Marshall 1987x rebuild

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Alfi27
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Marshall 1987x rebuild

Post by Alfi27 » Sun Apr 29, 2018 4:33 pm

Hello guys! This is my first post here, decided to register as I have heard that there's a lot of people with insane amounts of knowledge on here, and have also read more than a few interesting topics.

I currently have a Marshall 1987x, which is a cool amp but it's a one trick pony to put it mildly... The volume/gain sounds good at one point only, where the bright cap is perfectly blended in/out. And with the bright cap disengaged it can get some cool clean tones, but that's about it. Back in Norway I have a Ceriatone 2204, and it's the best amp I've ever had. After inspecting PTP layouts of both amps it's clear that they are very similar, and the 2203x utilises the exact same PCB as the 1987x. The problem is that I am quite the noob, when I see a circuit diagram just showing where the signal goes I get completely confused and I don't have the time to learn it at this time, busy times and all that. I plan on eventually learning it, but I would prefer to not spend months reading up and down and sideways to do a small modification that I know I have the physical skills to do, I just don't know exactly what to do. Also I vastly prefer the learning-by-doing approach :mrgreen:

So I was wondering, do any of you have, could make or know anyone who could make kind of a a step for step guide to what I have to do to convert the amp into a 2204 with the existing PCB? I was initially considering converting it to PTP, but that is quite expensive and seems unnecessary at this point. Turning the existing PCB into a 2204 shouldn't cost more than £10 tops, so if i want to turn it into PTP for modification purposes later it's not loads of money lost.

PS: this isn't a pristine clean, mint condition 1987x. It has already been modified with a fat switch, bright cap switch, one wire mod (on a switch as well) and a PPIMV, but I intend to reverse all of it and replace the fx loop with a NFB knob and something else. Just so you know that I'm not gonna ruin a relatively valuable amp (although it's not even worth that much in stock and mint condition, here in the UK).
Last edited by Alfi27 on Sun Apr 29, 2018 7:34 pm, edited 1 time in total.

danman
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Re: Marshall 1987x rebuild

Post by danman » Sun Apr 29, 2018 7:16 pm

To make the 1987 a 2204 would also require some rewiring of the inputs since your amp is a 4-holer. You could do a one wire mod which will cascade the circuit just like the 2204 does. Our member "neikeel" also has a layout for a switchable 1987/2204 mod but I can't seem to locate it right now. Maybe he will show up soon and post it for you.

Alfi27
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Re: Marshall 1987x rebuild

Post by Alfi27 » Sun Apr 29, 2018 7:33 pm

danman wrote:
Sun Apr 29, 2018 7:16 pm
To make the 1987 a 2204 would also require some rewiring of the inputs since your amp is a 4-holer. You could do a one wire mod which will cascade the circuit just like the 2204 does. Our member "neikeel" also has a layout for a switchable 1987/2204 mod but I can't seem to locate it right now. Maybe he will show up soon and post it for you.
Thank you! The amp already has a one wire mod, but it's way too bright sounding and has some serious oscillation issues. I have to completely retweak the amp going from stock mode to the one wire mod and with treble and presence at zero it's still way too bright and brash. A switchable 1987/2204 would have been really cool, if it's actually an authentic 2204 circuit and not just a switchable one wire mod. In my opinion a 2204 with the bright cap disengaged can get really good lower gain tones similar to the 1987x though, but perhaps not clean without using the low sensitivity input or rolling off a bit on the guitar.

danman
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Re: Marshall 1987x rebuild

Post by danman » Mon Apr 30, 2018 9:03 pm

I saw your thread over at ampgarage but it will be easier to explain this here. The two circuits are very similar except for the wiring at the input jacks and v1 socket. If you compare layouts to both amps, you will see the difference in wiring at the input jacks and v1. The circuit boards used were also the same between the models on the earlier amps but i'm not sure if that is the case with the 1987x. If you study the board closely and look at the traces between the components, you will see that it basically follows the exact same path as the early amps with turret boards. Compare this to the layouts online and you will begin to see how the parts connect. I will link you to two layouts that you can follow. The two circuits are extremely similar but trying to explain the process in words would be very difficult. Here are the layouts and a link to instructions for a 2203 build which has an identical preamp to the 2204. It may help you with the build...http://www.mediafire.com/file/a762d69ga ... df.....The instructions are from the Valvestorm website which sells master volume kits in the vein of the old Metroamp kits.

danman
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Re: Marshall 1987x rebuild

Post by danman » Mon Apr 30, 2018 9:05 pm


danman
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Re: Marshall 1987x rebuild

Post by danman » Mon Apr 30, 2018 9:05 pm


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neikeel
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Re: Marshall 1987x rebuild

Post by neikeel » Tue May 01, 2018 4:00 am

This is the BEST method of getting flexibility form this amp, just the V1 bits

It is easy and is reversible, minimum parts, keep te wiring neat and it works well

use a 100pF 'bright cap for the 1987 (NMV side)

Image

http://www.marshallforum.com/media/neil ... .9247/full
Neil

Alfi27
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Re: Marshall 1987x rebuild

Post by Alfi27 » Thu May 03, 2018 8:13 am

Thanks man! I decided to try to turn it into a plain 2204 first, as it would be simpler and cheaper. When I say try, I mean it didn't work as expected when I wired it all up... The low sensitivity input doesn't work which obviously make the high sensitivity input compromised, it sounds "broken" in lack of a better word, and a huge lack of gain. Inspecting all the layouts they have some kind of nut that is probably a shield of some sort, but my amp doesn't have that and neither do the countless 2203 and 2203x I found gut shots off. There is a wire going across all the pots for grounding and it seems like a point on that wire was used instead of an actual shield. The two wires I'm unsure of are both supposed to go to that shielding nut... All of the pots work as they should so I probably only made on or two mistakes, but I have no clue what that or those two are.

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Re: Marshall 1987x rebuild

Post by Greg_L » Sat May 12, 2018 1:25 am

Alfi27 wrote:
Thu May 03, 2018 8:13 am
Thanks man! I decided to try to turn it into a plain 2204 first, as it would be simpler and cheaper. When I say try, I mean it didn't work as expected when I wired it all up... The low sensitivity input doesn't work which obviously make the high sensitivity input compromised, it sounds "broken" in lack of a better word, and a huge lack of gain. Inspecting all the layouts they have some kind of nut that is probably a shield of some sort, but my amp doesn't have that and neither do the countless 2203 and 2203x I found gut shots off. There is a wire going across all the pots for grounding and it seems like a point on that wire was used instead of an actual shield. The two wires I'm unsure of are both supposed to go to that shielding nut... All of the pots work as they should so I probably only made on or two mistakes, but I have no clue what that or those two are.
I did neikeel's 2204/1987x layout on a push/pull pot. Works beautifully. I love it. Follow the layout and be very careful with your lead dress and it'll work great.

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