problem with my car amp

[apex_1310]

First of all, english is not my native language, so if I make some grammatical errors, please don't be surprised.

Now. let's talk about my problem. Please stay with me, I know this type of post's are boring to most people, but i really need your help.

I have bought some oldscool amp on ebay (audioart), but when I turn my car engine on it makes a whine noise from alternator, I am focused on amp, because when i heard whine noise, instantly I have swapped that amp with amp that I have used before and there is no whining noise. "audioart" amps are very quality amps and I have not cross on any problem with AA amps on whole net, so I think that mine is faulty one.

Next I have disconnected the amp an measured resistance from the input RCA shields on the amp to amp's housing, on one channel i get 50Kohm on other i get "infinity" value.

I believe this is not OK and that my amp is having faulty input stage, but I want to hear from you, what do you think about this, and what do you suggest to try so I can find where the error is?

[apex_1310]

just to add that I have measured resistance from the input RCA shields on the amp to each of the non-bridging speaker terminals and value is 0 Ohm, is this OK?

[jol50]

First unplug the RCA and see if the noise is still there, if so it may be the power supply or grounding of the amp.

Should measure RCA shield to amp's negative power terminal as some the case is not directly grounded. Many amps are 1K ohm, but others are different.

Usually it is the deck that does not ground the RCA shields and causes noise, some amps are more sensitive to this than others. I would first check ohms RCA shield to the amp's ground, with RCA not connected to amp, to make sure deck is grounding the shields and RCA cables are good. Only takes a minute.

If that is good then look at the amp. First investigate if amp RCA plugs have a bad connection/solder/are broken. You could play it and gently move the RCA in the plugs and see if noise changes. If not then it would be time to look inside the amp.

[apex_1310]

When i disconnect RCA there is no sound.

RCA shield to amp's negative power terminal: first channel is 1Kohm, second is "infinite"

[Perry Babin]

Does it make noise if you plug the RCA signal cable into one input but not if you plug the RCA signal cable into the other input (only one plugged in at a time)?

[apex_1310]

Thank you for your fast replies, I really appreciate it.

I am currently unable to run more test, because I disconnected amp from the car, but I will reconnect it tomorrow and run some more tests, like you suggested and get back with info..

[apex_1310]

I have plugged separately RCA to one channel first and then to second channel and the result is same, on both channels I can hear whining, but I have found out that on my right channel one RCA is not having good connection, because when I turned amp on, speaker is making popping noise every second, and I can hear loud bruum from speaker. When I press RCA, then everything is back to normal except I can still hear whining, like on the other channel.

[apex_1310]

I wanted to make sure that whining is not coming from amp's SMPS, and I made muting RCA where + and - are soldered together like in pic bellow



Result is that there is no whining at all. So my guess is still that i have faulty input stage?

I am wondering if there is possibility that this prob is related to ballanced/unbalanced in/out's ?

[Perry Babin]

If you plug either RCA into the right input jack and it does what you described, you need to find the problem with that RCA jack. I can't see enough of the RCA jacks to offer any suggestions.

[apex_1310]

I will try to describe my system from start, for better understanding what I am talking about. Source unit is pioneer cd-player connected directly to amp, it's so simple setup. amp's power supply is connected directly to accumulator. First I thought that I have ground loop or bad ground. Tryed this RCA Shield Repair and whining is little attenuated, but not gone. Changed all cables, grounded head unit directly to accumulator. At last I plugged all out from my car and connected everything outside the car, but noise is still there. When I exclude amp from setup, everything is working fine. It's like that amp is passing alternator whine through whole system and I can hear on all car speakers freaking whining noise. When I change the amp and place my old amp in setup there is no noise. What could be wrong?