Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th January 2013, 11:54 PM   #11
prezden is offline prezden  Canada
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
  Reply With Quote
Old 16th January 2013, 03:15 PM   #12
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.
  Reply With Quote
Old 16th January 2013, 05:18 PM   #13
prezden is offline prezden  Canada
diyAudio Member
 
Join Date: Nov 2008
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
Attached Images
File Type: jpg 3122 detail 1.jpg (304.7 KB, 225 views)
File Type: jpg 3122 detail 2.jpg (362.7 KB, 216 views)
  Reply With Quote
Old 16th January 2013, 05:31 PM   #14
diyAudio Member
 
wushuliu's Avatar
 
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.
  Reply With Quote
Old 16th January 2013, 08:03 PM   #15
Budgie is offline Budgie  United States
diyAudio Member
 
Join Date: Jan 2003
Location: Not were I'm suppose to be......
Before changing caps (again), What power supply do you have running the the Sure board?
  Reply With Quote
Old 16th January 2013, 08:05 PM   #16
prezden is offline prezden  Canada
diyAudio Member
 
Join Date: Nov 2008
Power supply is a 24v meanwell
  Reply With Quote
Old 17th January 2013, 10:23 PM   #17
prezden is offline prezden  Canada
diyAudio Member
 
Join Date: Nov 2008
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
  Reply With Quote
Old 19th January 2013, 12:10 AM   #18
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.
  Reply With Quote
Old 20th January 2013, 11:30 PM   #19
prezden is offline prezden  Canada
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
  Reply With Quote
Old 23rd January 2013, 03:05 AM   #20
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).
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
New TPA3122D2 Kit cervelorider Class D 2 4th January 2013 04:58 PM
Class D TPA3122D2 Single sided, all thru hole components Zaaphod Class D 12 22nd September 2011 01:51 PM
TPA3122d2 Amplifier Problem galaxy786 Class D 17 16th July 2009 03:42 PM
TPA3122D2 based amp just clicking and hissing along cynric Class D 6 11th July 2009 01:22 PM
Tpa3122d2 Class D Audio Power aris69 Class D 0 24th June 2009 10:50 PM


New To Site? Need Help?

All times are GMT. The time now is 10:41 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2