LM3886 Parallel Use - Page 2 - 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 January 2002, 09:53 AM   #11
diyAudio Member
 
Join Date: Oct 2001
Location: .
trim each op amp individually on the -ve i/p
  Reply With Quote
Old 25th January 2002, 09:56 AM   #12
ssanmor is offline ssanmor  Spain
diyAudio Member
 
Join Date: Jan 2002
Location: Madrid
sorry, I don't understand your notation, could you be more explicit? :-) Thanks!
  Reply With Quote
Old 25th January 2002, 10:14 AM   #13
diyAudio Member
 
Join Date: Oct 2001
Location: .
apply a adjustable dc voltage to -ve i/p via a 1m resister
assume the op amp is in non-inverted mode
  Reply With Quote
Old 25th January 2002, 10:32 AM   #14
ssanmor is offline ssanmor  Spain
diyAudio Member
 
Join Date: Jan 2002
Location: Madrid
Ah, you mean applying a small (a few mV) variable voltage at the inverting pin of the LM3886's ?
That sounds good for the non-inverting stages, but what for the others?
I was thinking on building 4 identical stages, non-inverting, and adding a inverting circuit with an op-amp to excite two of them, so your idea can be suitable.
But do you think it is going to behave well as the offset changes with temperature?

Thanks!
  Reply With Quote
Old 5th February 2002, 06:09 AM   #15
rljones is offline rljones  United States
diyAudio Member
 
Join Date: Mar 2001
Location: california
ssanmor,

I'm now stuffing a new PCB I made up, doing what you've talked about. I've got on one board that's about 2 x 7 inches, 4-LM3886 devices, all running non-inverted (this gives better performance: you don't have the feed back 'bucking' the source that's driving the - input).

I based it on the schematic in the application link that AudioFreak listed above, but only using the top half of their schematic--that is, the non-inverted portion. I repeated the upper non-inverted portion for the 'bottom' half. Each output pair drives a resistor/inductor and then the load.

Next, I split the single input buffer op-amp into two, using one to drive the upper non-inverted pair with a non-inverted input signal, and the second to drive the bottom half with the inverted input. That is, each input polarity is running into a non-inverted AD8610.

12V regulation is provided for the input buffers devices separately from the regulated supplies for the LF411CN used in the DC servo circuit. (Instead of using two op-amps, I've also set it up to use a Jensen input transformer, with one secondary leg driving the + LM3886 pair and the negative leg the other LM3886 pair; it's always fun to compare!)

This means the whole amplifer, while bridged, is fully balanced and non-inverted. I designed the boards so that multiple units could be paralled to even further increase the low impedance drive capability. I was thinking that 2 or 3 boards, each with a two pair (4-LM3886), should drive a 2 ohm load with around 700 watts. (4 bridged units give around 150 to 200 watts into 8 ohms and 300-400 watts into 4 ohms; so 8 units should handle a 2 ohm load with 600 to 800 watts, depending upon the power supply and heat sinking.)

Hopefully, I'll have one board running by this weekend and if it tests out OK, I'll plug it into my system.
  Reply With Quote
Old 5th February 2002, 07:32 AM   #16
ssanmor is offline ssanmor  Spain
diyAudio Member
 
Join Date: Jan 2002
Location: Madrid
Default LM3886 parallel use

Thanks for the explanation. Could you send me a schematic of your whole amplifier for clarification?
I am also going to do some tests this week, I will tell you how it goes.
You can send the sch. to ssm07@tid.es or ssanmor@canal21.com

Thanks!!
  Reply With Quote
Old 5th February 2002, 02:22 PM   #17
diyAudio Member
 
Join Date: Oct 2001
Location: UW Stevens Point Campus
rljones,

I have been working on this very same design but have had some problems. I am unfamiliar with the dc servos and their function. The amp I built also runs way too hot. Could you e-mail me your schematics and pcb if possible.
My e-mail is bopppe069@uwsp.edu

Thank you in advance,


Opie
  Reply With Quote
Old 5th February 2002, 03:37 PM   #18
ssanmor is offline ssanmor  Spain
diyAudio Member
 
Join Date: Jan 2002
Location: Madrid
Default LM3886 parallel-bridge

My idea is this (I will try to explain it as clear as I can):
I am going to use four identical non-inverting amplifiers like the one shown in this picture. The output R in parallel with L is substituted by a 0.1Ohm/5W resistor, (all picked by-hand to minimize differences between them).
Then two of them are excited by the direct input signal from my preamplifier (with a gain=1 buffer). This signal is inverted by an inverting opamp with gain=1 and then drives the other two power stages.
The outputs of the two top stages are connected together and to the + terminal of the speaker; The outputs of the bottom stages are also connected together and to the - terminal of the speaker.

All the gain resistors are also picked by hand to match them within 0.1%

As you can note, I don't use servos. The stages are AC coupled, so they don't amplify the DC offset from the preamplifiers.

Does this set-up have any chance of working well? If you don't think so sincerely, please send suggestions.

Thanks!
Attached Images
File Type: gif lm3886basico.gif (29.8 KB, 2783 views)
  Reply With Quote
Old 5th February 2002, 05:47 PM   #19
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
If I was you, I'd insert some finite resistance in
series with the output of each device to prevent
the amps from arguing with each other.
  Reply With Quote
Old 5th February 2002, 05:55 PM   #20
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
Default Re: LM3886 parallel-bridge

Quote:
Originally posted by ssanmor
The stages are AC coupled, so they don't amplify the DC offset from the preamplifiers.
But it does not help with the DC offset from the amplifiers themselves. The 0.1 ohm resistors you're proposing may be too small to keep the two amps from "arguing" as Nelson says.
Didn't that App note from National warn about trying to do this without the servo?
If the two amps have, say, a 100mV difference in offset, this would be 0.5 amps through the balancing resistors (100 mV / (0.1+0.1))!
  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
LM3886 in parallel Denis.BR Chip Amps 11 12th August 2009 07:16 PM
LM3886 parallel PCB's jmillerdoc Chip Amps 0 27th May 2009 08:26 PM
parallel lm3886 question ryan750 Chip Amps 2 23rd October 2008 09:37 AM
Are two separate lm3886 = 2*lm3886 in parallel or bridge mode rs1026 Chip Amps 11 21st October 2004 10:24 AM
Can I parallel transformers for a LM3886? soundNERD Chip Amps 14 29th October 2003 01:34 AM


New To Site? Need Help?

All times are GMT. The time now is 11:54 PM.


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