Phase Revolution - Perf & PCB layout for R.G.'s Phase 180 Plus

[doc_drop]

There is no doubt that at certain settings this circuit can hiss like...an angry cat?...

I find the externalized bias pot can tame that by simply changing the range of the sweep, or backing off on the regen. I guess what appeals to me is that you can adjust things like that to get a personalized sound, but it leads to some noise issues as well.  Not to mention self-oscillation if you push it too hard.

[frequencycentral]

Not to mention self-oscillation if you push it too hard.

I added a 100K timmer to my build to limit the regen to just below self oscillation, easily done, just added it in series with R33. You do need to play about with the Bias and Width though, as their settings can subtly increase the regen.  In fact, if I were to build it again I'd replace R33 with a 100K trimmer. Actually I am planning to build another one to go into my modular synth, as a kind forumite has offered me a PCB of my layout, and I have two more sets of matched FETs...

I've got a few other experiments to run on this circuit, so I'll have a look at the noise reduction solution Mark suggests along the way. It's not as noisy as my Phase Evolution though, but I used some old 4558's in that build (which I'm planning to replace with NE5532's).

[frequencycentral]

I see that the schematic calls out for the Vref to be 3v. Right now mine is at 4.36v to 4.45v as I rotate the bias pot. Is there a reason you didn't try to get the 3v Vref? Would changing the zeneer to a higher voltage lower the Vref?

I just experimented with changing the vref. What I did was remove the zener, then I took jumpers from vref and ground to a breadboard. I added different sets of diodes.

- One 5mm amber LED plus two 1n4148 = vref of 2.97 volts
- Two 5mm amber LEDs = vref of 3.47

I tried some different combinations going to ~2 volts and ~6 volts. The phaser effect gets more subtle the lower/higher the vref goes, and each different voltage requires a different position of the Bias pot to get the same effect.

The conclusion I have drawn is that I'm happy to stay at 4.09 volts. There's nothing to be gained from the option of having the vref switchable (to 3 volts for example), as the Bias control is king, it does the job for you.

.......and now I know that there's no reason not to use two 5mm amber LED's in place of the zener next time I build a FET phaser.  

[doc_drop]

Thanks for posting the info., Rick. I also tried replacing the zeener with a couple of other values with similar results, but neglected to post the info.

My only experiment left to try is to power it with 12v. I know you power all your pedals with 12v, so I am curious to see if it helps with headroom. I have a nice regulated 12v adaptor in the mail, supposed to get here tomorrow, so I'll post in a couple of days what my results are.

[doc_drop]

So, I received my new 12v 500mA regulated adaptor yesterday. I went ahead and powered the circuits I was playing with on my work bench with it, instead of the 9v cheapo switching adaptors I had been using. The whole "rig" definately sounded better. Everything was a lot cleaner, and I had more headroom. The phaser was deeper, although I had to fight back the self-oscillation a bit. But it definately is more usable at 12v.

All in all the one adaptor was powering my diy Ruby-ish amp, a Mosfet booster, a Tonemender, an MXR dist+, an Orange Squeezer, a Magnus Modulus and our friend FC's Phase Revolution. Aka lots of home built circuits. I am really happy with the clarity and headroom I got. I think it is 12v for me from here on out...

[frequencycentral]

Finally got a chance to iron out a couple of things that always bugged me about this pedal:

• I implemented the mix control from the BYOC Phase Royal. The issue I had with the stock mix control was a variation in volume through the sweep of the pot - very annoying as the pedal should always be at unity. Using the Phase Royal's mix control the effect is the same volume wherever you set it. Here's the Phase Royal schematic: http://dl.dropbox.com/u/967492/PhaseRoyalSch.jpg


• The pedal has always had very slight background distortion with humbuckers (I think this is endemic of Phase 90 varients?), sorting out the mix control left the effect's volume above unity, so the logical thing to do was to attenuate the input signal until the output is at unity. So, I've added a 100k trimmer to ground from between the 10k resistor and the 0.01uF cap at the effect's input. Tweaked for unity, the distortion disappears. Nice.

This pedal is now as perfect as I can get it. Sounds great now. I've done so many tweaks to it over the last nine months that I'd need to RE it to draw up a final schematic! Funny how solving a few of small but niggling issues can make you fall in love all over again............

[Beo]

FC, I have a list of phaser questions for you. Hopefully you have some time to respond to these.

1.   Have you needed to use the suggested filtering methods to tame hiss on any of your phaser designs? E.g. Feedback cap on every fourth stage? RC filtering in regen path?
2.   In the Phase Revolution you have used trim pots to dial in the regen just below oscillation, and also to tame hot HB input distortion. Do you still use this technique on some of your more recent designs? Do you tailor fixed resistor values (ie. socket)?
3.   To add a fixed stage to any phaser, is the basic circuit you have used on the two ends of the causality design usable as is (e.g. following a P45 or P90 series of swept stages)? Do the resistor/cap values need to be tailored depending on the phaser stage circuit?
4.   I'm planning on using the RG's P180 design (ie. Phase Revolution) and adding four fixed stages at the tail end. What do you think would be more useable switching: 4/8/12 (4 swept, 8 swept, 8 swept + 4 fixed) or 8/12 (4 swept + 4 fixed, 8 swept + 4 fixed) or something else. Or do you suggest switching different regen paths as more usable unique sounds? Also, any benefit to splitting fixed stages to front and back instead of stacking at the end? (Note, I'm not real keen on dedicating any stages just to the regen path, but if you think this is a more usable option, I'd like your thoughts on it. Mark has commented on this a few times.)
5.   I was going to use a SPDT switch and use the two outer positions to ground out the unwanted stages. (e.g. one position would ground input to output for the second set of swept stages, eliminating it from the path) Do you foresee any problems with this approach, meaning I'd have to use dual pole switching instead?
6.   What are your thoughts on various LFO circuits? Do you have a favorite for phaser, or do they all serve the purpose? The P90 LFO is nice and simple, but there are lots out there, some of which are easily adapted with a shape control as you've done in the causality.
7.   For the mix control borrowed from the Phase Royal, do the 22k resistors work for the dividers, or did you use a different value? Did you have to adjust anything on the input/output circuit or the regen path with the change to this mix circuit?

I'm going to experiment on breadboard, but I'd like to reduce the number of variables if I can. Note that my end goal is a somewhat traditional P90 based phaser sound with more depth and a little versatility/uniqueness... but not a knob crazy Phaserlab. I have a hundred 2N5952's on the way, so I'm hopeful to match a set or two of 12.

Thanks,
Travis

[clamup1]

hey im having probs printing this out at the right size so that the sockets fit right. what are you guys using to print this out. i have gimp and ms paint

[Govmnt_Lacky]

This pedal is now as perfect as I can get it. Sounds great now. I've done so many tweaks to it over the last nine months that I'd need to RE it to draw up a final schematic! Funny how solving a few of small but niggling issues can make you fall in love all over again............

Hey Rick...

Have you been able to get a FINAL revision of the PCB for this project? I am very interested in getting this one built.

Thanks as always 

[jmwreck]

very nice, may i know what other options can be done for the BC557 ?