Marshall 4x12 cab and KPA PowerRack

  • Requesting some advice on using PowerRack with a Marshall 4x12 please.


    I did my first shows with my brand new KEMPER PowerRack this weekend. I have a Marshall Celestion loaded cab wired in series rated at 16 ohms, and , I must be honest and say this set up isn't very powerful at all.... I am not a very loud player but my old rig, an old ADA MIDI preamp into Rocktron 300w poweramp then into the same cabinet blew the KEMPER into the middle of next week.


    I rarely had the ADA and Rocktron amp above 4 on respective volumes but the KEMPER was running almost on full power to make it comparable to my old rig on less than half of its capability.


    I obviously checked the speaker out was being used, checked speaker cable, engaged the poweramp boost, checked input and output settings, made sure MONO was set on monitor out, I pushed up individual output volumes of the rigs in performance mode, made sure cab was taken out of Monitor output, disengage noise gate... I got through the shows but I am not happy running the KEMPER at almost full throttle, it doesn't give me the same confidence I had with my old rig.


    I assume that I could rewire my cab into 8ohms but would this fix the lack of volume issue?
    I tested the cab with the ADA and Rocktron setup and the cables and the output volume achievable really is at least twice that of my PowerRack set at almost full.... I am confused and slightly worried....


    Any advice is welcome - thanks :)

  • Hi brother, no 4 ohm input jack, it is an old Marshall cab with a single jack and four old greenbacks wired at 16 ohm.


    I am intrigued as to why the 300w Rocktron solidstate poweramp is infinitely louder than the KEMPER powerack through the same speakers!


    CHEERS x

  • If the monitor volume (which is essentially the power amp volume) in the output menu is not turned up as high as it could, it will compromise the volume. What you can do is to max the master volume, and then go into the output menu and make sure the monitor volume is maxed out as well. If that is not enough, there is a power amp boost that can be increased to 12db from the default setting (6db). That should make a noticeable difference!


    That being said, if it is a regular Marshall 1960A there are a few things working against the Kemper: 16 ohm (less power available), and the speakers have a slightly scooped nature and 97db sensitivity. Compared to a V30 for instance, which has really cutting higher mids and 100db sensitivity, there will be a quite big difference.


    The first thing I would do is to check everything I mentioned in the first paragraph, and try the 4 ohm input on the cab. I did a band practice with a loud band using my Kemper Powerhead and a 1960A connected to the 4 ohm input, and it totally blew the other guys away with volume at about 6.

    Edited once, last by Alfi27 ().

  • Thanks for the input guys... sorry about the pun !


    My cab is a really old 16 ohm Marshall, no 4 ohm sockets, just a regular single input.


    I would have thought that maxing out the power amp volume AND the poweramp boost would be adequate for my needs... but the rig was still not cutting it at bigger venues.... plus, I dont like the idea of having everything on full throttle, I want to control the overal output with the Master Vol which is quick and efficient in a live scenario.
    The idea of relying on editing individual performance profiles for volume changes sounds a most horrendous way to go.


    I am aware that my issue is not totally relevant but I am genuinely intrigued as to why my Rocktron 300w poweramp is far louder and solid sounding than the KEMPER. going through the same 16 ohm cabinet....


    Kind regards to all :) x

  • I own the Rocktron 200W rackmount stereo poweramp that I used as a backup for some time. I could try out the difference between this and the powered toaster if you'd like to know.. though my cabs are all 8Ohm I think.

  • Thanks brother, it may be not necessary as my cab is 16 ohms.... all I can say is my ADA/Rocktron combo is pure power, I never had the volume above 4 and have played some big shows, I fear the Kemper PowerRack will struggle to give me the horsepower I need at open air events.... admittedly it was the first outing for the Kemper this weekend, the sound was awesome but the lack of volume is worrying, especially as the KEMPER cost almost 10 times more than the current rig that I have been using !!!

  • I had the exact same issue with my powerhead running into 16ohms.


    Marshall 4X12 300 watt cab running at 16 ohms barely cutting it volume wise live at full volume and power amp boost running at stock + 6.0db. Turn the power amp boost up to +12 made a bit of a difference.


