Marshall JCM1H or JTM1H schematics

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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 25 Jun 2016, 13:55

Apparently , there is no reason that this circuit does not work. Do not worry about the fixed Bias, thus is simpler.

Do not expect a similar sound to JTM1 or JTM45. But you will have a good study amplifier.

Cheers
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 26 Jun 2016, 01:39

Matec, so good to see you posting here again!

That jcm1 schematic turned out to be a fun build. Wish I had followed it from the beginning of my build, but the schematic wasn't complete then. I did find that R29 which is a 1meg resistor, should connect from V1A pin 7 to ground. It is shown as being connected between C22 and R28 to ground.

A buddy of mine actually cloned his own jcm1 and had boards made up. He sells his clone on eBay. They are built into lead 12 sized chassis and fit right into your own lead 12 combo or head. Search eBay for jcm 800 clone silver jubilee.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 26 Jun 2016, 01:44

Cloned jcm1. Search eBay
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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 26 Jun 2016, 16:53

Hello mavrim.

I doubt there is a big difference between R29 connected between the ground and the V1a grid, and R29 connected between the ground and the C22-R28 node.

There will be many clones of Marshalls 1W, manufactured by talented people. This is really good. Your friend seems to be doing a great amplifier.

Cheers.

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mavrim (30 Jun 2016, 01:17)
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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 31 Aug 2016, 15:16

Hello everyone.

Here is a video and sample of axehack, who set up his own JTM1.

Link: https://www.youtube.com/watch?feature=player_embedded&v=bL4m4kCeHAE

The description is in TDPRI Forum at this link: http://www.tdpri.com/threads/jtm-1-clone.650255/

Have fun!

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Re: Marshall JCM1H or JTM1H schematics

Postby bmxguitarsbmx » 18 Sep 2016, 20:01

Fatmoocow wrote: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.

[ Image ]

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.



Hey fatmoocow,
This is cool, but there may be some figuring to do first.

The classic marshall long-tailed par circuit has gain of ~ 25 (good for driving el34's)

the cathodyne phase splitter has unity gain.

The 12au7 needs much less drive to reach full power than el34's do, so a phase splitter with gain may not be helpful.

Hope that's helpful :)
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Re: Marshall JCM1H or JTM1H schematics

Postby Electrochimp » 03 Dec 2016, 06:06

What effect on the second triode plate does that 100nf and 4.7m have ? thanks
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