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Wow Tark, don't know what to think. First I'm sorry if I'm keeping you up at night Great info and most interesting to be sure. I know that even when I was getting a small amount of phasing if you recall I said the feedback pot didn't do anything that I could hear. Of course my circuit is not working to specs to begin with but since I was getting a small phase out of it I would have thought the feedback pot would at least change something I could detect.

I didn't get to this last night. I'm working on a customer request on something and I wanted to kick it out to him as soon as possible. I'll report back once I pull those parts.

I need to thank you guys again for spending time on this. I very much appreciate it.

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Actually its kinda cool, I have learned a great deal about how phasers work through simulating the Phase Royal and the Soaring skillet.

I could have made a mistake or misunderstood something, but I have tried everything I know to make the Resonance circuit elements in the Phase Royal do anything useful and I just can't.
The worst effect of this that I can see is, as I have said, that the Resonance components actually appear to degrade the performance of the Phase Royal even as a straight phaser, without the Resonance control turned up.

The Soaring Skillet appears to have a much better implementation of a Resonance or Phase Feedback control. What is significant about that circuit is that the Phase Feedback is applied as positive feedback around the entire circuit from the final output of the four phase shift stages back to the input buffer, with the amount of feedback controlled by VR1 (the Phase Royal tries to get away with just a few passive components wired between the fourth phase shift stage and the second phase shift stage). What the Resonance control is supposed to do, in addition to the two notches in the effects response created by phase cancellation, is to add a resonant peak to the response rather like a wah-wah pedal in between the notches. Under the control of the LFO these two notches with a peak between them sweep up and down the frequency response of the pedal. Before I simulated all this I was under the vague impression that perhaps the Resonance control simply deepened the phase cancellation notches.

What is a bit disappointing about the Phase Royal is that it has a spare unused op-amp which could have been used for a similar feedback scheme. The input buffer would need to be re-wired to have an inverting input and then the spare op-amp wired as an inverting buffer for the Resonance control. The output of that buffer would need to go to the new inverting input on the input buffer - the two inverting stages together resulting in positive feedback around the effect.

If that had been done you would have the option (with an extra switch) of a 2 notch phase with 1 peak rolled in on the resonance control, a 3 notch phase with 1 resonant peak or a 3 notch phase with 2 peaks. Depending on whether you switched the top of the Resonance control to the output of the 4th or 6th phase shift stages.

I have done some further simulation work so here is a summary of where I am at now. I would stress that I haven't built the BYOC Phase Royal for real and therefore I haven't tried any of my suggestions on a physical circuit. On the other hand SPICE simulation has been used in the electronics industry for many years so I reckon my sims are probably pretty reliable. If I wasn't short of cash right now I'd buy a Phase Royal kit and try this out.

BYOC Phase Royal improvements

1. The single transistor output stage is poorly biased and can cause distortion.
2. The Vref zener diode is current starved resulting in a low and unpredictable Vref.
3. The Resonance feedback network actually degrades the depth of the phase cancellation notches.
4. The FET bias trimmers useful range is limited to the top 1/5th of its rotation, making it very sensitive to setting.

1. The output transistor can be re-biased by fitting a 68K resistor between base and emitter. This output stage is powered from Vref on its emitter and a low Vref exacerbates the poor biasing. The current biasing scheme limits the output stage headroom before clipping. Some kit builders have complained of distortion.

2. A typical 500mW Zener diode (BZX79C5V1 for example) might have a Zener voltage tolerance of 5% - so between 5.355 and 4.845 volts. In the BYOC kit the Zener is fed from a 10K resistor from a nominal 9V battery. So the current flowing through the Zener is between 0.52mA and 0.39mA (depending on the actual voltage across the zener) which is really too low to produce a full and stable Zener voltage.
This type of Zener is tested at 5mA for its rated voltage.
The Zener is used to provide Vref to numerous points throughout the Phase Royal circuit - it sets the bias voltage point for all of the modulation FETs, all of the op-amps and the transistor output stage.
If Vref is low it has a critical effect on the operation of the entire circuit. Kit builders have reported Vref readings of 3.8V and 4.1V. The suggested fix is to change R37 from a 10K to a 2.2K.

