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?
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?
ziling said: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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traw said:
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 said:
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
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