https://www.diyaudio.com/community/...alas-ultrafsp-riaa.354704/page-5#post-6236358
You can‘t get any better!
You can‘t get any better!
OK, my rustiness and my now old eyes decided to bite me. On initial power test one board LEDs didn't light, and one did. Both of the 1R resistors in the PS connected to the diodes to the chassis ground smoked. No measurements were taken before power down. After power down determined on the board that LEDs lit, I have Q1 in the BIB installed backwards. I get Megaohms in the M1/R1 junction to ground. In the board that LEDs didn't light, Q1 is installed correctly, but I believe M1 may be bad as I only get 100-200 K to ground. Any suggestions or measurements I should test before replacing the M1 and Q1? Also, I suspect I will also need to replace the 1 ohm resistors.
Yes it had a fuse. It's a fast blow probably at 1 or 1.5A from when the chassis I used for the PS was a tube phono pre. It didn't blow. I've replaced the M1 and M2 on the board that didn't light, and the Q1 on the other board. Haven't powered up yet. Here are some before and after pics of the PS and after pic of the signal. I'll replace the 1R resistors, but not sure why they would have smoked. I ran the PS and tested voltages at ~44 volts unloaded before connecting initially with no issues.
Attachments
Most probably some fault current run through the resistors to the PE (protective earth). Those 1R connect the ground returns from the channels to the fat yin yang diodes that lift earth until a fault current drops >0.6V on the 10R that straddles them. At that point they conduct and the fault current diverts through the diodes. Its a safe ground lift scheme.
I somehow miss wired the B+ for one channel at the input jack. All working now. I "checked" it a couple of times before recognizing it just blind to it. I just swapped at the board for that channel for now. I'll fix the jack when some more 1 ohm resistors get here. Can I use 1.4 ohm resistors instead, as I have some here, or is that too far out of spec? Couldn't reach 4v at 34 volts, but no problem at 32 volts. Sounds very good so far. Very smooth with detail and clarity too.
49 so the eyes have really started getting old last few months and not used to it yet. I used to wonder why my Grandma always asked me if I needed to turn on a lamp whenever I was reading. I understand now. It had been a few years since I built anything.
49 so the eyes have really started getting old last few months and not used to it yet. I used to wonder why my Grandma always asked me if I needed to turn on a lamp whenever I was reading. I understand now. It had been a few years since I built anything.