#1 · Aug 15, 2008 21:56 UTC
The power stage, in the Marshall is pretty much the same design as what you'll see in the Fender Twin (135 watt). Well, OK, the tubes are different... 6 versions versus EL versions... but, conceptually the design is THE same, with a difference in tubes and output transformer. There are still 2, or 4, tubes in the stage. A splitter feeds those tubes, the tubes amplifier in Class AB1 design, pushing and pulling the signal through the transformer and driving the speaker. There are differences in the EL-series tubes and the 6V/6L series of tubes, but they don't contribute as much as what we'd like to think, to the final sound of the amp. There'll be more of that later when we talk about transformers and "power bandwidth" of those transformers... oh, and impedance matching. THAT, more than the tubes, makes a HUGE difference in the final sound. You can't just plug 6-version tubes in an EL-based amp (even with that nice little switch there) and expect it all to sound the same... Yes it sounds different but it's not just the tubes, at play.
Marshalls, like Fenders, went through a bunch of different splitter designs and, quite frankly, they contribute a bit to the sound of the amp, but once they're in there, they're hard to mod and make right... The largest difference between the Fender Bassman 5F6-A, that the Marshall topology is based on, and the Marshall power section lies in the feedback loop.
Marshall typically taps the feedback off the 16 ohm tap of the output transformer. The IMMEDIATE result, here, is that the initial voltage fed into the feedback loop is nearly double that of the voltage fed into the Fender loop. Marshall also has a much HIGHER value resistor at the bottom of the feedback loop, dropping MORE voltage back into the splitter which reduces gain considerably more than the Bassman, creating a much "tighter" response, overall, and much more linear. This also makes the Marshall power amp sound more "brittle" and "dry" than what the power amp in the Bassman sounds, as the power amp is highly damped and tightly controls the speaker movement. Of course, when the amp is driving 8, 12" speakers, there's a LOT more back EMF generated by the speakers and it takes a LOT more work to "control" all that than what it did in a 1, or two, speaker Fender amp. Even the smaller 10" speakers in the Bassman would have generated significantly less back EMF...
But, long story short, the Marshall amp has a great deal more feedback and it's more "tightly controlled" than its Fender counterpart. That said, it'd be hard to find something as tightly controlled as the high powered Fender Twins... at least you could, eventually, get a Marshall power stage to break up. Those Twin's never did.
In truth, those are the major differences between the Marshall power stages and the Bassman it copied... higher voltage being fed into the feedback loop. More voltage being fed back into the splitter... tighter control over the speakers in the cabinet. Again, designs varied, a bit, over the years but, eventually, Marshall created a power amp topology that was comprised of 50 watt and 100 watt stages that rarely ever changed...
That's about it, for the Marshalls... just remember 720Hz and more feedback... and you've got them licked! That's what makes a Marshall a Marshall.
Dar
Marshalls, like Fenders, went through a bunch of different splitter designs and, quite frankly, they contribute a bit to the sound of the amp, but once they're in there, they're hard to mod and make right... The largest difference between the Fender Bassman 5F6-A, that the Marshall topology is based on, and the Marshall power section lies in the feedback loop.
Marshall typically taps the feedback off the 16 ohm tap of the output transformer. The IMMEDIATE result, here, is that the initial voltage fed into the feedback loop is nearly double that of the voltage fed into the Fender loop. Marshall also has a much HIGHER value resistor at the bottom of the feedback loop, dropping MORE voltage back into the splitter which reduces gain considerably more than the Bassman, creating a much "tighter" response, overall, and much more linear. This also makes the Marshall power amp sound more "brittle" and "dry" than what the power amp in the Bassman sounds, as the power amp is highly damped and tightly controls the speaker movement. Of course, when the amp is driving 8, 12" speakers, there's a LOT more back EMF generated by the speakers and it takes a LOT more work to "control" all that than what it did in a 1, or two, speaker Fender amp. Even the smaller 10" speakers in the Bassman would have generated significantly less back EMF...
But, long story short, the Marshall amp has a great deal more feedback and it's more "tightly controlled" than its Fender counterpart. That said, it'd be hard to find something as tightly controlled as the high powered Fender Twins... at least you could, eventually, get a Marshall power stage to break up. Those Twin's never did.
In truth, those are the major differences between the Marshall power stages and the Bassman it copied... higher voltage being fed into the feedback loop. More voltage being fed back into the splitter... tighter control over the speakers in the cabinet. Again, designs varied, a bit, over the years but, eventually, Marshall created a power amp topology that was comprised of 50 watt and 100 watt stages that rarely ever changed...
That's about it, for the Marshalls... just remember 720Hz and more feedback... and you've got them licked! That's what makes a Marshall a Marshall.
Dar