My DMM is possessed !! was: How to measure a pr
Discussion
Hi all,
I am back to ground zero, no pun intended as I actually wish this were the case
.
Using my Fluke DMM set at it's lowest resistance setting, I get a reading of 0.03 Ohms at the grounding point for my stereo/amp ground distribution, but when I turn the ignition key to ACC, the reading jumps to 1.5 Ohms. Further, when I turn on the HU/Amp, the reading jumps higher still to 4.5 Ohms. Checking resistance at the negative battery terminal to engine block, I get a reading of 1.5 Ohms.
I think I know the answer, but rather than prejudice yours, I'll wait for your replies. Hope you can get me grounded. My new Nakamichi seems very sensitive to a proper ground, much more so than my previous Alpine unit. TIA!
Happy Motoring! ...Jim'85TE
I am back to ground zero, no pun intended as I actually wish this were the case
. Using my Fluke DMM set at it's lowest resistance setting, I get a reading of 0.03 Ohms at the grounding point for my stereo/amp ground distribution, but when I turn the ignition key to ACC, the reading jumps to 1.5 Ohms. Further, when I turn on the HU/Amp, the reading jumps higher still to 4.5 Ohms. Checking resistance at the negative battery terminal to engine block, I get a reading of 1.5 Ohms.
I think I know the answer, but rather than prejudice yours, I'll wait for your replies. Hope you can get me grounded. My new Nakamichi seems very sensitive to a proper ground, much more so than my previous Alpine unit. TIA!
Happy Motoring! ...Jim'85TE
Trying to measure resistance while applying load will corrupt your readings.
To check under load use the voltage setting. For example to check the earth battery terminal to chassis measure the voltage between these two points. Should be zero.
There should be ideally 12V across any load you have. To determine any loss measure from +ve terminal to +ve side of load and -ve terminal to -ve side of load. Any reading will show where the poor connection is.
Many years of owning old Italian cars has given me much practice
Graeme
To check under load use the voltage setting. For example to check the earth battery terminal to chassis measure the voltage between these two points. Should be zero.
There should be ideally 12V across any load you have. To determine any loss measure from +ve terminal to +ve side of load and -ve terminal to -ve side of load. Any reading will show where the poor connection is.
Many years of owning old Italian cars has given me much practice
Graeme
Hi Jim,
Graeme is correct about the presence of voltage in a circuit where voltage and/or current is present since the DMM applies a voltage across it's leads to determine resistance, and a live circuit will interfere with it. Ideally, measure resistance in a circuit without any voltage or current.
Try taking the measurements with the battery disconnected, and let me know what your meter reads along with the test points in the circuit you are measuring across(I wasn't sure what you're other test point was when you got the 0.03ohms).
Try measuring the voltage across the HU and amp as close as possible to the equipment while you're listening to something, and then go back to the battery and measure the voltage across it's terminals for comparison. If they're not pretty close then there's a high resistance somewhere in the circuit. First check the voltage (with the stereo still on) between your ground distribution and the negative terminal of the battery to see if that's where the voltage drop is coming from. If that's where the loss is, then the problem is in the ground circuit. If the voltage drop in the ground circuit is not enough to account for the loss, then measure from the positive terminal of the battery and the positive lead of the HU and amp to see if that's the portion of the circuit where you're losing it.
I can think of a couple of scenarios that might be the source of your trouble:
1) Some of the wiring to the HU/amp are of too small a gauge for the current demands (I'm assuming that the amp was just added to the setup creating more current draw than your Alpine HU did), or
2) There is a bad connection in the circuit that, while under load, will warm up causing an increase in resistance and a corresponding voltage drop across it.
regards,
Bill
'95 S4S
Graeme is correct about the presence of voltage in a circuit where voltage and/or current is present since the DMM applies a voltage across it's leads to determine resistance, and a live circuit will interfere with it. Ideally, measure resistance in a circuit without any voltage or current.
Try taking the measurements with the battery disconnected, and let me know what your meter reads along with the test points in the circuit you are measuring across(I wasn't sure what you're other test point was when you got the 0.03ohms).
Try measuring the voltage across the HU and amp as close as possible to the equipment while you're listening to something, and then go back to the battery and measure the voltage across it's terminals for comparison. If they're not pretty close then there's a high resistance somewhere in the circuit. First check the voltage (with the stereo still on) between your ground distribution and the negative terminal of the battery to see if that's where the voltage drop is coming from. If that's where the loss is, then the problem is in the ground circuit. If the voltage drop in the ground circuit is not enough to account for the loss, then measure from the positive terminal of the battery and the positive lead of the HU and amp to see if that's the portion of the circuit where you're losing it.
