Some Rockman X100 Mods

[Eb7+9]

I'm posting this to assist those wishing to add flexibility to their X100 unit ...

My goal was threefold: to provide generalized routing between the front-end circuit blocks and filters for yielding new tone flavors, to provide some parametric tweaks in a few key places (front-end gain, compression threshold, plus chorus speed and wet/dry mix), and the option of using essential Comp/Distortion circuits without either Chorus or Verb for better overall Signal-to-Noise ...

My mods focus on the primary board which holds the Compressor/Limiter, Distortion, Timed Gate (ignored) and Doubler/Chorus circuits - the second board holds the reverb circuit which I'm discarding even though it's quite an interesting circuit ... refer to US Patent number 4584700 for a block description of the X100 ... some of the lingo in the patent is intentionally misleading it seems - similarly, the schematic description of the compressor and fuzz blocks are unlike what's on the board like I said previously, while the other circuits in the Patent text are fairly close or identical to what's on the actual board ...

Primary board picture - note: (i) jack and switch labels match Patent jack/switch numbering, (ii) flex cable order matches Patent bus numbering, (iii) only VR101 and R163 are removed at this point ... VR101 sets gain in first inter-stage AC divider network, while R163 sets the speed of Doubler/Chorus ...



The next two pictures are flipped so you can more easily visualize the connectivity of the components over the traces - see my work-sheet at the bottom ...



this next BW drawing is what I used to doodle on ...take out your color markers !



The next hand-drawn schematic shows parts of the corrected Comp/Limiter and Distortion circuit minus the component value plus the resulting circuit with my mods in place ... so this schematic is not exactly representative of the board circuit - please note these are just my own rough notes detailing  my mods ... maybe someone can come up with a better drawn version with the distortion circuit values filled in ...

http://www.lynx.net/~jc/x100modSchem.gif

Notice the low-pass network before the distortion circuit, this part of the circuit is responsible for giving a cleaner clipping waveform as per Tom's explanations ... incidentally, this circuit block alone will not give the characteristic Boston sound, it's meant to be pre-filtered by the AC divider sitting before the comp circuit so together they produce an overall BP response prior to clipping ... note also that the variable eq in the Patent's Comp circuit is missing on the board ...

In my modded circuit I use a 25k bias pot on the Limiter FET to replace the stock  12k/3k switched combo found on the board - I wanted to go below 3k and above 12k to see what would happen, this is probably not optimum ...you'll have to follow what's on the board to understand what I mean ... in particular that 3k resistor in one switch position ties the bottom part of the interstage AC devicer to ground (actually it does very little in that position) and in the other position shorts out the said 12k bias resistor ... not sure why it was done this way ...

the gain trim has been replaced by 250k (forget what the original was) - 100k is probably plenty, this gives lots more gain - driving the comp and fuzz harder ... gives a variety of interesting variations in front-end circuit behavior ... btw, because there's no linearizing resistors across the Limiter FET the comp circuit can get fairly dirty - which accounts for the gritty sound quality in the first two gain position (fuzz is bypassed in those two positions) ... the increased gain trimmer and variable threshold on the limiter FET allows for more overall dirt in that mode ...

the routing options are fairly simple as they allow for filter and gain combos not available in the stock unit ... here I'm allowing for switchig between chorus and non-chorus modes with output volume pots from each feed - reason being the complexe filter and bypassed output levels as well as doubler outputs give signals of varying compatibility, so if one were to use footswitches to toggle the chorus circuit these pots could be used to even out the outputs, plus there's a mix control for blending amounts of wetness on the chorus ... the output controls are also useful depending on how much input gain is produced by the increased trimmer replacement pot ...

The chorus speed resistor R163 is given a high value to produce a high speed "warble" limit - there's other ways of modding this circuit but I think it's the most straightforward ... having it go close to zero in resistance also allows the Chorus circuit to go quite a bit slower than stock - yielding a subtle effect ...

I'm including my work-sheet (1.6Meg) - no doubt, it's quite the mess ... was never meant for public consumption ...

http://www.lynx.net/~jc/x100mainBoardComponents.gif

let me know if/what needs clarifying ...

~jc

[Steve Newton]

Cool! I have a spare X100. My original one has gone into one of those aftermarket "rockmount" rack cases. And the one that came in that is now floating around doing nothing. My original one is less less flakey so I swapped them over.

I had thought about opening the spare up. It would be nice to access the individual circuit blocks and be able to combine them in different ways. And add more variable control, better quality jacks etc.

[uberchoob]

Hi!

     I just bought a x100 off ebay and I'm itching to use it, but I have a feeling I wont be satisfied with the tweakability this unit offers.  You've got some awsome ideas for the rockman, but I was wondering, do you think you could provide us a couple pictures, inside and out, of your finished mods??  It's kind of a stretch, but if you happen to have a full schematics chart/service manual, I could really use it.  Thanks!

     uberchoob

[Dave_B]

It's kind of a stretch, but if you happen to have a full schematics chart/service manual, I could really use it.  Thanks!

That might be a tall order.  I had to send mine back to SRD when the reverb died in the late 80's.  I couldn't get it fixed locally.

[uberchoob]

I guess what I really want is just some information/guide on how to ad pots, etc., to make things adjustable, such as the echo (delay time), chorus (depth/rate), compression/limit, distortion, and output levels, etc. .  Perhaps even an EQ circuit as well?
I really am a newb in this area, so I can't really make heads or tails of this thread.  I guess the first step would be to take a look at the original patent (and learn how to read schematics  ).
I know people have done it in the past, but I doubt that anyone that has is surfin' the web for threads like these.
Any help would be great.  Thanks!

     Uberchoob

P.S.  If anyone knows how to effectivly run one of these things through a set of speakers, please share your knowledge!!

[the4thmark]

I'm posting this to assist those wishing to add flexibility to their X100 unit ...

I know this post is about 4 years old, I stumbled upon it while searching the web. is there any way you could helpfully post some pictures of the other board in the rockman? also, could you help me identify the components that cant be seen clearly? thanks in advance!

[John Lyons]

Your best bet would be to get a hold of JC via his site viva analog.
(unless he see's the post here...)

[Eb7+9]

Hi John and friends of the X100,

I keep getting emails from interested musos on this ...
and I must apologize for not finishing what I started

I unf. recycled the board last summer after finding myself w a small mountain
of electronics w nobody to pass it off to ... so, it's gone now
but if I had time for it I would have ripped up a few caps that were installed
face down to keep the values hidden ... sorry for the bad news

maybe somebody's damaged board can be used
to fully reverse it one day ...

there are a number of patents to be found on this circuit and its derivatives (...?)
w intentional misleading info/values here and there

4,584,700 primary patent
check out 5,133,015 to compare values (I forget if this is right)
please double check

that's all I can offer at this point ...
if anybody decides to jump in pm-me here if you want

thx // gd luck
~jcm
http://www.lynx.net/~jc/pedalsX100.html

[jimitrader]

could i get a quick answer on this unit? in the photo of the board it shows some leds does anyone know the size? they seem smaller than 3mm?

[Cybercow]

could i get a quick answer on this unit? in the photo of the board it shows some leds does anyone know the size? they seem smaller than 3mm?

Yes, the LEDs in an X100 are 3mm.