Help on NE5532 preamp Noise FREE

[pra3718]

With the help of sr. members I have developed preamp (attached file) but I could not make 100% noise free or clean sounding. Sometimes I see the speaker's cone movement is not matching to music strock. Overall some correction is required to my attached circuit. Please help me.

Thank you.

[Xoc1]

In Your Circuit diagram pin 4 is not connected to ground.
Also add some local decoupling to the op amp. A 100 uf 16v bi-passed with a 0.1 mkt will help the sonic performance and keep things stable.

[pacificblue]

Hi, pra3718,

please help us with a more precise description.

Could the cone movements be very low frequent music signals that the speaker reproduces below the listening threshold? http://en.wikipedia.org/wiki/Equal-loudness_contour

The noise you have is hum, right? Use the search function. There are many threads dealing with that, because there are many possible sources for hum, e. g. inductive coupling from the transformer, ground loops, bad solder joints, to name just a few.http://sound.westhost.com/troubleshooting.htm#earth

[pra3718]

Thank you.

Your approval is needed. Pl find my altered schematic. Alteration is in RED colour.

Prior to addition of Cap 0.22uf on Pin 1-2, there was SSSSSSSS type of sound. for this type of sound I have to open mouth & SSSSSSS. Cap 0.22uf on Pin 1-2 is removed this SSSSSS.

Now if I shut the mouth & sound by my nose like HAMMMMMMM yes, this type of sound is present now. I thought this HAMMM is comming from my source(DVD Player) but not I tried with remove all connection with DVD Player. One more thing if I touch the Subsoofer with no sound I can feel the vibration/hammm.

Pacificblue, another question is you know my PSU right? For Preamp I am using IC:7812 (regulated) If I add IC:7812 to PSU and if common supply <regulated supply> to all TDA1554q & NE5532 so is that HARM ?

Thank you & Regards.

[sangram]

There is a joint between the supply midpoint generator (2x10K) and the top of Ci (100uF near the inverting input). Since you have not labelled the parts I find it exceedingly difficult to point it out to you.

The connection needs to be broken, as it is feeding half the supply voltage to the inverting input through the feedback resistor network and may be a source of hum. I've made this remark on your earlier thread but it is still not corrected.

Unless, of course, it's a mistake in the drawing.

[pra3718]

Sorry, I could not understand you sangram. Why don't you download my schematic, ALTER it & post it again. Can you do it for me.

Thank you & Regards.

[poynton]

Why do you need a preamp with a gain of ~4 between a DVD player and amplifier??

It sounds to me as if you have too much gain hence hum and hiss.

The capacitor 0.22uF is acting as a top cut and will result in muffled sound.

Where is the volume control?? Before or after the preamp?


Andy

[sangram]

@Poynton - he's using it for a subwoofer amp, hence cutoff is not an issue. However the sub must be much more inefficient than the rest of his satellites, needing the higher gain.

@pra - I will defer the help till tomorrow evening, if someone else can do it great. I'm posting from a phone now. Impossible for me.

[jackinnj]

1) The 7812 regulator should be replaced by an LM317 adjustable regulator. Decouple the "Adjust" pin with a good quality 1uF film capacitor (or a 10uF electrolytic). This will dramatically reduce the noise at the artificial ground node on the non-inverting input. Bob Pease at National Semi wrote an entire white paper on the bypass for these regulators.

2) Consider reducing the values of the gain and feedback resistors. If your CD player can stomach it, use 22K.

[pacificblue]

Originally posted by pra3718
Sorry, I could not understand you sangram.

The 100 µF capacitor must only be connected to the 4.7 k resistor, not to anything else. In your schematic there is a connection also to the two 10 k and the 47 k resistors, which you have to interrupt.

Originally posted by jackinnj
1) The 7812 regulator should be replaced by an LM317 adjustable regulator. Decouple the "Adjust" pin with a good quality 1uF film capacitor (or a 10uF electrolytic). This will dramatically reduce the noise at the artificial ground node on the non-inverting input. Bob Pease at National Semi wrote an entire white paper on the bypass for these regulators.

2) Consider reducing the values of the gain and feedback resistors. If your CD player can stomach it, use 22K.

Noise at that level is not an issue with this setup. It is based on a multi-channel car radio TDA.