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

Software Tools SPICE, PCB CAD, speaker design and measurement software, calculators

Howto - Distortion Measurements with REW
Howto - Distortion Measurements with REW
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 18th July 2019, 10:44 AM   #221
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Howto - Distortion Measurements with REW
You might try adding a 1uF cap to AC couple it and see if that helps. I have had strange behavior sometimes when using the sound card’s own audio output to drive the amp under test. In which case, a standalone unit like Akitika eliminates that. Some sort of feedback issue.

That’s very cool that you have a Lotus and you get to take it on a track. Is this a Lotus 7?

I only get to race on a simulator but have tried several different Lotuses and they are all wonderfully nimble balanced cars to drive.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 18th July 2019, 11:03 AM   #222
enochRoot is offline enochRoot  United States
diyAudio Member
 
enochRoot's Avatar
 
Join Date: Mar 2004
Location: Midcoast Maine
Another thing to mention about the UM2 is that the max input is 1V RMS. Mine seems to overload just shy of that. I wondered why everything I tested seemed to have the distortion go apeshit right around a volt.

Does anyone know the max input level from the Focusrite Solo?
  Reply With Quote
Old 18th July 2019, 11:11 AM   #223
JohnYang1997 is offline JohnYang1997
diyAudio Member
 
Join Date: May 2016
Quote:
Originally Posted by enochRoot View Post
Another thing to mention about the UM2 is that the max input is 1V RMS. Mine seems to overload just shy of that. I wondered why everything I tested seemed to have the distortion go apeshit right around a volt.

Does anyone know the max input level from the Focusrite Solo?
22dbu or 10V at minimum gain for solo.
However what you can do is to add an attenuator to control the input level. Unless you want to measure noise(still useless), you don't need much input level.
The proper way to measure noise is to make a clean 20db to 40db preamp run on batteries, and subtract the gain after it.
  Reply With Quote
Old 18th July 2019, 11:17 AM   #224
enochRoot is offline enochRoot  United States
diyAudio Member
 
enochRoot's Avatar
 
Join Date: Mar 2004
Location: Midcoast Maine
I do have an attenuator on the input, but wanted to know the distortion at various output levels and was hoping I wouldn't have to make some sort of voltage divider.

And how does this noise test setup work?
  Reply With Quote
Old 18th July 2019, 11:32 AM   #225
JohnYang1997 is offline JohnYang1997
diyAudio Member
 
Join Date: May 2016
Quote:
Originally Posted by enochRoot View Post
I do have an attenuator on the input, but wanted to know the distortion at various output levels and was hoping I wouldn't have to make some sort of voltage divider.

And how does this noise test setup work?
It's very common to see distortion at higher level. Most adc will have optimal distortion at around -20db, and will rise after -15db and may start to saturate after -6db.

The attenuator I meant was the voltage divider you mentioned. That's very common way to measure distortion if notch filter is over kill.

The noise setup is separate from the distortion measurement setup. Mentioned here http://www.ti.com/lit/ug/tidu016/tidu016.pdf
  Reply With Quote
Old 18th July 2019, 12:30 PM   #226
elwood625 is offline elwood625  United States
diyAudio Member
 
elwood625's Avatar
 
Join Date: Jan 2013
Location: Illinois
My 1964 Lotus Elan, one of my first DIY projects.
When I get back I'll pay close attention to the test procedure.
Attached Images
File Type: jpg avatar lotus.jpg (53.2 KB, 66 views)
  Reply With Quote
Old 19th July 2019, 10:31 AM   #227
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Howto - Distortion Measurements with REW
Beautiful car. I know you know, but most people do not realize that Colin Chapman, the founder of Lotus, is the inventor of the mid engine as stressed member F1 car layout that is still used today (over 50 years later). The Elan had a beautiful double “Y” backbone chassis. Car weighs only 1500lbs as I recall.

Click the image to open in full size.

Ok, back to our regular programming.

Has anyone made measurements of their amps yet? I see mostly loopbacks posted here.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio

Last edited by xrk971; 19th July 2019 at 10:36 AM.
  Reply With Quote
Old 19th July 2019, 11:23 AM   #228
warrjon is offline warrjon  Australia
diyAudio Member
 
Join Date: Feb 2011
Location: Terang Vic
Quote:
Originally Posted by Panelhead View Post
Looks good. You might try changing the plot and sampling. The plot is a little “ragged” looking as it is.
I have been traveling, but have sorted the loopbacks out for a Focusrite Clarett. Ready to hook up some amplifiers and do the RTA analysis of them.
That was without averaging and 87.5% overlap. With averaging and 50% overlap noise floor dropped.

I'm building a dual mono preamp (buffered - no gain) so this will be handy for THD and channel separation measurements. I'm still waiting for parts, I live 200km from the nearest city so all my shopping is online. Once I have it built I'll post the measurements.

Last edited by warrjon; 19th July 2019 at 11:25 AM.
  Reply With Quote

Reply


Howto - Distortion Measurements with REWHide 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
Distortion and Other Measurements ????? SyncTronX Equipment & Tools 8 29th April 2014 06:57 AM
Distortion measurements, THD, IMD-what card? Eugene Dvoskin Solid State 24 1st January 2011 06:11 PM
Distortion Measurements Nikon1975 Tubes / Valves 8 1st March 2010 12:57 PM
How to do IM distortion measurements? Conrad Hoffman Parts 1 28th May 2007 06:09 PM
Distortion measurements Vg Multi-Way 5 13th August 2004 11:32 AM


New To Site? Need Help?

All times are GMT. The time now is 01:23 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki