Stereo Setup; Power amp: 100W Mosfet (3210) VS 80W+80W Valvestate (8008)

  • In theese days I'm trying different Power amp and I don't undestand one thing.

    maybe someone coudl give me an answer.


    I have theese cabinets and I was trying differnt combination for stereo live stage propose,


    the head on the top right of the pictures is 100Watt Marshall Mosfet 3210.pdf

    I use to connect the Monitor out of KPA into the return of its loop FX so I use it Only as Power amp..and it Works (better than the other 3 heads for sure.. IMHO)

    so I connect 2 cabinet to its Speakers Out.


    In this way I run 2 Cab but the signal is still Mono.


    In order to have a Stero Setup,

    I thought to connect the Direct Out of KPA (and switch ON the Monitor Stereo Function) to another external power amp, so I've recently got a Stereo 80W+80WattMarshall 8008.pdf

    that have 2 separate output of 80Watt each to connect to antoher couple of Cabinets


    in this way I can play 2 full Stack in stereo BUT the problem is this:


    the 100Watt Head is Louder than the 80+80 rack power amp, and honestly I don't figure out why:


    I guess that If use 2 cabinet connected to the 100Watt Head I could get Maximum 50Watt on Cab A + 50Watt on Cab B

    so I've thought that the 80+80 Watt Would have to be Louder but it's not like this

    Why ?

  • Hi Sollazzon,


    100Watt Marshall Mosfet 3210.pdf

    What are the impedances of the two cabs?

    What is inside the cabs (what speakers)?


    80W+80Watt Marshall 8008.pdf

    What are the impedances of the two cabs?

    What is inside the cabs (what speakers)?


    If all the cabinets (and speakers) are the same, I would not expect to hear very much difference between the 100 watt Marshall and the 80+80 watt Marshall. 80+80=160 but at best, you might get +3 dB SPL (Sound Pressure Level) more than 80. That's not very much louder.


    You may be putting more power into the cabinets driven by 80+80 but the cabinets getting 100 may be more efficient.

    OR

    100 watts into two cabinets 8-ohm cabinets connected in parallel are presenting only a 4-ohm impedance to the amp. Note: Marshall Mosfet 3210.pdf output is 100 watts into 4 ohms, and 80 watts into 8 ohms.


    The Marshall 8008.pdf document does not tell us if it is 80 watts into 8 ohms or 4 ohms. But if is like the Marshall Mosfet 3210.pdf then you get:

    80 watts into 4 ohms

    64 watts into 8 ohms


    I'm not surprised the Marshall Mosfet 3210.pdf is louder than the Marshall 8008.pdf, but I wouldn't be concerned. I would just turn down Volume control on the 3210 so you get a better balance.

  • HI ST! thanks for Your reply.


    I've already made many test but let's do it simple:

    I'm not taking as example the 2 full stacks of 4x12 because they have differnt (selectable) impedence, differents speakers with different effiiceint values.


    Let's take as example the 2 Stacks far form center.

    Those cabs Have the Same Speakers and the Same total impedence (8 Ohm each) in fact they are 2x12; w/G12-75T

    So I'm runnig each power amp with a pair of cab of 8 ohm: so any power amy has a total oad of 4 homs


    - the 3210 100W splits the total output in parallel so I Agree:

    Quote

    100 watts into two cabinets 8-ohm cabinets connected in parallel are presenting only a 4-ohm impedance to the amp. Note: Marshall Mosfet 3210.pdf output is 100 watts into 4 ohms, and 80 watts into 8 ohms.

    (that's why I consider 50W to each cabinet of 8 Ohm)




    - the 8008 has two output at 4 Ohm of 80W for each of the 2 channels, or at laest this is what I've understoot,

    in fact the manual says:

    ''The Connected cabinet Load sould not be less than 4 Ohms''


    but in any case I would expect as You wrote at least:

    Quote

    The Marshall 8008.pdf document does not tell us if it is 80 watts into 8 ohms or 4 ohms. But if is like the Marshall Mosfet 3210.pdf then you get:

    80 watts into 4 ohms

    64 watts into 8 ohms


    So I still do Not understand why the two cab connected to the 3210 are always Louder than the 2 connected to the 8008.

    Said That..


    Quote

    I would just turn down Volume control on the 3210 so you get a better balance.


    Unfortunaly this is not possible because the LoopFx Return of the 3210 goes straight into the Output Power section

    .



    There is no Pot on the 3210 to control the fx return level.

