Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 26th May 2010, 05:28 AM   #1
ss007 is offline ss007  United States
diyAudio Member
 
Join Date: Dec 2009
Default Simple stereo gain stage

I'm in the process of putting together a system with a Audio Sector Gainclone kit and a Pass Labs B1 input buffer. My main sources are a phono pre and a CD player. I will also have a mini jack input for my ipod or computer output for streaming audio such as Rhapsody or Pandora. Both my ipod and computer have a pretty low output. I want to be able to match the gain on that input to the level of the CD player which has nice output and the phono pre that has a gain control. I'd like to have all the levels equal before they go through the selector switch and then into the B1.

Is there a simple gain stage circuit with a pot that I can run the ipod/computer through to give it a little boost to match the rest of the sources?

Thanks, Scott
  Reply With Quote
Old 26th May 2010, 06:19 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Easiest solution is a simple opamp gain stage... do you know how to configure one ?

http://users.ece.gatech.edu/mleach/e...4/OpAmps01.pdf
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 26th May 2010, 06:34 AM   #3
ss007 is offline ss007  United States
diyAudio Member
 
Join Date: Dec 2009
Quote:
Originally Posted by Mooly View Post
Easiest solution is a simple opamp gain stage... do you know how to configure one ?

http://users.ece.gatech.edu/mleach/e...4/OpAmps01.pdf
Thanks Mooly! I thought that might be it.

I have no idea how to configure one, I've just started learning about electronics and DIY audio. Any help would be greatly appreciated.

Scott
  Reply With Quote
Old 26th May 2010, 06:45 AM   #4
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
An important question is where will this preamp be located... what power supplies do you have available ?
The opamp needs (preferably) a split supply of -/+ 9 to 18 volts or so.

The circuit is easy... I'll post one in a few minutes.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 26th May 2010, 06:56 AM   #5
ss007 is offline ss007  United States
diyAudio Member
 
Join Date: Dec 2009
I'll have an 18v supply that will be used for the B1 buffer.

I would like the pre to come before the input selector switch to the B1.

My intention is to have all the sources adjusted to equal level before entering the Buffer, then on to the Gainclone.
  Reply With Quote
Old 26th May 2010, 07:00 AM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Here's the normal circuit...
The input impedance is set by Rin, so a normal value would be say 470k. That give a high input impedance that won't load any source you connect.

The gain is given by the formula Rf + R1 / R1.
So using standard values if RF were 22k and R1 were 10k the voltage gain is 3.2
What gain do you need... the only realistic way to find out is to use a pot for R1 and see. Then select a fixed resistor to fit in it's place (preset pots are horrible in audio circuits )

The two caps... are good practice C1 certainly.
C2... I would say yes. The output of the opamp will be at zero volts DC... but again it's good practice to include it, however if the opamp is already feeding an AC coupled circuit then omit. The resistor R2 just defines the end of the cap to ground (100k).

Power supplies. You have to decide whether you want two single opamps or a dual.
Attached Images
File Type: jpg Opamp.jpg (16.6 KB, 1335 views)
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.

Last edited by Mooly; 26th May 2010 at 07:02 AM.
  Reply With Quote
Old 26th May 2010, 07:02 AM   #7
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Is that a single 18 volt rail ? In other words ground and +18 volts ?

If so, it's no problem...
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 26th May 2010, 07:11 AM   #8
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Another thought is to use the virtual earth configuration.
Have a look at this, which is the circuit I designed for my amp. Forget the FET's which are for electronic input selection.

R1 sets the input impedance. The gain of the opamp stage is just -R2/R1 (- because it inverts). The second stage inverts it back again.

This configuration is a "mixer" and each input has it's own R1 which allows each input to have it's level set to what is required. Different value of R1 for each input.
Attached Images
File Type: jpg Pre Switch Copy.jpg (55.3 KB, 1799 views)
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 26th May 2010, 07:17 AM   #9
ss007 is offline ss007  United States
diyAudio Member
 
Join Date: Dec 2009
Quote:
Originally Posted by Mooly View Post
Is that a single 18 volt rail ? In other words ground and +18 volts ?

If so, it's no problem...
Yes, just an 18 volt wall wart.
  Reply With Quote
Old 26th May 2010, 07:21 AM   #10
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
I'll redraw it for a single rail... now you can make this as simple or complex as you like, but for a single gain stage we'll keep it simple.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  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
Simple 12v gain stage dublin78 Solid State 10 14th April 2008 03:37 PM
Simple gain question maxw Chip Amps 8 12th May 2006 11:05 PM
Heretical Unity Gain line stage PLUS a little gain ? yagas Tubes / Valves 7 24th January 2006 01:30 PM
Problems With Simple Gounded Cathode Gain Stage dr._sleep Tubes / Valves 4 23rd January 2006 08:31 PM
simple BJT gain stage hihopes Solid State 2 22nd September 2005 08:19 AM


New To Site? Need Help?

All times are GMT. The time now is 03:40 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