I heard one of these old Magnatone amps the other day and I like the true vibrato sooooooooo much more than tremolo. So I thought I'd try to do a solid state version of it but I'm an idiot - got nowhere with it and just wasted a lot of time. It sure would be cool to be able to get that sound in a little box though. I suppose the varistors could be approximated by an LED/LDR combo (if I could ever get the LFO to actually work) but I don't know if the circuit would even work the same with soon to be completely extinct FETs. Seems like this is one case where you actually have to use tubes because of their unique characteristics (and the secret spec varistors). Or am I once again wrong?
This seems to be in the same category as a Tube Driver starved plate sound using solid state devices, kinda not really do-able. I'd be happy to be wrong about all this... and please inform me if I am so I can feel normal again.
A sidebar: The way that the reversed transistor on the input of the Vox Repeater acts like a variable resistor, can something like that be done to approximate a varistor? That MPSA18 thread got me thinking about this whole thing again, which is why I started this new topic. I might be nuts (well I am) but I thought I'd ask these questions anyway.
The Magnatone vibrato is done with two (IIRC) stages of all-pass phase shift implemented with tubes. Like all phasers, it generates the wobbling phase shift with all-pass filter stages, using the varistors as the variable resistors. Phasers first generated limited phase delay, then generate a notched semi-comb filter by adding the original signal so there is cancellation at frequencies where the shift is ultiples of 180 degrees.
That is, vibrato can be generated by not adding the dry signal to the phase delayed signal in what would otherwise be a phaser.
There's no magic in the varistors, as you figured out. They act like variable resistors. You can do this with LDRs easily enough.
The variable resistance can be FETs. Or even bipolar transistors or diodes, if you design within the limitations of whatever element is being used as a variable resistor.
The MPSA18 as a variable resistor in the Vox repeat percussion is a special case, or we would use reverwe-mode bipolars for all of our variable resistors. Reverse-mode bipolars have a very limited range of signal sizes for which their distortion is low enough. Diodes can act as variable resistors too - if you are willing to restrict the signal size across them to under 25mV or so to keep the distortion down.
A whole lot of pedal technology (other than distortions, of course) amounts to a search for and adaptations to some method of coming up with an electronically variable resistor.
I recently made myself a stereo unit, following the Magnavibe schematic, and I can not recommend it highly enough.
In general, the more stages of phase shift one uses, the wider the pitch shift in the vibrato. The Magnavibe uses one stage, which simply lends a bit of "nervousness" to the sound, rather than turning your guitar into Buffy Saint-Marie or Stevie Nicks. The Magnatone Panoramic amp also provides stereo vibrato, but uses a single inverted LFO to countersweep the vibrato in each channel of the amp back and forth. I decided to use a separate LFO for each vibrato circuit, with a dual-ganged pot for adjusting the speed and intensity of the two circuits at once. The nice thing about having independent LFOs is that they are rarely in sync, removing most of the periodicity of the modulation.
In stereo, the sound is lush and immersive, and most importantly from where I stand, not distracting. Much the same way that you may only want normal tremolo here and there but don't mind leaving harmonic tremolo on for extended periods, this is also something you don't mind leaving on for a while.
Time Escobedo's "Wobbtron" can do a decent job, though some may prefer using an LDR rather than JFET as the variable resistance. The second schematic provides a gain-recovery stage, and the pot on the collector allows for adjustment from vibrato to something more in the tremolo range. You may note some similarities with the EA Tremolo in the design of the LFO circuit. It's a classic.
Can one mix the two vibratos down to a mono signal? Yeah, I suppose. You can also listen to a JC-120 or a Leslie speaker or Axis: Bold as Love in mono as well. But you know damn well it's not the same experience.
(http://www.diale.org/tpe123/wobbletron.gif)
(http://i63.tinypic.com/35i9bn9.png)
Quote from: Mark Hammer on February 14, 2019, 11:24:05 AM
I recently made myself a stereo unit, following the Magnavibe schematic, and I can not recommend it highly enough.
