Rockman X100 - Make it a DIY Pedal

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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Carvindc125
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Post by Carvindc125 »

jarrodthebobo wrote: 05 Dec 2020, 12:43
Carvindc125 wrote: 05 Dec 2020, 05:34
jarrodthebobo wrote: 04 Dec 2020, 23:48 Just a heads up;

100% do not try and sub the 2n4339 in this circuit for other fets; I finally caved and purchased a couple and the difference in performance is rather dramatic (and much easier to bias now). I had 100% confidence that a j201 would be a suitable replacment for the 2n4339 since their data specs are quite close in terms of cutoff voltage and such but, save yourself the frustrations of trying to throw something. Upon plopping this tranny in, even without rebiasing it initially, the compression circuit works a hell of a lot better, the distortion 'feels' better under the fingers, less pumping artifacts, more natural decay, and for some reason, more highend (no idea why but a blanket has been lifted so to speak), although I'm not sure if the high end being reintroduced has something to do with the clipping circuit perhaps seeing a more appropriate signal, or the jfet itself having some sort of odd effect.
Nice! Thanks for the heads up.
Did you use a 10M trim/pot to bias?
I had used a combo of 2meg trimpots and 5.6m resistors in series with them in replacement of the two biasing resistors that go to the transistors in order to have a finer level of control over the bias selection. I also tacked on some 2meg resistors in parallel to try and see if dropping the overall values of the bias resistors made a change for the better for alternative jfets but it didn't for the most part.

The other bias method should be sufficient, but two trimpots just gives you the ability to drop pretty much anything in the circuit and get it 'working' at least :mrgreen:
WOW! It looks like you can still get that JFET but it cost around $12.00!!!! They are a lot cheaper on ebay but you risk fakes.... :?
I agree with you something about the arrangement with that particular JFET brings in the "Sparkle" using any other JFET sounds dull.
Interesting. But dang between that and the mn007 chip your going to be $24.00 out just on two chips!
Ive heard chorus pedals that sound very close to the "Normal" setting on a Rockman so perhaps some breadboarding is in order. If the effect can be mimic with just a stereo chorus circuit then we will drastically cut part count down and save some money too.
FYI someone has made a Rockman Distortion Generator in a pedal and it sounds really nice! It lacks the compressor and incredible clean 1&2 sound though.
https://www.youtube.com/watch?v=i_u880r71j8

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Carvindc125
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Post by Carvindc125 »

anyone in this thread is welcome to join our Rockman group on Facebook
https://www.facebook.com/groups/852250755526904

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Carvindc125
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Post by Carvindc125 »

Is R176 mistakenly going to -6V There is no need for a bias resistor when an IC op amp is running in bipolar power mode also this doesn't occur again in the schematic so I was just curious.
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Carvindc125
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Post by Carvindc125 »

Carvindc125 wrote: 09 Dec 2020, 14:20 Is R176 mistakenly going to -6V There is no need for a bias resistor when an IC op amp is running in bipolar power mode also this doesn't occur again in the schematic so I was just curious.
Ok I think it is correct and I think I figured out why its there.
I think its changing the sustain on the Compressor. R176 comes in to play on Clean 1&2 but not in the Edge/DST section so i'm thinking when its added its changing the discharge rate of the diode affectively changing the compressor settings on the Clean tone vs Distortion.

Per Tom Scholz
"The diode and the capacitor are a feedback loop that sends a strong negative voltage when the input signal is strong, thus reducing the gain, and a low negative voltage when the audio signal is low, thus raising the gain."

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Carvindc125
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Post by Carvindc125 »

Have done TONS of research since joining this thread.
I dont have time to elaborate but there are proven mistakes in the rev 10 Schematic on both the Distortion and Clean tone.
Someone had pointed this out after trying to build a rockman from scratch. Here is a Schematic of the ACTUAL preamp an distortion section. The values we changed are good. Just the layout is different and makes both the clean schematic I posted wrong and the distortion schematic OP drew wrong.
NOW R176 connected to -V makes sense! Also the distortion and edge is different C103A, C137 and R177 and only added when Edge is switched on. When distortion is switched on those components are deleted and IC101A becomes a Buffer! IE the left side dist and edge switch are NOT connected together. Please see below and get your breadboards back out!
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FeVeR2112
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Post by FeVeR2112 »

Carvindc125 wrote: 03 Jan 2021, 14:33 Here is a Schematic of the ACTUAL preamp an distortion section. The values we changed are good. Just the layout is different and makes both the clean schematic I posted wrong and the distortion schematic OP drew wrong.
Can you post a corrected schematic? I am unable to see the image you just posted properly (I have vision issues).

