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Effect of Output Impedance on Speaker Output
Posted: Thu 08/05/21 1:35 pm
by junior marbles
Several threads addressed the sonic effect of the three different output transformer strappings available in the Marshall 1974x.
But what has not been addressed: is there a difference in speaker output SPL between 4, 8, and 16Ω amp settings, provided I mount the corresponding 4, 8, and 16Ω Celestion Greenbacks?
Re: Effect of Output Impedance on Speaker Output
Posted: Thu 08/05/21 2:14 pm
by JMPGuitars
junior marbles wrote: ↑Thu 08/05/21 1:35 pm
Several threads addressed the sonic effect of the three different output transformer strappings available in the Marshall 1974x.
But what has not been addressed: is there a difference in speaker output SPL between 4, 8, and 16Ω amp settings, provided I mount the corresponding 4, 8, and 16Ω Celestion Greenbacks?
Welcome to the site!
If nominal speaker impedance is matched, there is no perceivable output difference. If it is mismatched, there will be a difference.
Side note: the circuit is 1974. 1974X is the reissue version.
Thanks,
Josh
Re: Effect of Output Impedance on Speaker Output
Posted: Thu 08/05/21 2:25 pm
by junior marbles
Thanks. I was referring to the 1974x Reissue, which I own.
Besides, I would love to find an original Marshall schematic for the mid-1960s 1974. If you know a source: it would be interesting to see how much the two schematics overlap or differ.
Re: Effect of Output Impedance on Speaker Output
Posted: Thu 08/05/21 7:06 pm
by JMPGuitars
junior marbles wrote: ↑Thu 08/05/21 2:25 pm
Thanks. I was referring to the 1974x Reissue, which I own.
Besides, I would love to find an original Marshall schematic for the mid-1960s 1974. If you know a source: it would be interesting to see how much the two schematics overlap or differ.
Ha, you're the first that got it right then when making that reference.
Sure, check our downloads section, it's there.
Thanks,
Josh
Re: Effect of Output Impedance on Speaker Output
Posted: Thu 08/05/21 7:55 pm
by junior marbles
Sure, check our downloads section, it's there.
Not seeing anything but a hand-drawn copy of what may or may not be the original mid-sixties 1974. Anyone have an official, Marshall-generated schematic?
Re: Effect of Output Impedance on Speaker Output
Posted: Fri 08/06/21 2:22 am
by Daviedawg
It is my understanding that any differences between individual units produced at the time was due to component availability not circuit design. I say that as an owner of a Watkins Scout which is one of the closest "ancestors" of this amp. The only differences are in the trem circuit which continued to change through Dominator versions as well.
I believe that the hand drawn schematic of Colin's 1966 amp is as accurate a representation of the Marshall circuit as you will find.
Dd
Edit: it is likely any official schematic would have seen the light of day given the exposure the circuit has had over the years.