DIY Audio Projects Forum

with an 8 ohm 10w resistor across the binding post I get 0.0mv
thanks so much for the help, onto stabilizing the bias
cheers!

Wow, thats making me proud
Firstly I have made a try on a piece of wood but got too much hum from the input.
After installing everything in a proper enclosure there is absolutely no hum (and i have very sensitive speakers).
The temperature is higher than with the ZCA: the enclosure gets approx. 50° Celsius.
The sound is much more direct, some sort of punchy. The best match to the Fostex i can imagine.
I have not heard a lot of that directly sounding systems even on HighEnd exhibitions.

I enjoy a lot!
Best regards
Stefan

Thanks for your inputs regarding the choice of transistors. I decided to go for the BDY20 2U50 and I dont regret - it sounds very nice!! Highly recommendable for as an amp for daily indoor use. Depending on the input device (in my case a Focusrite Scarlett 2i2 (max. output voltage: 1.2V pk-pk @ 1kHz)) it's easily loud enough to disturb neighbours

The housing just contains the amplifier and a small RC input-filter with 1 Ohm and 10mF on each side. Very handy! A mid-size fanless CPU-chiller sinks the heat of both 15Ohm resistors:



For the moment, I use my switching mode lab power supply and there is no hum at all. A CLC-supply (20mF-50mH-20mF) is close to be ready to use, too.
By driving the input at 28V, I burn almost 50W.

Playing with the input voltage, I only observe a clip in the positive half wave. Is this normal?

Because the MCA shows an amplification which is over a wide range independent on the input DC-driving voltage, I think I reduce it to say 15VDC, reset the bias and burn only a bit more than 10W all the time. Does this change the overall performance drastically (sure, I will shift the Q-point by some volts, but is this a 'serious' thing?)? My ears and my oscilloscope say it's fine as long as the input voltage is restricted by the preamp such as in my case to a relatively small value of 1.2V pk-pk. Unfortunately, I don't really have a detailled idea about the distortions and how to measure them..

In general, I'm curious how to calculate/estimate the damping factor, that will be provided by this circuit. Anyone an idea?

Thank you!