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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > AUDIO/VIDEO + BLUETOOTH + Electronics/Alarm/Software > Help, annoying "Hiss" after amp upgrade



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      03-07-2009, 09:32 PM   #67
sierrajulietgolf
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Today I spent some time working on the setup. I tried a few more ground points and isolated the amplifier from the car chassis, still have the problem.

I am almost certain that it is being caused by either the ground wire or the power wire. To describe the noise in a little more detail...it is a constant hiss with a high pitched whine. The whine does not fluctuate with the car RPMs though. The noise and whine exist at no volume and high volume from the HU. Also, the noise is present at the same level with electrical on/engine off and also with engine started.

Tonight I was driving home and noticed something else... when I use the window controls the whine changes pitch briefly and the illumination and exterior lights dim leading me further to believe this is a problem with the electrical setup of the amplifier.

Any suggestions?
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      03-29-2009, 12:02 AM   #68
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If you have a noise which does not change with RPM, I doubt you have a ground loop issue. If you have a component of the noise which does change with RPM, you have a slight ground loop issue. Where is it grounded?

I suspect that you have the input gains on the PDX too high. If you lower them, does the noise floor shift? (I recognize that the sound may be too low for you, but it is an important test...)

Also, is your amp close at all to the grounding bracket on the driver's wheel well?

Did you run your HU ground back to the amp? Always a good idea.
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      04-27-2009, 12:01 PM   #69
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OP, did you ever figure this out? I just installed my PDX-5 last night and I think I have the exact same problem.
I hear "hiss" as soon as I tune up the volume > 0, if volume is 0, I don't hear it.
The noise is constant as op described, won't change with rpm, but I did notice that if I step on the brake, it is louder. Help please.
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      04-27-2009, 12:55 PM   #70
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Quote:
Originally Posted by scanboy View Post
OP, did you ever figure this out? I just installed my PDX-5 last night and I think I have the exact same problem.
I hear "hiss" as soon as I tune up the volume > 0, if volume is 0, I don't hear it.
The noise is constant as op described, won't change with rpm, but I did notice that if I step on the brake, it is louder. Help please.
How the PDX-5 is connected to the OEM system? Are the gains of the PDX-5 all the way down?
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      04-27-2009, 12:59 PM   #71
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Quote:
Originally Posted by Technic View Post
How the PDX-5 is connected to the OEM system? Are the gains of the PDX-5 all the way down?
Not sure what your first question is asking, but I replaced the OEM amp with the PDX-5 and the input to the PDX is str8 from the HU and there's no other equipment, just the PDX.
The gains of the PDX-5 are all the way down.
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      04-27-2009, 01:19 PM   #72
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Originally Posted by scanboy View Post
Not sure what your first question is asking, but I replaced the OEM amp with the PDX-5 and the input to the PDX is str8 from the HU and there's no other equipment, just the PDX.
The gains of the PDX-5 are all the way down.
... just to make sure that there is nothing between the OEM HU and the PDX-5.

Is this PDX-5 brand new? If so, bought on eBay? Did it came with the "birth sheet"? What about removing the inputs of the PDX-5, still hiss?
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      04-27-2009, 02:15 PM   #73
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Quote:
Originally Posted by Technic View Post
... just to make sure that there is nothing between the OEM HU and the PDX-5.

Is this PDX-5 brand new? If so, bought on eBay? Did it came with the "birth sheet"? What about removing the inputs of the PDX-5, still hiss?
I see. Yup brand new and from eBay with "birth sheet".
Hmm, haven't try removing the inputs, I'll give that a shot later tonight. So what would the out come of this tells me? if I don't have the hiss after removing the input, what should I do? and if the hiss still exist after removing inputs, what does that mean?
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      04-27-2009, 02:28 PM   #74
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Quote:
Originally Posted by scanboy View Post
I see. Yup brand new and from eBay with "birth sheet".
Hmm, haven't try removing the inputs, I'll give that a shot later tonight. So what would the out come of this tells me? if I don't have the hiss after removing the input, what should I do? and if the hiss still exist after removing inputs, what does that mean?
If by removing the inputs the hiss is gone then the hiss is coming from your OEM HU/wires connection; you could try the JL Audio wire-to-RCA cables soldered to the OEM ouput wires to minimize any noise if you are not using them right now. If the hiss is still there after removing the inputs then it is coming from the PDX-5/ground connection. This one is more difficult to fix, as most probably it is a bad amp.

I asked about whether the PDX was new and from eBay as I got a PDX4.100 without "birth sheet" that was noisy as hell from eBay right out of the box. The replacement (with the "birth sheet") is dead silent...
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      04-27-2009, 03:27 PM   #75
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Quote:
Originally Posted by Technic View Post
If by removing the inputs the hiss is gone then the hiss is coming from your OEM HU/wires connection; you could try the JL Audio wire-to-RCA cables soldered to the OEM ouput wires to minimize any noise if you are not using them right now. If the hiss is still there after removing the inputs then it is coming from the PDX-5/ground connection. This one is more difficult to fix, as most probably it is a bad amp.

