Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on September 23, 2014, 01:08:08 pm

Title: Marshall JMP 2204
Post by: Leevi on September 23, 2014, 01:08:08 pm

Are the inputs correctly marked in the Marshall's schematic below?
It looks that the High sensitive channel has less gain.


http://el34world.com/charts/Schematics/files/marshall/Marshall_2204%20JMP%20Master%20Volume%20Lead%2050watt.gif (http://el34world.com/charts/Schematics/files/marshall/Marshall_2204%20JMP%20Master%20Volume%20Lead%2050watt.gif)


/Leevi

Title: Re: Marshall JMP 2204
Post by: sluckey on September 23, 2014, 01:49:27 pm

That particular 2204 belongs to the JMP series. The preamp is the same as the JMP 1987 (Plexi) except only two input jacks. The High input should be called Bright and the Low input should be called Normal.

The high gain JCM-800 2204 that we usually think of came later. It actually cascades the preamp tubes when using the High input jack for a high gain circuit.

Title: Re: Marshall JMP 2204
Post by: Leevi on September 23, 2014, 01:54:49 pm

Quote

The High input should be called Bright and the Low input should be called Normal.

Yes, that's true



Thanks
Leevi

Title: Re: Marshall JMP 2204
Post by: simonallaway on September 23, 2014, 02:26:16 pm

My JMP 2204 which was made in 1977 has the inputs labeled 'High' and 'Low' with the word 'Sensitivity' between them. See attached.

Title: Re: Marshall JMP 2204
Post by: Leevi on September 23, 2014, 02:41:08 pm

Here as well


https://reverb-res.cloudinary.com/image/upload/a_exif,c_limit,fl_progressive,h_620,q_85,w_620/v1399657814/fsudouyc26opuhidavdh.jpg (https://reverb-res.cloudinary.com/image/upload/a_exif,c_limit,fl_progressive,h_620,q_85,w_620/v1399657814/fsudouyc26opuhidavdh.jpg)


/Leevi

Title: Re: Marshall JMP 2204
Post by: simonallaway on September 23, 2014, 02:47:14 pm

I never could understand why Marshall kept the 220x model numbers for the JCM800 series when is wasn't quite the same circuit.

Title: Re: Marshall JMP 2204
Post by: Leevi on September 23, 2014, 03:05:00 pm

There is not any logic in their amp naming.
They even use years like 1959, 1986, 1987, 1992, that are probably not meaning year models?
I think the company did not exist in 1959.


/Leevi

Title: Re: Marshall JMP 2204
Post by: simonallaway on September 23, 2014, 03:29:56 pm

I'm a software engineer, so I'm used to arbitrary naming schemes. Over the years I've seen all kinds of numerical based (and movie names, dwarves, Hobbits etc) used for software releases. The source doesn't matter as long as it is consistent. I knew Marshall's numbering wasn't meant to reflect the inception date.

I just wish they were consistent over time!

Title: Re: Marshall JMP 2204
Post by: Backwoods Joe on September 23, 2014, 08:17:39 pm

Don't forget about the JMP 50 Master MKII. It had 2 inputs. one marked high and one marked low sensitivity, cascaded preamp stages and was basically one of the last amps or the last amp before the JCM800.