Defective amp?

[jmw703 10+ year member]

Ok, so i orginally posted a few weeks ago because my new system , 2 kicker cvrs and hifonics brz1200 were not playing very loud.

I ended up finding out there was a weak rca signal, i assumed it was from the head unit, i installed a pac turbo signal booster and used a multi meter to set the voltage on the speaker terminal of the amp to 40. It worked great for a few days but then i noticed the system got a whole lot quieter.

I checked the voltage output on the terminals again to find out only 25 volts were being put out by the amp at the gain setting which previously achieved 40. I assumed the signal booster stopped working so i took it back and decided to buy a new head unit, Alpine cde-123 with 3 4v outputs as opposed to the previous single 2v on my old cde-100. The problem persists, with the gain set at 4v the sub volume is very low, even at 2v+ (to achieve the 40 v output) its no louder than my previous 10 inch pioneers that were only getting 90 rms a sub from a crappy lightning audio 2 channel amp.

The amp is getting 13+v of power from the battery and the ground is secure

The Hu settings have the sub set on and SW level to +15

It is NOT the rca wiring, i switched the cheapo wire i had for RFK rca wire, there was a noticable difference but it clearly wasnt the problem

My question is, is my amp most likely the source of the problem? I got this system a few weeks ago and i havent been able to get it to work correctly, im very annoyed at this point.

EDIT: JUMP TO PAGE TWO THE AMP IS NOT THE PROBLEM.

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[Spooney 10+ year member]

Have you pulled the subs yet to check the wiring? Maybe you lost a tinsel lead or a speaker wire and your amp isn't running as low of an ohm load as it was and is now putting out less power? When you are measuring this power output are your subs hooked up?

 

[jmw703 10+ year member]

Have you pulled the subs yet to check the wiring? Maybe you lost a tinsel lead or a speaker wire and your amp isn't running as low of an ohm load as it was and is now putting out less power? When you are measuring this power output are your subs hooked up?

The subs were checked, they are in phase and wired correcly. This wouldnt explain the sudden drop in voltage at the speaker terminals.

And no the subs were disconnected when i mesasured voltage at the terminals

 

[Spooney 10+ year member]

The subs were checked, they are in phase and wired correcly. This wouldnt explain the sudden drop in voltage at the speaker terminals.
And no the subs were disconnected when i mesasured voltage at the terminals

It would explain a drop in voltage if the subs were hooked up when you were testing for voltage at the speaker terminals and they had lost a lead or connection somewhere which is why I asked. Trying to help rule some things out. Hard to be helpful when you don't know the whole picture.

 

[jmw703 10+ year member]

It would explain a drop in voltage if the subs were hooked up when you were testing for voltage at the speaker terminals and they had lost a lead or connection somewhere which is why I asked. Trying to help rule some things out. Hard to be helpful when you don't know the whole picture.

I used a voltage meter directly with the amp terminals , sub wire was disconnected, sorry if i was unclear. So this would not explain the drop.

 

[jmw703 10+ year member]

It would explain a drop in voltage if the subs were hooked up when you were testing for voltage at the speaker terminals and they had lost a lead or connection somewhere which is why I asked. Trying to help rule some things out. Hard to be helpful when you don't know the whole picture.

I used a voltage meter directly with the amp terminals , sub wire was disconnected, sorry if i was unclear. So this would not explain the drop.

 

[Spooney 10+ year member]

Is the amp mounted in a way where it would be subjected to excessive vibration? Like on a sub box or maybe not mounted down at all? Maybe internally one of the rca inputs has lost its connection and you are only getting half of the signal into the amp that you were previously?Is the output still clean just not the volume it once was? If the output is still clean I would be inclined to say the issue lies in the preamp section of your amp which could make it a cheap fix or if it is under warranty I'd just return it.

 

[jmw703 10+ year member]

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Is the amp mounted in a way where it would be subjected to excessive vibration? Like on a sub box or maybe not mounted down at all? Maybe internally one of the rca inputs has lost its connection and you are only getting half of the signal into the amp that you were previously?Is the output still clean just not the volume it once was? If the output is still clean I would be inclined to say the issue lies in the preamp section of your amp which could make it a cheap fix or if it is under warranty I'd just return it.

Yes it is mounted on top of the box and yes the signal is clear it is just VERY low with the gain set to match the HU, this was the first system i installed myself and my previous system was installed this way, i didnt know that it was bad for the amp. The amp is still under warranty so if your saying that its either defective or was damaged internally by vibration ill probably send it back and mount it elsewhere.

