Rockman X100 - Make it a DIY Pedal

bmxguitarsbmx · Post by **bmxguitarsbmx** » 03 Nov 2020, 22:45

FeVeR2112 wrote: ↑03 Nov 2020, 05:09
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.
Oh... I see you are referring to the Soloist circuit. I found that schematic and started the comparison. Interesting how the circuit changed in some areas around the compression and EQ.

I will breadboard this X100 circuit and compare to the soloist circuit as well.

Its on the PCB layout of the X100. It is often standard practice to put errors in schematics that are not so large that the device can not be repaired, but are large enough to foil cloning. But, yes! As connected in the soloist.

bmxguitarsbmx · Post by **bmxguitarsbmx** » 03 Nov 2020, 22:49

The "Factory selected to match" resistors are part of the decay circuit, but they are also for cancelling the distortion that the JFET introduces.

jarrodthebobo · Post by **jarrodthebobo** » 04 Nov 2020, 08:49

So I have a odd issue going on here; I've gotten a dirty little veroboard layout going for the first 3 stages, or 1.5 of the 4558s (just ignoring the eq for now), but no signal passes unless I have my input pot set at a very specific sweep.

I have a 10k going to input, but a 250k pot wired as a variable resistor in front of it. Bypassing the pot yields no signal... But if I turn down the volume pot of my guitar, a specific range allows signal to pass again...

Im assuming there is some odd impedance thing I'm missing here but I can't quite figure out what it is.

Also, I have the clipping led diodes on a switch... And when theyre engaged, 1 of them is always lit even without signal passing; which I feel probably indicates some other issue I'm not seeing...

Anyone have any ideas, or where I should be probing voltages and such? I'm getting 9v on the vcc pins so at least it's likely not a PS issue.

deltafred · Post by **deltafred** » 04 Nov 2020, 09:53

As drawn the circuit is designed to run from split supplies (-v. 0v, +v), if you are only using a single 9v supply then the biasing on all 3 opamps will be wrong (biased hard one way) instead of to half supply voltage.

I would AC couple the input (DC coupling is usually not necessary in audio circuits) and create a pseudo 0v (Bias voltage) that all the ground points connect to.

A bit of supply decoupling would also be advisable, something that is often overlooked on pedals.

jarrodthebobo · Post by **jarrodthebobo** » 04 Nov 2020, 13:50

deltafred wrote: ↑04 Nov 2020, 09:53 As drawn the circuit is designed to run from split supplies (-v. 0v, +v), if you are only using a single 9v supply then the biasing on all 3 opamps will be wrong (biased hard one way) instead of to half supply voltage.

I would AC couple the input (DC coupling is usually not necessary in audio circuits) and create a pseudo 0v (Bias voltage) that all the ground points connect to.

A bit of supply decoupling would also be advisable, something that is often overlooked on pedals.

Ahh!! Gotcha! I had no idea that this circuit used a split supply. That makes sense as to why everything is behaving so oddly. I'll be tackling this a bit further along today after all my university classes have ceased. I've never had to create a 'pseudo 0v' in a circuit such as this before as I typically just try and follow the directions correctly the first time around

so this is going to be an interesting little undertaking.

Time to hop back onto the research train I guess!

EDIT: Also, since I'm using a unipolar supply, I HAVE to use an input cap, correct? I may be wrong in my thinking, but I know in terms of power amps if you use a unipolar supply, you need an output cap. Not sure if my thinking is flawed here though; my background is based in pharmacology, electronics is but a passion

ALSO, I have a pot wired up on the supply voltage to act as a divider; the parts I've used in my build are all overkill; including my selected opamps, in order to have the ability to use a higher source voltage; I'm assuming I'd need to generate my bias supply AFTER this pot correct? Would there be any associated consequences towards dropping voltage in this manner (with my fairly robust power supply, and huge 4700uf filter cap)

deltafred · Post by **deltafred** » 05 Nov 2020, 13:30

If your power supply is 30v or less this is what I would do.

Get a couple of 10 to 100k resistors and connect them in series across PSU +ve and PSU 0v. Connect a 10 - 100uF (25v) capacitor across the resistor that is connected to the PSU 0v (-ve side to PSU 0v).

You have now created a pseudo 0v (often called "Bias or Vb" on pedals schematics)

From now on the PSU 0v will be known as -ve supply (because it is more -ve than your pseudo 0v).
The junction of the resistors is the pseudo 0v.
The PSU +ve remains the +ve supply.

