That’s the cutoff frequency without load. Concerning the lowpass, the source resistor and load impedance act as in parallel, so the cutoff frequency will be a bit higher.
Hi,
I’m wondering if tgis design has been tested by someone and has been found safe to use?
Well, I’m still alive and uninjured 
I did figure out that the distortion above 75% volume is due to my amp, not the transformers, since it also occurs on a pure resistive load. Maybe it’s possible to go up to 100% on a higher supply voltage, but I definately don’t need that much power.
Thanks for sharing this nice project. One question, what kind of power supply did you used? Ali has a lot cheap switched supplies but, I don’t think its a good idea to use one?
I’m using a USB-C PD trigger board to get 12V from a power bank. This guarantees isolation from mains. I would not trust any cheap power supply from aliexpress.
These amplifiers usually take any voltage between 9V to 24V, so another option is to use a battery from a power tool.
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Thanks, Iam going to use a power tool battery
can we have a backside picture of your circuit so we can see how to wire it on the board cheers.
Sure. Here’s front and back of the updated design with capacitors on the low-voltage side.
If I make another, I’d use unipolar electrolytic capacitors; those are much smaller.
I wanna try your setup with small transformer.
Can you please ceck my picture , if i am right with the transformer soldering?
Yes. On the primary side you want to connect either the red dots or the blue dots, not both.
Here’s the backside of my first iteration (trode outputs on column A, rows 4-7):
Thx for your help. I will tty it soon .