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gruni 21st January 2012 02:21 PM

Grounded Bridge Chipamp (using LM4780)
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Hi everybody,

I just ported the Grounded Bridge design invented by Crown to the LM4780 amplifier chip. I added the schematic to this post. Will this work or will the LM4780 protection circuits prevent the chip from working?

gruni 21st January 2012 02:24 PM

1 Attachment(s)
oops, i missed the voltage reference for the inverting amplifier. added it in this schematic

AndrewT 21st January 2012 02:56 PM

I can follow chip A. Gain 21times, Rin = 10k, driving a load connected to audio ground.

gruni 21st January 2012 03:09 PM

thats right. chip B's output is connected to ground directly, shifting the power supply (that has no reference to ground) so that the output can effectively swing the full supply voltage in both positive and negative directions. a good explaination of this topology can be found here:

geraldfryjr 21st January 2012 03:53 PM

Sunn had used this output configuration in their Concert series power amplifiers before Crown did, I believe.

I had just posted this earlier, But I had to delete it because the link was to a revised version and I think that it was incorrect.

This is the correct print to the two versions I have of this amplifier in which are slave amplifiers.

enjoy !!

jer :)

gruni 21st January 2012 04:27 PM

you're right that seems like being the same design, altough its obviously transformer-coupled(?)

anyway, does my implemention of that design using lm4780s work? using ne5532 as opamp instead of lm4780s works properly, but into very little load of course. so the only problem i see are the protection circuits in the chip.

geraldfryjr 21st January 2012 04:47 PM

The output devices are driven by a transformer,But the output devices are configured as bridged and ground on one end.
It took me a long time to realize how this configuration worked ,But it is very simple really.

If it works with a regular low power opamp I see no reason that it wouldn't work with a power opamp.

Is the input ground Referenced to GND?

jer :)

gruni 21st January 2012 05:10 PM

yes of course input ground is connected to gnd.

geraldfryjr 21st January 2012 05:51 PM

Okay,That's what I thought.

Very interesting configuration indeed !!!

jer :)

jcx 21st January 2012 06:09 PM

my guess is that you need to look at stability, the power chip amps are only stable for Acl > 10

some Spice macromodels will fail by showing stable operation when the circuit isn't

you may need "noise gain" compensation added to the "gnd" amp

and I hate it when people don't just put the image in their post instead of linking a pdf

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