Summer is coming and a lot other occupation on me. I suppose autumn is when more things should happened.
I have some question regard the parts and part values:
- Value range for: R31, R32, R33, R34, R36, R62 (2.2 ohms now)
- Value range for: R13 (3.3 ohms now)
- Value range for: R12, R45, R46, R47, R48 (6.8 ohms now)
- P1 value is 1K1 so it must be 2K trimmer
- What is 2SC2240/2SA970 alternative.
- What is 2SC3503/2SA1381 alternative. 2SC3423/2SA1360 ok?
- R37. I think i must be a high watt resistor, right?
- Does C34 needed?
- Does thermal track NJL3281 && NJL1302 transitors will be use in this design?
Thanks, all my questions was answered! I hope this project will be test and PCB will available soon for DIY fellow soon.
When you design the PCB make space for a resistors in series with D13 and D14, lets say 2.2R. This small value will not influence the VAS function but can be used to measure VAS current.
I have another question: I don't understand how to connect the DTTD diodes ( those diodes in output transitors? ). I saw there are four in the spice image but not sure which is which.
Use two from NPN/PNP output transistors for the bias spreader and other two between the drivers emitters. Do it as you think is better for the layout. You can look how I did it in my VFA TT TMC amp.
I noticed now, you can use for Q17 BC560C and for Q18 BC550C and not those high voltage transistors as on the schematic.
Yes Q19 not Q18. My 200W CFA MOSFET amp use very similar compensation and IPS and it is working, I don't expect problems here.
C9, C10, C12, C14, C5 - silver mica or polystyrene
C15, C16 - ceramic C0G (N0P), you can use silver mica here but not needed, to be as close as possible to the drivers base - collector
C34 - polypropylene
C24 - silver mica or polystyrene
Here are two amps, one is CFA with low impedance feedback network connected to the low impedance negative input, other one is the same amp but with high impedance negative input and thus with high impedance feedback network. The Loop Gains look very similar, distortion, PM and GM are very similar.
Does second one became a VFA or is still CFA??
Damir
Does second one became a VFA or is still CFA??
Damir
Attachments
Hi Damir
Confirms several points, that "CFA" is a poor description.
And that it's all in the Loop Gain😉
I am interested in rational "CFA" optimisation but previous threads, despite efforts from Andrew, have been too full of unsubstantiated rants to learn much from.
Except your nice work, of course, you have any links or references to useful information?
Best wishes
David
Hi David,
Thank you for your nice word.
I am not sure what you seek, I am still in the dark trying to understand myself. PM your email I will send you something (you probably have that already).
Best regards
Damir
Thanks to Bob, D. Self and the work they built upon, for VFA we have a nice explanation of the basic blocks of the amplifier.
So we understand well the basic LTP, the effect if we add a Current Mirror or a cascode to it, the effect of an EF buffer in the VAS and so on.
For a "CFA" much is similar, especially the Output Section, but there are some different decisions in the earlier sections.
No Current Mirrors but perhaps current sources in the IPS, perhaps the lower impedance feedback point favours one type of compensation implementation compared to another.
Some of this was discussed in the "CFA" threads but the useful discussion was buried under so much noise.
Clearly you have made some excellent choices in your own circuit so I hoped for your ideas.
Best wishes
David
Hi David,
What do you think about to open a new thread where we can discus, suggest, criticize ..a CFA building blocks: input part, VAS/TIS, compensation and OPS even if an OPS could be quite similar to those used in the VFA, but as VAS/TIS is symmetric there could be some improvements/simplifications. I suggest to start with complementary symmetric circuit.
I will try to show how I decided what circuits to use, but I need a time to collect all my different simulation burred in to many files.
Best regards
Damir