Amp noise !!! Please Help !!!

Ford_V6 · 29th May 2003, 06:13 PM

Hy !

I have a big problem:

I built from scratch an amp based on the TDA7250 and TIP142/147.

I have found a transformer that i have rebuild to get 32-0-32 and 11-0-11. I have rectified the 32-0-32 trough a 25 amps bridge and filtered trough 2 x 10000 Uf caps. I got 44-0-44 V

The 11-0-11 is rectified trough a 5 amps bridge and 2 x 4700 Uf caps.

Now from the 44-0-44 i feed the amp and from the 14-0-14 (rectified) i feed a computer cooler and a LM1036N tone control.

I have put all in a case and it looks pretty good. It sounds great but . . . . i have a very loud noise with the cooler on. With the cooler off i have the same noise but smaller.

What can i do to get rid of the noise and enjoy my amp ?

Thnaks in advance.

JOE DIRT® · 29th May 2003, 07:00 PM

Hi Ford... have you bypassed your large filter caps with smaller ones>???.....and what type of grounding arrangement are you using with source and signal>????.....it sounds to me like a ground problem

technics · 29th May 2003, 09:39 PM

Quote:

Originally posted by Ford_V6
I built from scratch an amp based on the TDA7250 and TIP142/147.

Hi,

Could you please post the schematics of this amp?

jeffreyj · 29th May 2003, 11:50 PM

Make sure that your main ground is not where the filter capacitors connect together! Also, sometimes a star ground is not the best solution when something dirty, like a fan is connected there. It is best to connect all sensitive circuits to one star ground and then the noisy stuff to another star ground. A pigtail from the junction of the reservoir capacitors to these two stars completes the circuit. The chassis, by the way, should be connected to earth on the mains side. It is optional to join the circuit ground to the earthed chassis.

Hope this helps and good luck with your amp!

Ford_V6 · 30th May 2003, 07:22 AM

Here is the schematic !

The file is *.ACE format. Use winace

Ford_V6 · 30th May 2003, 07:33 AM

The main ground of the amplifier is conected where the two large caps get together. The ground of the tone control is the same as the amplifier for the in and out ( signal ) but the power ground of the tone control is connected together with the ground of the fan where the 4700 caps go togheter.

Can somebody describe me a better grounding scheme for my setup ?

raindog · 31st May 2003, 08:00 PM

buna, cred ca problema e la circuitul lm1036 incearca eventual sa vezi cum merge fara el; coolerul ar trebui alimentat separat fiind o sursa serioasa de perturbatii

Ford_V6 · 1st June 2003, 03:37 PM

It's ok now. I have disconected the power ground from the tone control and it's working good only with the signal ground. The noise is gone. Thanks for help.

P.S. N-am vb. in romana sa nu zica lumea ca ii injuram. Oricum merci de sfaturi.

29th May 2003, 06:13 PM	#1
Ford_V6 diyAudio Member Join Date: Mar 2003 Location: Bucharest	Amp noise !!! Please Help !!! Hy ! I have a big problem: I built from scratch an amp based on the TDA7250 and TIP142/147. I have found a transformer that i have rebuild to get 32-0-32 and 11-0-11. I have rectified the 32-0-32 trough a 25 amps bridge and filtered trough 2 x 10000 Uf caps. I got 44-0-44 V The 11-0-11 is rectified trough a 5 amps bridge and 2 x 4700 Uf caps. Now from the 44-0-44 i feed the amp and from the 14-0-14 (rectified) i feed a computer cooler and a LM1036N tone control. I have put all in a case and it looks pretty good. It sounds great but . . . . i have a very loud noise with the cooler on. With the cooler off i have the same noise but smaller. What can i do to get rid of the noise and enjoy my amp ? Thnaks in advance.

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29th May 2003, 07:00 PM	#2
JOE DIRT® diyAudio Member Join Date: Apr 2003 Location: Brantford, ON	Hi Ford... have you bypassed your large filter caps with smaller ones>???.....and what type of grounding arrangement are you using with source and signal>????.....it sounds to me like a ground problem

29th May 2003, 11:50 PM	#4
jeffreyj diyAudio Member Join Date: May 2003 Location: Tampa, FL	Make sure that your main ground is not where the filter capacitors connect together! Also, sometimes a star ground is not the best solution when something dirty, like a fan is connected there. It is best to connect all sensitive circuits to one star ground and then the noisy stuff to another star ground. A pigtail from the junction of the reservoir capacitors to these two stars completes the circuit. The chassis, by the way, should be connected to earth on the mains side. It is optional to join the circuit ground to the earthed chassis. Hope this helps and good luck with your amp!

30th May 2003, 07:33 AM	#6
Ford_V6 diyAudio Member Join Date: Mar 2003 Location: Bucharest	The main ground of the amplifier is conected where the two large caps get together. The ground of the tone control is the same as the amplifier for the in and out ( signal ) but the power ground of the tone control is connected together with the ground of the fan where the 4700 caps go togheter. Can somebody describe me a better grounding scheme for my setup ?

31st May 2003, 08:00 PM	#7
raindog diyAudio Member Join Date: May 2003 Location: Timisoara	buna, cred ca problema e la circuitul lm1036 incearca eventual sa vezi cum merge fara el; coolerul ar trebui alimentat separat fiind o sursa serioasa de perturbatii

1st June 2003, 03:37 PM	#8
Ford_V6 diyAudio Member Join Date: Mar 2003 Location: Bucharest	It's ok now. I have disconected the power ground from the tone control and it's working good only with the signal ground. The noise is gone. Thanks for help. P.S. N-am vb. in romana sa nu zica lumea ca ii injuram. Oricum merci de sfaturi.

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