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What about this amp-CFA or VFA?
What about this amp-CFA or VFA?
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Old 29th March 2013, 06:08 PM   #1
dadod is offline dadod  Croatia
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Default What about this amp-CFA or VFA?

Is this amp of CFA or VFA type?
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Old 29th March 2013, 09:33 PM   #2
magnoman is offline magnoman  United States
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CFA I like it.
Daughter and I are making a very similar all bjt version (but more conventional output followers) for ipod speakers (I cant stand seeing earbuds or even headphones on for hours at a time).

Thanks
-Antonio
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Old 30th March 2013, 08:39 AM   #3
ivanlukic is offline ivanlukic  Serbia
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This is very promising CF circuit, distortion is most certainly very low. Somewhat overdone circuit, a bit more complicated than necessary, and finding J and K output mosfets specified is now difficult. But I like it, too.

BTW, I think that your proposal from other threads to use inverting input in VF amps has some merit and should be examined in more detail. At least, with power amps, it is easy to solve the problem of absolute phase by inverting connections at one side of loudspeaker cable. A number of people reported that VF amps sound better when inverting mode is used. Few years ago there were many amps with power ICs that used that kind of circuit. And John Linsley Hood promoted idea of using shunt feedback in MM phono RIAA stages as better sounding in spite of having 10dB more noise.
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Old 30th March 2013, 09:20 AM   #4
ivanlukic is offline ivanlukic  Serbia
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Damir,

Is this some kind of trick question? I am not EE, and circuit is drawn in such way that it is somewhat puzzling to me.
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Old 30th March 2013, 09:42 AM   #5
Lazy Cat is offline Lazy Cat  Slovenia
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Clearly CFA. Q11, Q12 are simply just bias providers for Q3, Q4 tracking cascodes. Nothing special about the circuit, only to complex for resulting performance. A big question remains how it would sounds, so build and listening test is of utmost necessity.
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Old 30th March 2013, 10:46 AM   #6
ivanlukic is offline ivanlukic  Serbia
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If I may add, circuits with this level of complexity are notoriously difficult to stabilize. This circuit asks for SMD pcb implementation which is not diy friendly. I wish that you could have a look inside Cyrus Straight Line amp (complicated CF topology). PCB is more like some PC card, you need magnifying glass to see all tiny SMD parts. That is why we, audiophiles with some diy inclinations, prefer simple CF circuits.
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Old 30th March 2013, 12:32 PM   #7
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ivanlukic View Post
This is very promising CF circuit, distortion is most certainly very low. Somewhat overdone circuit, a bit more complicated than necessary, and finding J and K output mosfets specified is now difficult. But I like it, too.

BTW, I think that your proposal from other threads to use inverting input in VF amps has some merit and should be examined in more detail. At least, with power amps, it is easy to solve the problem of absolute phase by inverting connections at one side of loudspeaker cable. A number of people reported that VF amps sound better when inverting mode is used. Few years ago there were many amps with power ICs that used that kind of circuit. And John Linsley Hood promoted idea of using shunt feedback in MM phono RIAA stages as better sounding in spite of having 10dB more noise.
I built inverted gain clone long time ago(non inverting too) and used input buffer to overcome low input impedance and a source impedance gain influence(JLH simple buffer).
I can't say which one sounded better, never did listening comparison, both sound quite good.
Damir
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Old 30th March 2013, 12:38 PM   #8
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ivanlukic View Post
Damir,

Is this some kind of trick question? I am not EE, and circuit is drawn in such way that it is somewhat puzzling to me.
It is not a trick question, I am not sure were to put it as the gain part is a current conveyor. A current conveyor has very low intrinsic distortion and to find equaly good output stage it's not easy.
This is just simulated project not ready to be built, main problem is to get close to zero volt at the output, probably neads servo to solve that.
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Old 30th March 2013, 12:51 PM   #9
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Lazy Cat View Post
Clearly CFA. Q11, Q12 are simply just bias providers for Q3, Q4 tracking cascodes. Nothing special about the circuit, only to complex for resulting performance. A big question remains how it would sounds, so build and listening test is of utmost necessity.
You are correct nothing special, just my try to use current conveyor as a gain part.
Here is modified VSSA with JFETs, also nothig special. I was in preprations to convert my JLH MOSFET amp(I have two) to CFA to compare it with JLH VFA type, but not desided yet on the circuit.
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Old 30th March 2013, 02:43 PM   #10
Lazy Cat is offline Lazy Cat  Slovenia
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Dadod, what I would do on last sch is to leave BJT pair at the input, cascoded with j-fets, BJT VAS/TIS with 470 ohm base and 10 ohm emitter resistors and no gate stoppers at output mosfets. Compensation with smallest possible Miller caps and remaining necessary cap compensation to GND or to OUT, just enough to stabilize it.
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