LTSpice project

[Aelxis]

Hi everyone,
I am a beginner and i need help with modeling and setting up my SPICE circuit. I’m working on the “Death of Zen” Class-A amplifier (Project 70)
I’m not sure how to correctly define all the sources and connections in the simulation.
Here’s what I have so far:
I need to add an analog signal source at the input (IN), but I’m not sure what the correct syntax or parameters should be.

I also need a +35 V power supply where the schematic shows “+35 V”, but I think it should be referenced to ground — I’m not sure if I connected it properly.

At the output (where the speaker should be), I placed a resistor as the load, but I’m not confident it’s set up correctly or if I chose the right value.

Another issue is that I don’t fully understand how to perform the .tran analysis and parametric sweeps (like varying component values).

I would really appreciate some guidance on how to model and declare everything properly, and how to run those analyses correctly.

Thank you very much for your time and help!!!!
i attached the circuit

[Zero999]

Please post the .asc file (the forum accepts files with a .asc extension), along with any models and symbols (append .txt to .sub .asy .lib filenames), of what you've tried.

[Aelxis]

alright, this is what i tried:
Edit: i forgot about a node between E Q3 and R13. i edited it right now(sorry)

[Ian.M]

Your voltage sources were totally messed up.  You also had a few crossed connections (literally, joined where wires should jump over each other), and once those had been sorted so it matched the original schematic you posted  and some incorrect components changed (the diodes, and R13 Q3's emitter resistor), it started to show signs of life.  I then found Project 70 and  tweaked the choice of Zeners to get 3/4 of the supply at the top of R1, after which the setup procedure in the article works and I got amplification.  LTspice sim attached + screenshot of the main part of the schematic.

Note that the two potentiometer settings interact, so after you've adjusted VR1 so Out is at at half Vcc, you need to go back and tweak VR2 for 200mA through the supply resistor (i.e. 2V drop across it), then check if you need to tweak VR1 a tiny bit.

[ledtester]

Attached below is the schematic with some fixes.



Note:

- variables resistors are implemented with two regular resistors (VR1 and VR2)
- wire dot between R4 and C2 was removed
- input signal (V1) moved to correct location
- extra ground symbols removed
- R13 changed to 100 milliohms
- 35V power supply (V2) corrected

[Aelxis]

Thanks a lot for your help! It really made a difference. Every time i get through one of these challlenges I feel more motivated to keep learning and pushing myself further. I know i ve still got a lot to figure out, but i m excited to keep improving step by step. U re a Hero

[Aelxis]

Thank you so much!!!!

[Zero999]

They should be zener diodes.

Here's to sweep the potentiometer.

[Ian.M]

Also see: https://www.eevblog.com/forum/beginners/simulating-potentiometers-using-ltspice/

Finally, there is a convention that wires join with a dot.   Unfortunately crossing wires can be ambiguous.  In the old days of hand drawn schematics, you'd draw a little half-circle where one wire 'hops' over another, but that's tedious and in the era of computer drafting has more or less gone away.  If two wires cross without a dot, they are NOT connected to each other.  However JPEG (and other) image compression, and in the old days photocopying, can cause a small blob where lines cross that looks just like the dot for joined wires so best practice is to avoid any four way wire junctions by offsetting the wires. e.g. see just above R8 and below R13 in the original, and how I've handled them.   One of your crossing wires mistakes was an unwanted junction between the bottom of R4 and Q1 collector which was preventing RV1 from working to set Out at 1/2 Vcc, and also stopping it amplifying.  Zero999 spotted the connected cross and vertically offset the wire to the left, but didn't notice it was a fault, unconnected in the original.