Amps

[Desert_Fox]

Hey i know this is not a pedal related question, but i know i can get some straight answers from everyone here. so my question is whats the difference between a rackmount amplifier and a head unit?  if you know any differences between how they're wired than please do tell, i'm quite interested in the specifics.

cheers.

[O'malley's Alley]

as far as I know, most rackmount amps are just Preamps.  Such as the Marshall JMP-1.  This means you need to buy a poweramp as well.  many people like it cause you can mix up different pre amps and poweramps.  I know I have seen people put their heads in with their racks, but I think the rack amps you are thinking of are just serperate power amps and preamps...

[Rodgre]

Or the opposite....

Are you talking about rackmount power amps?

Roger

[The Tone God]

This is a form factor question. In general a head is just a chassis with a cabinet to hold it much like a speaker cabinet. A Marshall head would be an example. A rack mount is a chassis that is installed to a racking system which then serves as the cabinet.

In terms of wiring they can both be the same. There are no real special requirements that different between the two.

Preamps and power amps are another topic.

Andrew

[Desert_Fox]

when i say head unit, i meant something like a marshall jcm-900, compared to a rackmount power amp. can one be used in place of the other?

[Hal]

some bass amps come in rackmount cases...never seen it with gutar amps, though.

[petemoore]

Part of the 1/2 stack full stack sound is the interaction between the head being in contact with the cabinet.
 You probably won't notice it much unless it's cranked, maybe not even then.
 There is a microphonic feedback element to amp/cab, and combo amp setups that is supposeldy part of the engineering.
 Combo amp 'do' this even more, and as a result, more often tend to get unwanted microphonic acitivity in the preamp tubes earlier than 'head' units, but this interaction is part of the sound or mojo of the design.
 Rack mounts are just different, It doesn't seem that the microphonics element is intended to be highlighted in these chassis.
 Reverbs respond differently when 'rattled' by the speaker.
 You may find, at some point, that you can use your input tube as a crude microphone...try yelling at it with the amp sorta cranked.

[Paul Marossy]

A rack mount power amp is only that. It does the output from whatever. You would also need a preamp of some sort to go with it. Two pieces of rack mount gear.

A Marshall head (or any other) has the preamp and power sections combined in one cabinet.

[william]

Yea, a rack mounted amp, meaning something with both the pre-amp and poweramp, (such as the SLO100R or the Mesa/Boogie rack mount kits) are the same beast as the head versions.  I've never understood a rack mounted amp.  On the other hand, you see lots of rack preamps, and rack power amps.  That makes sense to me, because of the options provided by diffrent combinations of the two.

[MarkB]

My Rivera head is a rackmount - and I'm glad it is... racks often have wheels, and this thing is WAY too heavy for a typical amp handle.

(the thing is about 65lbs according to the manual)
"-)

[RedHouse]

Having built Marshall 2204 type circuits into both cabinet and rack units I can tell you there is no difference in sound, no mojo, just form factor, the sound is exactly the same at all volume levels.

Rack units can get hotter if not carefull (may need fan) as there is less free air circulation that a cab  style enclosure (cab w/back removed)

[Desert_Fox]

thanks very much to everyone who responded, i feel less ignorant.

cheers.

[MarkB]

you're right, Redhouse - my Rivera has a big fan in the back.
"-)