Need Concert Slave advice

[SteveBass]

My Sunn Concert Bass head, played though a single 15" (4 ohms) cabinet, wasn't cutting through the clutter, so I added a 2-10 cabinet (8 ohms) to add definition and punch. It sounds great -- but the head was getting hot because of the impedence. (Went below the 4 ohm limit. Not good to do.) So, following advice from a music store and past posts in this forum, I found a Sunn Concert Slave, which I figured I'd use to drive one of the cabs while using the Concert Bass head to drive the other. My question:

How exactly is this slave supposed to work? I'm plugging my bass into the the Concert Bass head, like I've always done. Then I run a cord from the "pre-amp out" jack on the back of the Concert Bass head, plugging it into the "line in" jack on the front of the Concert Slave. I then use each of these components to drive one cabinet apiece. But....

The Slave has only one control knob, for "input sensitivity," and it doesn't seem to do much. I have to tuurn it to 10 to get a full sound out of the attached cabinet; anything below about 7 or 8 and it might as well be turned off. That means I cannot separately turn up or down that cabinet or use the Slave as a separate amp with any control over the volume (and not that much volume comes out, either). The entire setup seems to be entirely controlled from the Concert Bass head. So far as I can tell, I'm not getting any sort of big boost out of the slave. I suppose it will keep me from frying the Concert Bass head (because of the impedence issue). Am I missing something?

[JoeArthur]

Don't know what you are missing... your description of the wiring of the components seems to be correct.  

You didn't mention which speaker is attached to which power amp.  The 4 ohm speaker can be driven with the full 150 watt output.  The 8 ohm speaker will reduce the power amp output to something like 60 percent of 150 watts... roughly around 100 watts.

Speaker efficiency might be another consideration.  Whichever speaker "sounds louder" is the one I would use with the slave so that I could use the sensitivity knob to balance the outputs.

One thing you might be missing is that the slave is just another power amp section, almost exactly like the one in the amp.  The sensitivity knob is really only useful when you are feeding a hotter signal into the slave than what is coming out of the standard preamp - which by the way, is being fed to the internal poweramp at full sensitivity... well, it would be if your internal power amp had a front end sensitivity control.  What this means, is that you really want to run the sensitivity control full up or pretty darn close to it when you are feeding the slave the concert preamp output.

[SteveBass]

Thanks. That helps. What I was missing was, I figured that if I added a slave, I'd have some sort of big boost in volume (like going from 150 watts to 300 watts) But I guess I'm also pushing back the impedence -- from about 2.3 ohms with both cabs attached to the Concert Bass (and risking frying it) to 4 ohms with the Concert head and 8 with the slave, or vice versa if I switch them around. (Which I'll try.) Thanks for that tip.

[bcomnes]

if you open up your slave and look at the wiring you will find that the input  jack goes straight  to a pot, with one side out to the slave the other side goes right to the the output jack...that's it..... its basically a balance knob , so all  other things equal you twist the knob "sensitivity"  (remember this WAS the 60's) until both cabs are in "balance"......as mentioned in a previous post different impedances can skew the balance point.

the power sections of the slave and the main amp are alway both full on and for the most part the same circuitry..therefore any change in volume (and tone stack) is from the output of the preamp section of your main amp which, as mentioned above is split between the two power sections based on the senitivity setting.

hope that helps