    My 8ohm 2X12 (120 watt) cab and the same 4X12 cab used at 4 ohms was much louder at about 60 percent master volume than full volume when running at 16ohm even with power amp boost set to +6.0. I've never ran out of headroom at 8 or 4 ohm.


    Originally in the 2X12 I was running two gt12-75 at 16 ohm and also struggled with volume. Wired it to 4 ohms problem solved. Changed the speakers to Neodymium Creambacks wired at 8hms to perfect match the Kemper and never had the issue with those either.

  • Sounds like it would be a good idea to rewire the cab then to get 8 or 4 Ohm.


    btw: how's the ADA MP-1 like? I own a few preamp units but not one of ADA and I'm thinking about getting one if they're worth it.

  • Sounds like it would be a good idea to rewire the cab then to get 8 or 4 Ohm.


    btw: how's the ADA MP-1 like? I own a few preamp units but not one of ADA and I'm thinking about getting one if they're worth it.

    I borrowed my friends for a month or two whilst I was looking to buy something new years back. I ran it through a Marshall 9005 power amp and a Marshall 1960 cab. Sounded very 80's hot rod Marshall. I liked it. Wasn't a super high gain machine, but very tight and had good strong high mids for cutting through live. Was quite noisy from what I remember.

  • I run basically the same step up - high gain profile on Powerhead into a 16 ohm vintage Marshall cab (with mix of Black and Creamback's, approx. 120 watts) and it is loud as f*@k, at least inside... as I recall I did need to go thru all those settings / menus a couple times to sort out the outputs... check em again? Probably something simple. I'll check my parameters tonight and post back.


    PS: outdoors you might have to dime it...

  • If the 16 ohm cabinet has four 16 ohm speakers wired in series/parallel, those four speakers cannot be rewired to achieve an 8 ohm load.


    The four 16 ohm speakers can be wired in parallel to achieve a 4 ohm load. Or, two of them can be wired in parallel to achieve an eight ohm load.

    Yeah, right.

  • Just as an aside (and might not apply at all to solid state power amps) but my amp "guru" insists that a 16 ohm load will sound better , at least on the amps he builds / mods.... In my completely informal, unscientific, non systematic experiments with cab loads, I haven't noticed that big of a volume difference, everything else being equal.

  • He said there was no 4 Ohm input at his cab..If everything fails you could rewire the speakers to reach another Ohm-value. Perhaps it'll help

    Looks like I missed a few things there, haha! Well, Greenbacks are certainly not scooped speakers, I was referring to the G12-T75 speaker found in modern day's 1960A cabs. Getting the cab rewired to 8 or 4 ohm should do the trick, I've had no issues running my Kemper with a 2x12" Creamback 65M loaded cab in a band setting, even though they are 97db sensitivity speakers as well! One thing to keep in mind though, is that a healthy powered Kemper is fully capable of blowing four Greenbacks at 4 or 8 ohm, dependent on if the speakers are 20 or 25w each. If they are 20w I would advice you to be especially cautious with the master volume :)

  • Sounds like it would be a good idea to rewire the cab then to get 8 or 4 Ohm.


    btw: how's the ADA MP-1 like? I own a few preamp units but not one of ADA and I'm thinking about getting one if they're worth it.

    Mate, the ADA is monstrous, I am seriously reconsidering the idea of selling it and the Rocktron to pay towards the KEMPER. I had one back in the early 90's and used a Kitty Hawk PowrAmp and Aless Quadraverb with my Marshall wired in stereo. I could hold any note and it would feedback in perfect tune... doing Gary Moore feedback trick or Nazareths, 'This Flight Tinight' was a doddle :)


    More recently, after retiring my old 5150 to studio duties I bought an old ADA on EBay and got a used Rocktron 300w poweramp, the sound isn't quite as good as my old valve poweramp rig but it is really is tight, sustains with clarity and cuts through the band like a razor.


    The KEMPER has far more depth of tone and variation but this issue with lack of volume and the fear of smashing up a £1600 piece of kit on the road is unnerving to say the least !


    Cheers x