I modded my Class 5

Marshall Class 5

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Crunchifyable
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I modded my Class 5

Postby Crunchifyable » 19 Dec 2017, 21:14

After some frustration trying to record with my class 5, I decided to finally mod it.

I added a master volume, a 470pf cap around R14, and a bright input (940pf cap in series with input jack...idea taken from Supro amps to avoid messing with the PCB).

I'm pretty happy with the result. It's not quite the sound of a 2203, but very reminiscent of a plexi. And MUCH brighter than the stock amp.

I hope to add a power amp in (effects return / preamp bypass) next, to work with the 2203 preamp I'm building.

This amp gets most of it's gain from the pre-amp section. In fact all of it really. Cranking the master doesn't really add distortion, just colors the tone.

(about 3 db clean boost)






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Re: I modded my Class 5

Postby djw171 » 02 Jan 2018, 03:57

Any pics of the mods / info re the Master Volume location in the circuit?

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Re: I modded my Class 5

Postby Crunchifyable » 02 Jan 2018, 16:23

This is my mods on a schematic.

Image

I have been playing around with 470pf vs 940pf on input (in series with input). Both seem ok. 470pf is more Marshally (cuts below 720hz IIRC)....940pf in theory matches up with the amp better (similar HPF in later gain stage, 330hz IIRC). I haven't physically added the "bright input" yet but have plans to...in the mean time, allegator clips and 1" guitar leads do my bidding.

I'm also toying with the idea of putting the caps in a pedal...but this amp really needs a high pass filter on input, or near it, to kill the lows that muddy up the gain stages and give it a more vintage tone. Slightly reduces gain a bit, but worth it to me.

The master volume is simply two wires soldered to the opposite legs of R26, attached to a 1meg audio pot (I put in place of the indicator light). I left R26 in place...volume may be reduced a bit but this amp has plenty of power for me.

I added a 470pf over the legs of R14. This is a subtle (3db+) shelving boost of everything over 720hz. But not really enough.

This is all stuff I did while waiting for my amp build components to come. Now I'm working on a 2204/1987 dual.

When that gets done I'll probably get around to the bright input jack drilling and taking more pics.

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Re: I modded my Class 5

Postby 6B4G » 03 Jan 2018, 02:59

There are a number of good mods you can do to this amp, many posted on the internet, however I discovered that there is a German self build company offering a kit called The "Jim", https://www.tube-town.net/cms/?DIY/LoW-Projekte/Jim it contains all the best mods to the amp from the internet, many of which I had done individually to my amp. I enclose the circuit diagram of the German amp as it's really the Class 5 with all the best mods, just review the Marshall Class 5 Circuit to the Jim and then implement the mods that you think you will like, or just do the lot, makes the Class 5 a great little amp when completed. Not sure how they get away with selling this amp as it's identical to a Marshall Class 5 with a few mods here and there. I'm not going to list what all the mods do, there is so much on the net regarding this, all I will say is that if you change your Class 5 to match this circuit you will not regret it one little bit.

The last mod I did was the Master Volume, as the attached diagram, you have to cut the PCB track and use screened cable to the pot wherever you decide to mount it, I put mine on the back panel as I did not want to drill the face-plate. One thing that this mod did which surprised me was to seriously reduce the hum the amp had, it wasn't bad originally, but not good either, inserting the Master Volume mod now makes it very hard to tell when the amp is switched on, great job. Whilst you will never get JCM800 sounds from this amp, it's not designed to be high gain, you can get some nice low volume warm tones from the amp. With all the mods I did, I really like the amp now, it what I always hoped the amp would be, works well with Single Coil or Humbuckers now, before I only liked it with single coil, too muddy and dark for my taste originally. Whilst as always sound is a personal thing, all the mods do make the amp much more flexible than the original Marshall design (sorry Steve - no personal criticism intended).
Attachments
jim-schem_layout.pdf
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Re: I modded my Class 5

Postby surfnorthwest » 03 Jan 2018, 07:56

Your clips sound really good, nice crunch nothing over the top. Thanks for posting.
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Re: I modded my Class 5

Postby Crunchifyable » 03 Jan 2018, 09:03

surfnorthwest wrote:Your clips sound really good, nice crunch nothing over the top. Thanks for posting.


Thanks. All I wanted to do was adjust the "tone" of the amp without trying add anything, and I guess it was successful. There's not a ton of distortion on tap but that's the idea with this amp anyway.

Regarding that German builder, I find it strange that someone would copy the design and sell it (with their modifications), but I guess Steve should feel flattered. Seems like a simplified design.

This is what it looks like now...I may rewire the master wires (I know it looks bad) and tidy things up eventually. I just didn't want to mess with the PCB, so that means a lot of mods are off the table for me, which is fine, I like it as it sounds now. I wanted to keep it very simple.

With the way I set it up, the master does not require editing the PCB or using special wire....it just grounds out more of the signal through an existing pathway.

Image
Image


To get a bright sound I simply wire a cap in series with the input and it sounds much more in line with what you would expect from an old amp, perhaps. Eventually, a separate jack piggy backed off the main input with 470pf or 940 pf capacitance to roll off the low end.

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