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

Solid State Talk all about solid state amplification.

Proper way to servo a balanced receiver
Proper way to servo a balanced receiver
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 3rd December 2008, 03:44 PM   #1
00940 is offline 00940  Belgium
diyAudio Member
 
00940's Avatar
 
Join Date: Sep 2003
Location: Liège
Default Proper way to servo a balanced receiver

I'm wondering how to properly integrate a servo in a classical "one opamp" balanced line receiver. Is the schematic attached the proper way to do it ?

I'm a bit surprised to not find anything about this by searching this forum. CDPs output stages after a balanced output DAC often use coupling caps for example
Attached Images
File Type: png sans titre.png (3.7 KB, 208 views)
__________________
Ben.
  Reply With Quote
Old 3rd December 2008, 09:07 PM   #2
Steve Dunlap is offline Steve Dunlap  United States
diyAudio Member
 
Steve Dunlap's Avatar
 
Join Date: Sep 2008
Location: Here
I believe this or something similar is what THAT CORP. is doing in their balanced line receivers. If implemented correctly, the circuit shown should work. It did for me 20 years ago.
  Reply With Quote
Old 4th December 2008, 08:07 PM   #3
00940 is offline 00940  Belgium
diyAudio Member
 
00940's Avatar
 
Join Date: Sep 2003
Location: Liège
Thanks for the comment

Actually, from what I saw on the THAT website, they're either using a way more complicated four-opamps system (high performance solution) or simpler one-opamp receiver. They are not servoed at first sight. But they certainly look interesting (very nice thd and rejection figures).

In this case however I want to use a discrete amplifer as U1 and an opa134 or opa227 for U2.

Btw, this is not the receiver described in the Walt Jung opamp applications book: http://books.google.be/books?id=dunq...C&pg=RA6-PA454
__________________
Ben.
  Reply With Quote
Old 4th December 2008, 09:52 PM   #4
Steve Dunlap is offline Steve Dunlap  United States
diyAudio Member
 
Steve Dunlap's Avatar
 
Join Date: Sep 2008
Location: Here
I should have paid more attention to your schematic the first time. If you have drawn this as you intended you are only amplifying the differences in your input. This is not a conventional balanced line receiver. Since your Vin's are different you will have a signal, but you will have no low frequencies (because of C1).

It is also possible that I am confused about exactly what you are trying to do.
  Reply With Quote
Old 5th December 2008, 12:46 AM   #5
00940 is offline 00940  Belgium
diyAudio Member
 
00940's Avatar
 
Join Date: Sep 2003
Location: Liège
In the schematic :

U1 + R2/R3/R4/R45 is the usual difference amplifier.

R1 is the load

V3/V4 are the input voltages, with different DC offsets (2 and 1.8VDC). On the schematic, ac signal is at 0v/1khz

U2+R6/R7/C1 is the servo.

In simulator at least, 20hz signals are not attenuated. The servo controls the the usually grounded leg of R3 and feeds there a DC offset to balance the offsets at the input.

What I had in mind was to guarantee 0v offset at the output of the receiver, despite varying offsets at the inputs, instead of just a trimmer. Sorry I wasn't clear.
__________________
Ben.
  Reply With Quote
Old 5th December 2008, 07:03 PM   #6
Steve Dunlap is offline Steve Dunlap  United States
diyAudio Member
 
Steve Dunlap's Avatar
 
Join Date: Sep 2008
Location: Here
My mistake was in thinking the 1.8V and 2V were the AC signal in with 0 DC offset. It did not make sense that they were in phase and would cancel with only the .2V to be amplified. Now that your explanation has cleared that up, yes this is one of the ways to servo out the DC. It will also remove low frequencies just like a cap in the output. At what point this happens depends on the cap value and the impedances around it.

You have shown the amp (U1) as unity gain. I assume this is what you intended. Still, with positive feedback at low frequencies you may have a problem with oscillation. You can avoid this problem by making U2 non inverting and routing the output to the inverting input of U1.
  Reply With Quote

Reply


Proper way to servo a balanced receiverHide 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
Balanced Driver / Receiver arigy Solid State 11 14th June 2010 10:26 AM
Balanced shunt pot in front of a differential receiver 00940 Solid State 3 9th September 2008 01:09 PM
Balanced receiver and offset adjustment ? 00940 Solid State 2 30th March 2006 07:24 AM
Balanced DC servo for balanced stage ? CheffDeGaar Solid State 8 9th July 2003 03:39 PM
rod's balanced driver & receiver hugobross Solid State 2 19th March 2003 09:36 AM


New To Site? Need Help?

All times are GMT. The time now is 07:19 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki