How to lower the gain of this headphone amp - diyAudio
 How to lower the gain of this headphone amp
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 27th May 2012, 11:18 AM #1 diyAudio Member   Join Date: Oct 2010 Location: Sydney [Solved] How to lower the gain of this headphone amp Hi. Currently with these values the gain of this amp is 11: The problem is, I've no idea how to change the gain to, for example, 2? Which resistors to what value should I change..? I hope someone understands this better than I do. Thank you. Last edited by eimis; 27th May 2012 at 01:08 PM. Reason: Problem was solved.
 27th May 2012, 11:48 AM #2 diyAudio Member   Join Date: Mar 2006 Location: Budapest Hi, To reduce gain, R3 has to be decreased. With value equal to R2 (10k) you'll have the gain of 2. To maintain stability, a small (eg. 100pF) cap can be connected between inverting (-) input and output of the OpAmp. Regards.
 27th May 2012, 11:54 AM #3 diyAudio Member   Join Date: Oct 2010 Location: Sydney Thanks! So the formula is R3 / R2 + 1. As I understood, it's better to change R3 and always leave R2 at its original value? Thanks again!
 27th May 2012, 12:17 PM #4 diyAudio Member   Join Date: Nov 2009 Location: algeria/france In principle R1 should be equal to R3 to get lower output DC offset wich i think is even more important parameter with a phone amp than with a speakers amp.
diyAudio Member

Join Date: May 2011
Location: Virginia
Quote:
 Originally Posted by eimis Thanks! So the formula is R3 / R2 + 1. As I understood, it's better to change R3 and always leave R2 at its original value? Thanks again!
For lower noise, you can change both R2 and R3 to 1k. If you do this, you should increase C2 to something really big like 470uF.

Last edited by dirkwright; 27th May 2012 at 01:03 PM.

diyAudio Member

Join Date: May 2011
Location: Virginia
Quote:
 Originally Posted by wahab In principle R1 should be equal to R3 to get lower output DC offset wich i think is even more important parameter with a phone amp than with a speakers amp.
R1 = 220k is really huge.

Is this a circuit board you got from China?

Depending on which op amp you use, you may not need the input coupling cap. If not, then I'd replace the coupling cap with a 1k resistor, and replace R1 with 220pF capacitor. This will form a first order filter to keep RFI out of the op amp.

 27th May 2012, 01:07 PM #7 diyAudio Member   Join Date: Oct 2010 Location: Sydney Thank you gurus. I set the gain to 1.91 and am very happy.
 27th May 2012, 01:08 PM #8 diyAudio Member     Join Date: May 2002 Location: The great city of Turnhout, BE Blog Entries: 8 Since the input impedance is determined largely by VR1 here, you can easily decrease R1 to something like 50k. Then make R3=50k as well for low offset, and adjust R2 for the gain you want. The noise is determined by the parallel value of R2//R3 and since R3 is largely limited to whatever R1 you use, those are your play limits. The small cap across R3 is also a good idea. jan didden __________________ Music is dither to the brain; lets me think below the usual chaos - me Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher
diyAudio Member

Join Date: Oct 2010
Location: Sydney
Quote:
 Originally Posted by dirkwright Is this a circuit board you got from China?
It's a DIY clone of a popular headphone amp that I've already built. It had some serious hum issues at first but I solved them by putting capacitors between ground and +/- rails. I also put a cap between ground and smoothing capacitor plate. That shut up all hum. I've no idea what happened there because I'm not an engineer but I'm happy it solved the issue. At the moment the amp has original values, except for R3 which is 9.1K and the amp sounds absolutely fine.

diyAudio Member

Join Date: Oct 2010
Location: Sydney
Quote:
 Originally Posted by janneman Since the input impedance is determined largely by VR1 here, you can easily decrease R1 to something like 50k. Then make R3=50k as well for low offset, and adjust R2 for the gain you want. The noise is determined by the parallel value of R2//R3 and since R3 is largely limited to whatever R1 you use, those are your play limits. The small cap across R3 is also a good idea. jan didden
The amp uses NE5532. Are these 50k values fine with it?

 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 OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Dxvideo Headphone Systems 30 10th September 2011 02:05 AM PeteMcK Tubes / Valves 43 12th February 2011 04:49 PM eskimo hunter Headphone Systems 4 2nd August 2009 05:38 PM aljordan Pass Labs 10 8th January 2009 08:26 PM saurus Headphone Systems 5 16th December 2005 06:56 AM

 New To Site? Need Help?

All times are GMT. The time now is 02:12 PM.