DiyMobileAudio.com Car Stereo Forum banner

1 - 20 of 48 Posts

·
Banned
Joined
·
2,895 Posts
Discussion Starter #1
So I just got my brand new Arm DSO nano o-scope in the mail and i was using it to test the ouputs on my MB Quart Q 4.150. The test tones i was using were provided by a frequency analyzer app for the I-phone.

I started by testing the app for clipped signal. With the HU (Pioneer DEH 690UB) set halfway (32 of 62) and the o-scope leads on the amp outputs (gains still at normal settings), I slowly turned the volume up on the frequency analyzer (160hz test tone) app up to 9 (max output) the signal showed no signs of clipping. Then i proceeded to test the HU by slowly turning the volume up with the 160hz tone playing. At 50 out of 62 i stopped to sdjust the settings on the DSO Nano so i could view the wave better. while doing this I thought I saw a flash of light in the amp. I stopped what i was doing and listened to the tone but couldnt hear any distortion whatsoever, plus the top of my amp is opaque black so I didnt know if a spark would even be visable. So I figured it was the sun light and continued. I guess I was wrong cause a minute later I heard a pop and the speakers started playing some wierd mechanical interference type noise (alot like a poor quality 2 way radio signal). I immediately turned it down and the sound went away but the front right channel sounded like it was playing a half octave higher than before, so i cut the keys.
after a minute or so i turned my truck back on and heard alot of background noise and clicking with the volume all the way down, so i tried to play some music and when I slowly turned the volume back up the music sounded normal (front right back to normal) except for the terrible background noise and clicking. All speaker seem to be working fine as well.

I never once noticed a clipped signal or drove the amp past what ive done before.

So how bad is it?
 

·
Registered
Joined
·
6,376 Posts
It all works but noises? Sounds like a ground loop issue. Check the RCA again, test the HU RCA shield for ground, check speaker wires for ground shorts to car...or test with DMM to ground on speaker wires and on RCA shields at amp. The HU should be grounding the shields to the amp, the speaker wires should not be to ground (not 0 ohms).
 

·
Registered
Joined
·
1,741 Posts
unplug the rcas at the amp if the noise goes away well then thank pioneer for not grounding the rcas right.
I had a similar episode when i went into walmart about week ago.
Walk out crank the car up and damn wtf is that pop pop pop engine rev pop fast forward a week and a kenwood no noise dead silent fu$k pioneer.
 

·
Banned
Joined
·
2,895 Posts
Discussion Starter #5
unplug the rcas at the amp if the noise goes away well then thank pioneer for not grounding the rcas right.
I had a similar episode when i went into walmart about week ago.
Walk out crank the car up and damn wtf is that pop pop pop engine rev pop fast forward a week and a kenwood no noise dead silent fu$k pioneer.
I hope it is that simple. But I doubt it's the pico fuse. I dont think blown pico fuses smell burnt. :(

Any body else?
 

·
Registered
Joined
·
6,376 Posts
If the amp smells, thats not good however they usually stop working. It might have burned a ground trace inside easy to fix usually.

If the speaker wire shorts you put a DMM on it and test to ground, you will see ~0 ohms. Most DMM are not exactly 0 just touch the leads and it should be close to that. If it shows 0 on the amp take the wires off the amp and test the wires to ground to verify. If the HU pico puked you unhook the RCA at the amp and test the shields the same way to ground but they should be grounded by the HU, you should see ~0 ohms.

A signal is useless without a reference, the amp reads the HU signal compared to HU ground. Without it is like measuring how tall you are without using the floor and freaks out the preamp. The amplifier itself has its own power supply and ground, if the speaker grounds a wire that makes two grounds and a ground loop.
 

·
Banned
Joined
·
2,895 Posts
Discussion Starter #7
If the amp smells, thats not good however they usually stop working. It might have burned a ground trace inside easy to fix usually.

If the speaker wire shorts you put a DMM on it and test to ground, you will see ~0 ohms. Most DMM are not exactly 0 just touch the leads and it should be close to that. If it shows 0 on the amp take the wires off the amp and test the wires to ground to verify. If the HU pico puked you unhook the RCA at the amp and test the shields the same way to ground but they should be grounded by the HU, you should see ~0 ohms.

A signal is useless without a reference, the amp reads the HU signal compared to HU ground. Without it is like measuring how tall you are without using the floor and freaks out the preamp. The amplifier itself has its own power supply and ground, if the speaker grounds a wire that makes two grounds and a ground loop.
If I burned a ground trace inside the amp would the be something that would cause a visible flash? I still think a may have seen a spark through the dark tinted glass top at some point.
 

·
Registered
Joined
·
12,054 Posts
sparks and flashes are never a good sign. yes a burned trace can cause a flash.

how did you have the oscope connected? just across the speaker leads on the output? was the sound really loud? like louder then you normally listen to it?
 