Connect a capacitor to the input. For testing purposes anything between 0.1uF and 10uF (25v) will be fine. If you use an electrolytic connect the +ve side to IC1A pin 3.

On your vero isolate the IC -ve supply pins (pin 4) from your signal 0v.

Connect the -ve supply to the IC -ve supply pins (pin 4).
Connect the pseudo 0v to the circuit signal 0v.
Pin 8 of the ICs should already be connect to +ve supply.

To be strictly correct don't leave the inputs of the unused opamp open circuit. Connect pins 6 & 7 together (as a unity gain buffer) and connect pin 5 to pseudo 0v with a 100k resistor (value not critical) to prevent it picking up electrostatic interference.

Double check everything before switching on.
Good luck.

jarrodthebobo · Post by **jarrodthebobo** » 05 Nov 2020, 17:54

Thanks for the additional info!

I realized I was over-complicating things yesterday when I asked that question and completely forgot how easy it is to generate an additional supply voltage via a voltage divider and cap. I usually work with tube circuits (as they're so much easier to work on

) and have had the need to do so within those circuits as well, but felt a similar idea may work a bit differently within the world of small component electronics.

Anyways, I got the circuit to work properly (for a while) yesterday before my constant tinkering (and messy wiring) rendered something that doesn't pass signal, but that was to be expected the way I prototyped this thing. However, before it 'passed away' I was able to get a decently useable distortion tone out of the box, alas with what I perceive as far too much high end cut. I'm not 100% sure if this is just a part of the circuit, or if I used an incorrect value somewhere, but it appears that somewhere between the high and low eq sections of the opamps, there is a great deal of cut to the highs. Taking signal before these two stages yields a very nice, crispy, and SEXY lead tone that appears almost perfectly eq'd (albeit not the rockman/boston tone).

Additionally, I cannot get the compressor circuit to work correctly; I've been messing around with that french rockman compressor circuit that I've seen posted around in order to implement a more common jfet within the compressor circuit, but none of the one's I have tested have yielded a suitable result. I've tried a j201 (the tranny that they used in the documents), 2n5484, 2n5485, 2n5457, j112, j113, and some other random Jfets I've had laying about. Signal passed, the LED that is used in the feedback loop lights when heavy signal passes, and when NOT using an additional 1meg resistor from the wiper of the 1meg pot used in the french article to control compression/bias the jfet, I can turn the GAIN of the circuit down along with volume, but perceived compression does not appear greatly effected. Using that additional 1 meg resistor leads to a pot control that does near nothing, in my build at least. However, I cannot chuck this up to a design flaw just yet, as I DID make an incredibly messy, and super uncoordinated prototype board that was wildly overpopulated and incredibly hard to trace, so the issue was likely my own.

When I finish up some of my other projects I'll be attempting to create small protoboards for each chip in this circuit in order to better diagnose potential issues and maybe implement some cool bypass/switching/channel options.

In further news, the tone stack circuit from the Randall Rg100es seems to work quite well after the rockman circuit in terms of better controlling/eq the overall tone. My values are a bit tweaked from the stock circuit; using a 1k mid pot, 25k treble pot, and 50k bass pot, .44uf bass+mid caps, and 2000pf treb cap (I may have to double check these values, this is just off of memory). I used 2 2n5484s (as I've purchased 50+ of them since I love the way they sound) as seen in the stock Randall Rg100es schematic. I've left out the presence circuit as of now as I'd like to try and implement some sort of active presence control at some point.

deltafred · Post by **deltafred** » 05 Nov 2020, 18:02

Sorry if I explained it as if you were a total noob but on the net you never know the level of knowledge of the person you are talking to.

jarrodthebobo · Post by **jarrodthebobo** » 06 Nov 2020, 02:47

deltafred wrote: ↑05 Nov 2020, 18:02 Sorry if I explained it as if you were a total noob but on the net you never know the level of knowledge of the person you are talking to.

No no not at all!! That bit of information is incredibly important and I'm sure people looking through this thread in the future will get a hell of a lot of help from that write up you put there!

Like I said, I myself completely forgot this was a thing you could do to generate a bias voltage; its so simple that its hard!

