frusciante89 wrote: ↑Wed Jun 24, 2026 9:35 am
Ok so I retook some measurements but with a 4ohm dummy load (the 8ohm was getting quite hot as the resistors were not of the proper wattage, so decide to place two in parallel).
I'm running it at 40W, hence shooting at the ouput jack for a voltage of ~9V Rms -> sqrt(40W*4ohm/2)=8.94V
These are the updated scope measurements at K1 and K2: ...
Here's the scope connected to the output jack: ...
You're showing 20W at the output, which corresponds to the equation above where you used 40W for Pout Max.
What do you mean? The output I see at the scope is ~25VPP, meaning ~40W by inverting the equation. Unless I'm missing something?
Vpp = sqrt(40*4/2)*2*sqrt(2) = 25.22V
For reference, here's the final tuning at 40W. Was looking for sqrt(40*4)~12.6VRms. Got quite close with the trimming (293mV and 297mV)
Thanks Martin for the help!
Great job! That's a very cool portable oscilloscope.
Looks like you got 40 watts clean headroom before the sine wave was just starting to lose its clean sine wave. Small notch forming at the top right.
I am sure it would easily hit 50 watts when pushed into distortion wave.
Also if you are using a dummy load (resistor) for the speaker jack that tends to make the sine wave distort a little earlier than an actual speaker.
I was curious what power transformer you were using?
Cheers
G
Last edited by Guy77 on Fri Jun 26, 2026 1:34 pm, edited 5 times in total.
Guy77 wrote: ↑Thu Jun 25, 2026 2:47 pm
Great job! That's a very cool portable oscilloscope.
Looks like you got 40 watts clean headroom before the sine wave was just starting to lose its clean sine wave. Small notch forming at the top right.
I am sure it would easily hit 50 watts when pushed into distortion wave.
Also if you are using a dummy load (resistor) for the speaker jack that tends to make the sine wave distort a little earlier than an actual speaker.
I was curious what power transformer you were using?
Cheers
G
Hi G, transformers used are from InMadOut, Italy. The models are (prices from 2020):
