Low gain x circuit - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 28th April 2004, 03:21 PM   #1
diyAudio Moderator Emeritus
lumanauw's Avatar
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Default Low gain x circuit

What do you think of this design? I wanted it only using single differential, Xcct, and push-pull VAS/Output stage.
The differential is working at low ccs, only 2mA, output stage is working at 10mA, due to modified current mirror.
Can this be classified as low gain design? Since I think the gain is coming from the differential + modified current mirror only.
Attached Images
File Type: jpg mydesign.jpg (32.2 KB, 451 views)
  Reply With Quote
Old 28th April 2004, 04:10 PM   #2
Electrons are yellow and more is better!
diyAudio Member
peranders's Avatar
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
This circuit is rather suitable for you to simulate and for trying different component values. Download the freeware LTSpice and start messing around.
/Per-Anders (my first name) or P-A as my friends call me
PA03 LM4780 amplifier group buy, SIGN UP HERE for the group buy 0 boards left. 118 paid.
  Reply With Quote
Old 28th April 2004, 04:22 PM   #3
diyAudio Member
Join Date: Feb 2001
Location: Columbia, SC
If current mirrors you must have, why not simply use one across the differential? And why the difference in currents from one side to the other?
Or, put another way, I don't see that Q4, Q6, Q7, and Q8 actually contribute much towards your goal.
Low gain? Loading a gain device with a current source--which represents a pretty high impedance--generally yields a lot of gain. Unless you were planning on burning it off with feedback, which isn't the same thing at all.

  Reply With Quote
Old 28th April 2004, 04:26 PM   #4
diyAudio Member
Join Date: Feb 2001
Location: Columbia, SC
Actually, on looking at it again, you're taking the output for each phase from different points on each side.

  Reply With Quote
Old 29th April 2004, 01:29 AM   #5
diyAudio Moderator Emeritus
lumanauw's Avatar
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
This is what I think when drawing this design. First, I'm much inspired by low gain design (that will lead to low feedback). The current mirrors can be replaced by folded cascode, but I choose to use current mirrors.
The differential is Q1 and Q2, fed by 2mA ccs. Each leg is connected to current mirrors, so I have 1mA flowing down at Q4 to Q7 and also from the most right transistors. The function of this Q4-Q7 (the same with the most right transistors), is to shift the current to Q8 and the left down transistor (which Re is 200ohm).

I wanted push pull output. I can replace Q8 by CCS, but that will lead to single action only by Q6. If Q6 is "push" then I wanted Q8 tobe "pull", not steady like ccs. That is why I have Q3-Q4-Q7-Q8 for shifting the "pull" action from the other leg of differential.

I modified the current mirror Q5-Q6 so I can have bias of 10mA from 1mA differential leg. If I use the same 2k for Re, then the bias is too low, only the same as differential, 1mA.

Maybe the drawing is confusing, because I first I draw it single ended, but Jam mentioned something about X cct. So I put additional current mirror and output stage to have X cct. Using current mirror is good in this design, because I can

1.Level shift the single differential outputs to have push-pull action .

2.I can still use single differential to have X cct.

I really hope this is qualified as low gain design. And with good output for X cct qualification.
  Reply With Quote


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
Unity Gain op amp circuit? jetbat Solid State 3 5th May 2009 12:29 AM
Dual pot in a mono gain circuit Netlist Solid State 2 8th October 2007 05:15 PM
suggest circuit with gain of 60 AudioGeek Tubes / Valves 17 14th April 2004 04:16 PM
DC controlled gain circuit maylar Solid State 7 15th February 2004 07:04 PM
Need help designing high-gain amp circuit! electec Chip Amps 2 13th November 2003 01:01 AM

New To Site? Need Help?

All times are GMT. The time now is 01:23 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2