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Old 21st September 2012, 08:17 PM   #21
AndrewT is offline AndrewT  Scotland
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Cannot be biased into ClassA.
It's an IC chipamp !
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Old 21st February 2013, 07:26 PM   #22
alexbio is offline alexbio  Russian Federation
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Quote:
Originally Posted by juma View Post
I used OPA549 as an audio amp too, in Nelson's Super Symmetry topology. That's the only AB class amp that I kept and still listen to occasionally - it regularly surpasses the expectations.

Here is the sch. (small error - 220p caps should be 5-10 times smaller)
Click the image to open in full size.
Hi Juma!
1) Could you explain why feedback capacitor (220p) should be 5-10 times smaller? Will 200p cap attenuate signal at higher frequencies?
2) Question about the amp based on Walt Jung's paper on composite amplifiers
Click the image to open in full size.
Could it possible to increase R1 to 3.32 kOhm. Firstly, I have a this value on hand in contradistinction to 3k. Secondly, is it OK to increase R1 so that LT1361 will amplify voltage, and OPA549 will amplify current?

Last edited by alexbio; 21st February 2013 at 07:41 PM.
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Old 21st February 2013, 08:17 PM   #23
FoMoCo is offline FoMoCo  United States
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Quote:
Originally Posted by AndrewT View Post
Cannot be biased into ClassA.
It's an IC chipamp !
What he said.
Well... Maybe a current source of several amperes tied from output to a rail. Then there's that pesky heat problem...
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Old 23rd February 2013, 08:55 PM   #24
juma is offline juma  Germany
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Quote:
Originally Posted by alexbio View Post
Hi Juma!
1) ...Will 200p cap attenuate signal at higher frequencies?
2) ...Could it possible to increase R1 to 3.32 kOhm. Firstly, I have a this value on hand in contradistinction to 3k. Secondly, is it OK to increase R1 so that LT1361 will amplify voltage, and OPA549 will amplify current?
1) Yes
2) it's OK to make R1=3k3 and R2=10k so that in total gain LT1361 contributes with gain of about 6 and OPA549 with gain of 3. If you use OPA549 with unity gain (current only) the output power will be lower since LT1361 works with maximal supply voltage of +/-18V and OPA549 can go up to +/-30V.
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Old 23rd February 2013, 09:11 PM   #25
jcx is offline jcx  United States
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Quote:
Cannot be biased into ClassA.
It's an IC chipamp !
maybe not one - but 2 can:

...I explained some Class A push-pull op amp output bias concepts in my (jcx) posts:
AD8397-class A?

... higher power class A amps could be made similarly with "GainClone" power audio amp chips which are monolithic power op amps

simplified Class A push-pull output bias circuit:
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