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Old 10th November 2009, 21:10   #1
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Default What is this Shhhhhh... sound ?

hello friends,
i got a twin amp setup installed in my swift recently, a jbl monoblock( gto3501) and a full range jbl (gt5-s644), both of these amps are mounted on the backside of the rear seat, the rca is bt series audison 4 channel for the latter amp and stinger basic for the monoblock( soon to be changed to audison), mains by an audison distributor 0-4 gauge to two 4 gauge, powering the amps, grounds are connected on the floor of the car, headunit is pioneer 6950 ib.
now my problem is that i am getting a sshhhh sound through my rear coax speakers( the only pair of speakers in my car which is soon to be changed to front comps), i an quite surprised and disappointed, even after getting audison rcas, still im getting this sshhh kinda sound which i think is most probably electrical interference, am i right? before getting the second amp i was using only the monoblock with the coax speakers conected directly to the hu, at that juncture i wasnt getting this sound/ static, now what to do friends, this sound is prominant at high volumes and at the short interval when the hu is turned on and before the track sounds playing, it is there while the track plays too, help me fellows what to do? where did i went wrong?
p.s. right now this distributor is installed in the rear between the 2 amps and the power( mains wire) is running on the left side of the car and the rcas from the middle section( near handbrake)

Last edited by makanaka : 10th November 2009 at 21:30.
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Old 10th November 2009, 22:01   #2
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You should check Grounding of Amp here. The four channel one..

Last edited by Piyush_Vroom : 10th November 2009 at 22:03.
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Old 10th November 2009, 22:05   #3
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maybe your gains are set too high
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Old 10th November 2009, 22:52   #4
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Looks like the HU problem (pioneer) many members had faced the similar problem check check all the groundings and search the forum this had been discussed many times.

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maybe your gains are set too high
Does gains play any role in humming sound ?
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Old 11th November 2009, 00:09   #5
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Quote:
Does gains play any role in humming sound ?
the way he describes it it seems more like a noise floor problem and not a humming sound, that wouldnt sound like "shhhh" ..... rather it would sound like "Brrrr" which is the pioneer electronic type hum more like a machine gun firing but if it sounds like a tap left on running a high speed stream of water then its a hiss

if its a hiss then definitely its noise floor, but only way to really know is for him to describe it properly or to hear for oneself
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Old 11th November 2009, 14:44   #6
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Check the grounding of the RCA cables. Also, the gain may be set quite high.
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Old 11th November 2009, 15:28   #7
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Quote:
Originally Posted by makanaka View Post
before getting the second amp i was using only the monoblock with the coax speakers conected directly to the hu, at that juncture i wasnt getting this sound/ static, now what to do friends, this sound is prominant at high volumes and at the short interval when the hu is turned on and before the track sounds playing, it is there while the track plays too, help me fellows what to do? where did i went wrong?
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Originally Posted by DerAlte View Post
Check the grounding of the RCA cables. Also, the gain may be set quite high.
You got a Pio HU. Try grounding the 4 RCA out from the Pio HU. There is a pic of that on this forum somewhere. One of the google masters will be able to help you with that.
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Old 11th November 2009, 20:17   #8
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hello friends,
naughty, the gains are approx set at 55-60 percent which i dont think is too high, or are they ?
piyush when u said grounding of the amp, did u meant that check the connection of wire which supplies negative current to the amp, if you meant that then the wire is properly attached to the floor of the car, with the paint pealed off from the contact area with proper gauge wire, moreover there is no dimming of lights at very high volumes which i think means that atleast the wire is of proper gauge and supplying proper current, right?
i earlier had a pair of mico bosch horns which when honked used to create an interference in the rear coaxs, it sounded like a loud crackling sound when i removed those and restored the factory fitted horn the problem was gone, i still am running the factory fitted horn which dosent interfere with my coaxs, this sound is exactly like mild ssshhhh, very mild to be precise but can be noticed, i will post a pic tomorrow of my setup maybe then u guys might be able to help me more. till then il try the grounding of rcas, what i understand of grounding is to attach a small wire to the hu,s body and another end to the outer metal round part of rca , right? do i need to do this for all the 4 rcas or only 2 rcas , one of each output?
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Old 11th November 2009, 21:59   #9
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update:- got the pic where all the 4 rca's were grounded, tried that, still no difference whatsoever, the noise is still there!
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Old 11th November 2009, 22:09   #10
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Quote:
naughty, the gains are approx set at 55-60 percent which i dont think is too high, or are they ?
where the gains seem to be is not the way to judge how high they are set, gains are there to match the output voltage of the headunit with the input voltage at the amplifier 98% of people including installers set the gains incorrectly

