Semi O.T./ technically, is this O.K.?/R.G.?

[guitarhacknoise]

Hello,
I've been running this set-up,
Marshall 50W mkII head into a 16ohm 4x12,
Then I take a shielded line from the Marshall's D.I. and run it into a Sunn Concert Slave which moves air via a second 4x12 @16 ohms as well.

1) What does this mean to the Marshalls pre-amp, being tapped by a second power amp?
2) Subsequently, What does this mean to the Marshalls Power amp?

3) At times, I was experiencing what would commonly be described as "poor tracking"
Where as I would play a single note and at the end it sounded like when you play sloppy with an octave pedal. What would explain this?

Basically.............
Slave amp, Bad parasite or just a good way to blow out your ears?
I Thank You in advance.
-Matthias

[niftydog]

taking a signal feed from a DI output should in no way affect the operation of any part of the amplifier.

However, DI outputs are low impedance, balanced lines, usually at an amplitude akin to a microphones output. This makes them quite different to your typical guitar output.

Still, if your 2nd power amp is designed to accept microphone level balanced signals, it shouldn't present a problem. BUT, usually power amps accept LINE level balanced signals which are considerably higher in amplitude - so while it obviously works, it may not be giving the optimum performance.

[guitarhacknoise]

thanks for the response nifty,
I think I hear what you are saying, but I thought that this was the way that these slave amps were utilized. i.e. to run a second cabinet without pulling down the output vs. one head and two cabinets.
What is a slave head really for?
or rather, is there a difference between a slave and a power amp.

[guitarhacknoise]

Wait, wait.............

[guitarhacknoise]

o.k. so,
Marshall 2204 owners manual,
"17. D.I. Input.
jack socket carrying low level version of amplifier output, suitable for connection to recording and P.A. mixing desks, or into slave amplifying systems."

which I basically equate to what nifty said.  except for the "or into slave amplifying systems." part.

I may need to bring the D.I. output up to line level before the slave amp?
how much would be too much?

[guitarhacknoise]

O.k.,
So, with more searching and reading and trying to think. I found more "Nifty" words that I think may help me:
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=19640&highlight=low+level+line+level

So, if the D.i. is low level, for P.A.'s and such, it's not really at the same level as what is going into the onboard power-amp, right?
So, would a small pre-amp, ie. McTube, before the slave head be the right approach?
Or am I totaly off base here?

[niftydog]

if the D.i. is low level, for P.A.'s and such, it's not really at the same level as what is going into the onboard power-amp, right?

Right, not necessarily the same, but who knows what rules they follow inside an amp. The important thing is what goes on outside!

Just to restate, it works, and there's nothing necessarily wrong with that setup - it may not be the cause of the problem.

So, would a small pre-amp, ie. McTube, before the slave head be the right approach? Or am I totaly off base here?

For starters, the DI output is balanced, remember? And, I would imagine that the power amp is expecting to see a balanced signal at it's input too. So a simple, unbalanced pre-amp is not the best approach either.

Are you using a straight XLR to XLR cable to connect the amp to the power amp?

I think I need to know some more about your amp. Is there an online manual or even just some detailed pictures of front and back somewhere? What's the exact model number?

I'm thinking that if it has a DI output that there might also be a more appropriate output to use for this application.

[guitarhacknoise]

o.k.
you can find the manual here:
http://www.drtube.com/marshall.htm#JCM800
the model # is 2204
it is a 50watt MKII head
the D.I. is a 1/4 jack, which Is where I think we lost each other as far as balanced and unbalanced. Unless it is posible to run a balanced signal through a Stereo cord?

At the moment I can't find the Info on the concert slave but I did find this, which seems to go along with my original plan: http://www.dangpow.com/~sunn/phpBB2/viewtopic.php?t=2001&highlight=concert+slave
-Matthias

[guitarhacknoise]

as far as a "more appropriate output for this application", The D.I. is the only output available, minus the speaker outs.

Now, if a balanced line has two separate phases and a common ground, and was being sent out of a stereo 1/4" jack and I used a mono cord, one of the phases would go to ground, I would lose some amplitude and gain some noise. Correct?
I guess, I will need to start opening things up.

[guitarhacknoise]

Well, I can tell you this.......
The sunn Concert slave accepts a unbalanced input.
First off it is 1/4", and second it's a mono jack.
The only pot on the thing which is entitled "sensitivity" is just a variable resister.
what signal passes goes on to the poweramp.
Good thing I opened it up, real dusty/dirty, three out of six stadoffs are busted, the board had shifted forward so much that it has pulled the power resistors out of thier heatsink clips!
How in the world does something get mistreated so badly?
for what ever it's worth, date of manufacture is 11-3-72.

[niftydog]

Unless it is posible to run a balanced signal through a Stereo cord?

a balanced signal requires three conductors; hot, cold and ground.

I would lose some amplitude and gain some noise. Correct?

definately less amplitude, more noise? Maybe.

Still, as I say, if it works it works, and chances are it's not what is causing the "sloppy" sound. If you can, test the slave amp with a more conventional set up. Like the output from a mixing desk or something.

Basically, how you have it set up is the right way to do it given those pieces of equipment, but you have to work out wether it's your amp or the slave amp that's causing the "sloppy" sound!

How in the world does something get mistreated so badly?

let me guess, it smells like smoke too? Any PA gear that travels in band vans, gets lugged by drunk mates into smokey bars and gets abused by the sound guys is bound to be dropped, bumped, rolled around in the trunk etc etc.

Don't ever get into fixing mixing desks for a living, they are more often than not filthy, sticky and smelly.

[Paul Perry (Frostwave)]

I wonder if there is a phase reversal problem? Because if there is..... it could sound a bit weird, depending where your head is with respect to the two amp/speakers.

[niftydog]

yeah, nice thought Paul. I guess it's hard to diagnose because we can't hear the sound!