Bridge & Parallel 4 x LM4780 - Basic wiring diagram needed

[GAH]

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

 

[veteran]

Maybe this will help you:

LM4780 amp

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

LM3886 amp

An externally hosted image should be here but it was not working when we last tested it.

 

[Redshift187]

Look up the National Semi application note AN-1192. It details BR100, PA100 and BPA200 designs with schematics.

 

[GAH]

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.

 

[Redshift187]

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.

 

[renaguilar05]

nnnn

 

[chatziva]

hi there

i was planning on making my own bpa200:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=131216&highlight=

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

 

[chatziva]

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?

 

[Peter Daniel]

Re: Bridge/Parallel configuration

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/showthread.php?postid=636565#post636565
http://audiosector.com/lm4780 amp.pdf

If you don't have balanced signal available, you can easily create it with a simple transformer: http://www.diyaudio.com/forums/showthread.php?postid=1712724#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 😉

 

[GAH]

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)?
🙂

 

[AndrewT]

Hi,
if you plan to bridge an 8ohm speaker using chipamps then I suggest three channels in parallel rather then just two.
I am recommending that you build a BPA300 into 8ohm if you feel that you must use chipamps for your 200W into 8ohm loading.

 

[Peter Daniel]

Re: 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)?
🙂

I always avoid paralleling chips, they sound slightly inferior this way comparing to a single chip. I don't even want to think what 3 of them will sound like in parallel.

Besides, we are talking here about LM4780, since it is a dual chip, it is very inconvenient to use 3 halves in parallel.

A single LM4780 paralleled and then two of them bridged, will have no problem with 8 ohm loads.

There is a certain advantage to running chips in bridge: I find the dynamics improve and there is more body to the music, you can read more about it here: http://6moons.com/audioreviews/47labs5/gaincard_3.html

 

[AndrewT]

Yes Peter,
he could try running the dual chipamp in bridge mode and then parallel 3 of them to give the transient peak current ability into an 8ohm speaker.

But rather than build up 6channels of chipamp, go to a discrete output stage with discrete drivers using lme498xx series voltage amp driver stage or go fully discrete.

 

[Peter Daniel]

Yes Peter,
he could try running the dual chipamp in bridge mode and then parallel 3 of them to give the transient peak current ability into an 8ohm speaker.

But rather than build up 6channels of chipamp, go to a discrete output stage with discrete drivers using lme498xx series voltage amp driver stage or go fully discrete.

What I meant was to parallel each dual chip first and then run them in bridge, not paralleling brided amps which is completely impractical and unpredictable.

While going fully discrete may have certain advantages, using chip amps is quite tempting too and both approaches can produce very satisfying results.