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Carvindc125
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Post by Carvindc125 »

FeVeR2112 wrote: 04 Jan 2021, 09:22
Carvindc125 wrote: 03 Jan 2021, 14:33 Here is a Schematic of the ACTUAL preamp an distortion section. The values we changed are good. Just the layout is different and makes both the clean schematic I posted wrong and the distortion schematic OP drew wrong.
Can you post a corrected schematic? I am unable to see the image you just posted properly (I have vision issues).
Sure. I re-drew it peace by peace.
The only difference is I put a 10M trim in place of the two resistors at the JFET.
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Carvindc125
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Post by Carvindc125 »

FeVeR2112 wrote: 04 Jan 2021, 09:22
Carvindc125 wrote: 03 Jan 2021, 14:33 Here is a Schematic of the ACTUAL preamp an distortion section. The values we changed are good. Just the layout is different and makes both the clean schematic I posted wrong and the distortion schematic OP drew wrong.
Can you post a corrected schematic? I am unable to see the image you just posted properly (I have vision issues).
Hey man,
I made a slight change to the schematic as I realized R174-176 could be confusing as drawn so I spaced them out a bit.
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Post by Pedro Yi »

There is an error in this schematic diagram: there is no continuity between diode D117 and resistor R111 - the connection highlighted in green must be removed to have this circuit working, otherwise, it makes no sense. I realized this by comparing the schematic with the copper traces of a real X100 PCB. Just like Leonardo DaVinci, I believe Tom Scholz inserted small errors like these to prevent copycats from replicating his invention at the time.
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Post by Pedro Yi »

This schematic does not show any biasing voltage for the FET - in the original X100 schematic, the 2N4339 FET is biased with negative voltage from the -6 V rail via R176 (33Kohms).
Can you let us know whether this circuit has been verified on a breadboard? In theory, the negative cycles from the output of the op-amp could trigger the FET, but I think the FET would lag in attack time - the reason for biasing is to keep the FET somewhere within its "on" region so it rapidly reacts to any incoming signal. Feel free to correct me if I'm wrong.
Thanks.
Last edited by Pedro Yi on 12 Jan 2021, 06:57, edited 1 time in total.

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Post by Pedro Yi »

I don't think it is a mistake because the 2N4339 is an N-channel FET, which means it needs negative voltage at its gate to drive it towards the maximum pinch-off state (open circuit-like high resistance). My understanding is that it needs a negative voltage biasing to keep the FET within an intermediate region between the "fully on" and "fully off" states, in order to rapidly react to incoming signals from the op-amp output. In theory, the rectified negative portion of the output from the op-amp would be able to drive the FET, but not quick enough to serve the intended compression purpose (?). Also, the error in the same diagram, there is no connection between the resistor R176 and the output of the op-amp (pin 7 of IC101B).

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Post by Pedro Yi »

Carvindc125 wrote: 26 Nov 2020, 21:45 Is the compressor not used when clean 1&2 are engaged? Looking at the schematic it appears the compressor is built into the distortion/edge section and a diode blocks the compressor from hitting the clean circuit.
That is interesting because you hear people talk about how compressed the clean tone sounds on the rockman.
I believe the compressor remains engaged in both clean modes, but at a different setting compared to either Edge or Dist modes - you can conclude that because the biasing voltage for the 2N4339 FET changes as you switch between the clean tones to the distorted ones.

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Post by Pedro Yi »

Carvindc125 wrote: 09 Dec 2020, 19:24
Carvindc125 wrote: 09 Dec 2020, 14:20 Is R176 mistakenly going to -6V There is no need for a bias resistor when an IC op amp is running in bipolar power mode also this doesn't occur again in the schematic so I was just curious.
Ok I think it is correct and I think I figured out why its there.
I think its changing the sustain on the Compressor. R176 comes in to play on Clean 1&2 but not in the Edge/DST section so i'm thinking when its added its changing the discharge rate of the diode affectively changing the compressor settings on the Clean tone vs Distortion.

Per Tom Scholz
"The diode and the capacitor are a feedback loop that sends a strong negative voltage when the input signal is strong, thus reducing the gain, and a low negative voltage when the audio signal is low, thus raising the gain."
I don't think it is a mistake because the 2N4339 is an N-channel FET, which means it needs negative voltage at its gate to drive it towards the maximum pinch-off state (open circuit-like high resistance). My understanding is that it needs a negative voltage biasing to keep the FET within an intermediate region between the "fully on" and "fully off" states, in order to rapidly react to incoming signals from the op-amp output. In theory, the rectified negative portion of the output from the op-amp would be able to drive the FET, but not quick enough to serve the intended compression purpose (?). Also, the error in the same diagram, there is no connection between the resistor R176 and the output of the op-amp (pin 7 of IC101B).

