4 x LM4780 mono, OR 2 x LM4780 stereo: Will I notice the difference? - 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 23rd October 2013, 05:22 PM   #1
diyAudio Member
 
mondogenerator's Avatar
 
Join Date: Sep 2009
Location: City Of Villans
Blog Entries: 1
Default 4 x LM4780 mono, OR 2 x LM4780 stereo: Will I notice the difference?

I'm planning my active build, and have these ICs already.

I'm aware that for 4 ohm loads the parallel option is recommended, however my speakers are 8 ohm, and their lowest impedance is 6 ohm.

My plan is to either:

(1) Use one IC for L and R channel, bass on one 'half' and treble on the other.
(2) Use an IC per driver, in parallel mono.

Will i really notice a difference using 4 ICs rather than just 2 in stereo configuration?
__________________
Every new piece of knowledge pushes something else out of my brain - Homer.....................Simpson

Last edited by mondogenerator; 23rd October 2013 at 05:25 PM.
  Reply With Quote
Old 25th October 2013, 03:50 PM   #2
diyAudio Member
 
Join Date: Feb 2006
Location: On a hill, in a wooden shack, next to the woods, in Somerset.
It's not so much that you will notice a difference whether paralleled or not, though it will make life easier for the chips and there will be lower distortion (and you can go higher on the rail voltages), but more that you don't really want to be mixing signals (bass and treble) on the one chip. Both the thermal waves from large power draws at LF and any sagging (and signal) on the rails will be directly there on the treble section.

One of the advantages of active is that the LF part can clip or somehow run out of steam without taking the treble section with it as well. Ideally, or at some time in the future, you would have different supplies for treble and bass amps.

Depending on how loud you want it to go (and it won't be that loud into 8 ohm speakers) your two choices are two chips, one doing both basses and the other doing both trebles, or four chips in the same config but paralleled. Personally I would go for paralleled for two or three reasons. There is less chance to make a mess around the various V+ and V- with the decoupling caps there, you're more likely to avoid crosstalk in your layout, and you can get your rail voltages up to around +-40V, or a smidgeon more, while not putting the chips under any great pressure. A slightly better amp will probably come from +-37V and some of this loss of peak output will be made up by the fact that one amp can effectively add to the output of the other when spanning the crossover region which can't happen with a single amp. Having said that, I personally would probably be brave and get the very maximum I could out of the chips (Ie 42V, IIRC), knowing that they would be driving an equivalent 16 ohm load and that the arrangement is perfectly capable of driving a 1.5 ohm actual load!
  Reply With Quote
Old 25th October 2013, 03:58 PM   #3
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Okay, use one chip for bass. . . and then use a separate chip and separate power circuit for mids&treble. All of the effort strain and noise of big bass currents will not affect your mids&treble that way.

If you have only one transformer, then simply use a DC power board, and put diodes (or regulators or capmulti) in series to the DC power cable that goes to the mids&treble amplifier. Giving the mids&treble amp functional power decoupling may help block some of the noise from the bass amp so it doesn't get into the mids&treble amp.

P.S.
Since two different supplies would be better, in that case I would favor LM4780 bass amp teamed with LM1875 mids&treble amp.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 25th October 2013, 07:23 PM   #4
diyAudio Member
 
mondogenerator's Avatar
 
Join Date: Sep 2009
Location: City Of Villans
Blog Entries: 1
Default for a minute there I thought Id asked a daft question!

Thank you both for your responses!

This was one of those threads I almost wish I hadn't posted, but now I am glad I did!

PSU fluctuations and isolating that side of things hadn't occurred to me, and I agree Daniel, LM1875 for tops would be nice....but I don't have any!

I have 4780, 3875, 3876, 3886...

Both of your posts make a great deal of sense to me, and I was only just starting to consider HOW I was going to approach the PSU/s, I considered that shared PSUs wouldn't be ideal. I had no idea it was such a bad idea. Thank goodness I didn't try it.

