can I run my JCM900 into stereo?

[Indie P Bass]

If I put my 1960A cab into stereo mode, it's 150w@8ohm's a side, right? So, what if I run the two outputs of my JCM900 out stereo in 8ohms? Would there be any tone or volume changes? Or would it be the same as 1 16 ohm load?

[some_dude]

Re: can I run my JCM900 into stereo?

Try it and find out.

[Robert S.]

Re: can I run my JCM900 into stereo?

Two 8 ohm loads in parallel will be 4 ohms at your amp. I believe you need to set your amps output impedance to the total impedance.

The 900 is not a stereo amp but you may find it sounds better at 4 ohms. I like my 800 at 8 ohms better than 16.

There's probably nothing major to be gained, but it can't hurt to experiment as long as you get the impedance correct.

[Indie P Bass]

Re: can I run my JCM900 into stereo?

the 900 has two settings on the Ohm load, 8 and 4 (16), I assume that 4 (16) is actually 16, am I correct? or is it 16 if I use both outputs? The amp has two outputs.

[Robert S.]

Re: can I run my JCM900 into stereo?

Im not up on the 900s so I have to assume they are the same as all the other tube Marshalls I have seen. The outputs are parallel wired. This means that one 16 ohm cab needs to be run off of a 16 ohm tap. Two 16 ohm cabs will be seen as an 8 ohm load and the output impedance needs to be set to 8 ohms with 2 16 ohm cabs. Two 8 ohm loads will require the amp to be set to 4 ohms. Speaker cabs are also normally wired in parallel, so it doesn't matter if you string the cabs together or plug them both into the amp directly.

Having a 16 ohm 412 that has stereo 8 ohm taps confuses things a little, but two 8 ohm loads should still be considered a 4 ohm total load at the amp.

[Indie P Bass]

Re: can I run my JCM900 into stereo?

I still don't get it

[Robert S.]

Re: can I run my JCM900 into stereo?

To run two 8 ohm loads safely, you need to set your output impedance to 4 ohms.

[HolyDirt]

Re: can I run my JCM900 into stereo?

To run two 8 ohm loads safely, you need to set your output impedance to 4 ohms.

yup, rob (like always) is right. Since the outputs are wired in parallel, the 2 incomming impendences ( 8 ohms and another 8ohms in this case) have an overall load of 4 ohms. (formula for parallel impendences: 1st load X 2nd load divided by 1st + 2nd load, so in this case it's 8 X 8 = 64 , 64/(8+8) = 4)

[Indie P Bass]

Re: can I run my JCM900 into stereo?

ahhh... so... ok... also, on the back of my JCM 900 is a switch that goes from 8 to 4 (16) Ohms... which should I use? I usually ahve it on the 4 (16) side and plug into the cabinet's 4 ohm side.

[Metalman_666]

Re: can I run my JCM900 into stereo?

use the 4 (16) position

[Indie P Bass]

Re: can I run my JCM900 into stereo?

and should I plug into the 4ohm or 16 ohm side of the cabinet?

[Robert S.]

Re: can I run my JCM900 into stereo?

I need to do some research into how those cabnets are wired becayse I dont want to be the guy that helps you to fry your output tranny. My JCM 800 head and cab has 16/8/4 at the head and only the single 16 ohm (now 8) at the cab. I was assuming that your cab was either 16 ohm mono or dual 8 ohms stereo.

You appear to have something else going on. Run the head and cab mono at 16 ohms for now. Besides, there is really nothing to gain by changing the wiring to the head and cabnet, you will be mono either way.

[Indie P Bass]

Re: can I run my JCM900 into stereo?

ok... lemme explain this.... the back of the head has two "loudspeaker outputs" with two switches attached, a power switch has hi and lo, which I assume takes two of the power tubes out or something. Also, it has an impedance switch, "8" and "4 (16)"
now... my cabinet has two inputs 4ohms and 16ohms, then a switch that changes it to two 8ohm inputs and makes the cabinet stereo. Now, I'm running it the "4(16)" side into the 16 ohm input of the cab, is that correct?

[flank]

Re: can I run my JCM900 into stereo?

when i ran my twin through my 1960A cab with it set on stereo at 8 ohms and sound came from all 4 speakers..

are you trying to run 2 outs from the head into both inputs of the cab?.....cause it didnt effectly split my cab to 2x12 and 2x12, sound still came from all speakers...

im a bit confused about stereo and the question your asking lol

[Indie P Bass]

Re: can I run my JCM900 into stereo?

Well, I'm just wondering if running both the outs in my amp to the cabinet (with the cabinet in stereo) would increase volume, but, now I'm concerned that I don't have matching impednaces