I can think of a couple of scenarios that might be the source of your trouble:
1) Some of the wiring to the HU/amp are of too small a gauge for the current demands (I'm assuming that the amp was just added to the setup creating more current draw than your Alpine HU did), or
2) There is a bad connection in the circuit that, while under load, will warm up causing an increase in resistance and a corresponding voltage drop across it.
regards,
Bill
'95 S4S
Bill, Graeme,
Thanks for the primer. So far as the wiring is concerned, the Amp (100WX4 Nak PA-1004)is wired straight to the battery using 4AWG 0² Free insulated copper cable. The HU is wired into the stock wiring harness as was the Alpine (which made zero noise). Both units are grounded to a Ground Distribution block which is grounded via 4AWG to the chassis using the seatbelt attachment bolt. Ground wire to each unit is provided via 8AWG 0² Free insulated copper cable (direct to the Amp, but stepped down through the 14AWG ground wire in the HU's connecting harness). All connectors are quality gold plate crimp rings.
I do not get any alternator whine or ignition noise, just an annoying background hiss even with the HU internal Amp shut off and when the unit is set to Aux input (there is no Aux unit attached), but the hiss comes on when turning the volume from '0' to '1'. It stays constant until the unit is turned up past '50' on a scale of '60', when a slight antenna 'leakage' also occurs (antenna is well grounded and checks out on DMM).
Output voltage is 4+volts and the hiss intensifies with an increase in the gain level at the AMP, which is set so low to minimize the hiss as to alter the presence of the speakers (all Quart). The signal is carried via double insulated, gold plate Monster XT RCA interconnects and 14AWG 0² Free insulated copper Monster XT cable. All signal wire is routed well away from any power wires (a real feat in an Esprit believe me!)
This is very frustrating, I even returned my original Nakamichi HU thinking I had exhausted all possibilities save a defect in the unit itself which Nakamichi gladly and promptly exchanged, but the new one has the same issue. I did see some improvement when I removed the (-) battery cable ground and filed it clean and degreased the chassis, but not enough improvement to get all the sound Nakamichi is famous for. I have never had any electrical issues with the car whatsoever. I just hope I can locate it and reassemble my interior before the snow flies.
Happy Motoring! ...Jim'85TE
Thanks for the primer. So far as the wiring is concerned, the Amp (100WX4 Nak PA-1004)is wired straight to the battery using 4AWG 0² Free insulated copper cable. The HU is wired into the stock wiring harness as was the Alpine (which made zero noise). Both units are grounded to a Ground Distribution block which is grounded via 4AWG to the chassis using the seatbelt attachment bolt. Ground wire to each unit is provided via 8AWG 0² Free insulated copper cable (direct to the Amp, but stepped down through the 14AWG ground wire in the HU's connecting harness). All connectors are quality gold plate crimp rings.
I do not get any alternator whine or ignition noise, just an annoying background hiss even with the HU internal Amp shut off and when the unit is set to Aux input (there is no Aux unit attached), but the hiss comes on when turning the volume from '0' to '1'. It stays constant until the unit is turned up past '50' on a scale of '60', when a slight antenna 'leakage' also occurs (antenna is well grounded and checks out on DMM).
Output voltage is 4+volts and the hiss intensifies with an increase in the gain level at the AMP, which is set so low to minimize the hiss as to alter the presence of the speakers (all Quart). The signal is carried via double insulated, gold plate Monster XT RCA interconnects and 14AWG 0² Free insulated copper Monster XT cable. All signal wire is routed well away from any power wires (a real feat in an Esprit believe me!)
This is very frustrating, I even returned my original Nakamichi HU thinking I had exhausted all possibilities save a defect in the unit itself which Nakamichi gladly and promptly exchanged, but the new one has the same issue. I did see some improvement when I removed the (-) battery cable ground and filed it clean and degreased the chassis, but not enough improvement to get all the sound Nakamichi is famous for. I have never had any electrical issues with the car whatsoever. I just hope I can locate it and reassemble my interior before the snow flies.
Happy Motoring! ...Jim'85TE
Jim:
Just for the heck of it and for test purposes to try to rule out a ground issue, try this:
Connect your jumper cables from the battery to your stereo unit and amps. That is about the best connection you are going to get. It may take some fiddling to get the cables hooked up and not touching anything bad, like the + touching ground, etc. After it is all basically connected directly to the battery through the jumper cables, see if you get the noise. You can keep your existing wiring hooked up, just add the jumper cables and see what happens. You can even try them one at a time, that is, hook the ground cable from the negative battery terminal to the ground connection of your stereo. It is also a good idea to have all the grounds at one common point. Some heavy cable with a good connector on both ends.
From your description, it sounds more like an amp issue than a head unit issue, if I read you correctly: Turn it on, get small noise at all settings of the head unit volume and it stays about the same but goes up if you turn up the volume on the amp. Really, you can try grounding as described above, but my money is on a defective amp.
Keep in mind I don't claim to be a car stereo expert, but I know my radios pretty well, having earned a living with them for over ten years (in what seems like a past life now.)
Dr.Hess
Just for the heck of it and for test purposes to try to rule out a ground issue, try this:
Connect your jumper cables from the battery to your stereo unit and amps. That is about the best connection you are going to get. It may take some fiddling to get the cables hooked up and not touching anything bad, like the + touching ground, etc. After it is all basically connected directly to the battery through the jumper cables, see if you get the noise. You can keep your existing wiring hooked up, just add the jumper cables and see what happens. You can even try them one at a time, that is, hook the ground cable from the negative battery terminal to the ground connection of your stereo. It is also a good idea to have all the grounds at one common point. Some heavy cable with a good connector on both ends.