In general, the more stages of phase shift one uses, the wider the pitch shift in the vibrato. The Magnavibe uses one stage, which simply lends a bit of "nervousness" to the sound, rather than turning your guitar into Buffy Saint-Marie or Stevie Nicks. The Magnatone Panoramic amp also provides stereo vibrato, but uses a single inverted LFO to countersweep the vibrato in each channel of the amp back and forth. I decided to use a separate LFO for each vibrato circuit, with a dual-ganged pot for adjusting the speed and intensity of the two circuits at once. The nice thing about having independent LFOs is that they are rarely in sync, removing most of the periodicity of the modulation.
In stereo, the sound is lush and immersive, and most importantly from where I stand, not distracting. Much the same way that you may only want normal tremolo here and there but don't mind leaving harmonic tremolo on for extended periods, this is also something you don't mind leaving on for a while.
Time Escobedo's "Wobbtron" can do a decent job, though some may prefer using an LDR rather than JFET as the variable resistance.
I bet that does indeed sound very nice. Is the Panaramic doing a stereo vibrato? I didn't realize that.
I vaguely remember the Wobbletron... that's going back a few years. I think I might play around with that one a little bit, looks interesting.
Yes. The Panoramic does do a stereo vibrato. But it is applied to the two amp channels (which power separate speakers) in reciprocal fashion, due to the use of one LFO. Here's someone's demo of the 280.
Quote from: Mark Hammer on February 14, 2019, 11:47:46 AM
Yes. The Panoramic does do a stereo vibrato. But it is applied to the two amp channels (which power separate speakers) in reciprocal fashion, due to the use of one LFO.
OK, I get it. That's kind of what I thought as soon as I read "stereo", knowing what the schematic looks like. I kinda didn't follow that through all the way to the output. :icon_sad:
Magnavibe is awesome. I would make a two transistor (non-inverting) preamp with some amount of volume, then two of these stages, and you'll be good to go. Last time i messed around with any kind of Lfo, it was a modified lfo from univibe roughly adopted to 9v. Yes, it requires a dual-gang, but i feel like it is totally worth it, especially for this kind'a thing, and fairly easy to set up. I tried it with jfets as varistors, worked just fine.
Oh, there's also a fun thing to try with this type of circuit: since you have no dry signal mixed in, you don't have to worry about levels all that much, and what you can do is set emitter resistors lower than collector ones (in case you're going bjt of course), it should get less vibrato like, and more phaser/leslie like.
Well, like R.G. pointed out previously, Magnatone's vibrato circuit is basically nothing but a variable all-pass filter, which modulates the phase shift with signal from LFO. The Magnatone circuit is excessively complex due to using varistors as variable resistive element in the all-pass filter, and due to introducing the LFO signal in a "balanced" manner. Otherwise its just bread-and-butter all-pass filter with cathodyne phase splitting. Adding more phase shift stages was probably deemed too expensive at the time.
Using "modern" components the circuit can be simplified to a very rudimentary topology, which was actually also discovered by Bonham himself. By that time though, phase shifting effects were already becoming "known art" in the industry. Everyone was making them at that time. To make a case in point, Bonham's later solid-state version of the circuit was basically just a "Uni-Vibe" circuit. (e.g. SS Estey amps employ discrete BJT phase splitting and LDR as resistive element).
The phase shifting effect craze was actually so huge that some sort of phase shift "vibrato" became a "standard" feature of many guitar amps, along with the usual spring reverb and distortion, of course. Solid-state naturally setting the trend, as was customary in those days. Typical feature was to select between former (amplitude-modulated) tremolo effect and (phase shift modulated) vibrato effect. So when you ask if it has been done? Yes, something like 50 years ago!
In just a few years from that, designers started to add more phase shifting stages (it was waaaayyy more economical now) and feedback, and –like pointed out previously - discovered the so-called "phaser" effect.
Actually "solid-state" conversion of the circuit is the most trivial part of the design. Finding a proper resistive element can be problematical. Especially regarding any sort of matching. Varistors are somewhat "obsolete" along with OTAs and those electroluminescent cells, LDRs are "slow" and have no definite "impedance", BJTs and diodes have terrible input signal range characteristics, FETs and MOSFETs suffer from terrible inconsistency and are becoming obsolete anyway. A tube-based variable resistor? Now that would be something Magnatone actually never did. Anyway, trust me, least of your worries is how a vacuum tube "cathodyne" phase splitter converts to a solid-state "emitterdyne" (I made that up but you should get the point).