Quote:
this sound is exactly like mild ssshhhh,
this is basically noise floor caused by incorrect setting of gains

the problem with the pioneer headunit would sound more like a radio at the wrong frequency but sounding like a machine gun firing, whilst noise floor would just sound like a water tap thats on with a steady stream of water so maybe you need to describe the sound in more detail

Quote:
do i need to do this for all the 4 rcas or only 2 rcas , one of each output?
if the headunit is the problem then basically you might only need to do it for the higher frequency channels, if the sound remains you might need to do the other channels

a quicker and easier test is to drop the gains on the higher frequency channels slightly and play the headunit at a slightly higher volume - see if the noise disappears or remains. If it remains then only will you need to do all the grounding of the rca's

Last edited by naughty001 : 11th November 2009 at 22:13.
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Old 12th November 2009, 08:23   #11
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naughty can u tell me what is the appropriate gain settings for voltage on my headunit pioneer DEH-6950IB and amp JBL GT5-S644, the sound is more like a steady stream of water running from a tap fully open, one more example is when u want someone to keep quite u make that ssshhh sound, kinda like to a kid in a liabrary, its not a crackling sound, and is directly proportional to the volumes, the higher the volume the higher the sound, the lower the volume, the lesser the sound, if the hu is on mute or zero volume then there is no such sound.

Last edited by makanaka : 12th November 2009 at 08:27.
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Old 12th November 2009, 12:32   #12
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Quote:
Originally Posted by makanaka View Post
naughty can u tell me what is the appropriate gain settings for voltage on my headunit pioneer DEH-6950IB and amp JBL GT5-S644, the sound is more like a steady stream of water running from a tap fully open, one more example is when u want someone to keep quite u make that ssshhh sound, kinda like to a kid in a liabrary, its not a crackling sound, and is directly proportional to the volumes, the higher the volume the higher the sound, the lower the volume, the lesser the sound, if the hu is on mute or zero volume then there is no such sound.
Hi

setting gains PROPERLY is a bit of a black art, you could use a DMM (digital multimeter) but this gets you to the rated power of the amp and a more correct method would be to use an oscilloscope which would allow you to use clean (unclipped) settings which will allow you to use the maximum unclipped levels

my suggestion is to actually drop the gains a bit and see if the noise decreases, if it does then keep dropping till the noise goes away - if the noise remains then there are two possibilities :

1) i was incorrect and the noise is actually caused by the headunit, in which case you might need to try to ground the RCA negatives to chassis ground instead of to the headunit but AFAIK normally the blown microfuse issue would cause either alternator whine or a crackling type of sound, maybe it could just be less severe in your instance if this was the cause of your problem

2) you have either a defective amplifier or defective headunit and you will need to try out different replacement units in the place of the ones the ones that are there

Last edited by naughty001 : 12th November 2009 at 12:33.
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Old 13th November 2009, 21:37   #13
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hello friends,
after a lot of hit and trial i have set my gains at around 25 percent and the hiss is almost inaudible now, but it is still there, if i increase the gains the hiss increases and vice versa, i guess il have to use another hu to find out if my hu is faulty, if not then i dont know what to do?!
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Old 14th November 2009, 13:09   #14
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Did you check amp grounding?
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Old 14th November 2009, 13:21   #15
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Hi makanaka,

even i had the same problem in my swift, but here if i start the engine, and give accelartion,

even i am having the same problem,

http://www.team-bhp.com/forum/ask-gu...ift-s-ice.html

but when i changed the settings of the amp the sound was reduced but again comes in High RPM,

but if you follow the steps in the picture it will atlease reduce the sound.
Attached Thumbnails
What is this Shhhhhh... sound ?-alrernator_noise-1.jpg  

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