Balanced/unbalanced line receiver - Page 3 - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 11th February 2014, 10:26 PM   #21
diyAudio Member
 
Join Date: Feb 2014
Forgive the dreadful drawing!!

So what I tried to do here is show the two stages I built. On the left is my 'instrumentation amp' which I am hoping will operate as a balanced line receiver. So in balanced mode, my hot output goes to Vin+ and the cold output goes to Vin- . The two input IC's are the two halves of an INA2134 and with the resistors I used, I think the gain of this bit is =2. The differential amp is an INA137 with a gain of 1/2 so overall my 'receiver' has an overall gain of close to 1.

I have not tested this with a balanced input yet. BUT......

I did test this with the guitar (listening at Vout so without the 'buffer' cct that I have also drawn) and connected my TR cable tip to Vin+ and the Vin- to ground. So not a balanced cct obviously. And it sounds great!

The attenuation and 'muddiness' is gone and in fact I get a nice 'buffered' tone. Not surprising I guess, since I now have a nice high-Z input!

The circuit drives all my pedals so responds well and drives loads with varying input impedances of their own. So all good so far.

The buffer cct I have drawn was not used in these tests, to this point as I say, but sounded very good when I did add it after the 'receiver'

So I guess my question now becomes, do you think my 'receiver' circuit will cut it as a balanced line receiver when I do plug a balanced input into it or have I in someway compromised the whole thing? Assuming the answer is that it will function as a basic balanced receiver, does anyone have any suggested improvements?
  Reply With Quote
Old 11th February 2014, 10:32 PM   #22
diyAudio Member
 
Join Date: Feb 2014
Zero D thank you for your circuit btw. What you are drawing of course makes sense, but my goal is to have a single jack device with no manual switches.

So if I plug in a TRS lead from a balanced output, I get the benefits of a balanced receiver, and if I plug in a TR cable firect from the guitar, then ok it is not balanced, but I basically get a gain=1 signal out of the receiver. (and if fact a bit of a buffer based on the fact that I have a good Hi-Z input now.)
  Reply With Quote
Old 12th February 2014, 08:54 AM   #23
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Is your IC1 and IC2 actually an INA2134, or an OPA2134? As you cannot use an INA2134 in that scheme due to its built in resistors. Also, the hot and cold inputs will need some resistance to ground to bias them.

If you graft on the buffer circuit to the balanced input it will unbalance the circuit.

If you do not want a switch, I think your only option is a traditional balanced input using the resistor values I posted earlier. But looking at your circuit you have more gain for the guitar input, this can't easily be accomodated.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.

Last edited by richie00boy; 12th February 2014 at 08:59 AM.
  Reply With Quote
Old 12th February 2014, 07:24 PM   #24
diyAudio Member
 
Join Date: Feb 2014
Hi Richie, yes it's definitely an ina2134 I am using. I don't have anything connected to the sense or reference pins, so I figured that whilst I do have a small resistance on the negative and positive inputs it wouldn't be too big a deal. I did toy with using an opa2134 but don't have one handy.

The circuit is definitely working in some way shape or form. Without the buffer circuit attached, like I say I get close to a unity gain through the ina2134 and ina137 stages, which is what I thought I had calculated.

I am not grafting the buffer circuit onto the input of the balanced input, I have only used it on the output side of the balanced receiver, and really I only did this to see what happened. When I did this it all seemed to behave. I actually have a pot in the feedback of the op amp which acts as a gain control and then the pot on the output is like a volume control and as I say it seemed to sound ok. I think I may have confused the issue by making reference and drawing my buffer circuit, for now I probably won't use it and want to focus on the balanced/unbalanced hi-z input stage.

Back to the receiver itself I got a little confused when you said I need to bias the hot and cold inputs to ground. Could you explain why I would do this with different values? Also when you refer to a traditional balanced input, is what I have with the two ina chips significantly different to a traditional balanced input circuit?
  Reply With Quote
Old 12th February 2014, 09:53 PM   #25
diyAudio Member
 
Join Date: Feb 2014
http://http://www.douglas-self.com/a...d/balanced.htm

Figure 13 in this article sounds interesting. Is this what a traditional balanced receiver might look like?
  Reply With Quote
Old 13th February 2014, 04:20 AM   #26
diyAudio Member
 
Join Date: Feb 2008
Location: Melbourne
Hi,
I think a INA163 instrumentation opamp is what you need, with an RF filter and some biasing resistors on the input. The gain can be adjusted from 1 to lots! The INA163 is available from Mouser and/or Digikey for about $9.

See attached (poor) drawing.

Paul Bysouth
Attached Images
File Type: jpg INA163-example.JPG (88.2 KB, 102 views)
  Reply With Quote
Old 13th February 2014, 08:43 AM   #27
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
OK. You just won't be getting full potential with the inbuilt resistors being there.

All op-amps need a DC path to ground to meet their input bias current needs. When you plug a guitar in it's fine because the pickup is connected to ground, but once you connect something with a balanced output - which will have DC blocking caps - the circuit will go wild. It will also go wild without any input connected.

Figure 13 is what I would recommend you try as it offers a lot of the features you need.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 13th February 2014, 01:56 PM   #28
diyAudio Member
 
Join Date: Feb 2014
Paul, I like the idea of the INA163, and thank you for the sketch (your drawing is far better than mine btw ) Your proposal looks like a similar but neater and more compact version of the circuit I had stumbled towards but also with the additional information on filtering and biasing, this is an enormous help! Thank you again, can't wait to try it!.

Richie, that makes sense in terms of the bias, and I think Paul's proposal has this drawn in.

Guys I am so grateful for your input!!
  Reply With Quote
Old 13th February 2014, 09:33 PM   #29
diyAudio Member
 
Join Date: Feb 2014
Damn, the ina163 only seems to be available as surface mount
  Reply With Quote
Old 13th February 2014, 10:32 PM   #30
diyAudio Member
 
Join Date: Feb 2008
Location: Melbourne
There is also the INA103 which is available in a DIP16 package, but at almost twice the price of the INA163. Digikey have them in stock at the moment.

Paul Bysouth
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
line level unbalanced to balanced converter steevo Analog Line Level 17 16th February 2014 04:09 PM
Balanced to Unbalanced Line Conversion Loren42 Tubes / Valves 33 4th January 2011 06:31 PM
Unbalanced to Balanced Line Level XFMR wrenchone Solid State 8 22nd October 2005 09:06 PM
Balanced line stage, quistion's + unbalanced lykkedk Pass Labs 4 20th December 2002 12:58 AM
Zen Balanced Line Stage Balanced vs Unbalanced macka Pass Labs 28 11th December 2002 07:18 AM


New To Site? Need Help?

All times are GMT. The time now is 12:50 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2