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

Chip Amps Amplifiers based on integrated circuits

Chip selection for a fixed-gain low-voltage OPA+BUF
Chip selection for a fixed-gain low-voltage OPA+BUF
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 15th May 2018, 08:38 AM   #1
maxtch is offline maxtch  China
diyAudio Member
 
Join Date: Apr 2018
Location: From Shanghai with Love
Default Chip selection for a fixed-gain low-voltage OPA+BUF

This is intended for my DSP based multi-I/O headphone adapter module. I need a fixed gain OPA+BUF, but the chip selection is problematic.

Specifications (that I am certain) are:
* Upstream: analog output from ADAU1761. Can be differential, can be single ended. Contains a DC bias referenced from a pin on ADAU1761.
* Downstream: Apple EarPods
* Supply voltage: +3.3V only. Have to be RRIO for the sake of output range.
* No need to add volume controls. ADAU1761 has internal PGA for both input and output volume controls.

Questions:
* Is LME49721 OPA + LMH6623 BUF good enough?
* How to implement fixed OPA + BUF with a differential input signal?
* How to shift the DC bias level?
  Reply With Quote
Old 15th May 2018, 06:32 PM   #2
OlegSh is offline OlegSh
diyAudio Member
 
Join Date: Dec 2010
Location: Germany
Chip selection for a fixed-gain low-voltage OPA+BUF
Why wouldn't you use a single IC solution for headphone outputs? Just use OPA1688 or OPA1622 which are designed for such duty. The only drawback is that both require >4V supply.

For the differential input configuration look at the typical application diagram in the OPA1688 or OPA1622 datasheets. The op-amp + buffer config can be seen in the LME49600 datasheet. With the single rail supply you should not shift DC bias level since you need it for correct circuit operation and you should use an output coupling capacitor. Things become significantly easier if you can use bipolar supply for the analog output stage.
  Reply With Quote
Old 16th May 2018, 12:01 PM   #3
kokoriantz is offline kokoriantz  Lebanon
diyAudio Member
 
Join Date: Dec 2015
Location: south east asia
Have look to the latest opa837 single power supply from 2.7v to 5.4v 50Mhz 105v/us noise 4nv. As buffer I advise you the classAA of Technics.
  Reply With Quote
Old 16th May 2018, 12:07 PM   #4
kokoriantz is offline kokoriantz  Lebanon
diyAudio Member
 
Join Date: Dec 2015
Location: south east asia
Default classAA buffer

From Technics cd player manual .
Attached Images
File Type: png classaa buffer.png (159.0 KB, 58 views)
  Reply With Quote
Old 16th May 2018, 12:22 PM   #5
Mark Johnson is offline Mark Johnson  United States
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Chip selection for a fixed-gain low-voltage OPA+BUF
According to this very excellent table of headphone data, an output current of 60mA RMS is sufficient to drive all but the most ridiculously low sensitivity (Hifiman) headphones. So you need to see a datasheet Ioutmax spec of ~100mA, accounting for RMS-to-DC and margin-to-spec.

Operating from (3.3V, 0V) supplies, you won't be able to accept the two Vbe drops of a standard BJT Diamond Buffer circuit like BUF602 or BUF634 or LH0002. Instead you'll need to use a pair of high current, rail-to-rail opamps in push-pull ("bridge") configuration. This one might be a pretty good fit. 3.3V supply, RRIO, 220mA output current.
  Reply With Quote
Old 16th May 2018, 01:38 PM   #6
maxtch is offline maxtch  China
diyAudio Member
 
Join Date: Apr 2018
Location: From Shanghai with Love
Quote:
Originally Posted by Mark Johnson View Post
According to this very excellent table of headphone data, an output current of 60mA RMS is sufficient to drive all but the most ridiculously low sensitivity (Hifiman) headphones. So you need to see a datasheet Ioutmax spec of ~100mA, accounting for RMS-to-DC and margin-to-spec.

Operating from (3.3V, 0V) supplies, you won't be able to accept the two Vbe drops of a standard BJT Diamond Buffer circuit like BUF602 or BUF634 or LH0002. Instead you'll need to use a pair of high current, rail-to-rail opamps in push-pull ("bridge") configuration. This one might be a pretty good fit. 3.3V supply, RRIO, 220mA output current.
I cannot actually use that push-pull configuration doe tot he pinout of Apple EarPods. There is a common ground pin for both earbuds and the mic/remote.
  Reply With Quote
Old 16th May 2018, 01:58 PM   #7
Mark Johnson is offline Mark Johnson  United States
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Chip selection for a fixed-gain low-voltage OPA+BUF
Quote:
Originally Posted by maxtch View Post
I cannot actually use that push-pull configuration doe tot he pinout of Apple EarPods. There is a common ground pin for both earbuds and the mic/remote.
Then you are going to have a very difficult time driving the output to 4V RMS (5.6V peak to peak) as required by the Beyerdynamic T1 (and other) headphones, even after disqualifying the Hifiman weirdos.

If your output pin swings between Vmin (hoped to be 0V but higher in reality) and Vmax (hoped to be 3.3V but lower in reality) then its RMS output voltage is easy to calculate:
  • V_out_rms = 0.5 * (Vmax - Vmin) / sqrt(2)
When you crank the numbers I predict you'll find, that Vout_rms will work with about half of the headphones in the table
  Reply With Quote
Old 16th May 2018, 02:20 PM   #8
maxtch is offline maxtch  China
diyAudio Member
 
Join Date: Apr 2018
Location: From Shanghai with Love
Quote:
Originally Posted by Mark Johnson View Post
Then you are going to have a very difficult time driving the output to 4V RMS (5.6V peak to peak) as required by the Beyerdynamic T1 (and other) headphones, even after disqualifying the Hifiman weirdos.

If your output pin swings between Vmin (hoped to be 0V but higher in reality) and Vmax (hoped to be 3.3V but lower in reality) then its RMS output voltage is easy to calculate:
  • V_out_rms = 0.5 * (Vmax - Vmin) / sqrt(2)
When you crank the numbers I predict you'll find, that Vout_rms will work with about half of the headphones in the table
I actually don't intend to drive those hard ones at all - from the first post the intended target device has been Apple EarPods and compatibles. The design in question even have remote control decode logic for crying out loud, and I doubt if Beyerdynamic T1 would have one compatible with Apple's protocols...
  Reply With Quote
Old 16th May 2018, 02:28 PM   #9
Mark Johnson is offline Mark Johnson  United States
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Chip selection for a fixed-gain low-voltage OPA+BUF
I found this on the datasheet.

_
Attached Images
File Type: png screen_grabb.png (126.4 KB, 45 views)
  Reply With Quote

Reply


Chip selection for a fixed-gain low-voltage OPA+BUFHide 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
Unity Gain Power Amplifier Voltage Gain = 1 (0 dB) - where are these amps ? tiefbassuebertr Solid State 10 3rd July 2017 11:22 PM
Fixed Gain, Adjustable Output Impedance Power Amp? ballpencil Solid State 8 6th October 2016 05:03 AM
That 1512 fixed gain follow by a second stage lio nuite Analog Line Level 0 4th June 2012 08:16 PM
Transformer based voltage gain + unity gain stage? soundcheck Solid State 2 10th August 2010 02:44 PM
fixed gain ic? AudioGeek Solid State 0 20th May 2007 04:17 PM


New To Site? Need Help?

All times are GMT. The time now is 10:07 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