Home Forums GuitarPCB Build Support Modding Phaser circuits (Dr Phybes or the Vibe) to synch to CVs

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  • #11435
    mybud
    Participant

    Greetings all: I’m interested in principle in slaving either or both of these circuits to a clock CV (LFO and so on) from my modular setup to synch the overall phase rate to the system clock.

    I assume that one would add a 3.5mm jack across the existing pot to do this. If so, across what terminals would this be wired?

    If one built a new circuit from scratch incorporating this ability, would this entail removing the pot altogether?

    Question is whether one would need a basic starting point (i.e. 10k resistor to ground or what have you to accommodate the very slowest available rate).

    Hope this query makes a modicum of sense. Any advice gratefully received.

    #11436
    Cybercow
    Moderator

    mybud – being what it is, with electronics, there are at least 17 different ways to accomplish most any thing. I’m pretty sure using switching jacks to swap out the rate control on a Vibe or Phybes would work, but based on what I understand your approach intends, a bit more is required to achieve true synchronization. With each build having its own LFO circuit, using one master pot across two or more Phybes/Vibe builds will NOT guarantee that they will be in exact synch. Part tolerances will come into play and slight value differences in the LFO circuit of each will prevent a true synch.

    To achieve true synchronization, I would use a single LFO circuit instead; add a switching jack to engage\disengage R23 (as the injection point) when the 3.5mm jack is inserted; and use shielded wire on the 3.5mm connections.

    You could try ensuring that all the Phybes/Vibe LFO circuits are built to within 1% tolerances by carefully matching all the LFO circuit components between each Phybes/Vibe build and use the master potentiometer method. But I’m thinking that would NOT agree with more than one LFO circuit sharing the same speed/rate potentiometer.

    I do know that an LFO can act as a CV source, and I’m guessing that is what you are trying to achieve.

    It’s been a good while since I’ve worked with voltage controller (CV) circuits, and as such, I fail to see where a single CV injection point might be applied to the LFO of the Phybes/Vibe circuit. Perhaps I’ve completely misunderstood your entire questioning.

    #11437
    mybud
    Participant

    Yes indeed, Cybercow, there are at least seventeen ways, but first my apologies because I did phrase the question rather poorly. My intent was not to use both phase circuits simultaneously, but one at a time.

    LFO’s or ADSRs both seem to work as CV sources, but not connected across the pot as I’d originally thought. Thanks for the tip to try R23 on the Phybes (correspondingly on the Vibe). This works in both applications (i.e. LFO or ADSR).

    With the LFO at audio rate, one gets a ring modulation type effect. Bizarre, even by my standards.

    Thanks again, I’ll see if I can get some musically useful results from fiddling with R23 meanwhile.

     

     

    #11441
    Cybercow
    Moderator

    mybud – Just a point-in-fact . . . . R23 is the point where the overall circuit’s LFO is connected to the FETs. And TBH, I’m not sure if one would want retain the value of R23 and use it as the injection point – OR – bypass R23 and inject the CV where R23 connects to the FETs. Were I to tackle such a thing, I venture a guess that the high value of R23 suggests it is a current limiter and I would first try the injection at the bottom of R23 (as seen on the schematic) and thereby disengaging the internal LFO section.

    As for using the guitar\source signal as the LFO rate, I surmise it would indeed emulate a rather gnarly ring mod. For that, I would perhaps toy with using only one or two of the phase FETs for that option.

    Have fun and good luck!

    #11442
    wilkie1
    Moderator

    If I may add a thought to this conversation, I agree that R23 would be the point to insert a CV source.  This would replace the internal LFO in the circuit.  The variance of the voltage at that point is quite low.  I measured a variance of less than about 400 mV.  The steady voltage entering from R30 acts to balance the varying voltage from R23.  Since the trimmer is used to find the “sweet spot”, any voltage applied from a CV source would need to complement the fixed voltage as the LFO voltage at R23 does.  If you were to switch to another effect, the CV voltage might need to be adjusted/changed to fit that circuit.

    #11455
    wilkie1
    Moderator

    A good point Cybercow.  I agree.  Try retaining R23 if bypassing the LFO portion.

    #11459
    Cybercow
    Moderator

    Wilkie1 – you’ve brought up a point I’d not considered – the trimpot. Looking back again at the schematic, I’ve modified the LFO output section to include not only R23, but also R24 and P1 (the Rate pot) and a DPDT switch to exclude the internal LFO. The Rate pot may then be helpful in finding the CV reference to balance the CV swing at the FETs. (Potentially, as a better point at which to inject the CV. I present the modded schematic here for your consideration.

    #11460
    wilkie1
    Moderator

    P1 is the rate pot.  Since you are replacing it with the CV, I would think you could just use a SPDT switch with lug 2 attached to the lower leg of R23 and switching between C7,R24 and the CV.  The trimmer is adjusting the steady voltage going through R30 to the FETs.  Your thoughts?

    #11481
    mybud
    Participant

    Gentlemen: Your sound advice (pun intended) is greatly appreciated. I’ll try out Cybercow’s mod on a new build (from scratch) in due course. Just waiting for the quad 2N5952s to reach these shores. Thanks again, I have learnt a great deal from these exchanges.

    Best regards, mybud

    #11484
    Cybercow
    Moderator

    Wilkie1 – Ive modified my comment (but not the schematic mods) to reflect the reference to the “Rate” pot instead of the trimpot. Considering what you’ve pointed out, I still suspect the Rate pot could be used as a CV reference balancing control. And on further examination, perhaps the other end of the Rate pot could be grounded (calling for a 3PDT switch instead of the DPDT initially suggested) to potentially better help reference the CV balance. That way, with the trimpot left in tact, the trimpot need not be adjusted after finding that initial “sweet spot” and should retain its setting when switching between CV input and the internal LFO.

    So, it’s entirely possible the question in the OP may have been on target for using the “Rate” pot as the injection point.

    mybud – agreed! I find such exchanges quite stimulating. We hope you share what eventually suss out.

    #11507
    wilkie1
    Moderator

    Good point Cybercow.  WIth your mod, the Rate pot will become like a trimmer to help find the “sweet spot”.  Sounds good to me!

    Thanks to mybud for initiating this discussion.  You all know that “I just LOVE wires and sparks!”

    #11518
    mybud
    Participant

    I will surely let you know what develops, gentlemen. Thanks again and all best, mybud

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