I asked about whether the PDX was new and from eBay as I got a PDX4.100 without "birth sheet" that was noisy as hell from eBay right out of the box. The replacement (with the "birth sheet") is dead silent...
I see. I'm not currently using the JL wire-to-RCA cable so... another thing to test out tonight. I hope it is not a bad amp.
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      04-27-2009, 03:37 PM   #76
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Quote:
Originally Posted by scanboy View Post
I see. I'm not currently using the JL wire-to-RCA cable so... another thing to test out tonight. I hope it is not a bad amp.
I hope not as well... just check your connections.
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      04-28-2009, 11:29 AM   #77
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Ok, some good news (for me at least), when inputs are removed, hiss is gone.
I've tried cutting an RCA cable into half and use that for the connection, but the hiss is still there, is the JL cable better than regular RCA audio cable?
I am using this connector to make the connection,

http://www.molex.com/molex/products/...cts&Lang=en-US

so all my RCA wires to this connector and plug into the plug on the OEM side. Would this connector cause any noise? All the wires are solder onto the pins of the connectors, so....
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      04-28-2009, 12:55 PM   #78
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Quote:
Originally Posted by scanboy View Post
Ok, some good news (for me at least), when inputs are removed, hiss is gone.
I've tried cutting an RCA cable into half and use that for the connection, but the hiss is still there, is the JL cable better than regular RCA audio cable?
I am using this connector to make the connection,

http://www.molex.com/molex/products/...cts&Lang=en-US

so all my RCA wires to this connector and plug into the plug on the OEM side. Would this connector cause any noise? All the wires are solder onto the pins of the connectors, so....
I'm suspecting that the OEM HU 5V outputs could be the cause of the hiss, as the PDX-5 has a 4V max input sensitivity; that could explain the hiss problems with the OEM HU and the PDX amps in this thread (unless it is really a bad amp). Check what it says in Step 2 here about hiss and high voltage outputs:

Quote:
A constant ‘hiss’ will be heard if the amplifier cannot accept higher voltages.




My hiss in the PDX 4.100 was present even without inputs, but yours points towards the source. If using proper RCA cables doesn't reduce/eliminate the hiss then it is actually the source.

The last time that I connected a BMW OEM HU straight to a processor/amps I used a Matrix line driver just because of adjustability/control of the output level. You should be able to adjust the PDX-5 input levels to a point of no hiss at all with a line driver.

Of course, that should be the last resource if swapping RCA cables, revising the grounds or even using another amp for testing doesn't give you a solution.
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      04-28-2009, 02:26 PM   #79
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Thanks for all your input, Technic, that's some interesting info, didn't even know that HU output 5V.
From what I've read about ground loop, I don't think what I'm "hearing" is related to ground loop, but I'm not sure. I'll probably play with different ground points. Will definitely do some more testing on the RCA wires, if nothing works, will start looking for a line driver.
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      04-29-2009, 12:42 PM   #80
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Just FYI, I plug back my OEM amp and I hear the same "hiss" but just that I never pay any attention to it. However, it is more audible with the new amp, and I'm guessing after replacing the 4" speaker in the door, it's gonna be even more audible.
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      04-29-2009, 01:03 PM   #81
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Quote:
Originally Posted by scanboy View Post
Just FYI, I plug back my OEM amp and I hear the same "hiss" but just that I never pay any attention to it. However, it is more audible with the new amp, and I'm guessing after replacing the 4" speaker in the door, it's gonna be even more audible.
I got some slight hiss in my Individual Audio when it was stock, but by going thru a DSP processor now the hiss was radically reduced.

You can take care of that hiss by using a Matrix line driver.
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      04-29-2009, 02:47 PM   #82
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Quote:
Originally Posted by Technic View Post
I got some slight hiss in my Individual Audio when it was stock, but by going thru a DSP processor now the hiss was radically reduced.

You can take care of that hiss by using a Matrix line driver.
Thanks. That's pretty much what I plan on doing after reading your reply from yesterday. So the only thing that a line driver does is to control the gain? Sorry, new to these type of equipment. Anyway, do you know where I can get a good deal on that Matrix line driver?
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      04-29-2009, 03:32 PM   #83
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Quote:
Originally Posted by scanboy View Post
Thanks. That's pretty much what I plan on doing after reading your reply from yesterday. So the only thing that a line driver does is to control the gain? Sorry, new to these type of equipment. Anyway, do you know where I can get a good deal on that Matrix line driver?
I have one that I'm not using... you can have it for testing and if that solves your problem then we can talk about price. If not then you just return it to me. PM for details...

I'm also interested in knowing how it works with the E9x HiFi HU outputs...
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      04-29-2009, 05:41 PM   #84
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Quote:
Originally Posted by Technic View Post
I have one that I'm not using... you can have it for testing and if that solves your problem then we can talk about price. If not then you just return it to me. PM for details...

I'm also interested in knowing how it works with the E9x HiFi HU outputs...
Cool, don't mind if I do take you up on that, just PM'd you.
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      03-17-2011, 11:56 AM   #85
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Did the line driver fix the hissing from the aftermarket amp? I've got the same problem. It's an imput problem, because I get no hissing if I unplug the input from the HU/wiring or send input from another head unit in another car. Just wondering if/how you got it resolved.
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      10-01-2012, 12:13 AM   #86
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Hi, Any solutions to this hissing problem. I have the same exact problem after the JL xd600/6 install, i hear the noticeably hiss from my mids even when the HU is off ( ignition on ) or even when HU is playing CD at volume zero. I don't hear the Hiss if i disconnect the RCA's. Mine is HIFI system on E92 2009 model. I even hear the hiss even after lowering the input gain, but the hiss sound is little less but still noticeable.
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      10-02-2012, 05:31 PM   #87
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Hissing is very low or almost gone if my gain is set to zero for channel 1 to 4. does the amp / whole set up expect to sound good with the gain set to zero? the JL user manual says to raise the gain until i get a 17.4 volts per channel for a 4 ohm speaker connection.. just wondering if some one can help posting their setting for the above combination
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