"Knocking" sound

diarav · 9th October 2006, 02:13 PM

Hi,

Problem:
I get a continous knocking sound on my speaker when connected.

History:
I built my LM3886 and connected my CD player source. Was working perfectly fine. When switching on initially, there used to be a knocking sound , and this died within a few seconds and the source played fine.
I later built a pre-amp using NE5532 and this boosted the output very well and I had no problems again except that this knocking sound on the 16 ohm speaker played for a few seconds initially and the source was in. I got some hum and the chip was also heating up. I switched off after about 3 to 4 minutes.

Next day I switch on the same setup (no reconnections ) and connected my source again. This time I dont hear anything except the continous knocking sound which occurs something like two thumps per sec. its something like |^^_|^^_|^^_| where ^ determines the knocking, one second duration between | and |.

The schematic is from ESP site's http://sound.westhost.com/project115.htm . R7 value was 10K.

Any inputs on what the basic problem could be? I am actually planning to rewire the whole thing, but any suggestions would help.

Thanks
Din

Tube_Dude · 9th October 2006, 02:31 PM

Quote:

Originally posted by diarav

The schematic is from ESP site's http://sound.westhost.com/project115.htm . R7 value was 10K.

It look to me as oscillation in the output stage , the culprit must be R7 that can't be greater than 10 Ohms and you are using 10K Ohms...

diarav · 9th October 2006, 02:56 PM

Oh I'm sorry I did not make it clear in my earlier post. The R7 I was referring to was the one in the PreAmp (R7LA). All other values are as per schematic.

Could I suspect the pot? I was having problems with this ? Can an 'open' pot cause this?

Thanks
Din

Tube_Dude · 9th October 2006, 03:11 PM

Quote:

Originally posted by diarav

Could I suspect the pot? I was having problems with this ? Can an 'open' pot cause this?

I don't believe that the problem is in the pot.

Are you using in the power section, the R4-22K Ohms resistor?

diarav · 9th October 2006, 03:18 PM

Hmm. Yes . the R4 22K is there.
The problem is, it was working initially and now it is not.

I'll try disconnecting the preamp and check individually both the amps.

Thanks
Din

9th October 2006, 02:13 PM	#1
diarav diyAudio Member Join Date: Dec 2004 Location: Bangalore India	"Knocking" sound Hi, Problem: I get a continous knocking sound on my speaker when connected. History: I built my LM3886 and connected my CD player source. Was working perfectly fine. When switching on initially, there used to be a knocking sound , and this died within a few seconds and the source played fine. I later built a pre-amp using NE5532 and this boosted the output very well and I had no problems again except that this knocking sound on the 16 ohm speaker played for a few seconds initially and the source was in. I got some hum and the chip was also heating up. I switched off after about 3 to 4 minutes. Next day I switch on the same setup (no reconnections ) and connected my source again. This time I dont hear anything except the continous knocking sound which occurs something like two thumps per sec. its something like \|^^_\|^^_\|^^_\| where ^ determines the knocking, one second duration between \| and \|. The schematic is from ESP site's http://sound.westhost.com/project115.htm . R7 value was 10K. Any inputs on what the basic problem could be? I am actually planning to rewire the whole thing, but any suggestions would help. Thanks Din

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9th October 2006, 02:56 PM	#3
diarav diyAudio Member Join Date: Dec 2004 Location: Bangalore India	Oh I'm sorry I did not make it clear in my earlier post. The R7 I was referring to was the one in the PreAmp (R7LA). All other values are as per schematic. Could I suspect the pot? I was having problems with this ? Can an 'open' pot cause this? Thanks Din

9th October 2006, 03:18 PM	#5
diarav diyAudio Member Join Date: Dec 2004 Location: Bangalore India	Hmm. Yes . the R4 22K is there. The problem is, it was working initially and now it is not. I'll try disconnecting the preamp and check individually both the amps. Thanks Din