Frying bacon

[Sean S]

Hi there,

I built two J99's with Hardy 990c's, they have been working fine and sounding great for the last two or three weeks. Last night I plugged them up and I got a sizzling/popping noise on one of the channels that seemed to come and go.

Inspecting further this morning, the channel is quiet for about thirty seconds at power up and passes audio fine, but then after that the noise shows up. A brief inspection of the board shows no shorts anywhere.

Any ideas?

[Sean S]

I took the bad channel out of the chassis last night for closer inspection. Nothing looked suspect, but I went ahead and reflowed all solder joints anyway. Noise was still present.

I checked the voltage at U2 pin 6 while clicking through gain steps, the voltage was no longer falling to 0V like it did when I first calibrated. I removed the opamps and checked the supply voltage, it was still a solid +/- 24.0V.

I put the opamp back into U1 and set jumpers and conn1 up for bias current adjustment. I could not get the voltage to be less than 5-7V difference between min and max gain positions. I tried the second opamp in the U1 position and i was able to get the voltage dead on. I removed that opamp and put the first one into U2. I experienced the same large difference in voltage as I did when it was in the U1 position.

Am I safe to assume that I have a bad 990c? If that is the case, what do you think could have caused it to suddenly go bad after three weeks of perfect operation?

[tpryan]

Sounds like you have a bad op-amp. If they're going to fail, they usually fail early on just as you've experienced. John will probably replace it for free.

[Sean S]

Hey there, I justed wanted to follow up on this thread. I spoke to John after posting here, told him the situation, and he said he would send me out a new 990c before I even had a chance to ask.

I had to remind him a couple of times over the last few months, but I finally received the new opamp yesterday. I popped it in and was able to calibrate everything normally. I tested it with audio briefly last night, and everything is back to working properly and sounding great.

I noticed that in my haste of posting my problems, I neglected to mention how great these preamps are. When I first built them, the first test was with a blumlein pair in the middle of the room during band practice that evening. Listening back to the audio afterwards, everyone agreed that it sounded like a frickin' record. Even the drummer noticed how good it sounded . It's hard to say, but I think I like these more than my n72 and a12's.

So, once again, great product Tim, and thank you!