Simple hybrid amplifier (35W/8Ohm)

kacernator · 03:54 PM

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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.

kacernator · 19th January 2013, 08:43 AM

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.

revintage · 19th January 2013, 09:09 AM

I am a little puzzled. Wouldn´t it be easier to lessen the feedback of the OPA548 to get 20dB gain instead of zero and skip the tube section?

kacernator · 19th January 2013, 09:22 AM

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.

revintage · 19th January 2013, 09:37 AM

Can´t see the difference. What you have is a tubepre capacitorcoupled to a 90dB feedbacked chip amp ;-).

kacernator · 19th January 2013, 09:39 AM

There is difference in what will amplify voltage. Either tubes or transistors in chip, I prefer tubes for voltage amplification.

revintage · 19th January 2013, 09:44 AM

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.

kacernator · 19th January 2013, 09:54 AM

Opamp is configured as buffer, it does not amplify voltage, just current.

0feedback · 19th January 2013, 10:24 AM

...why not a couple of vmos sorce follower?

kacernator · 19th January 2013, 10:30 AM

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 don´t want because of so much heat.

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19th January 2013, 09:09 AM	#3
revintage diyAudio Member Join Date: May 2007	I am a little puzzled. Wouldn´t it be easier to lessen the feedback of the OPA548 to get 20dB gain instead of zero and skip the tube section?

19th January 2013, 09:22 AM	#4
kacernator diyAudio Member Join Date: Jan 2008	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.

19th January 2013, 09:37 AM	#5
revintage diyAudio Member Join Date: May 2007	Can´t see the difference. What you have is a tubepre capacitorcoupled to a 90dB feedbacked chip amp ;-).

19th January 2013, 09:39 AM	#6
kacernator diyAudio Member Join Date: Jan 2008	There is difference in what will amplify voltage. Either tubes or transistors in chip, I prefer tubes for voltage amplification.

19th January 2013, 09:44 AM	#7
revintage diyAudio Member Join Date: May 2007	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.

19th January 2013, 09:54 AM	#8
kacernator diyAudio Member Join Date: Jan 2008	Opamp is configured as buffer, it does not amplify voltage, just current.

19th January 2013, 10:24 AM	#9
0feedback diyAudio Member Join Date: Feb 2010	...why not a couple of vmos sorce follower?

19th January 2013, 10:30 AM	#10
kacernator diyAudio Member Join Date: Jan 2008	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 don´t want because of so much heat.