No global feedback preamplifier - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 18th December 2011, 06:57 AM   #1
diyAudio Member
 
Join Date: Aug 2011
Default No global feedback preamplifier

Hi,
I'm currently designing my new pre amplifier.
The aim to have below features.
-No global negative feedback.
-Direct coupling.
-Class A.
-Simple design.
My designed as here. but unfortunately I can't acceptable with it's voltage gain.
I would like to have 5-10 times gain, but it is actually 100 times voltage gain.
So can anyone give me an advise, or the a suggest schematic.

Click the image to open in full size.

Last edited by smithomo; 18th December 2011 at 07:00 AM.
  Reply With Quote
Old 18th December 2011, 07:33 AM   #2
Elvee is online now Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Load it
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 18th December 2011, 01:00 PM   #3
diyAudio Member
 
Join Date: Aug 2011
[QUOTE=Elvee;2825348]Load it[/QUOTE

Thanks that a nice one but it is a global feedback one with easy to specify the voltage gain.
  Reply With Quote
Old 18th December 2011, 01:28 PM   #4
CBS240 is offline CBS240  United States
diyAudio Member
 
CBS240's Avatar
 
Join Date: Aug 2005
Location: K-town
Ohms law. Reduce VR1 and VR9 by reducing the resistor value. This will reduce the change in voltage of the emitter resistors of Q5 & 8, reducing the output current change vs input voltage. But because your output is from the dependent current source of the transistors, that being the collectors, there must be a specific load impedance in order to control voltage gain. If the load Z is not constant, then you may need some form of FB be it current or voltage FB, to achieve constant voltage gain.
__________________
All the trouble I've ever been in started out as fun......
  Reply With Quote
Old 18th December 2011, 01:31 PM   #5
Elvee is online now Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by smithomo View Post
Thanks that a nice one but it is a global feedback one with easy to specify the voltage gain.
Do you call a resistor between output and node 0V a global feedback?
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 18th December 2011, 02:30 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
As Elvee said, all you have to do is load it. You have built a transconductance amplifier - it outputs a current so you need to convert it to a voltage. A rough calculation suggests a bit below 1mA/V, so perhaps a 1k2 load would give unity voltage gain.

You will need input and output DC blocking capacitors, unless you can guarantee that the adjacent equipment already has these and can cope with a potentially large DC offset. Note that the DC offset might not show up in simulation if the complementary pairs of BJTs are regarded as true complements - in real life they won't be.
  Reply With Quote
Old 18th December 2011, 02:31 PM   #7
knutn is offline knutn  Norway
diyAudio Member
 
Join Date: Mar 2006
Location: Oslo
Like Elvee says, connect a resistor between the output and ground. A value of 8.2k will give you a gain of 20 db (10 times). However, with your design you will have serious offset problems...
  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
JLH without global feedback? rmgvs Solid State 8 24th December 2013 04:56 PM
All CFP Non Global Feedback Amplifier Havenwood Solid State 0 7th August 2011 03:17 PM
Global vs Local Feedback ervinl Solid State 7 12th July 2011 03:11 PM
Which point to connect the global feedback? neazoi Solid State 9 2nd April 2011 06:49 AM
Articles on Global Feedback albertli Tubes / Valves 4 1st February 2010 05:57 AM


New To Site? Need Help?

All times are GMT. The time now is 08:11 PM.


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