The FM Tube Modulator Jimi Loved

[Eb7+9]

finally, here's a vid that details some of the technical aspects of the latest single-channel build ... it's long and boring, but it shows some of the subtleties obtained from playing with OFFSET/DEPTH combinations ...

again, the demo features a basic dry/wet stereo mix

notice the high S/N obtained in the gtr case ... and low distortion specs, etc etc
the vibrato seems palatable for organ playing as well ...

https://youtu.be/Wt-FEEWUMZk

~jcm

[Tek465b]

[Eb7+9]

another milestone ...

the pwmGate version of William Wayne's CTP single-channel test is up and running, not perfectly flawless (as to be expected with a pure PWM-gate system on the first pass) but more than just good enough // actually, quite great in the middle of the Depth range - with a "tikking" issue near the extreme (0% and 100%) PWM limits // something the optical version has none of (since its resistance variation is more continuous) ... the Phaser option works very well and produces an interesting "mono" effect // with the Vibrato signal I can 50-50 mix in dry signal that is either in-phase or out-of-phase for two slightly different qualities of Phasing (it's subtle) ... there is also an input for an external (SPEED control) expression pedal, and the AVR module now has a calibration routine to accommodate for various EXPRession pedal ranges // with a push-button and LED "calibrate" indicator (mounted on the side) ... all in all, it's pretty rockin' as I have it working now

by and large it's a success IMO // maybe some extra tweaking/padding is needed around the gates (hmmm ...) ... I wonder if other peeps will come out this way and pursue the idea further (the MXR pwm designs were never much explored by clonesters either, PWM-gate resistance is a very math thing and also requires a very specific design approach) ... so, now we know that the pwm-Gate version of the William Wayne pitch shifter works, as expected ... this was a very useful experiment for me, besides being a fun design/build challenge ... if there is any interest I might well turn this over to the DIY community and see what others do with the idea

as a parting thought here, I will say that if a full four-channel rendition is meant to happen it will // I've got an interesting take on the BP filters drawn up, etc ... for now, my board maker is on a 3-month sail-boat trip around the north-west pacific and further prototyping opportunities will have to wait // plus I need to get back on track with the "amp" side of things ...

thanks to Tek465b for the hard work and unwavering diligence to get the AVR board working flawlessly,
and special thanks to Dave Weyer for the inspiration, hope you get better soon ...

c'y'all in the future //
~jcm

[ArrogantOwl]

I'm witnessing something great here. What that something is I don't know, but I like it!

[daveweyer]

Bravo as well, glad to see some folks come forward to notice how cool this is. No telling where this will all go, but I'll bet it is not over.

[Xplorer]

the clip i've heard is really amazing, such a great work ! you should post it here !
your kits project proposition should be greatly appreciated. it should deserve also some understanding of what we've seen here, but it's really high level ..

[Tek465b]

This one?(it was posted above):
https://www.youtube.com/watch?v=Wt-FEEW ... e=youtu.be

[Xplorer]

oups, sorry, indeed, i maybe needed some sleep lol.

[daveweyer]

It might be the new girlfriend......

[Xplorer]

He ha ! well, you guessed right ! girls like that .. it's like a nervous Lamborghini or a roller coaster lol

[daveweyer]

Not exactly on-topic, but you ought to post a pic of her so the forum can see why you are so preoccupied. Definitely worth a look I'd say........

[Xplorer]

He he he, thank you but no, i won't post it here

[daveweyer]

Too bad for the forum readers.........

[Eb7+9]

I'm witnessing something great here. What that something is I don't know, but I like it!

my apologies for not being more clear ... thing is, I'm not sure what that is either

in the process figuring out how to implement Willian Wayne's basic "frequency shifting" concept using current SS circuit design thinking I ended up building a couple of variable speed single-channel units

high headroom Vibrato circuits ... nothing more than that really

what interested me originally was the three-phase modulation approach
because it did not rely on optical elements, or BBD chips ...
it sounds different ...

that is the mid 50's after all ... all done with tubes
but at fixed running frequencies

Wayne's later patent showed a solution that did use photocells ... still fixed speed

so, with Tek465b's help I built a variable-speed equivalent to replicate the function of a single Freq-Shift channel

and then did another one that uses CMOS gates to replace the photo-cells ...
that one worked fine but had minor issues (as these types of circuits often do)

so far, the optical version sounds the best ... at this point I think it's flawless in operation
the second one was useful for confirming parametric values, simulation estimates, technical matters, etc ...

if anything I would say that it is somewhat similar to a Hammond (Vibrato scanner) in function
I think that's the main thing here

this system is based on three phases, while in the Hammond scanner there are twelve
still, there's a similarity in my mind ...

so, ok ... I got a nice three-phase vibrato circuit that can operate in an
old-school FX loop (passive/un-buffered/un-attenuated, etc ...)
so that it can be used to produce near-perfect noise specs ...

you may ask, now what ...?

like I said before, the next step is to see if a full Chora-tone emulator can be designed and built ...
but without costing an arm and a leg

I've discussed this with Tek465b and he design AVR code that can provide all the necessary cock outputs from one Arduino board ... he can easily make them all locked together, or not ... so, in principle a modern CTP emulation is possible by duplicating the opto version that I recently built ...

but that would also require 4 or 5 matched triplets of cells ... now that can be a real bitch for most peeps to deal with, even for myself I must say ... I don't think I have that many left in my "calibrated" stock

these are not cheap, and to get 4 or 5 well matched triplets might require buying maybe 30 cells (I'm guessing)

it would be doable ... but a little pricey, and quite an involved project

I'm hoping to find a simpler solution still ...

at the moment I'm considering a more basic counter-multiplexer approach
if I can get the edges to slew I might be onto something here ...

the idea is to get a more modest speed adjustment compared to the AVR approach
for example the 1hz, 2hz, 4hz, 8hz and 16hz clocks might drop by a factor of 1/2 only

speed range restrictions in exchange for considerable design ease ...

it's something I thought of recently (especially since it's something Dave mentioned a few times before)
and thought I might wanna try ... ie., hard(er) multiplexing of the Lattice signals

in contradistinction, the AVR provides progressive fading in and out of the phases via triangle wave drive
a bit more similar to a Hammond scanner with its rotating plates ...

I'm curious if a hard-chop/digital approach would give good results ...

I'm not at the point where I have something drawn up that begs building
I'm still mulling things over ...

but if it did work I'd have the easier approach to building a full CTP emulator I'm looking for

stay tooned ...
~jcm

[daveweyer]

JC,
I'm sorry to have to be the one to bring attention to this, but I loved the imagery of, "THE NECESSARY COCK OUTPUTS". I knew this was a sexy circuit, but that really says it all.

In dealing with gated outputs as you probably know, the thumping is more pronounced because there are harmonics in the modulating frequency. If you've ever triggered a gate at an 8HZ rate you can hear it easily. If that problem could be dealt with, then there would be many advantages in design. I'm thinking of 70s synth circuits, which could be gated on quickly and very musically. Four quadrant multipliers work well for this.

I have not given up on the idea of 6 tubes, the acorn types, extremely small, low current and voltage, cheap to procure, and can run off a switched supply which would be very small.
Everything else in the circuit could be SS. It may sound daunting, but considering it would take care of the oscillators and gating (modulating) all at the same time, the complexity and matching of all the other parts would be greatly reduced, and, you would get the exact voicing of the original modulations.

The first unit you made however is commendable, and I encourage any further design steps, no matter which road they may take.