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 February 2012, 11:00 AM   #1
diyAudio Member
 
Join Date: Feb 2005
Location: Topsfield, MA
Default LM3886 vs STA540

I recently learned about the STA540 via SparkFun. Bought one and am very happy with it so far. My application is a whole-house, 8 to 12 channel amplifier. I'm driving bookshelf and in-wall speakers in each zone, and want about 20-30W per channel. The current system uses 8 channels of LM3886 amplifiers. The sound is fine, but the 8 channels use 24W of quiescent power. That plus the fact that LM3886 provides no means to power down unused channels means that it uses more power than I like. Really it should have a fan just for the quiescent power burned.
  • 2 amplifiers per chip vs. 1 for LM3886, less than 1/2 the price per channel
  • 30W vs. the LM3886 50W. Good enough.
  • No Zobel or L-R network needed with long speaker wires
  • Single +12V to +20V power supply
  • Lower quiescent current and power
  • 5V Power down control: draws <1mA in shutdown.
  • Diagnostic output pin indicated clipping, overload, thermal problems, etc. on a single LED
  • Good distortion and noise specs
  • Simpler board layout, fewer parts....
It has a clever power amplifier configuration that they discuss in the data sheet. Unlike most amplifiers, it uses complimentary, common emitter output transistors. This has several benefits:
  • The output swings very close to the power rails
  • Clipping is very clean
  • No instability from capacitively-loading emitter followers: no Zobel needed
  • Amplifier efficiency is improved
A problem with multi-zone stereos is the crosstalk caused by running multiple amplifiers on a single power supply. I solved this OK for the LM3886 but will likely require another solution for the STA540. Iíll keep you posted. Here is my LM3886 solution Dave's Multi Zone Stereo / STM32 Design Challenge page

People have complained that the STA540 is sensitive to power supply. Since it is a single supply amplifier and is bridged, it draws all its power from one supply. That means that to provide the same output to a speaker it needs twice the supply current. Made worse with 4 or 6 of these on a single supply. Car batteries maybe? ;-)

The Sparkfun STA540 amplifier is here. Dual/Quad Power Amplifier - STA540 - SparkFun Electronics You can get the STA540 data sheet there too.

For the chip alone, Sparkfun only charges $2.95, just over half of what Digikey asks. How, I wonder?

Peace,
Dave Erickson
  Reply With Quote
Old 25th February 2012, 01:55 PM   #2
mikje is offline mikje  United States
Soakin' up the Sound!
diyAudio Member
 
mikje's Avatar
 
Join Date: Feb 2008
Location: Bismarck, ND
Quote:
Originally Posted by djerickson View Post

People have complained that the STA540 is sensitive to power supply. Since it is a single supply amplifier and is bridged, it draws all its power from one supply. That means that to provide the same output to a speaker it needs twice the supply current. Made worse with 4 or 6 of these on a single supply. Car batteries maybe? ;-)
So, please correct me if I'm wrong, but this doesn't need a CT transformer? This is pretty interesting, and it has a number of configurations to make it that much more fun. Is it stable to 2 ohms in any configuration?
I think I see one of these in my to-do list soon.
Mike
__________________
Marantz PM8003 amp, Jolida SJ502A, Squeezebox Touch, MLTL Continuums, DIY Carmichaels (Dayton, TangBand, Vifa); Sony STR5800SD, MarkAudio CHP-70s
  Reply With Quote
Old 26th February 2012, 12:49 AM   #3
Ipanema is offline Ipanema  Malaysia
diyAudio Member
 
Ipanema's Avatar
 
Join Date: Jun 2004
Location: KL
You can use a signal sensing circuit to mute 3886 when it is not playing. Save quiscent power.
  Reply With Quote
Old 26th February 2012, 10:51 AM   #4
diyAudio Member
 
Join Date: Feb 2005
Location: Topsfield, MA
Quote:
Originally Posted by mikje View Post
So, please correct me if I'm wrong, but this doesn't need a CT transformer? This is pretty interesting, and it has a number of configurations to make it that much more fun. Is it stable to 2 ohms in any configuration?
I think I see one of these in my to-do list soon.
Mike
Yes, some transformers have separate windings which would need to be wired in parallel, or a center tapped transformer. Or just a single lower voltage winding. I haven't done the power supply calculations or found a suitable transformer yet.

As far as 2 ohm loading: The STA540 is a 4 channel amp that can be bridged with no external parts to a 2 channel amp. Since it is a single supply design, in 4 channel mode output coupling capacitors are needed. These are not needed in 2 channel mode.

When you bridge an amplifier, each amplifier stage essentially sees 1/2 the speaker impedance that it would see as single ended. So a bridged amp driving 2 ohms is would see a 1 ohm load and would probably go into current limiting. My application will use all 8 ohm speakers and will use the STA540s in bridged mode.

Thanks,
Dave
  Reply With Quote
Old 26th February 2012, 11:19 AM   #5
diyAudio Member
 
Join Date: Feb 2005
Location: Topsfield, MA
Quote:
Originally Posted by Ipanema View Post
You can use a signal sensing circuit to mute 3886 when it is not playing. Save quiescent power.
The problem I have with LM3886 is that it draws full quiescent current even when muted. I incorrectly assumed that the mute pin lowered the quiescent current, so was surprised to learn that it does not. It only mutes the amplifier which still draws full quiescent. The data sheet doesn't say this explicitly, but since it doesn't specify quiescent current while in mute, one must assume that it is the same. Unfortunately it is the same as when not in mute. I learned this the hard way after laying out and building circuit boards.

The LM3886 quiescent current spec is 50mA typ, 85mA max. When operating from +/- 25V supplies, 50mA x 25V x 2 = 2.5W per channel. Since I have 8 channels, that's 20 watts when the power is on and not playing music. Worse if the amplifiers are close to their 85ma maximum. With my dense packing of the amps, they get too hot and waste too much power even when not playing music.

The STA540 draws 80ma typ. from a single +20V supply, but that is for 2 channels. So its quiescent power is 80ma x 20V / 2 = 0.8W per channel. That's a more reasonable 6.4W for 8 channels. In standby it draws a miniscule 100uA for 2 channels.

Thanks,
Dave
  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
STA540 - works, but clips with bass heavy sources MegatronUK Chip Amps 5 2nd January 2012 09:12 PM
Need help with LM3886 pradeeppk Subwoofers 2 10th October 2010 07:32 PM
why are LM3886 used here? henry zhang Chip Amps 4 12th November 2008 05:42 AM
Are two separate lm3886 = 2*lm3886 in parallel or bridge mode rs1026 Chip Amps 11 21st October 2004 10:24 AM
lm3886 MKK Chip Amps 5 3rd July 2003 08:53 PM


New To Site? Need Help?

All times are GMT. The time now is 07:41 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