MY LM4780 Amp

[ziling]

MY LM4780 to 3 link Amp

[traw]

hmmm.... have something similar before in regards to an opamp up front driving them with an outer feedback loop. Not myref but a commercial 'bpa300' implementation. Except inner feedback was 56/1+1 and outter feedback 56/1+1.... It was a great sounding amp.

What is the philosphy of the opamp feedback wrapping the inner paralleled chips?

What does the cap + resistor across the inputs do? (my ignorance). On other i've seen was 470pf solely...

Paralleled 6 ? why not bridge to creat larger voltage swing?

[gootee]

Originally posted by ziling
MY LM4780 to 3 link Amp

Why do you have ~equal feedback to both + and - input pins of each chipamp? Is it some type of Howland current source topology?

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

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[gootee]

Originally posted by traw


What is the philosphy of the opamp feedback wrapping the inner paralleled chips?

Off the top of my head, there are a couple of standard reasons for putting a larger amp inside the forward part of the feedback loop of an opamp.

One reason is to use the larger amp as a current/power booster for the opamp, often implemented with the gain of the larger amp = 1, so it's a buffer, but with much higher power output capability. If the larger amp is configured as a Howland-type current source, the whole thing can become a voltage-controlled current source, with relatively higher current output capability. (I haven't analyzed the OP's schematic fully-enough to know if that is what he did, here.)

I have several power amplifier designs that put a chipamp into the forward part of the feedback loop of an opamp, solely to improve the performance of the chipamp. It can easily result in the improvement of the THD@20kHz by a factor of 15 or so, while also dramatically improving the transient response characteristics.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

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[ziling]

[Tolu]

@ziling:
How does it sound? In comparison to the well known candidates (3875, 3886, ...)!

Regards

Thomas

[ziling]

Gootee,thanks you for your explanation

[gootee]

Originally posted by ziling
Gootee,thanks you for your explanation

You're welcome. But please note that I'm not really an expert at these things, after many years of not working in the EE field. I have been playing around with chipamps, lately, though.

I also wanted to mention that by using several chipamps in parallel, inside of an opamp's feedback loop, there are ways to make a power amplifier that is amazingly good at driving very large capacitive loads, with truly-excellent transient-response characteristics, while still retaining extremely-low THD-20kHz.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html