Sure TPA3122D2 Mods - Page 2

prezden · 14th January 2013, 11:54 PM

I listed the caps in my first post. Will take some more photos and get them up later this eve.
Thanks for all your help

killerbobjr · 16th January 2013, 03:15 PM

The two input caps in the BOM appear to be mylar film caps. Replacing these with good polypropylene caps will improve the sound quality. The BYPASS cap (C14) is a mono ceramic. The BYPASS pin is the feedback loop bypass of the analog first stage. It definitely needs a quality polypropylene cap. I've found the change in audio quality to be noticeable.

The analog stage power supply isolation mod is a more subtle mod. The internal analog stage opamps theoretically should cancel out 100% of the power supply noise via common mode rejection. I've found this to be rarely the case. Further, the majority of the power supply noise is coming from the switching frequency of the digital output stage, which means the input stage opamps are doing the greatest amount of feedback at the output stage's switching frequency. If you think about it, the analog stage is doing the adjustment right at the point the digital stage is switching -- it's not a clean path for an audio signal. Adding a filter for the analog stage power supply reduces this potential for distortion.

The output caps (2x220uF) into an 8 ohm load roll off at about 44Hz, so increasing them to the recommended values lowers the roll off to about 9Hz, which will increase the amount of bass you'll be able to hear.

prezden · 16th January 2013, 05:18 PM

Here are a couple detail photos of what I have done so far. I thought I posted them yesterday but for some reason it didn't work

wushuliu · 16th January 2013, 05:31 PM

I personally would replace all those caps with the ones I mentioned earlier (muse, cerafine, silmic, etc). These TPA chips are very, very sensitive to PS cap changes and the better caps are still plenty affordable so no reason not to try them. The 1uf is a Panasonic X2? X2 are fine if you're using for AC power filtering but poor performers usually sound quality wise as input caps. Even a Solen or Bennic would probably sound better there. I also agree with earlier advice to use higher values for the PS caps.

I Agree w/ Killerbobjr.

Just my .02.

Budgie · 16th January 2013, 08:03 PM

Before changing caps (again), What power supply do you have running the the Sure board?

prezden · 16th January 2013, 08:05 PM

Power supply is a 24v meanwell

prezden · 17th January 2013, 10:23 PM

Thanks for all your suggestions.
I have another question if I may:

Quote:

The BYPASS cap (C14) is a mono ceramic. The BYPASS pin is the feedback loop bypass of the analog first stage. It definitely needs a quality polypropylene cap.

What size cap would you recommend? And just C14 leaving C13 & 15 as they are?

Dumb question #2- Are the power caps and the rail caps the same thing

I think I need a Amplifier Design for Dummies book

Thanks

killerbobjr · 19th January 2013, 12:10 AM

Rule of thumb -- make the BYPASS cap value the same as the input cap value. The input cap value should be based on your required bass cut off, which is determined by the input impedance, which is controlled by the amp gain. The minimal input impedance at the 36dB gain selection is 9Kohm, while the maximum impedance is 60Kohm at 20dB gain (all this is in the TPA3122D2 data sheet). Use the standard filter formula to determine this value:

C = 1 / (2 * 3.14 * frequency * impedance)

where 'frequency' is how low you want your bass response to be (20Hz is pretty standard), and 'impedance' is the input impedance based on the gain selected (look it up in the data sheet).

For terminology, "Power supply voltage" = "voltage rails" = "V+" and/or "V-". These all generally refer to the same thing.

prezden · 20th January 2013, 11:30 PM

I was going to order some Panasonic KA caps but not sure what to order.

My understanding is that the rule of thumb is to replace power caps with ones of the same or greater voltage. Please correct me if I am wrong. The KA's and Muse caps at 470uf are only 4v where as the ones specified for the board are 35v. Which is more important (uf or v). I was targeting 470uf because they will fit on the board.

cheers

killerbobjr · 23rd January 2013, 03:05 AM

Your power cap voltage ratings should always be more than your maximum power supply voltage. If I remember my rule of thumb with an unregulated power supply, you add a 20% margin on the maximum expected unregulated voltage for safety's sake. If you have a regulated power supply, (a 24V laptop switching supply for instance), you can use 25V rated capacitors and not worry about it.

The power supply capacitance values are based on two things: A. Ripple rejection on an unregulated supply; and B. the low frequency cutoff for your output impedance load. You need to calculate the minimum capacitance required for both. I generally like keeping the ripple to less than 1% at full load and the cut off frequency of the rails an octave lower than the cut off of the signal path, whichever is the larger capacitance value (i.e. if I calculate 100uF for a 10Hz cutoff, but 200uF for a 1% ripple, I use 200uF).

