Current conveyor as a voltage amplifier

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Well, that's why I made my suggestion. In the schematic in post 117 you could add my name next to yours. In any case, the idea was yours and you are doing the testing. I helped refine the design.

Not meaning to demean, I just really like this circuit. It deserves good documentation.
 
OK here it is.
 

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Here is what I think to use for shunt regulator to power GainWire. I don’t have spice models for IRF610/9610 mosfet so I used what was close enough just to simulate it. Input voltage is +-42V because I have such transformer. I like to use quite simple circuit to get good shunt regulator. This one is similar to the Borbely simple shunt reg, just I did not want to use zener diode, so here is CCS + resistor instead. I am not sure that 1.3V is enough to get JFET CCS to work properly, but some use just 0.65V. I simulated one more complex circuit and did not get significantly better result.
dado
 

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Can you show output impedance?

I like this design. However the bases of Q10 and Q12 see an impedance of 10k. It's like having 10k base stoppers. You may try bypassing R3 and R12. Even something as small as 10p may work well. I have not actually studied it however.

IIRC Salas made a DN2540 model, and I'm guessing that is what you should use. I'm no expert on shuntregs like this, but if you can make sure it's stable then the circuit looks great to me.
 
Hi Dadod,
thanks for the exciting designs you're presenting in this forum.
Regarding your schematic in post #128 I think Q13, Q14 (and Q21, Q22 on the the negative side) will face an undefined biasing state on startup (chicken - egg situation).
I would suggest a 100k (or higher) resistor from Q13 base to V+ (same from Q22 base to V-).
Best regards,
George
 
Hi Dadod,
thanks for the exciting designs you're presenting in this forum.
Regarding your schematic in post #128 I think Q13, Q14 (and Q21, Q22 on the the negative side) will face an undefined biasing state on startup (chicken - egg situation).
I would suggest a 100k (or higher) resistor from Q13 base to V+ (same from Q22 base to V-).
Best regards,
George

Thanks for suggestion George. Actually I was listening to this circuir http://www.diyaudio.com/forums/anal...onveyor-voltage-amplifier-10.html#post3314435 as I made PCB beffore all other improvement were simulated (by the way simulation did not show an undefined biasing state). As just now I am designing my shunt regulator and when finnished I will test all those different combinations and I'll report result.
Damir
 
I think Q13 needs some initial base current to act as a cascode for J3, thus causing the necessary voltage drop on R17, turning on Q14 and providing more current for zener D1 and Q13.
Haven't built the circuit though, just based on my understanding of the circuit.
Best regards,
George
 
After some simulation attempts here is output impedance graph.
I would like to hear opinions if output impedance between 2 and 6 miliohm is low enough, or Ishould go for more sophisticated circuit.
dado
 

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That is already quite low. More importantly, compare the output impedance with an inductor. How much output inductance does it have?

At this point you may as well start building it. The circuit is so powerful that you will probably need to get layout sorted out before you can stabilize it, and it will need to be stable before anything else will ever matter.

R14 and R5 may be redundant because the FETs are already driven by a large source impedance. I wonder if they could even worsen stability.

What is the output impedance up to 50MHz? Have you included the ESL of C3 and C1?
 
If the output buffer fails to turn on at startup, you'll notice it when signal is first applied, at which point the output will initially snap to the triggering level and then act as though it never happened. This may not be audible and should not destroy anything, but you should check zener voltage right after startup to see if it turns on by itself. Something like gagnou suggests would fix it.
 
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I have download the ltspice file that you post , and have tested , there are alterations that i would like to propose, if you guys do not mind.
First is to lower the voltage , it does not make much sense that hight voltage, you will be ok with minus/plus 15 volts , less power waste. And less thermic problems with the circuit. Other is to change the mirrors transistors (bc550c) with bc327-40 and bc337-40, they should be better in dealing with the current that the circuit use, the distortion will be lower.

The 2sa1381 and 2sc3503 is a very good choice , but the cordell models are a bit to much optimist in respect to early voltage, so expect a litle more distortion in reality that with the simulation, but in the overall it seems a good circuit .

I use current sources instead of mirrors , I get even lower distortion that this circuit post here:

http://www.diyaudio.com/forums/digital-source/217459-dac-i-v-convertion-very-low-distortion.html
 
I brought up similar points in the beginning of this thread.

In your circuit, Q7 and Q8 cause the same function of the Baxandall cascodes in this circuit. Difference is, your circuit has a very high output impedance so it can't be compared with this one. Adapt your circuit to give similar Zin, Zout and gain and then we can toss boulders.

Early voltage of the A1381/C3503 should not matter if the Baxandall pairs do their job.
 
That is already quite low. More importantly, compare the output impedance with an inductor. How much output inductance does it have?

At this point you may as well start building it. The circuit is so powerful that you will probably need to get layout sorted out before you can stabilize it, and it will need to be stable before anything else will ever matter.

R14 and R5 may be redundant because the FETs are already driven by a large source impedance. I wonder if they could even worsen stability.

What is the output impedance up to 50MHz? Have you included the ESL of C3 and C1?

This simulation is with small Miller capacitor connected to Q1 and Q2 and it is up to 1GHz, and should be stable.
Looking at phase there is no significant inductance up to 20kHz.
One think were I have my concern, jfet CCS between Q1 and Q2 bases. In the simulation it looks good, but does 1.3V is enough for 2SK170 to behavs as good CCS at 1.7mA??
dado
 
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