 

[Spooney 10+ year member]

Vibration is terrible for amps. Some amps are constructed better than others but even a little vibration over a long period of time can cause major failures. There are people that would argue this to no end with me but I have repaired my fair share of amps and have seen plenty of amps fail because of vibration. You'll see things like legs snapped off of mosfets and connections pulled completely out of the board or cracked solder joints. Not guaranteeing that is what happened here but it is a possibilty. If you are saying that its taking approximately twice the input voltage that it was previously to get to the same output and you are confident your rca's and all other wiring are good then I would be pretty confident of a failure of the amp internally and if its within warranty there is no good reason not to send it back. Have you tried plugging in just one rca plug at a time? Like try plugging in the left one and see how that works and then powering the amp down and trying the same thing with the right one? Do you find that you only get sound when you plug in the left and nothing when you plug in the right or vice versa?

 

[jmw703 10+ year member]

Vibration is terrible for amps. Some amps are constructed better than others but even a little vibration over a long period of time can cause major failures. There are people that would argue this to no end with me but I have repaired my fair share of amps and have seen plenty of amps fail because of vibration. You'll see things like legs snapped off of mosfets and connections pulled completely out of the board or cracked solder joints. Not guaranteeing that is what happened here but it is a possibilty. If you are saying that its taking approximately twice the input voltage that it was previously to get to the same output and you are confident your rca's and all other wiring are good then I would be pretty confident of a failure of the amp internally and if its within warranty there is no good reason not to send it back. Have you tried plugging in just one rca plug at a time? Like try plugging in the left one and see how that works and then powering the amp down and trying the same thing with the right one? Do you find that you only get sound when you plug in the left and nothing when you plug in the right or vice versa?

If i pull one out it cuts to half volume and vice versa.

 

[Spooney 10+ year member]

Well that would rule out the rca connection if they are both working and the output is halving when one is removed. I'd return the amp . It seems like you've done everything necessary to rule it out at this point.

 

[jmw703 10+ year member]

Well that would rule out the rca connection if they are both working and the output is halving when one is removed. I'd return the amp . It seems like you've done everything necessary to rule it out at this point.

Yeah im going to check the wiring on the subs once more before to double check. If everythings in order then it has to be the amp. Theres just nothing else it could be.

 

[jmw703 10+ year member]

i checked the sub wiring and leads, they are are fine. It must be the amp. If its not im just going to sell the whole system, im sick of this.

 

[akheathen Premium Member]

also, try cycling the amp adjustments through their range and back to where they are now (with amp off, of course) and check the output voltage again. and, just to clarify, you are checking the source voltage at the amp itself, while not playing, but on, and while on. also, the rca voltage was re-checked, too?

 

[jmw703 10+ year member]

also, try cycling the amp adjustments through their range and back to where they are now (with amp off, of course) and check the output voltage again. and, just to clarify, you are checking the source voltage at the amp itself, while not playing, but on, and while on. also, the rca voltage was re-checked, too?

Even when I set the voltage on the amp to 40 it still sounds very weak , the gain has to be set to 2 v or higher to achieve that voltage anyways when I'm using a brand new 4 v HU. Either the problem lies in the amp or something is drawing alot of voltage from my HU. I have the alpine mini amp installed on my HU , the ktp 445 if that would make a difference

I Check the voltage on the amp while the subs are disconnected playing a 50 hz tone with HU at about 3/4 volume

 

[jmw703 10+ year member]

Ok so i just hooked up my subs and amp in my friends car.. everything works..

The problem is NOT:

The head unit

the subs

the amp and all connections to the amp (power wire, ground, rmt, speaker, rca )

the rca wire.

Meaning the problem lies behind the HU in the wiring which i personally did not do (other than installing the new HU). Im starting to think the local car audio shop which installed my first system did something, because now that i think of it my old system which i bought used had to have the gain cranked in order to be very loud and this was with my old HU with a single 2v pre out. I just didnt know what to expect because the system was used and very old, not very high rms too.

I have a ktp 445 alpine mini amp wired to the HU could that in anyway draw signal or power from my HU since it has no dedicated power/ground wire of its own?

It is directly between the factory harness of my car and the HU.

Or a bad ground connection at the HU? i simply cut the previous connections from the old HU and crimped the new harness to the side of the KTP 445, the ground as well so i did not ground it myself.

Other than what i listed above what could cause this weak signal im getting, im really confused right now.

Any thoughts or suggestions would be greatly appreciated!

 

[akheathen Premium Member]

this is why i suggested taking rca voltage readings to compare. try tapping into the ground connections at both the back of the head unit, and vehicle harness connector. do the same for the main power (yellow) see if you have a voltage drop.