A12 and R33 problem
Posted: Sun Feb 26, 2012 5:28 pmI assembled 4 preamps, the SCA A12, N72, C84, and T15. They all were assembled great and sound great. While building my T15, I had a small problem with getting my phantom power to get to 48 volts. In the beginning due to poor soldering, I only measured 12 volts, but eventually I got it working to 48. Just to compare and contrast I decided to do the same test on my fully working A12 preamp.
Now, I've used the A12 on many projects, it sounded great. But, While locating pins and points to measure the phantom power (just for fun), I don't know EXACTLY what I did, but I saw some spark that made the R33 (150 ohm carbon resistor) burn and eventually just cook. I replaced it with the exact one and turned it on again, only to find out that now Q1 was burning (A06 transistor). So, I replaced Q1 and Q2 (A06 and A56 transistors), however now the preamp just no longer passes sound. What exactly happened and how can I fix this?
Now, I've used the A12 on many projects, it sounded great. But, While locating pins and points to measure the phantom power (just for fun), I don't know EXACTLY what I did, but I saw some spark that made the R33 (150 ohm carbon resistor) burn and eventually just cook. I replaced it with the exact one and turned it on again, only to find out that now Q1 was burning (A06 transistor). So, I replaced Q1 and Q2 (A06 and A56 transistors), however now the preamp just no longer passes sound. What exactly happened and how can I fix this?