I go ahead with try to find why I have 0v in a channel on v0, I found that on q3 in the middle pin I have 0v otherwise in the other channel I have 11,5. The other two pins are at 24v. What I have to check?
on the road, so typing on phone, thus brain working even less than usual;
just in case - buzz test with amp not powered
just in case - buzz test with amp not powered
Thanks nicoch58. Less than proper soldering noted! Will re-flow - especially as I recently received Fire Metall, and have recovered from my post newborn fugue state - when much of the initial work occurred.
ZM - Buzz test notes above completed with amp unpowered. Thanks for looking out!
ZM - Buzz test notes above completed with amp unpowered. Thanks for looking out!
I desoldered the irf9520 and I measured the resistance between the pins, found 2,2Mohm from source to drain, in all other combinations I found open circuit. Is it dead?
Removed and measured the other one and found same value so irf9520 are good, other suggestions?
Looking at the bottom view of the entire board: lower right, near the "+". There is solder blob on the + side of CL4 extending onto the ground plane. The blob might not penetrate the insulating layer to the ground plane, but it shouldn't be there in the first place.
Look for article or youtube video on how to test N channel and P channel Mosfets using multimeter.
Thank you Kevin, I checked as per various videos the irf9520 and it is defective!
I have 2 pair of Harris 9520/520 left. As I understand, you have one bad 9520, correct? I can send you a pair, but we need the determine the root cause of the transistor failure. No sense throwing good transistors into a circuit that's going to burn them up.
I also have matched pairs of Vishay 9520/520 which I can send. Once you're reasonably confident the board is safe I would install those first to make sure.
BTW, the Vishay parts sound fine in the ACA Mini. You just don't get the same distortion spectrum as with the Harris parts.
Thank you Kevin, can you suggest me some test to understand if the board is safe and correct?
Only the 9520 is bad, the 520 seems to be ok. I wanna change also the 1k trimmers. By comparing the circuit voltage between the other side the only difference is the 0v on v0, all of other measurement was the same.
All 4 fully ccw.
Can I use an irf9520 from eBay for validate the circuit, without matching with the irf520?
Yesterday I had finished my Acamini build after about an hour of work. Firing up and letting stabilize the bias took me longer than that. It was quite warm in my roof room and I set bias to 290 mV. Today in the morning - temperature fell during the night - bias was down to 230 mV on both channels. Jim once mentioned, that one should set bias at the amps later permanent location. I would add: rebias it on a warmer day.
Thanks for the design and kit. I'm looking forward to listening later this weekend.
Cheers, Ernst
Thanks for the design and kit. I'm looking forward to listening later this weekend.
Cheers, Ernst