Perhaps then I should use one 4780 parallel per channel for bass, and then either:

A single 4780 for highs, with separate PSU(Crosstalk shouldn't be too bad?
its a stereo IC isnt it?)

Or just a pair of 3875/6/3886 instead.

hmmmmm

Thanks again guys
__________________
Every new piece of knowledge pushes something else out of my brain - Homer.....................Simpson
  Reply With Quote
Old 25th October 2013, 11:13 PM   #5
Banned
 
Join Date: Jun 2013
Location: Melbourne
Hi,
I am planning on using paralleled LM4780 amps in my new build. The boards are designed to be used only in parallel and I will use five for a three way; a pair bridged for woofer and mid. They are 75 x 50 mm so that they will fit across a 300 mm wide heatsink.
Attached Images
File Type: jpg IMG_20131010_083522.jpg (269.6 KB, 280 views)
  Reply With Quote
Old 28th October 2013, 08:43 PM   #6
diyAudio Member
 
Join Date: Feb 2006
Location: On a hill, in a wooden shack, next to the woods, in Somerset.
Yes, they are stereo chips. To the point that the V+ and V- go separately to each of what is effectively a 3886 chip on board, so it's worth checking the paperwork to make sure you have this right.

I have to say that since you have got the thermal tracking already there by virtue of being on the same chip, I would also be very tempted to bridge them since they are driving an 8 ohm load. Then you can get some real headroom. Just one more thing to add to the thoughts.
  Reply With Quote
Old 28th October 2013, 09:38 PM   #7
diyAudio Member
 
mondogenerator's Avatar
 
Join Date: Sep 2009
Location: City Of Villans
Blog Entries: 1
Hmm.

I confess i haven't really considered bridging as an option, although for no particular reason.

Perhaps it deserves more consideration, although i only have small speakers.

Definitely food for thought. Thanks.
__________________
Every new piece of knowledge pushes something else out of my brain - Homer.....................Simpson
  Reply With Quote
Old 28th October 2013, 10:00 PM   #8
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

IMO two chips parallel on the bassmids and single chip for
treble. 3 chips but thermally it makes the most sense to me.
Adding a 4th chip for the treble doesn't make sense to me.

Common supply but isolate the treble chip with series diodes in
the power supply lines to the local (to the chip) supply capacitors.

Some may argue but modest cap values on the PS board and
much bigger than usual caps near the chips is IMO a decent plan.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 28th October 2013 at 10:06 PM.
  Reply With Quote
Old 29th October 2013, 09:22 AM   #9
Banned
 
Join Date: Jun 2013
Location: Melbourne
Quote:
Then you can get some real headroom.
I can vouch for that!
  Reply With Quote
Old 29th October 2013, 11:18 AM   #10
diyAudio Member
 
mondogenerator's Avatar
 
Join Date: Sep 2009
Location: City Of Villans
Blog Entries: 1
Thanks Sreten, i also considered it a little wasteful to use a chip each for treble. Of course 3 heatsinks instead of 2, in order to equalise their heat dissipation, is a little awkward.

Bridging may indeed be on the cards now, although my aim in using parallel was to ensure i had ample current capacity at the limits of the amps power, for e.g. using 40V rails. Bridging means ill have to rejig gain to match the treble amp.
__________________
Every new piece of knowledge pushes something else out of my brain - Homer.....................Simpson
  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
Integrated dual mono lm4780 SoIL4x4 Chip Amps 143 1st September 2012 12:22 AM
Heatsinks for LM4780 in dual mono mattjuk81 Chip Amps 4 5th November 2010 01:11 AM
LM4780 dual mono -- boards jackinnj Swap Meet 1 1st October 2008 12:44 AM
mono power amp using LM4780 hypnotize Chip Amps 4 7th February 2005 07:50 AM


New To Site? Need Help?

All times are GMT. The time now is 06:39 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