WIRE AND BOLTED IT DOWN TO BARE METAL. I ALSO AM GETTING ENGINE NOISE AT LOW VOLUMES.
swez on 03/8/2006 13:02:37
CAPS = shouting... No need to shout.
Have you also tried grounding the HU to bare metal on either the floor pan or firewall?
Amp may have "loose RCA's" (Are they tightly secured, or wiggle a bit?) as inputs and losing the needed ground to amp chassis. If this is an older amp, rather common and if you are handy with a soldering pencil, 60/40 solder and get brite, shiney joints when finished, that would be the likely fix.
Also, clean the RCA input outer sleeves with a clean pencil erasure. This is a mild abrasive and is good enough to remove any oxides (rust) that may be on them. (We may not always see the oxides, but they do develope normally with age and use)
Finally, be sure the amp gains are matched to HU output voltage. (Ie: If the HU is rated at 2.0 volts output, set amp gains at 2.0 volts too)
Swez
JAYSQ on 03/8/2006 14:07:26
thanks Swez, sorry about the caps. The HU is grounded to metal. The amp's RCA's do wiggle a bit, and seem loose. All of the connections at the HU are ok and, it has 4.0 volt preouts. The amp gain is set at 3.5 volts. I also noticed that when a turn the gain knob it produces static also. The amp in question is a Kenwood KAC-921 which power wise matches up perfectly with the rms wattage of the component set at 100x2 at 4ohms.
swez on 03/8/2006 17:58:48
Noisy pots can be cleaned and de-gunked with a small shot of WD-40. Do this on a workbench with no power connected to the amp.
To get to the gain pot, you'll need to remove the amps outer cover, to get a good shot into the pot internal wiper and resistive pathway. Just a little shot will do, then work the pot back and forth a few passes in both directions for about 30 seconds. That should clean things nice. (WD-40 will not damage the pot, surrounding board or localized components)
Now, while you have the covers off, have a close look at the RCA jacks and how they are mounted on the PC board. If they wiggle at the board, (where the feet go into the PC board) the solder joint has been compromised. Here, the board may need to be removed from the casing enough to get a soldering tip in there to re-solder the joints.
The board is usually fastened to the lower casing with a number of small screws. Most of the main wiring harnesses have disconnect sockets if they need to be removed. (Make a sketch of what wires go where on the board, if they need to be removed before soldering)
Now, lift the board out of the lower casing enough to gain access to the location where the RCA's are soldered into it. You see at least 4 pins coming through the board, that attach to eyelits and copper tracings. If the pins are loose, (Like a wobbly tooth) they need to be re-soldered back into the board. A 25 watt soldering pencil should give enough heat to get the job done.
Here's what ya need for tools:
1. 25 watt soldering pencil
2. 60/40, rosin core solder (1/8" dia or smaller is great for this job)
3. Solder wick braiding (a small spool of flat, fine braided copper wire, will wick up the old solder when heated on the joints)
4. A wet paper towel (cleans the solder tip when it gums up)
5. A bright work light and a 10X magnifying glass (now you can see what old and fresh joints look like)
6. A small pair of needle nose pliers, forecepts or tweezers (may be helpful to keep things from getting to hot on the fingers)
7. An old toothbrush and some IPA (rubbing alcohol) to clean the yellowish residue (old fluxing agent) off the board as needed
That's the skinny on what is needed, how to do it and make effective repairs on your own. If you wish a soldering primer before tackling this one, have a look at this link:
http://www.bcae1.com/solder.htm
NOTE: We are shooting for bright, shiney joints after soldering is done. If grainy or grayish, it's a cold solder joint and needs to be re-heated.
Tips:
a. When soldering, we allow the pencil to heat up to operating temperature, apply fresh solder to the tip and wipe off excess with the wet paper towel. This is called "tinning" the solder tip. A soldering pencil works best with a pre-tinned tip as the tinning provides excellent heat transferto the board and components to be soldered.
b. For best results, we apply heat to the the component until the old solder is molten, then add fresh solder until it melts and flows a bit. Then, remove heat and allow the joint to cool to a nice shiney silvery look. (the whole process takes less than 30 seconds between contact of pencil to board) Much more then that and we risk overheating the joint and get a poor job)
Finally, inspect the joints after soldering so there are no soldering bridges (shorts) between each connecting pad. That's where the bright lamp and magnifying glass come in handy. If you see clean, round humps of fresh solder on each pad, you have done very well.
Ready to try it?
Swez
PS Radio Shack or WalMart should have everything needed for this little repair job. Under $15.00 for all materials noted.
Victor on 03/8/2006 18:10:10
That is a very explanatory and useful procedure swez suggested...
But before opening up the amp, can u just set the gain at 4 volts or even 4.5 volts and see the difference..It should ideally reduce a lot of unwanted noise.
Victor..
P.s . You have set the gains at 3.5v where as the Hu gives out 4v.
This higher sensitivity setting on the amp also works a lot on picking up static, alternator whine and a lot of unwanted noise.
Ideally the gains on an amp should be set at exactly the same volgate as the Output of the HU.
Most people mistake the gain setting as the volume setting, and in the process to make it louder they add loads of distortion to the sound. It could be that u have tried doing it, but whats the harm in trying it out again.
swez on 03/8/2006 20:21:07
If the amp gain was set on 2.0 volts and the HU output reaches ~2.25 volts or higher, (when you dial up the volume) the HU will drive the amp into much distortion and clipping mode. This level of sensitivity settings can also pick up engine and electrical noise as mentioned by Victor.
However, since your amp gain setting is very close to 4.0 volts and the HU is able to supply 4 volts, (at ~80% full volume) amp distortion should be minimal here.
I think your biggest problem may be the loose RCA's. If the grounds are loose or not well connected to the amp circuit board, humming and other strange noises are likely. That means a repair job, inside the amp as noted earlier.
Swez
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