    (Let's say it's always set and fixed to 10)


    So I thought:

    Ok, I dont' use the Fuction 'Monitor Stereo' on KPA and I'll set the Monitor Out as Master Left and the Direct Out as Master Right so I can adjust their two levels independntly.

    It Works and I've found a good balance with the 8008 at -16db an the 3210 at -24db (so 8 db of difference)

    BUT this can not be a good solution:

    - Mostly because I don't have the 'Monitor Cab Off' function on the Direct Out line.

    (and of course I can't disable the CAB section at all, because I need it on the Main Output!)

    - secondly because I don't have EQ specific/indipendent for the Direct out

  • Hi Sollazzon,


    On the 3210 - can you use the main input and set all the tone and presence controls flat? Then you can use the volume control.


    On the 8008, are you connecting like A or B or something else?

    A - each cab gets 64 watts (note - could be less)



    B - The two cabs get 80 watts in total. Each cab gets 40 watts


  • Hi ST,

    About the 8008 I connect like show figure A.


    About the 3210.. good idea!

    I have to try.

    I remember it has is a push pull pot that completely bypass the EQ section. Usefull in this case.

    Thanks for your help.

  • Hi, Sollazzon,


    "the 8008 I connect like show figure A."


    How are you feeding the input to the 8008? Are you using a splitter to provide a signal to 5 and 6?


    What setting are you using for switch #3


    "I remember it has is a push pull pot that completely bypass the EQ section. Usefull in this case."

    Great!


    ST

  • Hi ST,

    I feed the signal direct form Kpa Connecting to Direct Out Or Monitor Out. No need to split anything.

    On 8008 I use the B (5) input witch is liked to both output channel when A input is not engaged.


    I ve tried both settings and, as expected, I prefer to use the Linear mode and Not the Valvestate mode.

    I can't say This last is bad or not musical.. it just sounds more rounded and less louder, softer generally speaking. It s usable for sure but I Prefer the Linear one

  • yes, I have good memory: the Gain Input Pot on 3210 is a Push/Pull that enable or disable the Eq Section (9, 10,11) of the pre-amp

    ..but it works only if You engage the Boost channel, and to do this You have to Use the Footsitch (7) or the boost and the normal channels work in series,

    (and this is not specified in the Manual)


    In the end, unfotunatly, to use the Input of 3210 instead of the FxLoop Return it's not a good solution for my goal because, apart from EQ section, there are some others controls to affect and modify the signal in Input.

    first of all the Gain knob its self, witch on boost channel is really sensitive, (adding distorsion and also background Noise)

    than the Volume of the Boost channel (3),

    than the Tone (4), and finally the Master Volume (13)


    No, definetly not a good solution.


    Right Now, I've found a compromise to compensate the difference of Volume between 3210 and 8008:

    I use 3210 (the louder one) conected to the 2 Bottom Cabinets and the 8008 connected to the 2 on Top.

    The wrong aspect is that my ping -pong effect in not Left/Right, it's Up/Down ! DOH!X/


    Anyway, I guess the only Correct Solutions are:

    - Sollazzon buy another 8008

    - Kemper modify the OS to Let Sollazzon have the same actual controls of Monitor Out on Direct Out!

    (Level, Cabinet Off Option and Indipendent EQ, No more need to Monitor Stereo Option)



    The Second Solution is the Best one IMHO :thumbup:

  • Hi, Sollazzon,


    Here's another idea:


    Use the only the Marshall 8008.


    Connect Kemper Monitor Out to Marshall Input 5

    Connect Kemper Direct Out to Marshall Input 6



    This should be simpler and could still sound nearly as loud.


    If you try it, please let us know how it sounds.


    Thanks,

    ST

  • Humm.. to test it I should have to modify the connection of two Cabinets but it's not a bad Idea!

    I shoud have to replace this (only 1 Input)

    with something like this (1 Input and 1 Output)

    In my case I would have

    8+8=16 Ohms on each channel of the 8008

  • Hi Sollazzon,


    Oh, I didn't realize the Marshall cabinets do NOT have an output jack wired in parallel.

    Two cabs in parallel would present a 4-ohm load to the amp. That way you can get the full 80 watts x two from the 8008.


    ST

  • Hey ST I've found a good and simple solution!


    I've put a Volume Pedal Between the Direct Out of KPA and LoopFX Return of the 3210 and I keep it Closed just a little:

    something like 75-80%


    In this way I've found a Balance between the 2 different external Power Amps and I can regularly use KPA setted with Monitor Stereo option out

    (so I have on both Left and Right Channels the Monitor Cab OFF and the EQ)


    Cool!

    ..and Thanks For the time you've spent on this topic!