Bias Troubles

[Pajbassman81]

I was able to get the settings for U1 in a good operating range, but U2 has not been so easy. The pot for the bias adjustment of U2 doesn't seem to have as large of a range as the pot for U1. I can never get back to the first voltage before the clicking starts. Also, I'm using 990C's and the one in U2 seems REALLY hot. Hotter than U1. I have swapped them with no dofference. Still hot. Any help would be greatly appreciated. Thanks

[dclawson]

I am having the exact same experience while trying to bias the opamps.

U1 is fine, I can set it OK. U2, I can't seem to bring bias voltage down, it seems rather high, and U2 gets hot. Turning the bias pot for U2 makes a very small diference. Anyone know where to look or whats up?

[midimonster]

I am not quite having the same problem as you, but my 990C's are running very hot.

I can get the bias adjustment withing a couple of milli-volts for both U1 & U2, however U2's bias seems to jump around a little. When the Jumpers are moved from ADJ to the normal position both outputs drop to 0v, but it takes about 1 minute for this to occur. The directions say just a few seconds, so I'm not clear if this is a problem.

After the pre's have been on for a while both of the 990C's are extremely hot, almost too hot to touch. I am running them at +/-22V, but I think I may drop this down to +/-20V.

Even though they are running hot, they sound wonderful...

[tpryan]

U2, I can't seem to bring bias voltage down, it seems rather high, and U2 gets hot.

What is the DC voltage at the output of U2?

I can get the bias adjustment withing a couple of milli-volts for both U1 & U2, however U2's bias seems to jump around a little.

That's perfectly fine, don't worry about it.

[markwayne]

Yeah, I'm also thinking of backing off the voltage a bit. My 990s get too hot to touch after a period of time and I don't think I'm in any danger of maxing out the headroom. However, I don't want to compromise on this tone. The sound is flat out amazing. The J99 has already become my favorite mic pre for vocals and I've got a fairly nice collection here.

Oh, I should also add that my J99 is dead quiet. I was a little concerned with some of the noise issues I was reading about here. But I'm happy to report that, in addition to being my favorite pre based on overall tone, my J99 is also among the quietest. I'm impressed.

Thanks Tim,
Wayne