COMPLETE Rockman Ultimatum

Tantalums! You sir, are a radical. And Cyber, thanks for the blowback. If mine is any indication of the original it seems that the the compression is quite a bit relaxed from the Rockman and not in a bad way if used as a pedal. Part of the problem of using a RM thru an amp was the noise was horrendous. Probably my best recorded solo was back in the day and into a Rockman patched direct into a Tascam 4 track.

I'm really intrigued by the Acoustic now that I have a better understanding. It would seem that the grey button (SRD) is better than the blue button (Dunlop) but by most accounts is open to the unicorn factor. I'm busy boxing mine up with Robert's relay bypass but have been tempted to snag an Acoustic from eBay and toss it Robert's way.
 
fig said:
I see my MaryAnn walking awayyyyyyyyy….ahhhhhhhhh…AHHHHHHHHHHH [blood vessel bursts in forehead]


uYxO8cH.jpg


Robert
🤘
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I rarely listen to the radio in the car, but I did yesterday and this song was playing when I turned on the radio. I tried to sing along, but...

mars-attack-21.gif


...burst a blood vessel.





Just ordered my PCB for it...
 
Cybercow said:
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.
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If you are referring to X100 Rev10, I have to point out that the compressor most definitely does not remain consistent for all four modes. In DIST and EDGE, it is almost completely disabled (turned into a fixed gain stage) by biasing the JFET gate to around -1V (via the R175-R176 divider and through D117). This isn't just me looking at the schematic -- I also confirmed it by measurements on the bench. In DIST and EDGE, the compressor gain is pretty much constant (about 1+R104/R105) at almost any input level.

This part of the circuit (resistive divider) was not present in rev9 and earlier, and I'm not a fan of it -- I want my compressor on in all modes. It just feels better to play.
 

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JTEX said:
If you are referring to X100 Rev10, I have to point out that the compressor most definitely does not remain consistent for all four modes. In DIST and EDGE, it is almost completely disabled (turned into a fixed gain stage) by biasing the JFET gate to around -1V (via the R175-R176 divider and through D117). This isn't just me looking at the schematic -- I also confirmed it by measurements on the bench. In DIST and EDGE, the compressor gain is pretty much constant (about 1+R104/R105) at almost any input level.

This part of the circuit (resistive divider) was not present in rev9 and earlier, and I'm not a fan of it -- I want my compressor on in all modes. It just feels better to play.
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No argument here. The compressor is always on in the X100 rev 10. But in CLN1 & CLN2 modes, it becomes a more dynamic compressor when R174 (3K3) is added in parallel to R175 (12K), thus changing the bias level to accept the dynamic changes in the incoming signal. Did I miss something?
 
Cybercow said:
No argument here. The compressor is always on in the X100 rev 10. But in CLN1 & CLN2 modes, it becomes a more dynamic compressor when R174 (3K3) is added in parallel to R175 (12K), thus changing the bias level to accept the dynamic changes in the incoming signal. Did I miss something?
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No, that's how I see it too. It's just that you said something along the lines of "the X100 compressor stays constant in all modes", and at least in Rev 10, it does not. They used a different mechanism in earlier revisions, adding a resistor in series with the JFET, which reduced the maximum compressor gain in Dist and Edge. But Rev 10 takes it further, by almost completely disabling the comp in dist and edge. It barely kicks in with VERY loud input level.
 
Sorry for the unrelated questions but I see the experts are in the building at the moment. I had to order some of the exotic resistor values and accidentally got 1/8 watt. Is that ok in this circuit?

And as for the red, clipping LED's. I've got the red diffused from tayda on hand, are they in the ballpark or should i seek out diodes with a higher/lower Vf?
 
Roberman said:
Awesome! Thanks
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FWIV, the original LEDs have a Vf of around 1.6V. Most modern red LEDs are closer to 2V. I am currently playing with a 2V LED in series with one or two Schottky diodes. Experiment! Nothing will burn. (famous last words).
 
JTEX said:
No, that's how I see it too. It's just that you said something along the lines of "the X100 compressor stays constant in all modes", and at least in Rev 10, it does not. They used a different mechanism in earlier revisions, adding a resistor in series with the JFET, which reduced the maximum compressor gain in Dist and Edge. But Rev 10 takes it further, by almost completely disabling the comp in dist and edge. It barely kicks in with VERY loud input level.
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There is something else going on we can't see. If you add a pot in series with the 390ohm resistor that sets the attack time and set the pot where the attack time is so high the compressor never compresses you get just the extra gain characteristics in the DST. setting. Interestingly you can hear a difference. Its subtle but still enough to where you can hear it.
If there is one thing I have learned in the past several years of reverse engineering the rockman circuit there are lots of clever little Easter eggs happening that when looked at on paper and even measured make absolutely no sense.
 
drgonzo1969 said:
Interesting. do you notice a drastic difference when running it at 18v?
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I notice no audible difference when running at 18V, 12V or 9V.

Robert and I traced the Ultimatum at about the same time and we compared notes. And when I breadboarded the entire circuit, I ran it at each of three voltages and heard no difference. When I built several of them into enclosures (using Robert's "Proposition" PCBs, I ran them again at the 3 different voltages and heard no difference.
 
Cybercow said:
I notice no audible difference when running at 18V, 12V or 9V.

Robert and I traced the Ultimatum at about the same time and we compared notes. And when I breadboarded the entire circuit, I ran it at each of three voltages and heard no difference. When I built several of them into enclosures (using Robert's "Proposition" PCBs, I ran them again at the 3 different voltages and heard no difference.
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Thanks. I’m about to build my second proposition and I was curious.
 
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