Kern into QSC PLX issues

Hi all, this is my last bastion of hope before I call Les at Kern. I recently picked up a used Kern, but I can't seem to get useable volume out of it without damn near diming the preamp gain and output volume. With all other settings/cables/etc on my basses and PLX 2402 power amp being equal, my Read Purity only requires the preamp and master volumes to be at about 9:00-10:00. I've tried both the Main Out (has unbalanced 1/4" output) and Line Out (XLR out), and neither seems to give me anything more than the other. I've also tried swapping tubes, but replacing any one of the two 12AX7's or single 12AU7 did nothing for me.

I figure if something's wrong with the Kern, I'll have to send it back to Les. But the user before me reported no problems running it into his PLX 3002 from the 1/4" out, and so I was thinking that if there's a flaw with my setup, you guys could find it, or at least give me suggestions of things to try before I trust my preamp to UPS or Fedex.

Random thought: I know that some preamps don't work well with the QSC PLX's because of their relatively low sensitivity, and there are some people who have had their PLX's modded to accomodate lower input voltages. Those of you who have used Kerns into PLX's, is this for me? Have any of you Kern veterans noticed low output signal coming from them?

 

I agree with your first point; I should have rephrased that in my original post. The QSC does not have low sensitivity; however, there are several preamps that send outputs that are too low to fully drive the QSC. Many people have had mods done to their PLX's to accomodate these low input signals.

I highly doubt that the Kern suffers from 'gutless output'. There are enough rave reviews on this site and others to lead me to believe that a properly functioning Kern into any reasonable power amp is a perfectly formidable setup. I'm just trying to figure out where my weak link is.

Like maynard, I believe that inserting a separate EQ into my signal chain isn't a true solution, it's a sidestep. While I believe that you are right that it would help, I would rather fix the problem at its source (be it my setup, or the Kern) than work around it. Having said that, I really appreciate your suggestion, as it was only designed to help me. If you have any other thoughts, I would very much like to hear them.

Keep 'em comin', guys. I know a lot of you have experience with Kerns. David Wilson, Jae, Boogie, I'm lookin' your way.

 

Yeah, I bought my QSC from him, and I've read about that mod as well. He's an authorized QSC retailer/repairman, so any work he does should keep the warranty intact. There shouldn't be anything fundamentally wrong with my PLX, so I'd rather not modify it until I'm sure that everything else is as it should be. I'm still hoping to hear from some of the Kern gurus around here... I'd like to get a feel for their experiences with it (hopefully pertaining to a PLX, but if not, just their setup in general will do) to contrast and compare against my own.

 

Thank you so much man, that was really great of you! As you, Jae, and Bob Lee have suggested, I'm pretty sure that the fault is not with the Kern's design. I'm also reasonably sure that my setup is not to blame, unless there's a particular cable or output that I should be using. But, like I said, I've tested with both the 1/4" unbalanced Main Out and the XLR Line Out.

I played around with it some more today, and I noticed that there seems to be a huge volume swell at about the 1:30 position. What I mean by that is, if you leave either the gain or master volume high (this is true of either master volume, the XLR out when using it as well as the Main 1/4" out) and slowly crank the other control, it seems like the volume goes from minimal to HUGE somewhere between 1:00 and 2:00. With both the input gain and correct master volume knob high (about 3:00), the preamp sounds enormous, just like I would expect it to with everything cranked. It's just that when the volume knobs are at "normal" settings (anywhere between 9:00 and 12:00, since I'm just playing at home right now), there's just very little appreciable sound. After having performed this test about 30 minutes ago, my new suspect is that some, if not all, of the pots are of incorrect value. Thoughts everyone?

 

Just the laugh I needed this morning, Jae... thanks!

What do some of you other folks think of this volume-swelling-type dilemma here? Think it could be the pots, or another culprit that I've not considered?

 

And I'll be happy to provide them, just as soon as I get the Kern up and runnin'. The entire purpose in me buying the Kern was to A/B them, and see which one I prefer. I will sell the loser. I simply don't need two preamps, but sometimes I get that grass-is-always-greener feeling, so I like to try the competition whenever possible. This will help me decide which preamp is right for me.

I emailed Les (or whoever is on the other end of the email link on Kern's website), so hopefully I'll get a reasonably prompt response. In the meantime, additional thoughts about my predicament are more than welcome...