Hi guys,
The other week while wasting time on a lazy afternoon, I was inattentively doing a random search of a CFA amp schematic online. One schematic of which looks like of chinese origin at Pinterest site caught my interest. I took a quick screenshot on some parts of it (Pinterest won't let me see the whole schematic without registering). I tried to recreate it in LTSpice, with some changes in order to make it work accordingly (specifically IRFs for the outputs). It was surprising that the circuit displays a very good voltage/current balance, low THD and has a good gain and phase margin. The only drawback for me was that it is inherently H3 dominant hence I used low gain transistors (high gain transistors significantly boosts H3).
Fueled by a 'want to build one CFA', I modified the circuit in order to meet my preferences . Make it H2 dominant low THD and still showing good balance of currents and voltages. I humbly ask the more knowledgeable ones to check on my work if my circuit will actually work right when built in a real hardware. LTSpice simulation say's it will (sim files attached). This is my first CFA amp build if everything goes according to plan and the last build of my DIY Audio hobby.
Any thoughts folks?
Thank you!
Albert
The other week while wasting time on a lazy afternoon, I was inattentively doing a random search of a CFA amp schematic online. One schematic of which looks like of chinese origin at Pinterest site caught my interest. I took a quick screenshot on some parts of it (Pinterest won't let me see the whole schematic without registering). I tried to recreate it in LTSpice, with some changes in order to make it work accordingly (specifically IRFs for the outputs). It was surprising that the circuit displays a very good voltage/current balance, low THD and has a good gain and phase margin. The only drawback for me was that it is inherently H3 dominant hence I used low gain transistors (high gain transistors significantly boosts H3).
Fueled by a 'want to build one CFA', I modified the circuit in order to meet my preferences . Make it H2 dominant low THD and still showing good balance of currents and voltages. I humbly ask the more knowledgeable ones to check on my work if my circuit will actually work right when built in a real hardware. LTSpice simulation say's it will (sim files attached). This is my first CFA amp build if everything goes according to plan and the last build of my DIY Audio hobby.
Any thoughts folks?
Thank you!
Albert
Attachments
Therefore, it is not preferable to make CFA.
His only advantage is the high speed of growth.
Everything else is worse than a VFA amplifier.
His only advantage is the high speed of growth.
Everything else is worse than a VFA amplifier.
Nice circuit Sir Sandy, I'd like to run a simulation, perhaps replace those BC devices because they are not the popular kind here in my place. Thanks for sharing!
Albert
(and Yes I have simulated quite a number of CFA circuits, they are mostly 3rd harmonic dominant and the simpler ones displays quite a high dc offset and can be very hard to tame even in simulation).
Albert
(and Yes I have simulated quite a number of CFA circuits, they are mostly 3rd harmonic dominant and the simpler ones displays quite a high dc offset and can be very hard to tame even in simulation).
Thanks for your feedback Sir Andrew, I've never simulated a fully symmetrical circuit before, this is my first attempt and it comes in a CFA form. I did not realize that these types of circuit are very sensitive to dc offset balance, a small tweak here and there and dc offset jumps instantly. I now understand why some designers choose complexity because the added elements and stages helps in isolating each stage from possible 'disturbances' if ever a fault may exist in each stages. The smaller circuits that I have simulated displays such a wild behavior, a small bias adjustment and dc offset instantly jumps, not really good because if thermal drift may occur it can really be very destructive.
Albert
Albert
Meanwhile, I've modified the China circuit and revert it back to use BJTs for the output. Too high bias currents for the mosfet seems to be not a favorable setting in my part of the world where hot weather is experienced all year round. I've actually came up with two modifications, the China CFA and my CFA version (Sir Sandy actually gave me an idea) both circuits displays very good current/voltage balance, and now I have four circuits to choose from, sajti's V6, Sandy's CFA and these two mods that I've made.
By the way I'm calling it China amp because it comes with chinese (?) characters, not so sure though if the circuit was a clone but perhaps if anyone knows of exactly a similar design kindly post it here.
Thanks!
Albert
By the way I'm calling it China amp because it comes with chinese (?) characters, not so sure though if the circuit was a clone but perhaps if anyone knows of exactly a similar design kindly post it here.
Thanks!
Albert
Attachments
Has anyone had a spice model for 5.1v through hole zener diode? The closest I found on the internet was 5.6v and it seems it originated from an older spice program.
Thanks!
Thanks!
So I built it 🙂 this is my first time hearing a CFA topology amp. The only difference that is audible in comparison to my other DIY builds was the bass sound. This one is more controlled, punchy (or tight?) opposite to a loose/boomy sounding bass (or extended). DC offset is very low at 2mv at 14mv bias current test, very stable too.
Albert
Albert
