SOAP - Simple OpAmp Pre - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 December 2007, 08:10 AM   #1
zei is offline zei  Sweden
diyAudio Member
 
Join Date: Feb 2005
Location: Gothenburg, Sweden
Default SOAP - Simple OpAmp Pre

* Flamesuit on.

Thought i should give something back to the forum.

I wanted a small (tiny) preamp and found loads of schematics on the web.

Made a layout (my first) based on one of them and this is the result. It worked perfectly and sounds powerful and clean with my LM4780 chipamp.

On my prototype build i did,nt use the input/output caps. Neither the resistors on the output to gnd. Workes without them.

Be my guest to use it as you wish.

Click the image to open in full size.

Schematic
Copper
Silk


Best regards

/Zei
__________________
Tala är tiga, silver är guld
  Reply With Quote
Old 11th December 2007, 01:03 PM   #2
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
Zei, as opamps go, I like the OPA134/2134! This is a circuit that I built a while back. Note the 1K5 resistor going from output to the negative rail.

Click the image to open in full size.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 11th December 2007, 01:37 PM   #3
BWRX is offline BWRX  United States
diyAudio Moderator Emeritus
 
Join Date: Jan 2005
Location: Pennsylvania
Default Re: SOAP - Simple OpAmp Pre

Quote:
Originally posted by zei
Made a layout (my first)
Nice job on the layout Zei.
__________________
Brian
  Reply With Quote
Old 11th December 2007, 01:48 PM   #4
zei is offline zei  Sweden
diyAudio Member
 
Join Date: Feb 2005
Location: Gothenburg, Sweden
Thanx Brian.!

Nuuk, Please explain Why did you put the resistor between out and - supply?

Did i miss something important?

The cirquit is tested and it works very well But i can always make changes to the layout of course.

Regards

/Zei
__________________
Tala är tiga, silver är guld
  Reply With Quote
Old 11th December 2007, 03:43 PM   #5
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
I was told that the 1K5 resistor would bias the opamp nearer to class-A operation, It did sound very slightly better after I did so.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 11th December 2007, 03:47 PM   #6
Nisbeth is offline Nisbeth  Denmark
diyAudio Member
 
Nisbeth's Avatar
 
Join Date: Jan 2001
Location: Denmark
Yes, it does. Details here: http://tangentsoft.net/audio/opamp-bias.html


/U.
  Reply With Quote
Old 11th December 2007, 04:49 PM   #7
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
Nuuk, a few questions for you.....

I read on the tangent site that the lower the load R the higher the bias needs to be. What load range is the 1K5 good for with the OPA?

What is the purpose of the 33pf cap across RF?

I see your schematic doesn't use input or output resistors. What is the purpose of having a ~1k resistor on the input and under what circumstances should it be used?

I know what an output resistor is for, but why have you excluded one?

Thanks.
  Reply With Quote
Old 11th December 2007, 05:52 PM   #8
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
TAO - there are a few more details here but basically I just took advice from Carlos Machado and don't fully understand how it all works. I just try suggestions, and if I can hear an improvement I include them in the final version.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 11th December 2007, 05:55 PM   #9
zei is offline zei  Sweden
diyAudio Member
 
Join Date: Feb 2005
Location: Gothenburg, Sweden
Quote:
I was told that the 1K5 resistor would bias the opamp nearer to class-A operation, It did sound very slightly better after I did so.
Aah.. yes i read that but never tried it my self. It should be fairly easy to solder directly to the OPA pins i guess.

Thanx for the input Nuuk!

/Zei
__________________
Tala är tiga, silver är guld
  Reply With Quote
Old 11th December 2007, 06:19 PM   #10
zei is offline zei  Sweden
diyAudio Member
 
Join Date: Feb 2005
Location: Gothenburg, Sweden
Picture of an earlier layout before i settled with the one on the first post.

Just to show how small it realy is.

Click the image to open in full size.



Regards
/Zei
__________________
Tala är tiga, silver är guld
  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
SOAP MKIII (Simple OpAmp Pre) With onboard PSU zei Chip Amps 206 4th August 2009 12:55 PM
A Simple opamp question? Dxvideo Chip Amps 29 3rd April 2009 01:42 PM
Looking for Simple 12V supply dual opamp for kid's project chipco3434 Chip Amps 26 16th March 2006 07:13 PM
Designing a simple tube opamp? bradd Tubes / Valves 1 26th October 2005 06:24 AM


New To Site? Need Help?

All times are GMT. The time now is 06:03 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