Having confirmation in the form of your description on how to achieve this only further cements that I didn't do something stupid and somehow still ended up with a semi-working circuit

Thanks again for your help man, I'll likely be reaching out more-so as I continue debugging this.

jarrodthebobo · Post by **jarrodthebobo** » 06 Nov 2020, 17:30

Question: should I be terminating ALL grounds, such as the clipping diode grounds, cap grounds, etc, to the virtual ground, or actual ground? I know the + inputs need to be tied to vG in order to get a bias point but im unsure about the rest

deltafred · Post by **deltafred** » 06 Nov 2020, 17:55

I would take all signal grounds to virtual ground.

The ones that are AC coupled could go to actual ground but it is probably easier to isolate the IC pins 4 and connect those to actual ground and connect your existing ground to virtual ground.

jarrodthebobo · Post by **jarrodthebobo** » 09 Nov 2020, 09:28

So I've got it all built and working,for the most part. Super sweet singing lead tones for days, but the gain knob appears kinda odd in how its functioning; would it be possible to replace the current configuration with a voltage divider or keep it as a variable resistor and perhaps try a different taper?

The first 3 stages into a little power amp I built, and into a celestion ten seventy sounds absolutely killer, even without an eq currently set up. With the remaining 3 stages in place, too much high end appears to be lost ,but, this is probably designed as such so you can play direct through headphones which DOES sound pretty convincing. However, I do still feel it sounds a bit muffled; as as I will likely be playing this through an actual cab or a seperate vst cab sim, I'm not sure the analogue cab sim in the circuit will be neccesary.

Before I remove the cab sim from circuit, is there any easy change in cap value to reintroduce some highs? Im not very familiar with the functionings of the last 3 stages, or which caps perform which tonal function.

I'd hate to leave an opamp unused if I just go with leaving out the cab sim section; but I was interested in perhaps retaining that mixed feedback stage at the end, but I'm not 100% sure as to what its exactly doing tonally. Typically when I think of mixed feedback, I think of Mixed Mode feedback to try and increase damping to a power amp or something along those lines, but feel that this probably isn't exactly the same thing.

Additionally, I found a variable voltage pot to be incredibly usefull! This circuit sounds great at different voltages; with a hell of a lot more distortion at lower voltages, and more "amplike" behaviors at higher voltages, but I'm having taper issues with this pot as well, haha. Currently have a linear 10k as a voltage divider and it appears that only the last 3/4 of the pot contains any useable voltage levels for this circuit; perhaps I should place an additional resistor to ground in order to shunt less,voltage?

phatt · Post by **phatt** » 09 Nov 2020, 14:07

Hey Jarrod,
Just my observations,,
Change C112 from 12n down to 2n2 or similar that will flatten the mid hump.

Don't try grabbing more top end in this circuit,, You would be far better off hanging a tone stack on the end.
Also I agree with Mr BMXguitar the compressor is likely not that great so insert another in front or post cabsim.

I've had great results with Distortion > Compressor > Cabsim > tone stack > Amp.
But try out a different sequence to your taste.
my Cab sim is similar to the Rockman.
Phil.

jarrodthebobo · Post by **jarrodthebobo** » 11 Nov 2020, 13:59

phatt wrote: ↑09 Nov 2020, 14:07 Hey Jarrod,
Just my observations,,
Change C112 from 12n down to 2n2 or similar that will flatten the mid hump.

Don't try grabbing more top end in this circuit,, You would be far better off hanging a tone stack on the end.
Also I agree with Mr BMXguitar the compressor is likely not that great so insert another in front or post cabsim.

I've had great results with Distortion > Compressor > Cabsim > tone stack > Amp.
But try out a different sequence to your taste.
my Cab sim is similar to the Rockman.
Phil.

I'll try tweaking that cap value.

I do have a TMB tone stack after the cab sim circuit here; however the tone, at least out into a guitar speaker, sounds kind of odd. However, that's probably expected due to the fact that the cab sim is supposed to be run into full range headphones/speakers.

Bypassing the cab sim completely, and just running directly into the tone stack yields a VERY nice sound that is quite easily tweakable; at least running through a guitar speaker instead of full range speakers. However, I hear some oddities in the signal when doing so (swirling and additional distortions) but I may just be overdriving the 2n5484s that I'm using as buffers a bit too hard; Maybe I just need a dropping resistor, or additional volume control before the tone stack?

Another quick question; I'd like to be able to switch the cab sim in and out of circuit; ie bypassing it in one position and running through it in the other. What would be a good way to implement this switch-wise? When I used a spdt switch to switch the output of the cab sim away from the input of the tone stack, and have the output of the 3rd stage (after the clipping diodes+coupling cap), I get some oscillations and noise which goes away if I remove the last opamp+pull the pins up from the 2nd half of the 2nd opamp. Do I need to ground the inputs/outputs of the other opamps/completely switch break contact to the input of the 2nd half of opamp number 2, by utilizing a dpdt for example?

