#1
I'm putting together a hypothetical rig diagram before actually building my new pedalboard/amp set up and maybe blowing it all up, and something had just occurred to me... The two amps I want to use have different impedance >.<

I'll say now that I don't fully understand impedance matching, that may be why I'm stuck on this...

The two amp heads I want to use are a Marshall JCM900 (100w) and a Peavey Classic 50 (50w). The JCM900 has an "impedance select switch" with two options - the first is "(4) 16" and the second is "8". I use it set to 4, because the mono setting on my 1960A 4x12 cab is rated at 4. The Peavey Classic 50 (yet to get my hands on, tried a friend's combo unit and loved it so getting a head I can use with my own speakers) has the options of either 8 or 16.

I figure I can't set the JCM900 to 8 as it should be 4 to match the mono setting of my cab. But then what do I do about the Classic 50?

The two heads will be switched with a Tonebone HeadBone, which I figure doesn't do anything to change the impedance?

Any help would be appreciated!
PRS SE Chris Robertson
PRS SE EG
PRS SE Angelus Custom
Yamaha SF1000 (Both of 'em)

Laney L20H Lionheart
Marshall 1936 w/ Eminence

Rather large pedalboard..
#2
Seems like the JCM900 head only puts out 8 or 16 ohms (the combo is 4 or 8). I would suggest consulting the manual for the head/cab and make sure you are setting it up right before you worry about adding another amp in. It does seem like you could do it though, with both heads and the cab run at the 16 ohm setting.

http://www.marshallamps.com/handbooks/pdf/jcm900.pdf
http://www.marshallamps.com/downloads/files/Cabs%20Hbk.pdf
#3
Now you've said it that looks blindingly obvious and I feel I should've spotted that already... thanks dude!
PRS SE Chris Robertson
PRS SE EG
PRS SE Angelus Custom
Yamaha SF1000 (Both of 'em)

Laney L20H Lionheart
Marshall 1936 w/ Eminence

Rather large pedalboard..
#4
impedance matching just means the output of the amplifier has to be matched to the impedance rating of the cabinet. this is applicable to tube amps, the impedance output of the tube amp is dictated by the output transformer(OT). the the OT generally has one input and can have multiple outputs, the outputs are generally rated for multiple impedances (like 16 ohm or 8 ohm).

you have a JCM900, rated at either 8 ohm output or 16 ohm output (assuming you are using the head).

you will be getting a peavey classic 50, rated at 8 or 16 ohms (also assuming this is a head and you will be needing a cab for it).

you seem to have a 1960A cabinet and you have access to a radial headbone to switch it.

it looks like you have multiple options on how to set this up.

1) set the cab up for 16 ohm mono and use the 16 ohm outputs for each amp into the Headbone

2) use your cab on 8 ohm stereo mode and plug each head's 8 ohm output into a respective R/L side or the cab.

if you did have a mismatch between heads (like if the JCM900 only had 4 ohm and 8 ohm output) then you'd be stuck with using the cab in stereo mode and using each amp's 8 ohm output.
punk isn't dead, it's always smelled that way.

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