i realised i dont have emitter resistors to built the aca (the aca uses mosfets my but you get the point)
Last edited:
why becuse i think companies should just provide a thd vs power graph instead of using random numbers that are the most beneficial to them?
im building the aca but i realised i dont have the exact components. irf540 bf245 and bc237 with 1.1ohm "emitter" resistors
Well here is a simulation of the ACA. If you haven't got this model then add it to your list:
The NPN transistor is not critical and a BC237 should be fine.
The BF245 you will just have to try. In a simulation a 2N3819 works OK and also so does a high gain small signal NPN transistor. You will have alter the sim preset values to get those to work properly (adjust values to get the midpoint voltage correct).
The 'emitter' resistors as you call them are critical because they determine the bias current. Try different values in the sim. You can parallel your 1.1 ohm to get different values.
Code:
* IRFP240C VDMOS copyright Cordell Audio December 6, 2010
.model irfp240C VDMOS(nchan Vto=4.0 Kp=4.8 Lambda=0.0032 Rs=0.01 Rd=0.1 Rds=1e7 Cgdmax=2600p Cgdmin=10p a=0.35 Cgs=1250p Cjo=3000p m=0.75 VJ=2.5 IS=4.0E-06 N=2.4)The NPN transistor is not critical and a BC237 should be fine.
The BF245 you will just have to try. In a simulation a 2N3819 works OK and also so does a high gain small signal NPN transistor. You will have alter the sim preset values to get those to work properly (adjust values to get the midpoint voltage correct).
The 'emitter' resistors as you call them are critical because they determine the bias current. Try different values in the sim. You can parallel your 1.1 ohm to get different values.
Nothing is particularly oddball as far as I know. The input FET maybe is uncommon but everything else should be standard. Are you looking at strange resistor values somewhere on a diagram. Nothing is critical beyond those low value resistors determining the bias current.
There have been a few different papers for different versions over the years but apart from the low value resistors everything else can be common values.
In the early versions R12 was 68.1k. (use a 68k). This sets the gain with R11. The version I sim has R12 as 39.2k (use a 39k)
The voltage gain is R12/R11.
R10 at 332k (use a 330k)
R1,R2 and R3 and R4 do matter because the volt drop across these sets the bias current.
In the early versions R12 was 68.1k. (use a 68k). This sets the gain with R11. The version I sim has R12 as 39.2k (use a 39k)
The voltage gain is R12/R11.
R10 at 332k (use a 330k)
R1,R2 and R3 and R4 do matter because the volt drop across these sets the bias current.
at this point i finished the ab amplifier with some of my design choices, im gonna skip the proto board stage becuse i get way to lost with more complicated protoboard projects and i will start designing the pcb tommorow and actually planning everything and looking at what parts i have etc.
OK 🙂 You have to learn by doing. There are several things I would do differently on that design, however......
Go for it 👍
Go for it 👍
i also adjusted it for parts that i have. im also intrested if i could use something like NTE2320 for the differential pair.
That could be interesting, using the PNP and NPN's for the diff pair and the current mirror. I don't see why not as long as you observe the maximum voltage rating of the transistors.
You learn a lot building stuff 🙂 and this design is basically OK but as I pointed out before, there are things I would do differently.
Don't let that stop you making it though.
Don't let that stop you making it though.
decided to revisit this circuit in hopes of making a headphone amplifier but i have an issue with the dc operating point after applying the transistor models
You are making the same mistakes as in the others 🙂 but before you even look at those there are some big mistakes in the simulation.
Look at the current in R3
Look at the collector current of Q6
We've covered why the offset will be high. Also look at how much current you need in the output stage if it is only to drive headphones.
Look at the current in R3
Look at the collector current of Q6
We've covered why the offset will be high. Also look at how much current you need in the output stage if it is only to drive headphones.
If you get 0.04% distortion in the simulator on ideal components, then in the real world you will get 0.4%. This is a lot for such a complex circuit that works in class A. A few pages earlier, I gave a link to my project of the Hyperbolic amplifier - it contains half as many parts and at the same time produces distortions of 0.01-0.02% when operating in class A. These are measured distortions of the assembled amplifier, and not computer simulations.