Bridge & Parallel 4 x LM4780 - Basic wiring diagram needed - diyAudio
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Old 10th August 2009, 06:03 AM   #1
GAH is offline GAH  Fiji
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Default Bridge & Parallel 4 x LM4780 - Basic wiring diagram needed

I'm a newbie to gaincloning and have become hooked after successfully building a LM3875 and LM4780 dual mono Audiosector kits. I'm now interested to build a Bridge/Parallel amp configuration using four LM4780 chips (Audiosector). I'd appreciate a basic description and or wiring diagram to build such an amp. I intend to use two 300VA transformers with this amp.

Glen
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Old 10th August 2009, 10:41 AM   #2
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Maybe this will help you:

LM4780 amp

I'm building a similar amp but with the LM3886 (+ DC Servo)

LM3886 amp

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Old 10th August 2009, 11:23 AM   #3
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Look up the National Semi application note AN-1192. It details BR100, PA100 and BPA200 designs with schematics.
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Old 11th August 2009, 03:35 PM   #4
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Default Bridge/Parallel configuration

Thanks. I'm aware how to bridge or parallel two LM4780 chips. However is it possible to integrate four LM4780 chips for a stereo amp - two in bridge mode and two in parallel? If so which goes first and how are they wired together for a stereo output?

Thanks.
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Old 11th August 2009, 06:37 PM   #5
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Break it down. First off, forget "stereo". Think of a single channel. Then realize that bridged-parallel means one parallel on either side of the speaker. So you will use 2 parallel LM4780 per speaker (one for positive and one for negative). So technically, all 4 LM4780 will be set up for parallel mode and you will bridge them after.
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Old 11th August 2009, 07:58 PM   #6
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Old 11th August 2009, 08:53 PM   #7
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hi there

i was planning on making my own bpa200:

Wendy200 a gainclone based on the BPA200

but now i am also thinking of using the audiosector boards as i am not very confident in board design & etching

you can use a driver to drive your 2 lm4780 per channel, similar to alex's layout here:

http://www.shine7.com/audio/300W_diag_full.jpg

i would replace the drv134 with something more up to date such as ths4131

hope this helps
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Old 11th August 2009, 09:11 PM   #8
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oh i am also thinking of using a separate boards which will contain dc servos for the lm4780's.

it seems it's worth including servos as they won't cost much (compared to the cost of the rest of the amp) and you wont have to play with trimmers all time or buy very expensive 0.1% resistors

i plan to pretty much follow figure 13 in the national's application note (without the front end bit)

i hope there shouldn't be an issue with using a separate board for those if cables are kept short, any feedback on that?
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Old 11th August 2009, 09:32 PM   #9
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Default Re: Bridge/Parallel configuration

Quote:
Originally posted by GAH
I'm aware how to bridge or parallel two LM4780 chips. However is it possible to integrate four LM4780 chips for a stereo amp - two in bridge mode and two in parallel? If so which goes first and how are they wired together for a stereo output?

Each chip should be configured for parallel operation first, then use two of them per channel in bridged mode. For more info check this links:
http://www.diyaudio.com/forums/showt...565#post636565
http://audiosector.com/lm4780%20amp.pdf

If you don't have balanced signal available, you can easily create it with a simple transformer: http://www.diyaudio.com/forums/showt...24#post1712724 Chances are, it will work better than active circuitry methods.

With bridged configuration, DC offset is not an issue as long as you combine similar offset chips for both halves of balanced signal: the differential offset will be close to zero then
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Old 12th August 2009, 02:50 AM   #10
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Thumbs up Bridge/Parallel configuration

Thanks Redshift187 and Peter! Now I understand. With such a configuration is there any sonic benefits besides the extra power when using 6 to 8 ohm speakers (Harbeth SHL5)?
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