I'm terrible when it comes to switches; they just confuse me to no end for some reason or another! Just a mental block I guess, haha!

Also I learned my lesson in regards to using a normal ol' pot wired to the 24v supply as a variable voltage source; sparks and carbon stink! I now am using a lm317 regulator and am currently just trying to figure out the best way to wire up a pot to it (as I was also sending sparks flying on the pot even when using the regulator!). I used a small vero layout thats up on google in order to put together a variable voltage supply with the lm317, but I feel like it may be missing a resistor to ground on the pot in order to ensure 0ohms is never seen on the pot... but I'm not 100% with this either.

jarrodthebobo · Post by **jarrodthebobo** » 13 Nov 2020, 05:43

Got her boxed up and mostly finished; just need to find a better way to implement the voltage control since it sounds wildly different depending on how much juice you give it. In this demo I have it running off of only 9v, as with 24v I notice some odd little distortions and such that appear to be coming from the compressor circuit. The issue appears to disappear around 15vish and it sounds quite good at this voltage, but my pot broke again and I cannot get an "in-between" value until I fix it.

Running directly my DAW using the rockman cabsim that's built in (no additional IRs used), with some plate reverb, delay, and gobs of chorus. Sounds pretty killer with how its set up.

The post-rockman EQ is pretty essential honestly, as the cabsim can sound pretty odd without tweaks.

deltafred · Post by **deltafred** » 13 Nov 2020, 10:36

An LM7815 regulator is the easiest way of getting 15v from a higher voltage
https://components101.com/ics/7815-volt ... -datasheet or you could use an LM317 if you want to make it adjustable.

The demo sounds good, it pretty much captures the Tom Schulz's guitar sound.

jarrodthebobo · Post by **jarrodthebobo** » 13 Nov 2020, 13:47

deltafred wrote: ↑13 Nov 2020, 10:36 An LM7815 regulator is the easiest way of getting 15v from a higher voltage
https://components101.com/ics/7815-volt ... -datasheet or you could use an LM317 if you want to make it adjustable.

The demo sounds good, it pretty much captures the Tom Schulz's guitar sound.

I'm using an lm317 so it can be adjustable and am following the datasheet specs on how to do so, but I keep blowing pots for some reason and I can't figure out why...

phatt · Post by **phatt** » 13 Nov 2020, 14:19

Maybe check your pins are correct against the data sheet,, as they are different to LM78xx series.
Great playing BTW

and yeah,, close enough I'd stop tweaking for more top end as that will likely make it worse .
Phil.

deltafred · Post by **deltafred** » 13 Nov 2020, 14:29

I'd forgotten that you said you were already using a 317.
Can you post the schematic and layout as something is definitely wrong.

What voltage is the power supply that you are using?

jarrodthebobo · Post by **jarrodthebobo** » 13 Nov 2020, 15:18

[quote=deltafred post_id=283118 time=1605277792 user_id=16526,
I'd forgotten that you said you were already using a 317.
Can you post the schematic and layout as something is definitely wrong.

What voltage is the power supply that you are using?
[/quote]

I used this veroboard layout because I'm lazy

https://ua726.co.uk/2014/02/25/lm317-ad ... ly-layout/

The power supply I'm using is a small regulated power supply I made using a lm317 built into a pedal enclosure. This however, uses a fixed resistor to set the voltage and has no issue sitting at 24v. I have in the same enclosure, a 9v tap as well off another regulator. Has some giant filter caps in it to, 4700uf after the bridge rectifier off the 25vac supply, AND another 4700uf on the output of the lm317. I've used it with tons of other projects, pedals, and diy amps without issue.

In the rockman unit, I have yet another 4700uf cap as a main supply cap sitting on the dc jack, then I have the lm317 veroboard, with ANOTHER 4700uf input cap, and a 1000uf output cap. All caps are rated above 50v and above. Protection diodes on the veroboard are 1n914s as they were what I had laying around. The regulator works great for a little bit before the pot eventually shorts itself out; able to get a pretty wide range of voltages out of the 24v input supply. However, after playing around with pot positions for a bit, it eventually smells strongly of carbon and stops functioning as a variable supply, instead sitting at around 22ish volts which I assume is due to the remaining shorted resistance?