Hey folks,

first of all, I'm not familiar with speaker cabs, so please don't kill me if this is the stupidest question in history of mankind.

My amp is a Marshall AVT275X (that don't-kill-me thing is also applicable here) which has 2 75 watt outputs, each one drives one of the 2 speakers in the combo cab.

A friend of mine has a previous version of the valvestate, but with one output of 150 watt. He has a 4x12 cab which makes his sound a lot better than what I get (shh, valvestate).

So I was wondering, would it be possible to get this 2x75watt output to combine to 1 150watt output, so I can drive the cab with 150 watts instead of just 75 watt? Also, would it damage my amp to just use one output, and let the other unplugged?

Check your manual to see if one of those outputs is capable of running in mono (called mono or main output.) It probably won't hurt it to just run one cab out of one jack but I imagine it will cut the output of your head in half (unless the head has a mono option.)
I know it wouldn't sound better. It's just, why only be able to use 75 watt when I could use the full 150watt. I don't want to use 75watt through one of the speakers of the combo-cab, and another 75watt on an external cab, because I can imagine there would be a noticeable sound-difference (combo sounding thinner).

Manual can be found at warning, pdf link, get ready for insta-browsercrashing

Page 9 states:

2. Loudspeaker Jack Sockets
These connect the internal loudspeakers to the
stereo power amplifier outputs.
Always provide both with a load equal to, or
greater than 8 Ohms.

Can't find anything about a mono setting though.


I stumbled upon this link:

It's the Marshall 1960A (does not mean I would buy this one.. I *stumbled* upon it ). On this site, it states that you can select between a stereo and mono mode, with the impedances being respectively 8 and 16/4 ohms. Does this mean that I can plug in both of the speaker cables into one cab, and let that cab use both these inputs together?

All you would have to do is run one cable from one output jack into a mono cab. The impedance of the mono output is 8 ohms so any cab you use would also need to be 8 ohm. Some cabs have switchable impedance, so switch it to 8.
Then I would end up with the cab being driven with only 75 watt though, right?
That's exactly the problem, I want to feed it 150 watt. (so the only 'used' speakers would be those in the external 4x12cab)
I'm sorry. I was talking about the 1960A. On yours you would probably cut the output in half. Your only option would be to run two cabs (one for each output) or do some extensive rewiring.
Thanks for the explanation so far, uldhppi.

After searching a bit more about the 1960A cabinet, I found a photo of the rear panel

or http://i8.ebayimg.com/01/i/000/b3/c7/0e93_3.JPG
If you put the switch on stereo, you use both inputs (left & right), so this was what I was aiming for.

Now, what's next is saving some money, and hunting for a stereo 4x12 cab (maybe the 1960A, we'll see)

Last edited by sanderd at Sep 3, 2007,