Aquaticwombat
Member
My friend's dad is convinced it is the greatest distortion of all time. I think he might be a Boston fan.
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COMPLETE Rockman Ultimatum
- Thread starter Aquaticwombat
- Start date
Cybercow
Well-known member
I've conducted a lot of testing with the Rockman X100 compressor section and the Rockman Ultimatum Distortion Generator compressor section. And while they both have quite similar biasing configurations, it's the X100 that is far more fussy about biasing the JFET. In the X100, the JFET must be hand selected for a Vgs(Off) of between -0.88v and -1.05v - and in addition to the hand selected Vgs(Off) parameters, the biasing resistors often had to be adjust to get the test point to measure very near 2.65v (±0.25v) where the input is 1v PtP @ 1K Hz.
Because the Ultimatum's compressor only comes into action when the gain control is turned up, the parameters for setting up the compressor is not nearly as demanding. While the target Vgs(Off) range is virtually the same, the biasing resistors can both remain at the BOM specified 5.1M Ω - unless the selected JFET is outside the -0.88v and -1.05v Vgs(Off) range. The X100 is set up so the compressor is always on and remains consistent for each of the four modes - DIST/EDGE/CLN1/CLN2. The Ultimatum has no mode options and the compressor is integrated directly into the first gain stage of the circuit.
Because the Ultimatum's compressor only comes into action when the gain control is turned up, the parameters for setting up the compressor is not nearly as demanding. While the target Vgs(Off) range is virtually the same, the biasing resistors can both remain at the BOM specified 5.1M Ω - unless the selected JFET is outside the -0.88v and -1.05v Vgs(Off) range. The X100 is set up so the compressor is always on and remains consistent for each of the four modes - DIST/EDGE/CLN1/CLN2. The Ultimatum has no mode options and the compressor is integrated directly into the first gain stage of the circuit.
Throwing all caution to the wind (which is typically how I roll anyway) I soldered in a random smd J201 and went with PPCB's 5.1M for RB1 and 6.2M for RB2 and it sounds crazy close. The comp is definitely working. It sounds dead on to the X now into a clean solid state amp. The comp tends to suck out the bottom end a bit (per the original) so it might be worth exploring having the comp switchable. Without it the pedal has a bit more oomph but sounds less like a Rockman.
Now the big question is...did the Acoustic pedal from the same series mimic the CLN1/CLN2 settings?
The fact that I could pull all these parts out of my stash is a bit disturbing but outside of sweating the comp details this was a most enjoyable build. Now if only I had a 1590BB kicking around...
Now the big question is...did the Acoustic pedal from the same series mimic the CLN1/CLN2 settings?
The fact that I could pull all these parts out of my stash is a bit disturbing but outside of sweating the comp details this was a most enjoyable build. Now if only I had a 1590BB kicking around...
Bricksnbeatles
Member known well
Afaik it’s its own thing. I think just some EQ, yk? I think I wish listed it a while back since it’s a cool sound, but it’s nothing too special. I’ll probably buy one someday if I can get it cheap, just for the cool factor. But I’ve played thru one at a guitar fair once, and it was pretty much just an EQ afaik
Robert
Reverse Engineer
The compressor can be made variable but I wanted to keep things as close to stock as possible on this one. It'd be fairly easy to hack one in offboard though, since there's plenty of room for an additional knob.
I want to say the acoustic pedal uses a BBD for some sort of notch filter, but I may be confusing it with something else.
Cybercow
Well-known member
Gordo - based on what I've heard from other Rockman gear heads, is that the Rockman Acoustic pedal is supposedly the exact same CLN2 setting of the Rockman Sustainor without the bells and whistles like smart gate, phase notcher, etc
JTEX
Well-known member
That would make sense, as CLN2 sounds like an acoustic guitar simulator to me.
Cybercow
Well-known member
I tried making the compressor "variable" in this circuit when I breadboarded it. But it's different from the compressor in the X100 in that the gain of the associated opamp is fixed with a 160K neg feedback resistor in the X100. (Tom did the X100 that way in order for the compressor to work consistently in all four 'Modes' of that circuit. And that fixed gain tends to allow the compression to be varied by simply adding a B250K pot (in rheostat fashion) between the output of the Gain opamp and where the compressor section meet at the 470Ω resistor. (In the X100, that resistor is 390Ω)
In the Ultimatum, the neg feedback loop incorporates a filter that (if I've used the correct RC filter calculations) has a frequency knee at ~720Hz - and with the Ultimatum's compression section integrated into the configuration, the compression seems to activate only as the "Gain" control is turned up. The compression is far less evident as the Gain is turned down.
At least, those are my observations between the Ultimatum and the X100.
fig
Village Idiot
Yep. Vishay. There are a couple of SMs in there as well.
