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Old 25th December 2012, 08:33 PM   #1
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Default Simple hybrid amplifier (35W/8Ohm)

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Hi,

I have built tube / power opamp hybrid amplifier.
Tube preamp section is CCDA circuitry from John Broskie, which drives power opamp OPA548T connected as unity-gain voltage follower.

It sounds good, has that smoothness of tube and you can listen to the amplifier for long periods of time without any fatigue.
Attached Images
File Type: png CCDA Preamp.png (8.6 KB, 1110 views)
File Type: png CCDA PSU.png (19.3 KB, 1098 views)
File Type: png Hybrid 35W OPAMP PSU.png (9.1 KB, 1064 views)
File Type: png Hybrid 35W OPAMP.png (8.6 KB, 1067 views)
File Type: jpg DSC00464.JPG (741.7 KB, 1081 views)
File Type: jpg DSC00465.JPG (646.0 KB, 486 views)
Attached Files
File Type: pdf CCDA Octal.pdf (736.7 KB, 151 views)

Last edited by kacernator; 20th March 2013 at 03:54 PM.
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Old 19th January 2013, 08:43 AM   #2
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Default Project update

I have updated few things. Mainly, I have changed preamp to aikido with noval tubes, because of better availability of ECC83 and ECC82 than 6SL7.
There are also some changes in the power supply and power amp.

Thinking about adding EQ, because some people really need one with their speakers/listening conditions.
Attached Images
File Type: png Aikido Preamp noval.png (12.3 KB, 378 views)
File Type: png Aikido PSU noval.png (20.9 KB, 265 views)
File Type: png Hybrid 35W OPAMP PSU.png (9.1 KB, 209 views)
File Type: png Hybrid 35W OPAMP.png (9.2 KB, 221 views)
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Old 19th January 2013, 09:09 AM   #3
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I am a little puzzled. Wouldnīt it be easier to lessen the feedback of the OPA548 to get 20dB gain instead of zero and skip the tube section?
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Old 19th January 2013, 09:22 AM   #4
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Ofcourse you can do that. Then you have nice IC chip amplifier. But I want sound of tubes without output power tubes and output transformer.
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Old 19th January 2013, 09:37 AM   #5
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Canīt see the difference. What you have is a tubepre capacitorcoupled to a 90dB feedbacked chip amp ;-).
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Old 19th January 2013, 09:39 AM   #6
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There is difference in what will amplify voltage. Either tubes or transistors in chip, I prefer tubes for voltage amplification.
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Old 19th January 2013, 09:44 AM   #7
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You still have 90dB raw gain in the chip. The amplification inside the chip does not lessen with more feedback. But if you lessen feedback, fidelity usully gets better.
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Old 19th January 2013, 09:54 AM   #8
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Opamp is configured as buffer, it does not amplify voltage, just current.
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Old 19th January 2013, 10:24 AM   #9
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...why not a couple of vmos sorce follower?
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Old 19th January 2013, 10:30 AM   #10
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In class AB without feedback around mosfet source follower you will have much more distortion. You could use class AB BJT follower output stage, but it should have about 4 to 5 pairs minimum of parallel devices to have small distortion and high damping factor.

Simple mosfet source follower works better in class A, which I donīt want because of so much heat.
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