3. A SPICE simulation of the Phase Royal circuit shows that the simple Resonance circuit connected between pin 2 of IC3a and pin 1 of IC4a performs poorly. It introduces an unwanted phase shift that degrades the phase effect.
The suggested fix is to rewire the input buffer IC1a so that it has an inverting input and to use the currently unused half of IC2 to build an inverting buffer for the Resonance control. The output of this Resonance buffer would then feed the inverting input on the effects input buffer. This follows the feedback scheme used on the Soaring Skillet which performs well in simulation.
An extra switch can be added that switches the Resonance feedback between the 4 stage output and the 6 stage output to give further resonance peak options.

4. The adjustment range for the FET Bias trimmer is cramped up near one end of its rotation and the trimmer is sensitive and requires fine adjustment. The suggested fix is to replace the 250K with a 50K and to fit a 270K fixed resistor between circuit ground and one end of the trimmer. The typical bias range for the FETs is between Vref and Vref - 0.9V so it is quite small.

The attached plots below are for 6 phase stages and the Resonance at max.

Hey Tark, thanks for the ton of info. I haven't forgotten about this one. I'm clearing out a path so I can devote 100% of my time to it and taking a mental break from it. I'm about there though so I should tackle this before the week is out.

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I really hope all this info helps.

I guess it is worth mentioning to other readers of this thread that I posted more info in the Mods section of this forum.
It has been interesting analysing this circuit and if things work out the way the simulations indicate it should be possible to bring about a massive improvement in the performance of this pedal and to add further options by switching the Resonance circuit to a choice of phase stages. You could also add an MXR Phase 45 option by switching the mix input to the output of the 2nd phase shift stage as well as the 4th and 6th.

I'm almost inspired to knock one of these pedals up on perf. board. Maybe I will one day.

My recently built Royale has seemed a bit uninspiring as well. It seemed to kinda work (though volume seemed to increase significantly when engaged) and I got it to phase after adjusting the trimpot but now it doesn't seem to offer much phase. I haven't had any time to dig into it but I've been following the thread and will def apply all of the info from it when I feel like digging in and debugging.

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The thing to try first is to disconnect one end of R16 (as far as i can tell that is the 10K at top left of the PCB) and one end of C4 (which is the small ceramic cap to the left of the little sheep marking), disabling the Resonance circuit. The quality of the phasing should get dramatically better. If you weren't sure of the biasing before that you may need to re-adjust the bias trimmer since the phasing effect and therefore the effect of bias should be much more obvious. My sims show that the bias action is all in 1/5th of the rotation at one end of the trimmer (I'm presuming it is the clockwise end).

If you get much improved phasing after disconnecting the resonance components then that is practical confirmation of what I'm seeing in the simulations.

Though I really didn't have any reason to fool around with #'s 1, 2 & 4 of Tark's suggested mods (none of those things seem to be an issue on my Phase Royal), I did decide to give the "resonance control disconnect" a try--mostly out of curiosity about it's tonal impact, but also to see if his SPICE findings held water with the actual pedal.

The first observation that I would make is that if you're doing this on a Phase Royal that's already built, getting that little 220pf ceramic cap out of the C4 position is a significant PITA. The cap itself is tucked down between IC1 and IC3 and (unless you like to leave your component leads long) is almost impossible to get a hold on with your finger tips (you can try a needlenose pliers, but those little ceramics break quite easily). And on the back side of the board, the solder joints are right between the legs of VR2 and VR3, the Mix and Speed pots. After trying to get that sucker out in one piece for about 15 minutes, I finally just clipped the legs. Geez! Fortunately, removing R16 is a piece of cake. If you want to try this mod with a pedal you're just building, I'd strongly suggest socketing the two spots and trying the pedal with and without the resonance control connected.

