TDA2030 swith on thump

EBM_dude · 23rd August 2009, 11:33 AM

At the moment, I'm modding an "Audiophile AA-941" amp that is equipped with two TDA2030A. I plan on swapping the 2030s with TDA2050s. What bothers me is that extremely loud switch on noise. I'm afraid it will kill speakers on the long run. Is there any way to get rid of it or just make it less loud?

jaycee · 23rd August 2009, 11:44 AM

Best solution - add a DC protect circuit with a power-on delay

EBM_dude · 23rd August 2009, 11:54 AM

This is what I was thinking, too. But I didn't want to do it because I think that the TDA20x0 is "not worth it" and I'm shooting for a LM3886 in the future.

sangram · 23rd August 2009, 02:30 PM

Two SPDT relays, one BD139 and one capacitor, plus two resistors. All you need for a delay circuit (not DC protect, just the delay). I used two 12V relays hooked up in series to the +28V power line of a LM4766 + Alien DAC combined amp. The power amp was silent, but the Alien had some flatulence on switch-on. I tried to use the muting circuit on the 4766 to create a delay but it didn't work at all, and I had all the bits in my junk box so it took me all of 10 minutes to work into the circuit. Plus, it was on a separate board so using it somewhere else is a simple matter.

EBM_dude · 05:14 PM

I should have a few relays in my parts bin.Do you think I can substitute the BD139 with a Darlington transistor? I have some 2SD1415. That's a nice NPN Darlington used in car's ECUs to switch on injectors.

jaycee · 23rd August 2009, 05:00 PM

Just wondering how it's wired up ? Is it a single supply amp? The problem in that case is the output capacitor charging, which isn't easy to solve.

EBM_dude · 23rd August 2009, 05:13 PM

It's a split power supply using a 0-12VAC trafo. It doesn't have or need output caps. DC offsett is around 1.2 ... 1.5 mV.
From studying the TDA2050 datasheet, I think the caps for the inverted feedback DC decoupling are the culprit here. So that switch on thump is a design "feature". I wonder what will happen if I just short that cap....

sangram · 23rd August 2009, 06:06 PM

As long as the transistor has Ic ~200mA it should work fine.

How is the amp generating a split supply from a single transformer winding? The charging current at the midpoint is causing the thump. Look at the application notes for Single-supply applications from some of Nat Semi's power amp datasheets (LM3886 has it IIRC). It is not a very easy problem to solve.

The Ci which you have identified keeps the amp's DC gain at unity. Shorting the capacitor may create a slightly higher offset voltage than is normal. It's not safe to do this and tests with your actual speakers.

Dr.EM · 23rd August 2009, 07:39 PM

When I had my TDA2030 based amplifier, which also ran from split supply, I don't actually remember there being any turn on thump. I used a 15v, 0 15v dual secondary transformer (only to be used with 2030AV models and even then I had to drop a bit in reality!).

EBM_dude · 23rd August 2009, 10:27 PM

The darlington transistor can switch up to 7 Amps. Those (saturated) injectors it usually switches draw a bit more than 1 Amp. That's why some folks get fried ECUs if they swap their satured injectors (12-16 Ohms) with peak and hold ones (1-3 Ohms)...

The trafo and rectifier part of the amp looks like this:

23rd August 2009, 11:33 AM	#1
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	TDA2030 swith on thump At the moment, I'm modding an "Audiophile AA-941" amp that is equipped with two TDA2030A. I plan on swapping the 2030s with TDA2050s. What bothers me is that extremely loud switch on noise. I'm afraid it will kill speakers on the long run. Is there any way to get rid of it or just make it less loud?

23rd August 2009, 03:09 PM	#5
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	I should have a few relays in my parts bin.Do you think I can substitute the BD139 with a Darlington transistor? I have some 2SD1415. That's a nice NPN Darlington used in car's ECUs to switch on injectors. Last edited by EBM_dude; 23rd August 2009 at 05:14 PM.

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23rd August 2009, 11:44 AM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Best solution - add a DC protect circuit with a power-on delay

23rd August 2009, 11:54 AM	#3
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	This is what I was thinking, too. But I didn't want to do it because I think that the TDA20x0 is "not worth it" and I'm shooting for a LM3886 in the future.

23rd August 2009, 02:30 PM	#4
sangram diyAudio Member Join Date: Sep 2002 Location: India	Two SPDT relays, one BD139 and one capacitor, plus two resistors. All you need for a delay circuit (not DC protect, just the delay). I used two 12V relays hooked up in series to the +28V power line of a LM4766 + Alien DAC combined amp. The power amp was silent, but the Alien had some flatulence on switch-on. I tried to use the muting circuit on the 4766 to create a delay but it didn't work at all, and I had all the bits in my junk box so it took me all of 10 minutes to work into the circuit. Plus, it was on a separate board so using it somewhere else is a simple matter.

23rd August 2009, 05:00 PM	#6
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Just wondering how it's wired up ? Is it a single supply amp? The problem in that case is the output capacitor charging, which isn't easy to solve.

23rd August 2009, 05:13 PM	#7
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	It's a split power supply using a 0-12VAC trafo. It doesn't have or need output caps. DC offsett is around 1.2 ... 1.5 mV. From studying the TDA2050 datasheet, I think the caps for the inverted feedback DC decoupling are the culprit here. So that switch on thump is a design "feature". I wonder what will happen if I just short that cap....

23rd August 2009, 06:06 PM	#8
sangram diyAudio Member Join Date: Sep 2002 Location: India	As long as the transistor has Ic ~200mA it should work fine. How is the amp generating a split supply from a single transformer winding? The charging current at the midpoint is causing the thump. Look at the application notes for Single-supply applications from some of Nat Semi's power amp datasheets (LM3886 has it IIRC). It is not a very easy problem to solve. The Ci which you have identified keeps the amp's DC gain at unity. Shorting the capacitor may create a slightly higher offset voltage than is normal. It's not safe to do this and tests with your actual speakers.

23rd August 2009, 07:39 PM	#9
Dr.EM diyAudio Member Join Date: Oct 2006 Location: Swindon	When I had my TDA2030 based amplifier, which also ran from split supply, I don't actually remember there being any turn on thump. I used a 15v, 0 15v dual secondary transformer (only to be used with 2030AV models and even then I had to drop a bit in reality!).

23rd August 2009, 10:27 PM	#10
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	The darlington transistor can switch up to 7 Amps. Those (saturated) injectors it usually switches draw a bit more than 1 Amp. That's why some folks get fried ECUs if they swap their satured injectors (12-16 Ohms) with peak and hold ones (1-3 Ohms)... The trafo and rectifier part of the amp looks like this:

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