Amplifier Hiss!....what causes it?...its bothering me!

[form109]

i recently got an Aiwa Reciever....(Broken CD Player,Tape Deck)...but the FM/AM and Aux imput functions are intact...

anyway when theres no signal imput to the Reciever the speakers emit a Small but Auidble Hissing Noise...this Hissing Noise is Present from Volume 1 to 31...but dissapears at 0

what is this hissing noise and what Causes it?

is there something wrong with the amp?

[Keith Taylor]

Perhaps you could elaborate a little on the circumstances that give rise to the hiss. I take it that when you have the FM receiver selected and it is tuned off a station or has no antenna connected you are hearing it. Under these no signal conditions the receiver will output the noise generated in the tuner as it will be operating at maximum (RF) gain. When the signal level falls below a threshold value the mute circuit will operate to silence the noise. This is normaly done automatically, but it is conceivable that some receivers may have a switch to defeat the muting for people interested in listening to very weak signals.

The actual muting circuitry is generally a pair of transistor switches (one R channel, one L channel) that short out the audio. It is not quite that brutal as there is a series build out resistor involved to make an attenuator. Maybe the mute system does not completly kill the audio. If this describes your problem the answer would be to switch the amplifier to another input such as aux, as you are not listening to the radio anyway.

On the other hand maybe your problem is evident when the tuner is not selected and that you have leakage/crosstalk in the selector switch, or a combination of this and the fact that the mute circuit is not working. Some more advanced designs of selector switches have extra poles to ground the unselected inputs giving much higher isolation between sources. Sorry if I am being too technical. Let us know what position your input selector switch is in when you are hearing hiss.

Keith

[form109]

Originally Posted by Keith Taylor

Perhaps you could elaborate a little on the circumstances that give rise to the hiss. I take it that when you have the FM receiver selected and it is tuned off a station or has no antenna connected you are hearing it. Under these no signal conditions the receiver will output the noise generated in the tuner as it will be operating at maximum (RF) gain. When the signal level falls below a threshold value the mute circuit will operate to silence the noise. This is normaly done automatically, but it is conceivable that some receivers may have a switch to defeat the muting for people interested in listening to very weak signals.

The actual muting circuitry is generally a pair of transistor switches (one R channel, one L channel) that short out the audio. It is not quite that brutal as there is a series build out resistor involved to make an attenuator. Maybe the mute system does not completly kill the audio. If this describes your problem the answer would be to switch the amplifier to another input such as aux, as you are not listening to the radio anyway.

On the other hand maybe your problem is evident when the tuner is not selected and that you have leakage/crosstalk in the selector switch, or a combination of this and the fact that the mute circuit is not working. Some more advanced designs of selector switches have extra poles to ground the unselected inputs giving much higher isolation between sources. Sorry if I am being too technical. Let us know what position your input selector switch is in when you are hearing hiss.

Keith

The Imput is the Dual RCA Connections for an Auxillary connection....with NOTHING connected there is a Continious Hiss from the Amp going into the speakers..this hiss isnt present when the Amp is turned all the way down to its lowest Level which is 0 but can be heard immediately when the dial is turned to 1 and is Present Through all Volume levels up to the Maximum one which is 31....However...when there is an Active imput signal..the Hiss Cannot be heard...as the Audio is louder than it is.

[jaycee]

Short those inputs to ground. Does it still hiss?

[whitelabrat]

Originally Posted by form109

i recently got an Aiwa Reciever....(Broken CD Player,Tape Deck)...

It sounds to me that this is one of those inexpensive all-in-one stereos. All amplifiers exhibit hiss which is random noise. The lower that noise floor is the greater signal to noise ratio you will enjoy. Good components and design will usually give better results.

I suspect your stereo is operating as designed.

[form109]

Originally Posted by whitelabrat

It sounds to me that this is one of those inexpensive all-in-one stereos. All amplifiers exhibit hiss which is random noise. The lower that noise floor is the greater signal to noise ratio you will enjoy. Good components and design will usually give better results.

I suspect your stereo is operating as designed.

Yes it is Cheap...however i obtained it for Only 5 Bucks...so no Real Complaints here.

When there is an Active Signal the Hiss cant be heard anymore...as stated above.

overall i dont think theres much to complain about....the amp isnt the strongest in the Bass Register..but i can get Pretty Loud with very little distortion.

The Reciever has Digital Audio System labeled at the top...so i guess that means Digital Amplifier?

not sure of the Amplifier Class Though.

[AndrewT]

you can guess all you want.
I would recommend you ask for your 5bucks back.

[CBS240]

Try what Jaycee suggested. If it still hisses, gnd the input of the pwr amp PCB inside. The amp or the relationship to the input circuitry may be causing oscillations. HF oscillations can sound like 'hiss'. Do you have a scope?

Of course if it were me, for 5 bones, I would gut the pwr amp section and build a better amp in place.

[ticknpop]

It 's typical of an older reciever made with carbon film resistors, generic ( not selected low noise) transistors, a basic high gain output stage (With front end hiss- especialy if you turn it up all the way, but still is there at lower volume levels) and extra stages such as tone controls, and aging capacitors - most ( but not all) older mid market recievers will have hiss with efficent speakers from the residual hiss of these suboptimal active and passive components and circuit topology. Hi and mid range audio products have moved on to better resistors, active devices, and gain toplogies. Even mid-fi products typically now use metal film resistors which are cheaper and more readably available than when your reciever was made and have less hiss. You need better / newer equipment to solve the issue.

[form109]

Originally Posted by AndrewT

you can guess all you want.
I would recommend you ask for your 5bucks back.

Nope....keeping it...

Originally Posted by CBS240

Try what Jaycee suggested. If it still hisses, gnd the input of the pwr amp PCB inside. The amp or the relationship to the input circuitry may be causing oscillations. HF oscillations can sound like 'hiss'. Do you have a scope?

Of course if it were me, for 5 bones, I would gut the pwr amp section and build a better amp in place.

i dont Feel Like Gutting it....Yet....i might Replace the CD Changer Though....im not Worried about the Tape Deck...i dont use Tapes much anymore.