From your description, it sounds more like an amp issue than a head unit issue, if I read you correctly: Turn it on, get small noise at all settings of the head unit volume and it stays about the same but goes up if you turn up the volume on the amp. Really, you can try grounding as described above, but my money is on a defective amp.
Keep in mind I don't claim to be a car stereo expert, but I know my radios pretty well, having earned a living with them for over ten years (in what seems like a past life now.)
Dr.Hess
dr.hess said:
Jim:
Just for the heck of it and for test purposes to try to rule out a ground issue, try this:
Connect your jumper cables from the battery to your stereo unit and amps. That is about the best connection you are going to get. It may take some fiddling to get the cables hooked up and not touching anything bad, like the + touching ground, etc. After it is all basically connected directly to the battery through the jumper cables, see if you get the noise. You can keep your existing wiring hooked up, just add the jumper cables and see what happens. You can even try them one at a time, that is, hook the ground cable from the negative battery terminal to the ground connection of your stereo. It is also a good idea to have all the grounds at one common point. Some heavy cable with a good connector on both ends.
From your description, it sounds more like an amp issue than a head unit issue, if I read you correctly: Turn it on, get small noise at all settings of the head unit volume and it stays about the same but goes up if you turn up the volume on the amp. Really, you can try grounding as described above, but my money is on a defective amp.
Keep in mind I don't claim to be a car stereo expert, but I know my radios pretty well, having earned a living with them for over ten years (in what seems like a past life now.)
Dr.Hess
Doc,
Great advise! Unfortunately, I already tried that as well with the same result. I tend to disagree that the AMP is defective as I originally had a Rockford-Fosgate Amp (which was part of the original Alpine set-up) and had the same problem.
When discussing the possible defective HU w/ Nakamichi's Chief Tech, I described the entire system as I have here. He told me that while R-F made excellent Amps, they weren't especially compatible with Nakamichi's equipment. He said that due to my problem, they would sell me a 4-Ch Nakamichi Amp (PA-1004) for their best dealer cost (believe me when I say the mark-up on these things is unbelievable!). The cost to me was so good, I couldn't pass it up (about 1/3 the HU cost). When I got both units, which were checked by Nak prior to shipping, the same hiss was present. It is also present if I connect the speakers directly to the HU using only it's internal Amp (47W/Ch X 4) totally isolating it from the external Amp, so I have to believe it's a wiring/ground issue.
My suspicion is that I have some electrical accessory which is 'bleeding' into the ground if that makes any sense. Trouble is, I have no idea where/how to locate it w/o checking every circuit in the car. All accessories work properly and there doesn't seem to be any battery drain when the car is unused for extended periods. I replaced all the cables to the recently rebuilt alternator and cleaned the existing and added an additional engine-chassis ground cable (2AWG). I get 14.1 volts at the battery and Amp take-off which is well within the spec operating voltage for the Amp (10.0 VDC-15.0 VDC).
One other point, while the Amp and HU have a common ground point (distribution block), the power antenna has a separate ground (but I get the hiss even with the antenna disconnected), but the mounting sleeve for the HU also grounds through the steel center console frame - possible ground looping? I believe I pulled the HU and ran it apart from the console mount with no improvement (although to tell the truth, I can't keep track of what I have tried anymore).
But I'm pretty persistant when it comes to perfect sound, so absent any other suggestions, I'll just keep plugging away until I get it. Thanks!
Happy Motoring! ...Jim'85TE
Hey Jim,
You didn't mention trying it without the amp. OK, then, I agree that the amp is not the issue if you had the speakers hooked to the head unit _directly_ with the amp out of the circuit and still had the noise. Also, although I have never actually heard a ground loop, I seriously doubt it sounds like a hiss. Hiss noise is typically a leaky capacitor, but could also be a noisy transistor (or even diode) junction.
I would: Pull the head unit from the car, put on the bench, hook to a battery with some speakers. Noise? Y -> HU defective. Replace. N -> Car based noise. Put back in car. Start pulling fuses and relays one by one until the noise stops. Found the circuit. Go from there.
Just shooting in the dark here, but doesn't your car have one of those mechanical voltage regulators in the dash?
Dr.Hess
You didn't mention trying it without the amp. OK, then, I agree that the amp is not the issue if you had the speakers hooked to the head unit _directly_ with the amp out of the circuit and still had the noise. Also, although I have never actually heard a ground loop, I seriously doubt it sounds like a hiss. Hiss noise is typically a leaky capacitor, but could also be a noisy transistor (or even diode) junction.
I would: Pull the head unit from the car, put on the bench, hook to a battery with some speakers. Noise? Y -> HU defective. Replace. N -> Car based noise. Put back in car. Start pulling fuses and relays one by one until the noise stops. Found the circuit. Go from there.
Just shooting in the dark here, but doesn't your car have one of those mechanical voltage regulators in the dash?
Dr.Hess
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