DIY Brit Module Mod (gain stage add/remove , gain boost)

[matam]

Here's a mod for every Brit PCB (plexi, Sl+, Ultra etc.).
What i've done is put 2 switch (spdt On/On) to add a gain boost and a "channel switching" between hotrodded plexi mode and hotrodded jcm800 mode.
I tried to make it as simple as possible without cutting/rerouting traces on the pcb so it could be done by everyone who is cabaple to desolder/solder component without damaging the PCB itself;
if you're not happy or don't like how the mod sound you could roll it back to stock.

I thake no responsibility if you damage the pcb/module in the process, so do it only if you are comfortable with a soldering iron.


First a brief explanation of the mod:

I thake the signal after C3 and reroute to different parts of the board, so we can choose between 3 or 4 gain stage (hotrodded plexi/hotrodded jcm800).

The gain boost is an added resistor that trow part of the signal before the Gain knob to ground.


Here you can take a zip file containg the schematics, a layout of the PCB with the wiring of the 2 switches and a component list.
Where you read "No Parts" it means that if you have a cap, resistor or a bridge in that place you have to remove it.


My pcb Layout is the old Brit Board revision, it was a black stripe plexi module,
if you have the new revision just look at the layout then thake a look at your pcb, it may be a different name but it'll sit in the same spot. (Ex: R31 on old revision = r25 on new revision)

I'm sorry but since i don't have a new revision board i cannot provide a different layout/schematic/part lists for the new pcb revision, but if someone could give me a good picture of the board then...

In the schematic and component list some part of the module circuit are omitted, only the "real" preamp section is described.

The brit module is very nice to work with, this is the simplest way i finded to have switchable gain stages without messing around with added component to the board or cutting/rerouting existing trace.


I'd put some clip also, but i don't have a mic for recording...i'll see if i manage to borrow one.

If you're interested in it i could upload the schematics and board layout of the "general" Brit Module in diptrace format.

 

[tuna141]

Hi,

Welcome to the Board, and thanks for sharing your mod. It looks cool !

Looking forward to hearing the clips....

 

[matam]

Hi,

Welcome to the Board, and thanks for sharing your mod. It looks cool !

Looking forward to hearing the clips....

Thanks!

Tomorrow i'll upload a clip, too bad i couldn't manage to borrow a mic to record it properly.

I found a nice picture of the new revision board, so i'll upload an alternate schematic/part list file.

edit:

Here's the file for the new revision board (taken from a 1086 picture)
I couldn't figure where R18 is connected, but i think i get R23 right. (if someone is kind enough to check i'd really appreciate it)
With a picture of the bottom of the board i could trace the missing parts.

Clip coming later in the evening (CET).


reedit:

Heres the link to a youtube video

I play a couple of chord first with the plexi channel (green light) with gain boost off then on, then i switch to JCM800 channel (red light) and do the same: boost off then on.

Gain it's @ 9:30/10 on the module all the time, EQ and level @ 12:00.
Master an hair less than 9:00, presence 2:00 density 9:00.

The signal chain is:
Gibson Explorer Goth II with EMG 85/81 -> RM100 -> 2x15 (Eminence speaker, dunno wich one) thanks to my friend who plais bass in our band.
No effect or pedal used.
Module has 2x JJ ECC83S and the head have almost new EH EL34 (biased @ 32)

Sorry for the sloppy plaing and for the infamous recording quality.

 

[tuna141]

Sounds pretty good. All the modes have good gain and tone variation - especially the first 3 modes. You can hear the incremental gain increase as you step through the modes.

Since you left the tone controls the same for the demo, I'm sure you can get each mode to sound even better by tweaking the tone controls.

I'll have to give this mod a try when I get some free time. Thanks again for sharing.

 

[matam]

I managed to borrow a Shure SM58 so i'll redo a proper recording, the sound coming from my camera mic is very thin compared to the "live" sound and it add also some distorsion.
With the gain @ 9:30/10 in plexi mode with or without the gainboost engaged the module produce a very clean sound (a little on the edge with the gain boost on but still clean), in the video it seem it got always some distorsion...

Here's a little add-on for the mod, a tone stack switch between the two famous combo of 56K 250pF and 33K 500pF for the slope resitor and the bright cap.

When the switch is engaged the two component are added in parallel to the one present in the PCB, the resistance is lowered to 33K while te capacitance is doubled to 500pF.
Wiring is done this way beacause having always a cap and a resistor on board eliminates any switching noise.

I also studied a solution for changing the C3 cap when you change between plexi and jcm800 mode (3/4 gain stages) to have a little more lowend on the lower gain channel.
It can be done using a DPDT switch that does both channel and cap switching; i like this idea more than adding another switch only for the C3 cap changes.

I suggest you to add a 2200pF/0.0022uF cap there but you can experiment with higer value parts, my stock plexi module had a 0.022uF cap mounted on C3.

 

[Jacksauce]

Wow, incredible work - thank you! I'd be very interested in seeing the Brit Module in diptrace format

 

[matam]

Wow, incredible work - thank you! I'd be very interested in seeing the Brit Module in diptrace format

Sorry for the late answer, i was kinda busy these days;

Here you can find the schematics for the mod in diptrace format, and this is the custom library i've used for the drawing.

You could check, if interested, the other mod made for the XTC.

 

[Jacksauce]

Both are impressive and very well documented. Thanks Matam!