Once removed, I fired the pedal back up, and there's a definite difference in sound. I wouldn't say there was stronger phasing, but I would describe its character as clearer and more focused. I found that I did need to rebias the pedal a bit after disconnecting the resonance control. Yes, the effective phasing span on the trimpot is quite small and definitely over on the clockwise side of the sweep, but I don't find it particularly difficult to get a good, deep phase signal--just "dime" the Depth control and turn the Speed up around 2 - 3 o'clock, and you should be able to dial in the phasing without much trouble. Just use your ear. Again, if you want to do the trimmer mod that Tark suggests, the best time is when you're building the pedal, not after the fact. Probably not worth the trouble then, unless you find yourself really struggling to dial in a good phase sweep.

As to whether or not the pedal sounds better with the Resonance control disconnected, you'd have to judge that for yourself. If you're looking for more clarity or going for the classic MXR Script 90 tone, then this would definitely be something to try. What you'll give up is the Resonance control's ability to change the character of the sweep tone. Contrary to what the term "resonance" usually connotes in a modulation pedal, this implementation does NOT function as depth control--the pedal already has one of those. From what I understand, it's really intended as more of a voicing control, and is derived from a feedback loop used in later versions of the Phase 90. My experience with the Phase Royal bears this out--when I turned the Resonance pot between full down and full up, the phasing didn't seem to get any deeper--it just seemed to take on a huskier and somewhat darker character. So whether or not you like that character and find it useful is a judgment you'll have to make for yourself.

As for the more involved modification of the resonance control a la the Soaring Skillet version, somebody else will need to look into that, because it's nothing I'm interested in undertaking on my Phase Royal. Two reasons: (1) I have a Soaring Skillet, so I see no reason to take my P.R. in that direction, and (2) it's pretty "major surgery" in any case, and particularly so for a pedal that's already built. Hooking into the unused half of IC2 is no small task when the PCB isn't set up for it, though there are ways around that. Again, the more opportune time to undertake such an extensive modification would be during the initial build.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Cool! DVM, thanks for trying that out.

To add to the description of what the Resonance control does (or rather what it is supposed to do). While the phase effect is created by what are effectively deep filter notches swept by the LFO, turning up a properly implemented resonance control adds filter peaks in between the notches (also swept by the LFO). You can see these quite plainly in the graphs I posted in the Mods section and also the difference when Resonance is turned down. Should sound a bit like adding a wah wah. And, yes - it does not increase the depth or width of the phase cancellation notches.

Might be worth pointing out that like all these swept filter effects (phasing, flanging and chorus) the effect becomes more obvious with harmonically complex, wide frequency range inputs (ie - distorted and / or with treble)

Personally I would also recommend sorting out the Zener current and changing the bias on the output transistor. I think these could produce an audible improvement and they are mods that are not too tricky to do. DVM is right of course - it would be a lot easier to make all the mods during a new build.

Well, whether I ever get this thing running one way or the other, at least this thread was not in vain as there is some good info in here!

Thanks for the info Bob. At this stage I'd be happy with just getting a good phasing effect regardless of how.

Keith is sending me some matched JFets so whether or not that is the issue I'll at least be able to add swapping them out to the mix to see what happens.

Time to heat up that desoldering iron cuz it's about to get used and abused. Hopefully the board won't be abused

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Further info in the mods lounge: http://buildyourownclone.com/board/viewtopic.php?f=12&t=40729&p=352845#p352845

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Well, I got it working. It is the best it has sounded up to this point. I don't get any crazy phasing or anything still but I believe I'm real close to max of what it does. I would love to swap out the JFets but I never got them. If Keith does end up sending them I'll swap them out, otherwise I'll just let it ride.

I ended up swapping out everything in the LFO circuit. I replaced every pot, the toggle (which was a total bitch to get out of that board), all 5 IC's again, the trimmer etc... I didn't hvae a TL022 for IC2 so I just put another TL072. It was 7 resistors and 3 caps. Who knows what part was off/bad or whatever.

I meant to take some voltage readings and ran out of time this morning. I'm curious what everything looks like now that I'm getting it to work.

At the end of the day thanks again for everyone that spent time on this one.

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