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14th January 2013, 11:54 PM	#11
prezden diyAudio Member Join Date: Nov 2008	I listed the caps in my first post. Will take some more photos and get them up later this eve. Thanks for all your help

16th January 2013, 03:15 PM	#12
killerbobjr diyAudio Member Join Date: Sep 2004 Location: killer	The two input caps in the BOM appear to be mylar film caps. Replacing these with good polypropylene caps will improve the sound quality. The BYPASS cap (C14) is a mono ceramic. The BYPASS pin is the feedback loop bypass of the analog first stage. It definitely needs a quality polypropylene cap. I've found the change in audio quality to be noticeable. The analog stage power supply isolation mod is a more subtle mod. The internal analog stage opamps theoretically should cancel out 100% of the power supply noise via common mode rejection. I've found this to be rarely the case. Further, the majority of the power supply noise is coming from the switching frequency of the digital output stage, which means the input stage opamps are doing the greatest amount of feedback at the output stage's switching frequency. If you think about it, the analog stage is doing the adjustment right at the point the digital stage is switching -- it's not a clean path for an audio signal. Adding a filter for the analog stage power supply reduces this potential for distortion. The output caps (2x220uF) into an 8 ohm load roll off at about 44Hz, so increasing them to the recommended values lowers the roll off to about 9Hz, which will increase the amount of bass you'll be able to hear.

16th January 2013, 05:31 PM	#14
wushuliu diyAudio Member Join Date: May 2008 Location: Los Angeles	I personally would replace all those caps with the ones I mentioned earlier (muse, cerafine, silmic, etc). These TPA chips are very, very sensitive to PS cap changes and the better caps are still plenty affordable so no reason not to try them. The 1uf is a Panasonic X2? X2 are fine if you're using for AC power filtering but poor performers usually sound quality wise as input caps. Even a Solen or Bennic would probably sound better there. I also agree with earlier advice to use higher values for the PS caps. I Agree w/ Killerbobjr. Just my .02.

16th January 2013, 08:03 PM	#15
Budgie diyAudio Member Join Date: Jan 2003 Location: Puddletown, Oregon	Before changing caps (again), What power supply do you have running the the Sure board?

16th January 2013, 08:05 PM	#16
prezden diyAudio Member Join Date: Nov 2008	Power supply is a 24v meanwell

19th January 2013, 12:10 AM	#18
killerbobjr diyAudio Member Join Date: Sep 2004 Location: killer	Rule of thumb -- make the BYPASS cap value the same as the input cap value. The input cap value should be based on your required bass cut off, which is determined by the input impedance, which is controlled by the amp gain. The minimal input impedance at the 36dB gain selection is 9Kohm, while the maximum impedance is 60Kohm at 20dB gain (all this is in the TPA3122D2 data sheet). Use the standard filter formula to determine this value: C = 1 / (2 * 3.14 * frequency * impedance) where 'frequency' is how low you want your bass response to be (20Hz is pretty standard), and 'impedance' is the input impedance based on the gain selected (look it up in the data sheet). For terminology, "Power supply voltage" = "voltage rails" = "V+" and/or "V-". These all generally refer to the same thing.

20th January 2013, 11:30 PM	#19
prezden diyAudio Member Join Date: Nov 2008	I was going to order some Panasonic KA caps but not sure what to order. My understanding is that the rule of thumb is to replace power caps with ones of the same or greater voltage. Please correct me if I am wrong. The KA's and Muse caps at 470uf are only 4v where as the ones specified for the board are 35v. Which is more important (uf or v). I was targeting 470uf because they will fit on the board. cheers

23rd January 2013, 03:05 AM	#20
killerbobjr diyAudio Member Join Date: Sep 2004 Location: killer	Your power cap voltage ratings should always be more than your maximum power supply voltage. If I remember my rule of thumb with an unregulated power supply, you add a 20% margin on the maximum expected unregulated voltage for safety's sake. If you have a regulated power supply, (a 24V laptop switching supply for instance), you can use 25V rated capacitors and not worry about it. The power supply capacitance values are based on two things: A. Ripple rejection on an unregulated supply; and B. the low frequency cutoff for your output impedance load. You need to calculate the minimum capacitance required for both. I generally like keeping the ripple to less than 1% at full load and the cut off frequency of the rails an octave lower than the cut off of the signal path, whichever is the larger capacitance value (i.e. if I calculate 100uF for a 10Hz cutoff, but 200uF for a 1% ripple, I use 200uF).