lm4780 2.1 volume control? - 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 25th September 2010, 12:15 AM   #1
diyAudio Member
 
Join Date: Sep 2010
Default lm4780 2.1 volume control?

I am hoping someone can help me (and I searched the forums and google to no avail) I am about to put together an lm4780 dual mono amp, but in the future I may decide to add an extra mono channel using one lm4780 to drive a subwoofer.

My question is how would I connect the rca signal to the extra chip (subwoofer mono chip) is it ok to split the signal coming into the amp, to a seperate volume pot for sub volume control, or would this mess up impedance etc...?

The signal coming into the amp would not be going through a pre amp but direct from a DAC.
  Reply With Quote
Old 25th September 2010, 07:31 PM   #2
diyAudio Member
 
Join Date: Aug 2010
You'd take one channel spilt into two using a low pass filter on one line to provide the signal you need or the bass amp. You could even design the third amp to be active filter/amp.

Last edited by Mankysteve; 25th September 2010 at 07:33 PM.
  Reply With Quote
Old 25th September 2010, 09:28 PM   #3
diyAudio Member
 
Join Date: Sep 2010
Quote:
Originally Posted by Mankysteve View Post
You'd take one channel spilt into two using a low pass filter on one line to provide the signal you need or the bass amp. You could even design the third amp to be active filter/amp.
If I take just one of the stereo channel, then surely if the lower bass signal happens to be on the other channel in a certain piece of music then I would not hear it ?
  Reply With Quote
Old 25th September 2010, 10:00 PM   #4
diyAudio Member
 
Join Date: May 2008
In theory yes. In practice everything below 100 Hz is usually the same on both channels anyway.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 26th September 2010, 12:12 AM   #5
diyAudio Member
 
Join Date: Sep 2010
Quote:
Originally Posted by pacificblue View Post
In theory yes. In practice everything below 100 Hz is usually the same on both channels anyway.
Ah thats ok then, but wouldn't splitting a signal into two, make one of the stereo channels slightly quieter?
  Reply With Quote
Old 26th September 2010, 12:48 AM   #6
diyAudio Member
 
Join Date: Aug 2010
In theory your amp should have infinite input resistance so there shouldn't be any voltage drop. In reality you will loose a small amount of volume, how big or small this would be I'm not 100% never tried 2.1 my self so I don't really know.

I Can't think of any way of mixing both channels for a middle on with out loosing stereo ability.

Also in this case it's not true 2.1 but that's not really of importance.

Last edited by Mankysteve; 26th September 2010 at 12:56 AM.
  Reply With Quote
Old 26th September 2010, 07:25 AM   #7
diyAudio Member
 
Join Date: May 2008
Quote:
Originally Posted by mattjuk81 View Post
Ah thats ok then, but wouldn't splitting a signal into two, make one of the stereo channels slightly quieter?
Yes, to such a small extent that you won't notice any difference.

Quote:
Originally Posted by Mankysteve View Post
I Can't think of any way of mixing both channels for a middle on with out loosing stereo ability.
You are probably refering to crosstalk through the mixer. It does usually not affect the imaging too much. If you want to calm your conscience, use a stereo low pass and put the mixer after that. That restricts the crosstalk to the region below the filter frequency. It takes a few more op amp channels than the usual setup with the mixer before a mono low pass.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 26th September 2010, 04:18 PM   #8
diyAudio Member
 
Join Date: Sep 2010
Could I not take both stereo signals and use 2 resistors, and take a signal from the middle of the resistors?

or use this --|SMC-1|AUDIO CONVERTER, STEREO/MONO | CPC
  Reply With Quote
Old 26th September 2010, 09:35 PM   #9
diyAudio Member
 
Join Date: Aug 2010
You get cross talk between the two channels. say if you've gt a part of music where there nothing on the right channel and something on the left you'd get the left channel on the right.
  Reply With Quote
Old 26th September 2010, 10:02 PM   #10
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
You need a virtual earth summing op-amp circuit otherwise you will corrupt your stereo signals. Or take a look at the sub-woofer controller project on my website
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  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
Volume control on DVD player remote. Lose resolution at low volume? Circlotron Digital Source 2 10th June 2011 07:20 PM
i need preamp schematics w/o tone control or volume control hernanstafe Parts 7 30th January 2008 03:12 AM
can a volume POT be used in LM4780 PCB like those from P Daniel? jarthel Chip Amps 0 22nd June 2007 01:36 AM
The remote control paratactic volume control audio-gd Solid State 33 7th June 2007 11:16 PM
remote control motorised control for volume pot/knob CharlesY Parts 0 25th July 2005 11:12 AM


New To Site? Need Help?

All times are GMT. The time now is 10:53 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