Commercial amps
I read in a British mag about an amp that has IC output at low levels and goes to a discrete "booster" stage at higher demand. This is close to what you are asking for. Review said it sounded better at low power.
But I cannot see where more than say 40 volt rms swing would ever be needed. Current delivery is more of an issue with a LM3875 with most speakers. But there are always special cases.
George
I read in a British mag about an amp that has IC output at low levels and goes to a discrete "booster" stage at higher demand. This is close to what you are asking for. Review said it sounded better at low power.
But I cannot see where more than say 40 volt rms swing would ever be needed. Current delivery is more of an issue with a LM3875 with most speakers. But there are always special cases.
George
Leolabs said:
I'm not sure what you mean by "bootstrap topology".
If using a bridged configuration (doubling the voltage swing across a floating load) isn't what you need, you can easily boost the output voltage and/or current, by following the chipamp with a discrete "booster" stage, with feedback from the booster stage's output back to the negative input of the chipamp. (But, if you were going to do that, then maybe you might as well use a high-quality opamp instead of the chipamp, in many/most cases.)
Here are some application notes that have circuits that can boost the output voltage and/or current of any monolithic voltage amplifier, such as an opamp or chipamp:
AN-272 at http://www.national.com
AN18 at http://www.linear.com
And here's one that might also be of interest:
AN14 at http://www.apexmicrotech.com
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
I belive Leolabs refers to this circuit:
http://www.edn.com/articles/pdfs/EDN/19990513/07m4591.pdf as OP-Amp bootstrap.
this techniqe employed in PHONIC Max-250 amp, for example,
is known as class H.
http://www.edn.com/articles/pdfs/EDN/19990513/07m4591.pdf as OP-Amp bootstrap.
this techniqe employed in PHONIC Max-250 amp, for example,
is known as class H.
The LM3875 can do that as long as the difference in voltage between the two power pins (Vcc/Vee) does not exceed the ratings. So if the +rail goes up then the -rail will have to decrease to be sure the total is never more than the 84V in the datasheet. The question would then be, how good does it perform? The LM3875 doesn't have the greatest PSRR on the negative rail but it would be fun to test and see the results.
-SL
-SL
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