Marshall JPM 2204 50 Watt Cascaded Pre-Amp Schematic

adam79

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Feb 13, 2008, 4:10:34 PM2/13/08

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Are the JPM 2204 schematics with the cascaded preamps different from the JCM
800 2204 schematic? I think the JCM 800 has a whole different circuit board
than the JMPs. The only JMP schematics I've found are for the non-cascaded
pres.

thanks,
adam

west

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Feb 13, 2008, 6:29:29 PM2/13/08

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This JCM800 has the same circuit board as my JMP 50w master. My
voltages are much lower than his posted values.

http://mhuss.com/MyJCM/JCM800_2204.gif

jh

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Feb 14, 2008, 1:24:24 AM2/14/08

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adam79 schrieb:

Hi adam,
there was a posting with the origonal schem of a 78 cascaded 2204 in one
of your threads...

The mk2 board was identical for all units (1987,1959,220,2204) from
about 1977until they changed to the board mounted design in the mid 80s.

IIRC the pics of your amp shows exactly this kind of board...

What do you not like with your amp in the current state?

Jochen

Jim

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Feb 14, 2008, 3:56:12 PM2/14/08

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Check: http://tinyurl.com/2cn2e6

Even if the circuit is identical to JCM800, operation won't be, because
of lower plate voltages.

Peter Alerich

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Feb 14, 2008, 9:47:13 PM2/14/08

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http://www.alerich.com/2204-1976.gif

http://www.alerich.com/2204-1978.jpg

http://www.alerich.com/2204-jcm800.gif

adam79

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Feb 18, 2008, 4:31:52 PM2/18/08

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So let me get this straight before I show this guy the schematics..

http://www.alerich.com/2204-1976.gif is the non-cascaded JMP

http://www.alerich.com/2204-1978.jpg is the cascaded JMP

is this correct?

so my '77 JMP is like the '76 schematic (non cascaded), and i want it to be
like the '78 schematic (cascaded).

i just want to get this all down before i bring him the schematic.

also, from the other thread, you guys recommend I send my amp to someone
named Rich in NJ? he would do the best job, in your opinion? how do i get
intouch with him?

thanks for all the help,
-adam

jh

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Feb 18, 2008, 5:03:28 PM2/18/08

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adam79 schrieb:

> So let me get this straight before I show this guy the schematics..
>
> http://www.alerich.com/2204-1976.gif is the non-cascaded JMP
>

yup

> http://www.alerich.com/2204-1978.jpg is the cascaded JMP
>
> is this correct?
>

yes

> so my '77 JMP is like the '76 schematic (non cascaded), and i want it to be
> like the '78 schematic (cascaded).

if your amp is like the pic you posted weeks ago, you're correct.

>
> i just want to get this all down before i bring him the schematic.
>
> also, from the other thread, you guys recommend I send my amp to someone
> named Rich in NJ? he would do the best job, in your opinion? how do i get
> intouch with him?

look here for Rich Koerner...

and call him on the phone...

timelectronics.com

Jochen

Message has been deleted

jh

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Feb 19, 2008, 2:02:52 PM2/19/08

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adam79 schrieb:
> I just realized that the two schematics below ('76 and '78) are for the
> 2204s with 6550 power tubes. My 2204 was made with el34s. Does the
> difference in power tubes change the schematic, or will the schematic look
> the same no matter what the power tube?

almost identical...

I'm assuming all 2204s have 12ax7

yes

> pre-tubes..
>
> Also, I don't know anything about these schematics, but I looked them over,
> and the two are dramatically different all the way down the circuit board..
> will all of that have to be changed, or just the input side of the circiut
> board?

take a look at the board, the instructions are printed on it - not
kidding....

Jochen

>
> thanks,
> -adam
>
> "adam79" <ada...@toast.net> wrote in message
> news:13rjuao...@corp.supernews.com...

adam79

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Feb 19, 2008, 2:15:00 PM2/19/08

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jh,

so it doesn't matter that is says 6550 for the power tubes on the schematic
even though mine was made with EL34s?

thanks,
-adam

"jh" <jh-audio...@t-online.de> wrote in message
news:fpf8mo$nb7$03$1...@news.t-online.com...

jh

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Feb 19, 2008, 2:43:57 PM2/19/08

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adam79 schrieb:

> jh,
>
> so it doesn't matter that is says 6550 for the power tubes on the schematic
> even though mine was made with EL34s?
>
> thanks,
> -adam

only a few components different at the power tubes, the bias supply and
the negative feedback loop.

Tonally definately different, but no essential changes to the schematic
and the layout.

Jochen

Jim

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Feb 19, 2008, 7:15:04 PM2/19/08

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adam79 wrote:

> I just realized that the two schematics below ('76 and '78) are for the
> 2204s with 6550 power tubes. My 2204 was made with el34s. Does the
> difference in power tubes change the schematic, or will the schematic look

> the same no matter what the power tube? I'm assuming all 2204s have 12ax7
> pre-tubes..

Preamps are identical. Differences are bias circuit, tap for NFB loop,
and I think maybe screen resistors. ...but no worry for the preamp section.

>
> Also, I don't know anything about these schematics, but I looked them over,
> and the two are dramatically different all the way down the circuit board..
> will all of that have to be changed, or just the input side of the circiut
> board?

I've never compared the non-cascaded to cascaded. And, unfortunately, I
don't have time to do that at the moment.

Did you ever call Rich Koerner to ask him about doing the update? He's
definitely the guy to do it, but try to get firm time and dollar
commitments.

>
> thanks,
> -adam
>
> "adam79" <ada...@toast.net> wrote in message
> news:13rjuao...@corp.supernews.com...
>

adam79

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Feb 19, 2008, 9:13:37 PM2/19/08

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"Jim" <as...@beforeyousend.com> wrote in message
news:13rms84...@corp.supernews.com...

>
>
> Did you ever call Rich Koerner to ask him about doing the update? He's
> definitely the guy to do it, but try to get firm time and dollar
> commitments.
>

yeah, i talked to him today for like an hour. cool guy. i'm gonna take a
roadtrip down there at some point..