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Post by Carvindc125 »

Pedro Yi wrote: 12 Jan 2021, 07:09
Carvindc125 wrote: 26 Nov 2020, 21:45 Is the compressor not used when clean 1&2 are engaged? Looking at the schematic it appears the compressor is built into the distortion/edge section and a diode blocks the compressor from hitting the clean circuit.
That is interesting because you hear people talk about how compressed the clean tone sounds on the rockman.
I believe the compressor remains engaged in both clean modes, but at a different setting compared to either Edge or Dist modes - you can conclude that because the biasing voltage for the 2N4339 FET changes as you switch between the clean tones to the distorted ones.
Hi Pedro,
This is Josh from the Not Another Rockman Group.
You are replying to some old post.
I posted a corrected version of the schematic same as you. No worries though.
I think the next biggest hurdle is figuring out how to switch the CLN and DST in and out without using one of those slide switches. If you have ANY ideas update here and or in the Not Another Rockman Group.

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Post by phatt »

Rotary sw maybe?
https://www.jaycar.com.au/2-pole-sealed ... y/p/SR1212
Can be preset for 2 pole 2 position to 2 pole 6 position.
I have used these in several builds and work well.
Phil.

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Post by Yazoo55 »

I originally used a slide switch which was unreliable. I ended up using a set of 4 push switches to select between all four settings, the kind which deselects the other switches automatically. On ebay they are called interlock push button switches.

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Post by Carvindc125 »

Yazoo55 wrote: 16 Jan 2021, 00:30 I originally used a slide switch which was unreliable. I ended up using a set of 4 push switches to select between all four settings, the kind which deselects the other switches automatically. On ebay they are called interlock push button switches.
That is a GREAT idea.
Thank You.
On the compressor did you ever get anything else to work really good besides the stock 2n4339? Just curious since 2n4339s are super expensive these days.
I have the stock version breadboarded with a 10M trimmer.
Pin 1 goes to Source Pin 2 goes to Gate and Pin 3 is going out to the Diode/cap network. I haven't had much time to play with it but from what I see the 10M trimmer is the easiest way to get this compressor going so far. The only bad thing is 10M trimpots are hard to come by and are expensive compared to others. Have you found an easier or better way to bias it?

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Post by Yazoo55 »

I only ever used the 2n4339, I’m afraid. I’m not that knowledgeable so I played safe and stuck with this. I originally used 2 separate trimpots with series resistors but I couln’t get this to work. The single trimpot is much easier to use when dialling in the compression.

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Post by Carvindc125 »

bmxguitarsbmx wrote: 03 Nov 2020, 01:50 Connect R105 to R106. R105 is the discharge path to ground for the detector voltage. I made this comment earlier. If you check the PCB layout, you will see that it is so.
I breadboarded the Soloist Compressor last night and got it to fire up.
But I am having an issue. Voltage to the LED will slowly rise and never go down. It just keeps going up slowly.
Oddly the compression effect works fine but eventually I have to disconnect the power supply then turn it back on. The power will go back to 0 and start slowly climbing again. Im afraid to see how high it will go. at 2.0V I pull the plug so the LED doesn't blow.
I built the compressor as drawn below with all spec components including a 2n4339.
I assume my issue is due to no path to ground for DC as you describe.
But Where do you move R105? R105 is 560ohms Its connected to the Source/R106 already, and its helping to set the gain of the op amp.
To my eyes it looks like R111 (56K) should be moved and connected from Source of JFET to Ground? Or from R107 to ground in parallel to the cap?
What do you think? See schematic below.
Anyway any help here would be awesome! If I can fix this LED from trying to blow up I'll have a fully functional compressor!
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Post by Carvindc125 »

Yazoo55 wrote: 21 Jan 2021, 22:41 I only ever used the 2n4339, I’m afraid. I’m not that knowledgeable so I played safe and stuck with this. I originally used 2 separate trimpots with series resistors but I couln’t get this to work. The single trimpot is much easier to use when dialling in the compression.
Did you add a resistor or move one or anything?
I have breadboard the X100 and the soloist compressor they are very similar but in both cases The LED will draw power and that power will steadily increase.

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