Ok, so the 600W power amp in my powered KPA managed to make a 4x12 smell of burning the other day.... It was in a band scenario but I wasn't even pushing it that hard I don't feel...
What guitar cabinets are suited for this beast of a 600W solid state power amp...?
At at this point I'm considering swapping for a non-powered and picking up a 3rd party external, valve poweramp....!
Can you give details about your 4x12? What speakers are in it (i.e. what wattage each speaker) and what is the impedance of the cabinet? (Do you have just one input jack in the cabinet or do you have two jacks with the option of different impedance)? Also what was your Kemper master volume level?
Per the specs on the powerhead/powerrack, it is 600W into 8 ohms and 300W into 16 ohms. I'm running 4 Celestion large motor 30 watt greenbacks (model G12H(55), so my cabinet is effectively only a 120W cabinet, but I run it through the 16 ohm load with my output volume at 3.4, which is volume for a small bar/club situation (i.e. not earbleed volume). I've had no issues/no smell from the cabinet.
If perhaps your cabinet is a 4 ohm load, then (assuming the Powerhead/rack can handle 4 ohms; probably can as its solid state) you'd be putting around 1200W into the cabinet, so even had lower volumes, you could run the risk of heating up the speakers (if you are smelling something burnt, it would mean the voice coils are getting very hot, and the smell probably from the glue/enamel coating of the wire in the voice coil....and I work for a speaker company and know that smell!).
To answer your question of what guitar cabinets are suited for the powered Kemper, any cabinet rated from 280W to 300W with a 16ohm load input jack would work fine (assuming you need to play very loud, hence matching the cabinet wattage to the Kemper wattage at 16ohm load). Marshall 1960A (300W) or the 280W 1960AV are examples that have the 16ohm input option. I checked Mesa Boogie, but the recto and road king cabs are 8ohm/4ohm...I'd stay with 16ohm load cab.
The 412 that smelt of burning was at a practice space and wasn't even that cranked I didn't feel like. As for the speakers inside, I couldn't be sure but it's just some rundown, used&abused cheapo Marshall 412 like a 1960A or something (angled)...
My 412 at home is also a cheapo Marshall 412 I think something like the 8402 or whatever model it's called (I'll look for some photos I took of it once) again, can't recall the speakers inside and don't fancy opening it up to check to be honest... That doesn't get cranked anyways as its in my bedroom - (but I will likely use it for gigging so may look into the speakers when I eventually have to move it)
As for impedances, I'm always EXTREMELY careful to match them up correctly. All the cabs run at 8ohms (Mesa recto is 8ohm, the 412 at the praccy space I manually switch to the 8/16 ohm selection rather than 4/8ohm so that it is covered either way by the Kemper... And my Marshall 412 is actually upside down in a live-in flightcase and has a specially made socket w/hatch (that can only be run at 8ohm)
As for the Kmeper, it was my first time out with it in a band scenario (and I hadn't even finished tweaking the performance rigs so hadn't even looked into the outputs side of things in detail - for example, I have no idea what my main & monitor volumes were at (pretty sure they were linked to the master though as everything was still pretty much in factory defaults...) I have a feeling they were below -15dB and I had to crank the master vol all the way up to 10.0 to keep up with the drums... since then, because of the burning smell (and also some sparks appearing in one of the PA speakers because of 1 performance rig!) I've looked into these output calues in a little more depth, but still a bit confused by them all!
The PowerRack is 8/16ohm only. Think you are spot on there with the glue starting to heat up and smell ... Either way I turned down immediately and put the PA. a little higher.
Cant really afford/justify spending out anymore at the moment for a 16ohm cab but I have been searching for them Zilla/EVH 212's etc.
but since the Kemper has been designed so well I find it hard to believe they just whack a non-suitable power amp on the PowerRack that isn't actually fit for use with most cabinets on the market.... The wattage of MOST cabs generally sits around 100-150, unless you have some Celestion 4x 75w Dave Mustaine Marshall cab....which even then is only 300w!
The powered kemper does work with 100 to 150 watt cabs (my 120 watt cabinet is perfect example), but is dependent on the impedance of the cab and how much you crank the amp. As I mentioned, my master volume is 3.4 and that volume is enough to keep up with the drums in my cover band, and that volume level into a 120 watt 16 ohm cab is no issue. Now if I had to turn up to 9 or 10 and engage the full 300 watts of power by the kemper at 16 ohms, I'd be frying some speakers.
you mention running 8 ohm cabinets, which means the kemper has the ability to send 600 watts to the cabinet depending on your patch gain settings and if your master volume is cranked up.
somethings up if you think the kemper isnt that loud yet the speakers are getting hot. I suggest you get a multimeter and put a cord in the cabinet and measure the cab impedance by putting one lead of the meter on the tip of the cord and the other lead on the body of the jack and see what you get. You will be measuring DCR (resistance of the coil wires) but that is very close to impedance. If you measure 14~16 ohms, its a 16 ohm cab, if 6.5~8 then an 8 ohm cab, if 3~4, then 4 ohm cab.
also try to work out your gain structure
Thanks for the tips... Much appreciated!
Im certain my cabs are at 8ohms as I run them with a 100w and 120w tube amps no problemo.... And the one at the rehearsal space (which was the one that got smelly!) I manually select 8/16ohms before I use it each time.
With your master at 3.4 what are your dB levels on main & monitor out in the OUTPUTS page? And do you have them 'linked' or 'un-linked' ?
I have a feeling this may have been my problem and that they were set very low (as I'd been so busy cresting presets I hadn't had time to look into all the output options and so had to crank my master vol to 10.0 to keep up with drums...)
