Marshall JCM1H or JTM1H schematics

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

Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 28 Apr 2015, 20:29

The NFB maintains power a little more linear.

This is important to increase a little the headroom, and works well when the circuit is in the linear region. When the power goes into overdrive, then whatever. :roll:
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 28 Apr 2015, 22:09

Thank you for clarifying! Still undecided if I build JTM circuit or combine output section with another preamp design. I wondered how the amp would sound with a standard Marshall preamp design as used in those 18 watt builds.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 29 Apr 2015, 05:09

Matec,

I used google translate to read the original discussion on other forum.

I also listened to sound samples of the Marshall 1 watt amps. The JCM-1 was my first choice. I think I will build this amp. Would you happen to have a schematic drawn without the external tone boards? I plan to use a turret board, and would find it easier looking at a schematic with components shown fully connected instead of routed to other boards. Thank you!
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Re: Marshall JCM1H or JTM1H schematics

Postby HTH » 29 Apr 2015, 13:04

mavrim wrote:Thank you for clarifying! Still undecided if I build JTM circuit or combine output section with another preamp design. I wondered how the amp would sound with a standard Marshall preamp design as used in those 18 watt builds.


When I was messing around with the 1w output stage maybe 4-5 years back (back in the 'sewatt' forum days) I found I could bolt the 1w push-pull output stage on any preamp stage with no problem. You may need to tweak a little to your taste, but thats par for the course when building your own amps and pedals (and one of the major benefits as opposed to settling for a tone thats 'almost' perfect).

You could alternatively hook the 12AU7 up single ended (or parallel SE if you want to use both triodes) and you'll get slightly less overall volume - these 1w amps are louder than you think they will be. Maybe toy around with a self-split configuration too as its less efficient.

Lots of possibilities :hmmm: :scratch: :D

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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 29 Apr 2015, 16:23

mavrim wrote:Matec,

I used google translate to read the original discussion on other forum.

I also listened to sound samples of the Marshall 1 watt amps. The JCM-1 was my first choice. I think I will build this amp. Would you happen to have a schematic drawn without the external tone boards? I plan to use a turret board, and would find it easier looking at a schematic with components shown fully connected instead of routed to other boards. Thank you!


Hello mavrim.

I can draw up a scheme with that format. I take a few days. :hmmm:

Cheers.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 29 Apr 2015, 23:03

Thank you Matec!

It is so confusing when looking at the schematic and tone controls are so far from the circuit. Much easier to understand without those tone boards.

For my JCM-1 build, I will be using a gutted Marshall lead 12 chassis/head. I wish it was not inverted like a tub style, but the amp head will look like the real thing when done. Here is what I have done so far! I started with parts for a firefly 1 watt build. Transformer is 22k PP and made for use with 12au7 tube. I had to cut turret board to fit, only have 18 terminals on each side. Have to make everything fit!

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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 30 Apr 2015, 00:06

Hmmm ... 36 terminals is little, but I think you will find a way. :hmmm:

Your project is at least interesting. Are you sure the valves, when in their sockets, will not be very tall? :scratch:
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 30 Apr 2015, 01:01

I have already sold 2 of these type amp conversions that were single ended 1/4 or 1/2 watt. The tubes clear the upper head cabinet. I buy these amps for under $100 and then sell off the pcb to make my cost even less.

On the jcm circuit, that lnd150 fet or transistor is to boost the signal going into the tone stack, right? I may want to omit this or use another tube stage in its place. I have mounts for 4 tubes. Was planning on adding a tube effects loop, but not sure if I really needed that.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 30 Apr 2015, 01:10

Since I don't have a lot of realastate on that turret board, I probably should stay with the mahaffay plexi preamp circuit and feed that into the Marshall 1 watt output stage. Online the jcm-1 sounded incredible! I have one 10" celestion mounted into the matching slant cabinet. I found that I preferred the cheaper China celestion ten thirty speaker over the stock celestion.
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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 30 Apr 2015, 01:40

mavrim wrote:On the jcm circuit, that lnd150 fet or transistor is to boost the signal going into the tone stack, right? I may want to omit this or use another tube stage in its place. I have mounts for 4 tubes. Was planning on adding a tube effects loop, but not sure if I really needed that.


