Seventh Circle Audio

Arrgh, did the 2nd kit A12 today and everything went well, powered right up first try. (Two for Two!) I set up all the voltages, gave it a mic test and I was good to go!

I remembered later I never did the "After 15 minute warm up adjustment", so I opened it back up and let it run for 15 minutes. I kept slipping from pin 4 to 3 with my probe and it made a spark. Occasionally 6 to 5 too.

Well now pin 6 reads about 10v generally and now the preamp just outputs a loud hiss. The pin 4 to pin 3 now reads about 11v, while pin 4 to 5 reads 18. Take the op-amp out, and they are both 18v. It's got a little indentation by pins 3 and 4 on the epoxy which is probably where it got fried. Too bad I can't replace what went bad.(EDIT: Looking at the Schem, I'm guessing the caps C5 and C6 in the SC25 got killed) I swapped the op-amps and the voltage readings are fine.

Damn. Maybe Tim will take pity on me and sell me an SC25 for the kit price, or let me send this one if there's anything he can do with it. Guess I'll have to see what he can do. My first experience with these kits was going so well too!

Anyway guys be CAREFUL when checking that 4-6 Pin check at the very end. You can fry the Op-amp Like I just did!

Just wanted to give props to SCA. They took great care of me and the turn around time was nothing short of amazing! Now I can use my new A12's on my upcoming session. Very happy!

DAMN IT! I think this might have been what I did when building my A12. I had the same problem as you. But I sent the whole PCB back to be looked at on 3/22 and I'm still waiting to hear back
I should have just sent in the SC25 by itself, like you. I'm pretty sure that was the problem. And maybe I would have had a fast turn-around time like you did.

By the way,

Did you notice the Positive Regulator getting hot after you fried the SC25? That's what happened to me.

If I was more confident in my work, I would have just sent in the SC25. But it was my first kit, and I wanted to play it safe. But I'm pretty damn sure that we had the same problem. Maybe I'll check up with Tim. If they are backed up for a while longer, I'll ask if I can just buy another SC25 and have him send back my PCB. I've been Itching to use this pre!

Sinnerx96 \$m[1]:By the way,

Did you notice the Positive Regulator getting hot after you fried the SC25?

Yep.

NuSkoolTone \$m[1]:

Sinnerx96 \$m[1]:By the way,

Did you notice the Positive Regulator getting hot after you fried the SC25?

Yep.

,...And Pins 3 and 6 readings were bouncing around quite a bit as well?

That's it. I'm sure of it now. Thanks for sharing your experience! Now I know I'm not crazy! I was troubleshooting my A12 for Days, checking every single component on the board to see if I did something wrong. I should have known better than to think that the spark I saw, was inconsequential. DUH!