Lessons Learned: Failure and Success

[heddykevy]

I know there isn’t a lot of activity on this board in recent years, but I wanted to add my experience here for future builders. I am new to this scene of building SCA pres, but so far I can say that the SCA J99 is a great product. When I build the next one, I will have some additional experience to make the process go smoother. Hopefully my newbie experience with this board (v.3.6) can help the next newbie.

The only problem that I encountered with this project was with the 3rd Party Op Amps. The J99 would not pass audio, both Op Amps got VERY hot with power, and could not be properly biased. As a method of troubleshooting, I placed DMM probes on pins 4 and 6 (I think) the Op Amps were passing almost full voltage. (Something like 10v.) Once I took out the 3rd Party Op Amps, I carefully installed the included AD797 Op amps and additional resistors, and the unit was then easily biased and audio signal passed just fine.

Again, I am a complete newcomer to this project, so the following is probably obvious to a lot of you. One thing I learned the hard way is Op Amps are VERY fragile. I trust the builder of these Op Amps completely, so I am quite sure that they were shipped in brand new perfect working condition, but somewhere along the line, I did something to damage the Op Amps.

HANDLE THOSE OP AMPS WITH CARE. Make sure to use anti-static mats or wrist straps. Be VERY careful when placing the probes of your multimeter once the Op Amps are installed. All it takes is a little slip off of one pin and you can short the Op Amps.

Beyond that, the project went flawlessly. I followed the directions carefully. READ ALL DIRECTIONS FIRST before diving in, then re-read directions for each step. I made sure to carefully solder each connection, using 63/37 Kester solder. As recommended in the directions, I measured the resistance of each resistor with a DMM. Take extra special care to follow those directions in red/orange. I wore a wrist strap connected to ground, used an anti static mat, since the climate is very dry this time of year in Wisconsin. I was very careful to place DMM testing probes so as not to short anything.

I was a little intimidated to build this kit since I had no previous experience with soldering on a PCB, but it’s really not too difficult. The most important points I found were to carefully follow directions, connect to ground, be patient, pay close attention to detail, and be able to consistently solder a joint. That last point is especially important. I didn’t have any previous experience soldering on a PCB, but after spending some time reading about how to properly solder for this application, it didn’t seem very difficult.