Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Equipment & Tools From test equipment to hand tools

Passive Filter for Class D Amp Testing
Passive Filter for Class D Amp Testing
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 July 2015, 12:18 AM   #1
leadcoma is offline leadcoma  Canada
diyAudio Member
 
Join Date: Jan 2009
Location: Scarborough
Default Passive Filter for Class D Amp Testing

I'm testing a Class D amp with my computer sound card and I've been told I need a passive 20Hz-20KHz filter to limit the high frequency output of the amp. Audio Precision's AUX-0025 is an obvious choice but beyond my budget.

Does anyone know where I can buy a low cost passive filter for testing Class D amps?

Last edited by leadcoma; 13th June 2017 at 04:11 PM.
  Reply With Quote
Old 14th July 2015, 06:13 AM   #2
Samuel Groner is offline Samuel Groner  Switzerland
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
You probably mean Audio Precision, not Audio Control?

If the amplifier is well designed (in particular has low conducted EMI), you could very likely use a DIY active low-pass filter, or perhaps even get away without any filter (particularly if your sound card has good anti-image filters).

See also the post by Putzeys here: Stanford Research Systems - SR1 - Dual-domain audio analyzer - Experiences?

Samuel
  Reply With Quote
Old 14th July 2015, 06:31 AM   #3
Keruskerfuerst is offline Keruskerfuerst  Germany
diyAudio Member
 
Keruskerfuerst's Avatar
 
Join Date: May 2007
Location: Germany
Construct a high pass 20HZ and low pass 20kHz active filter. This can easily be done.
  Reply With Quote
Old 14th July 2015, 07:21 AM   #4
arnyk is offline arnyk  United States
Banned
 
Join Date: Jan 2014
Location: Grosse Pte Wds MI
Quote:
Originally Posted by leadcoma View Post
I'm testing a Class D amp with my computer sound card and I've been told I need a passive 20Hz-20KHz filter to limit the high frequency output of the amp. Audio Control's AUX-0025 is an obvious choice but beyond my budget.

Does anyone know where I can buy a low cost passive filter for testing Class D amps?
If the ultrasonics at the amp output aren't large enough to cause appreciable distortion in the measuring gear, you can do the low pass filtering in the digital domain, after you collect the signal and before you apply your measurements.

Or you can just identify the high frequency components you want to ignore and remove their influence from your analysis of the output signal.
  Reply With Quote
Old 14th July 2015, 07:21 AM   #5
caligulaminus is offline caligulaminus  India
diyAudio Member
 
Join Date: Oct 2014
Good paper, looking mostly at their "filter free" class D amps. http://www.ti.com/lit/an/sloa068/sloa068.pdf
  Reply With Quote
Old 14th July 2015, 09:46 PM   #6
leadcoma is offline leadcoma  Canada
diyAudio Member
 
Join Date: Jan 2009
Location: Scarborough
yes, Audio Precision. thanks for catching that and sharing the link.

DIY is an option but I'd rather purchase a low cost filter.

Quote:
Originally Posted by Samuel Groner View Post
You probably mean Audio Precision, not Audio Control?

If the amplifier is well designed (in particular has low conducted EMI), you could very likely use a DIY active low-pass filter, or perhaps even get away without any filter (particularly if your sound card has good anti-image filters).

See also the post by Putzeys here: Stanford Research Systems - SR1 - Dual-domain audio analyzer - Experiences?

Samuel
  Reply With Quote
Old 14th July 2015, 09:57 PM   #7
leadcoma is offline leadcoma  Canada
diyAudio Member
 
Join Date: Jan 2009
Location: Scarborough
Quote:
Originally Posted by arnyk View Post
If the ultrasonics at the amp output aren't large enough to cause appreciable distortion in the measuring gear, you can do the low pass filtering in the digital domain, after you collect the signal and before you apply your measurements.

Or you can just identify the high frequency components you want to ignore and remove their influence from your analysis of the output signal.
These are 250W Class D amps with significant 480KHz output that clips the sound card input buffers.
  Reply With Quote
Old 15th July 2015, 08:27 AM   #8
udok is offline udok  Austria
diyAudio Member
 
Join Date: Jul 2011
Location: Austria
Here is a simple passive filter which does what you need. Beware that
the 10 Ohm source impedance is important and that the values should be better than 2%.

Use Polypropylen capacitors and good wire wound inductors, ideally with an air core.

The second filter has a -3dB of 50 kHz and imperfections of L and C do not effect the audio band as much as the first version.
Attached Images
File Type: png PassiveFilt1.png (34.2 KB, 434 views)
File Type: png PassiveFilt2.png (32.7 KB, 421 views)

Last edited by udok; 15th July 2015 at 08:56 AM. Reason: added 2nd filter
  Reply With Quote
Old 15th July 2015, 08:58 AM   #9
arnyk is offline arnyk  United States
Banned
 
Join Date: Jan 2014
Location: Grosse Pte Wds MI
Quote:
Originally Posted by leadcoma View Post
These are 250W Class D amps with significant 480KHz output that clips the sound card input buffers.
One word: attenuator.

I build mine into the dummy loads.
  Reply With Quote
Old 15th July 2015, 11:17 PM   #10
leadcoma is offline leadcoma  Canada
diyAudio Member
 
Join Date: Jan 2009
Location: Scarborough
Udok, thank you for the filter designs! It looks like I may just need to build my own.

Arnyk, good suggestion. I will give it a try.
  Reply With Quote

Reply


Passive Filter for Class D Amp TestingHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Passive filter for loudspeakers - filter simulation torgeirs Software Tools 2 26th June 2015 07:47 AM
Passive filter at tube amp input WDYSUN Tubes / Valves 8 19th February 2010 08:23 AM
Active filter to Class-D amp. Cyberzim Class D 2 10th October 2009 06:06 PM
passive filter + non-inverting amp for output stage.. luigi_secchi00 Digital Source 3 12th March 2007 03:09 PM
Amplifier & filter testing palesha Solid State 1 1st December 2002 02:33 PM


New To Site? Need Help?

All times are GMT. The time now is 05:42 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki