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

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

How to convert unbalanced input to differential for an opamp filter
How to convert unbalanced input to differential for an opamp filter
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 24th September 2018, 12:40 PM   #1
ygg-it is offline ygg-it  Italy
diyAudio Member
 
ygg-it's Avatar
 
Join Date: Feb 2008
Default How to convert unbalanced input to differential for an opamp filter

I have the following filter working with an unbalanced source chip (DAC).

Now I have to change to a source chip (DAC) that has differential outputs.

Thus I will build a new filter.

Is there a simple way to convert the filter (maintaining identical design/performances/orders) using differential inputs, instead of unbalanced like now?

Is there any simple formula for the components? (Output should remain RCA unbalanced).

It doesn't matter to use two opamps or add an extra one.

(Components values in the schematic are dummy as I cannot reproduce true ones for copyright reason, but please use these one.)


Click the image to open in full size.
  Reply With Quote
Old 24th September 2018, 01:23 PM   #2
MarcelvdG is offline MarcelvdG  Netherlands
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
You could connect V4 to the bottom side of R4 and connect a resistor and a capacitor equal in value to R1 and C2 from the positive input of the first op-amp to ground, if the DAC can handle the load. The first op-amp is then used as a differential to single-ended converter.

Compared to the present circuit you lose a zero, but I'm not sure if you wanted it in the first place.
  Reply With Quote
Old 24th September 2018, 02:06 PM   #3
ygg-it is offline ygg-it  Italy
diyAudio Member
 
ygg-it's Avatar
 
Join Date: Feb 2008
Quote:
Originally Posted by MarcelvdG View Post
You could connect V4 to the bottom side of R4 and connect a resistor and a capacitor equal in value to R1 and C2 from the positive input of the first op-amp to ground, if the DAC can handle the load. The first op-amp is then used as a differential to single-ended converter.

Compared to the present circuit you lose a zero, but I'm not sure if you wanted it in the first place.
Thanks! That was exactly what I simulated, but I didn't get the same slope...

Any way to maintain all zeros?

What about to duplicate U1 and make U2 single ended converter (fed by two U1)?
  Reply With Quote
Old 24th September 2018, 08:53 PM   #4
MarcelvdG is offline MarcelvdG  Netherlands
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
Replacing C2 and the capacitor from the positive input to ground with RC series networks should do the trick. With R = 10 kohm and C = (34/44)*300 pF, for example. Changing the second stage into the differential-to-single-ended converter seems more complicated to me.
  Reply With Quote
Old 25th September 2018, 07:07 AM   #5
ygg-it is offline ygg-it  Italy
diyAudio Member
 
ygg-it's Avatar
 
Join Date: Feb 2008
You are a star! Thanks. This is the sort of help I like to receive from this forum! That works: same slope!

Now I'm trying to change the second stage, but, as you said it is very difficult.
Attached Images
File Type: jpg FRom unbalanced to differential inputs 1 st stage.jpg (195.5 KB, 75 views)
Attached Files
File Type: asc opamp balanced to unbalanced diyaudio.asc (5.9 KB, 6 views)
  Reply With Quote

Reply


How to convert unbalanced input to differential for an opamp filterHide 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
Is low differential input impedance of opamp not important? Alan0354 Solid State 4 16th July 2015 09:18 AM
Convert CD from unbalanced to balanced output? aps Digital Source 13 6th January 2011 10:51 AM
DM/CM RFI filter on instrumentation opamp input xiphmont Solid State 14 2nd January 2010 02:03 AM
Tube differential input/buffer /w opamp output gainclone aletheian Chip Amps 2 23rd August 2005 08:36 AM
Transformer at input of SOZ to convert unbalanced->balanced? psarin Pass Labs 29 29th December 2003 06:13 AM


New To Site? Need Help?

All times are GMT. The time now is 06:37 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki