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

OSVA - Open source Versatile Analyzer
OSVA - Open source Versatile Analyzer
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 29th June 2020, 09:39 AM   #121
JensH is offline JensH  Denmark
diyAudio Member
 
Join Date: Jul 2009
OSVA - Open source Versatile Analyzer
Quote:
Originally Posted by Frex View Post
Hello,

For now, the best results i have is with the ada4945-1, but adding some tweak because the part behavior is not well documented.
Hi Frex,

Could you tell more about your tweaks and experience with the ada4945-1?
I am close to mounting an ada4945-1 test board, which I plan to test as a driver for the AK5394A. Your findings could probably be very useful.
  Reply With Quote
Old 29th June 2020, 04:13 PM   #122
Frex is online now Frex  France
diyAudio Member
 
Join Date: Nov 2009
Hello,

I'm not very familiar with mechanical software, but even if FreeCAD seem a little bit difficult to use,
anyway after some time it do the job well and for now i can do what i want.
I must admit that i prefer to use in general open-source solution.
Another point is that there some tool allowing easy CAD interface between Kicad and Freecad.



JenSH,

First, there is an inconsistency between the AD datasheet and the eval board.
The bottom pad of the IC is connected to ground in EVM but the datasheet
say explicitly to connect it to negative rail !
You can look my complete post on AD support on link here,
you will see all the story. I hope that will help you.

Regards

Frex
  Reply With Quote
Old 29th June 2020, 08:25 PM   #123
JensH is offline JensH  Denmark
diyAudio Member
 
Join Date: Jul 2009
OSVA - Open source Versatile Analyzer
Thanks.
In my case I have connected the supply and the center pad to GND, planning to use a 5 V supply.
It will be interesting to see if using only a single sided 5 V supply will give any downsides.
Worst case I can probably still apply a -2.5 V and +7.5 V supply. I won't be able to use the clamp function though with the current layout.

So, not really a conclusion on your support question to ADI.
If it can be of any help, I can report some of what I experienced during the development of the RTX6001.
At some points in time I had instability in the input stage, leading to oscillation in the 8 to 9 MHz region, in one case around 12.5 MHz. In my case I could measure it with an oscilloscope.
It gave a result similar to what you have seen, with a large increase in the distortion level. In one occation it went from -127 dB THD to -95 dB.

My guess is that you actually have some instability, most likely caused by the long input traces. Perhaps it is only present in the input stage of the ADA4945-1, so that you don't see it on the output? The fact that it only occurs when you use the full bandwidth also points towards instability.
I don't have any practical experience with the device (yet), so don't take it for more than an attempt to help, based on experience with a similar problem although that was using a completely different circuit.

By the way, do you have any experience with performance differences between a 5 V only supply and a +7.5 and -2.5 V supply?
  Reply With Quote
Old 29th June 2020, 09:01 PM   #124
Joseph K is offline Joseph K  Hungary
diyAudio Member
 
Join Date: Dec 2004
Location: gran sasso
May I say that not by accident they have invented that FB node.. That it is brought out directly beside the input pins. These amps are not that high speed, and still, they can be more picky than a real high speed amp.
So by design it is intended that a 0603 or even smaller feedback resistance is put directly at the pins..
Instead I see that a full trip including the relay contacts is placed there.. I feel that it is stretching a bit too much.
If I would face this problem I would cut out everything, would place a single small feedback resistance as intended, and would try that way, if the instability is still there..
Also, I could not see how the ground layer is formed. Is it cut out in the input pins/traces zone? That had happened to us already once, too much dispersed capacitance on the input pins. (and that was without that extra amount of traces/ relay..)
I'm just thinking out loud, please bear it with me..

Usually this can be seen, but not with a scope. Best is a network analyzer, then a spectrum analyzer or a good scope with spectrum an. /FFT function.

Ciao, George
  Reply With Quote
Old 30th June 2020, 04:16 PM   #125
Frex is online now Frex  France
diyAudio Member
 
Join Date: Nov 2009
Hello,

II tried many things (some suggested by AD) without found any evidence
of oscillating behaviour.
I know that the signal path i use is quite large than it would be,
but the adopted topology i used require this and i have done it whith great care.
I my mind as Joseph K say the stray capacitance between feedback traces
and ground planes add some capcitance and i really thing that it disturb
the AD4945-1 input stage.

For finishing, i successfully cancelled the THD spurious by adding a small
RC network between IN+/IN- of the FDA, near it.
This work well in both operation modes of ADA4945-1.
(I tried a little in 0-5V mode and it work also very well).


Frex
 

Reply


OSVA - Open source Versatile AnalyzerHide 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
[Open source] TINA The total open source Audiophile Player based on Beaglebone Black DragonWar PC Based 7 18th December 2016 02:31 PM
Ultimate Open Source XMOS USB-I2S: The source to end all sources. krfkeith Digital Source 4 14th June 2013 03:54 PM
Volume / Source selector - open source project ? AuroraB Analog Line Level 22 22nd September 2012 02:21 PM
XTZ Room Analyzer - US source Zodiac Vendor's Bazaar 1 5th October 2010 11:58 PM
Open call for suggestions on Open Source DIY Audio Design gfergy Everything Else 1 15th April 2007 07:33 AM


New To Site? Need Help?

All times are GMT. The time now is 06:02 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki