Marshall JCM1H or JTM1H schematics

Tube or solid-state, this section goes to eleven!

Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 19 May 2015, 01:49

I have the preamp and output sections built on the turret board. I was worried about running out of room and the preamp section is squashed together. Would have liked to spread it out more. I have room in the center for more components, possibly the tone network or future tube effects loop.

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Re: Marshall JCM1H or JTM1H schematics

Postby cassoulet » 19 May 2015, 06:23

Looks pretty clean build. :applause:

What's the mahaffay schemo like? Any link to it? :hmmm:
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Re: Marshall JCM1H or JTM1H schematics

Postby cassoulet » 19 May 2015, 06:28

mavrim wrote:Awesome, makes it so much easier to understand!


Thanks. I used TinyCAD, this free software you talked me into if I remember well. :P
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Re: Marshall JCM1H or JTM1H schematics

Postby sturgeo » 19 May 2015, 12:43

Cassoulet, not sure if its a typo or a modification but on your HTM-1 schematic R9 is down as 56k?
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Re: Marshall JCM1H or JTM1H schematics

Postby cassoulet » 19 May 2015, 14:11

sturgeo wrote:Cassoulet, not sure if its a typo or a modification but on your HTM-1 schematic R9 is down as 56k?


Not exactly a typo. 56k is the JTM1 standard value, but for some reason Matec chose to raise it up to 560k. I kept the standard value on the schematic, but this is up to you to chose 560k like Matec. I will also try this mod.

Also, I noticed that Matec chose 2.7k for R31, while the standard JTM1 value appears to be 1.5k. I added this info in parentheses on the schematic.

One last deviation from the standard circuit is of course the addition of the TMB tonestack plus R202 to avoid a complete cutoff of signal when the three pots are turned all the way down.

I have an updated BOM that compares JTM1, HTM1, JCM1 and JTM145 (incomplete). Shaded gray shows where a value is different between the four. Shaded yellow indicates auxiliary stuff such as light indicator, ground lift, etc.
Here it is, please check for any error.

BOM-JT-JC-JTM.xlsx
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 19 May 2015, 23:52

cassoulet wrote:Looks pretty clean build. :applause:

What's the mahaffay schemo like? Any link to it? :hmmm:


http://freestompboxes.org/viewtopic.php?f=2&t=9445

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Re: Marshall JCM1H or JTM1H schematics

Postby cudaboy_71 » 22 Jun 2015, 02:03

cassoulet wrote:Hi Matec,

I am interested in your JCM1 schematic dated august 2014. Since then, have you been able to find the missing values for components on the external PCB? That is C101, C105, C106, C107, C108, R102, R106, R107, R108.

Many thanks for your work.

Cheers. :thumbsup


Hi All,

Been lurking for a while watching this thread. Just registered to ask a question. I see back on page 3, Cassoulet asked for the JCM1 schematic dated august '14. I looked back and see nothing posted on that date. Where do I find this schematic? does someone have link?
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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 22 Jun 2015, 13:00

Hi cudaboy_71

The process to obtain the diagrams of amps "Marshall 1W" was, and remains, long and confusing. :horsey:

I started in Handmades forum in Brazil - http://www.handmades.com.br/forum/index ... pic=5841.0
I got a lot of information at The Garage amp - http://ampgarage.com/forum/viewtopic.ph ... 44790e78ed
and also here in Freestompboxes,

Plus plenty of help from people who come in contact directly. :secret:

The information available in these forums will have to clarify many of your questions. :shock:

Happy reading.

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 01 Apr 2016, 01:01

After letting this project go unfinished since my last posting, I finally finished building it last week. Tonight I made a few final changes to clean up the turret board layout. In hindsight, I should have made the turret board longer and move the tube sockets to the rear. I am very happy with the sound of this amp! I used a combination of the JCM and JTM output stage coupled to a basic preamp circuit as shown in Mahaffay schematic in past post. The 50th anniversary models used more capacitors and resistors to shape the sound. My preamp resembles a standard Marshall preamp. I used vintage mustard caps. I notice a warmer sound compared to the green chicklet poly caps I use in my 1/4 watt builds.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 01 Apr 2016, 01:15

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 01 Apr 2016, 01:25

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 02 Apr 2016, 00:33

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 02 Apr 2016, 00:34

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 02 Apr 2016, 00:37

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 02 Apr 2016, 17:49

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Just spotted a Marshall JMP1 schematic on handmades website that was also reverse engineered by Matec. Wish I had this before building the JTM/JCM output section in my amp build.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 17 Jun 2016, 20:13

Where has everyone gone?

I rewired the turret board to fit the entire JCM1 circuit. I used a small perf board for the silver jubilee boost circuit. The circuit is not as neat and layed out as I had hoped. Had to stack and crisscross a few components to squeeze them in.

Amp sounds incredible!

I need to finish low power wiring and maybe a few tweaks. I used vintage mullard capacitors for the best tone.

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 17 Jun 2016, 20:17

JCM1 chassis
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 17 Jun 2016, 20:21

Turret board
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 17 Jun 2016, 20:34

Turret board
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Re: Marshall JCM1H or JTM1H schematics

Postby Fatmoocow » 24 Jun 2016, 19:50

This is a great thread. As a learning exercise I've been reworking the JTM1 to more closely match the real thing. Full disclosure I don't really know what I'm doing.

Thus far I've taken the power amp and added a long tail pair to split the signal in front of the 12au7. I'm not sure that this will work at all. In a perfect world we'd want fixed bias as well, but I don't have the skills for that.

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I'm going to add another 12ax7 and toss out the jubilee circuit for something that matches the JTM45 more closely.

Any feedback or ideas would be greatly appreciated.
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