·
Banned
Joined
·
2,895 Posts
Discussion Starter #9
sparks and flashes are never a good sign. yes a burned trace can cause a flash.

how did you have the oscope connected? just across the speaker leads on the output? was the sound really loud? like louder then you normally listen to it?
Yes, the probes were just stuck in the speaker outputs and it wasn't the loudest ive ever had it. The distortion caused wasn't as loud either.
 

·
Registered
Joined
·
12,054 Posts
you are sure that the probe leads didnt touch?

since I wasnt there is hard to say where and why the flash happened. but since you had a flash and now the amp sounds bad. I bet you blew something on it. the weird sound could mean you only blew half the fets on the output of that channel (meaning it is still playing half the signal) if it is not under warrenty still, open it and see what you see. a flash that visible will have caused a burned spot that you should be able to see pretty easy.
 

·
Registered
Joined
·
475 Posts
A scope unlike a meter doesn’t really have leads; it has a probe. I use scopes at work but never used a scope to check the output of an amp. I would think you don’t want to go across the speaker leads. Neither of the speaker terminals are signal ground. I would assume just leave the probe ground dangling while scoping the speaker leads.

Plus if you have a scope that’s connected to AC power and now your connecting the signal ground of the probe to the amplifiers output that could spell disaster, no?:confused:
 

·
Registered
Joined
·
12,054 Posts
A scope unlike a meter doesn’t really have leads; it has a probe. I use scopes at work but never used a scope to check the output of an amp. I would think you don’t want to go across the speaker leads. Neither of the speaker terminals are signal ground. I would assume just leave the probe ground dangling while scoping the speaker leads.

Plus if you have a scope that’s connected to AC power and now your connecting the signal ground of the probe to the amplifiers output that could spell disaster, no?:confused:
leads, probes. whatever you want to call them.

the one he used is a battery powered device. you have to have a ground referance or how is the scope gonna know where to referance the measurements from? since amplifiers dont have signal ground common with power ground, you HAVE to connect the scope ground to signal ground. even an AC powered scope would work this way, since the AC would be coming from your house and the amplifier power is coming from the car. there is no common ground at all.

I know what you are talking about and it doesnt apply here. if you are probing a circuit that is plugged into AC line voltage and you have a scope powered by AC line voltage. If you put the probe ground in the circuit somewhere you will be putting earth ground at that point in the circuit. NOT something you want to do 99% of the time. you will always want to put the probe ground on the circuit ground of the circuit under test.

This is also why you dont always need to connect the probe ground if both devices are powered via the same power source (IE: ac line voltage) they already share the same ground and the probe will get it ground from the earth ground between them. (take a DMM and measure resistance between probe ground and earth ground prong on the scope)
 

·
Banned
Joined
·
2,895 Posts
Discussion Starter #13
Ok, so I just unplugged the RCAs and all the nasty noise went away immediately. That's a good sign right?

So what could've caused the flash and smell I saw/smelled? Could a failure in the amp been the cause of a blown pico fuse?
 

·
Registered
Joined
·
12,054 Posts
very well could have been. try another source. plug your mp3/phone into the amplifier and see if it is ok. if unplugging the RCAs made the sound go away, then it is either a groundloop problem (could be HU or amplifier) or the HU is fried.

next is to test the HU. get a pair pf PC speakers that are powered by battery or AC (plugged in the house) and see if the noise is there.
 

·
the darkside is loud
Joined
·
6,092 Posts
very well could have been. try another source. plug your mp3/phone into the amplifier and see if it is ok. if unplugging the RCAs made the sound go away, then it is either a groundloop problem (could be HU or amplifier) or the HU is fried.

next is to test the HU. get a pair pf PC speakers that are powered by battery or AC (plugged in the house) and see if the noise is there.
Wow Fric, it just keeps getting worse huh?
Sorry for all your trouble.
Too nice a guy to have all this crap happen.
BTW, did they warranty the subs?

Bret
PPI-ART COLLECTOR
 

·
Banned
Joined
·
2,895 Posts
Discussion Starter #18
Ok, now I've hooked my iPhone directly to the amp and everything sounds normal minus the processing that my HU provided.

Could I assume I'm in the clear as far as my amp is concerned or is could my amp have incurred some damage that isn't apparent?
 

·
Registered
Joined
·
12,054 Posts
Ok, now I've hooked my iPhone directly to the amp and everything sounds normal minus the processing that my HU provided.

Could I assume I'm in the clear as far as my amp is concerned or is could my amp have incurred some damage that isn't apparent?
it could still have damage, but if it sound ok, prolly not. then next test is for the HU. if you have another amp, or the PC speaker test, I would try that and make sure the HU is ok. I suspect that the HU is causing it.

hard to know what that spark was, that still has me concerned.
 

·
Registered
Joined
·
17,149 Posts
It's important to add that IF using a AC powered scope.... that on most amplifiers the (-) is the driven leg on 50% of the outputs. The signal polarity is just inverted internally to facilitate easier bridging.

For example if the amp outputs look like this + - + - and you bridge to one + and one - then one of those -'s aint "ground," it's driven.
 
1 - 20 of 48 Posts
Top