Rahul,That is awesome, Alfi! Another great build. Congratulations!
How did you wire the Jensen's?
Looks very neat!
@Alfi, you skipped R101 and R201 too? connected directly to the a volume pot?Rahul,
I omitted R109/R209. I wired the primary of the jensen across the output of the PCB.
I wired the jensen's two secondaries in series for a 4:1 step down.
I believe this results in an overall gain of 2.5 for the headphone amp.
Try sticking a 30 pF cap across R2 in your sim and see what it does to your HF response. The spec sheet shows 9 pF with 400 volts across the part, but the graph shows about 30 pf with 10 volts across the part. It also varies a lot with the signal voltage in the range you will be operating it at.A little off topic, but thought George (@Tubelab_com) might be able to help me. I experimented with a power amp using the Schade method. Here's the schematic.
View attachment 1070781
I am getting very poor bandwidth at the top end. Probably not even making it to 10 kHz and quite a bit less than the sim. Getting good bit of gain. The device is an SCT10N120 with nice looking curves. It biases up exactly as shown. This is not an SCG topology, but it is identical to a Zen amplifier just with an SiC device. I even added 1000 ohms of source resistance to the input voltage generator, but the sim still shows very wide bandwidth.
The same device but with the inductor on the source and the output taken from the source pin sounds quite good. Okay, it is no VFET, but it sound like a decent class A amplifier. I pushed it to 1.5 amps and it was doing fine.
I made R1 into a 100k trimmer pot for easily changing the bias. It works nicely. The bias does wander a bit, but mostly stays close to where you set it. Certainly could be improved.
The inductor is the Hammond 193T. The chassis and setup was my choke-loaded VFET amp, but I pulled the VFETs for the OS2 amp and now using the setup for experimentation