The lnd150 prevents a part of the signal is lost, among other things. You can use without it, but the sound will be different. An effects loop would be something that many JCM1 owners would like. All tube so ... :horsey:

Cheers
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Re: Marshall JCM1H or JTM1H schematics

Postby HTH » 30 Apr 2015, 17:05

mavrim wrote:Since I don't have a lot of realastate on that turret board, I probably should stay with the mahaffay plexi preamp circuit and feed that into the Marshall 1 watt output stage. Online the jcm-1 sounded incredible! I have one 10" celestion mounted into the matching slant cabinet. I found that I preferred the cheaper China celestion ten thirty speaker over the stock celestion.


Nice tidy work, but just wondering why you don't mount the transformers on the other side of the chassis like all other valve amps. Same with the valve bases - use a chassis punch and mount them the normal way. I'd probably avoid punching the chassis for the can caps as holes that big are a pita to do - especially in those old steel chassis that Marshall had (I've done a SS-tube conversion too).
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 30 Apr 2015, 22:57

Nice tidy work, but just wondering why you don't mount the transformers on the other side of the chassis like all other valve amps. Same with the valve bases - use a chassis punch and mount them the normal way. I'd probably avoid punching the chassis for the can caps as holes that big are a pita to do - especially in those old steel chassis that Marshall had (I've done a SS-tube conversion too).


Thank you!

Marshall made tub style chassis for their solid state amp lineup. If I flipped the chassis over, the front and rear panels would be upside down. I have seen where people have made a top plate, but still hard to work from the back. When done, know one will know it is a tub style chassis. These 80's vintage heads offer that true Marshall look in a smaller scale.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 30 Apr 2015, 23:06

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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 30 Apr 2015, 23:17

This is my 1/4 watt plexi single ended tube amp built into a gutted Marshall G-10 combo.

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Re: Marshall JCM1H or JTM1H schematics

Postby sturgeo » 03 May 2015, 10:16

Did you stick with the JCM1 build or do the mahaffay plexi preamp? Any gut shots and did you stick with the transformers pictured?
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 03 May 2015, 18:02

sturgeo wrote:Did you stick with the JCM1 build or do the mahaffay plexi preamp? Any gut shots and did you stick with the transformers pictured?


That amp is my combo build. The other amp has not been built yet. I just showed the parts layout. I started laying out the turret board. It will be the mahaffay preamp with Marshall 1 watt output stage.
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 03 May 2015, 18:08

image.jpg


That's all I did so far with the turret board.
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Re: Marshall JCM1H or JTM1H schematics

Postby Matec » 03 May 2015, 22:42

Hello mavrim.

Here's JCM1 scheme without connectors or auxiliary boards.

It is only the circuit. As you can see, it's not a very simple circuit.


Good luck.
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Re: Marshall JCM1H or JTM1H schematics

Postby cassoulet » 14 May 2015, 16:29

Hi everyone,

Here is my own redrawn JCM1 schematic, from Matec's original. Details such as heaters and grounding are omitted on purpose to help clarify. Hope this helps.

JCM1.png


I also did the same kind of redraw for Matec's JTM1-HTM1. Here it is:

JTM1-HTM1.png


Hope this helps. Please let me know if anything is wrong. Matec, thanks again for your work.

Cheers
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Re: Marshall JCM1H or JTM1H schematics

Postby mavrim » 18 May 2015, 19:28

cassoulet wrote:Hi everyone,

Here is my own redrawn JCM1 schematic, from Matec's original. Details such as heaters and grounding are omitted on purpose to help clarify. Hope this helps.


Awesome, makes it so much easier to understand! I am still working on my amp build. I used the mahaffay preamp with the jtm-1 output stage. Much less components.
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