BTW, One clever trick exploits MOSFETs of CMOS logic chips (such as inverters). These integrated MOSFETs actually seem to be rather "matched" as is.
True hi-fi stereo Vibrato a la Don Bonham Magnatone 480
... circa 2005
www.lynx.net/~jc/stereoVibe1.html (http://www.lynx.net/~jc/stereoVibe1.html)
Hi, J.C. :)
Ah, memory lane. I think my first vibrato phase shifter was my clumsy copy of a circuit that I found in one of the giant Markus compendiums of circuits back in about 1972. Your pictures bring up memories. It was on perfboard and had the two LDRs facing a blinky incandescent bulb, much like that.
I think I still have the book. Perhaps I should hunt that up.
Teemuk's right - this stuff is old.
(apologies for un-necessary comments, shoulda taken the time to read RGs more carefully)
The higher voltage class-A stereo version sounds best of all the versions I've tried ... tho for slow speed stuff the stereo op-amp version produces a deeper panoramic sweep - esp good on bass
Matching optics is no biggie and not sure what Teemuk means by "no definite impedance" since biasing cells at a given mid-point is trivial ... what's this cmos trick ?!
Quote from: Eb7+9 on February 15, 2019, 02:47:50 PM
what's this cmos trick ?!
Early CMOS logic chips were un-buffered, and one of them offered access to the gates and drains of the actual inverter transistors. Hooking up the power supply pins (im) properly in activated the opposite polarity P-channel devices and allowed one to treat one chip as an array of N-channel MOSFETs with their sources tied together. They had the advantages of monolith construction for matching.
I can't remember whether I saw it first from Anderton or Lancaster. I'd have to go do some research to find the source I remember.
> A tube-based variable resistor? Now that would be something Magnatone actually never did.
RCA did. Commercialized around 1950, though probably developed in the late 1930s.
This was for BIG AM radio transmitters. You have a big power oscillator for the RF wave. You then try to modulate that with an audio signal. The classic way was a BIG audio power amplifier swinging the RF power amp's supply rail.
In the Ampliphase (https://en.wikipedia.org/wiki/Ampliphase) transmitter, you had two RF power tubes. Audio modulated a small RF signal which was phase-shifted 135 degrees to two signals which drove the two RF power tubes. When combined, RF amplitude varied from zero to 200%, making AM. This eliminated two big audio tubes and all high-power audio iron. The phase-shift stages used reactance-tube techniques to vary the resistance in a phase-shift circuit.
https://www.americanradiohistory.com/ARCHIVE-RCA/RCA-Broadcast-News/RCA-95.pdf pg 12
http://www.rossrevenge.co.uk/tx/ampli.htm
http://www.rossrevenge.co.uk/tx/block50.gif
Note that this scheme only aimed for 7.5 deg phase shift and near 1mc.
So, correct me here if I'm wrong, but neither of these techniques can be used to simulate controlled floating resistors (what's required in a Maggie emulator) ... and the later could only produce very limited phase shift ...
so not of any real use here / and not worthy of mention other than vague annectodals
—-
To get back on topic, adapting the Maggie to SS naturally involves either using optics say Univibr style like I did above / ie., bulb and cells or opto-isolators operating differential (using current drive as I did in another couple of projects). or using pwm'd Analogue gates operating in a similar manner - as I'm experimenting with these days using a non-linear CV bender to smooth out the hyper ness of the 1/x transfer function
Again, to recap, there are no other (practical) methods that will provide four or more decades of variable floating redistance // what's necessary for produce a full depth emulation that is plenty adequate speed wise as well
My memory made me rediscover this, that you might be interested in:
(https://i.postimg.cc/D8X3ZXB9/phasevibrato.jpg) (https://postimg.cc/D8X3ZXB9)
Pretty much a simplified univibe, i think it's worth a shot.
It is interesting that it has 3 stages, i guess to keep the circuit in phase, but if i were to make it, i would simplify first stage, or simply not modulate it.
On the other hand i don't know, maybe 3 stages will be awesome.
That's a cool idea, but what a dump of transistors ....
It would be interesting to rework the circuit using something like mpsa13 darlingtons; that alone would cut the transistor count in half. And all the bootstrapping excess could be imho reduced with a better high-z biasing arrangement, cutting down the cap-count significantly.
Lastly, it would be quite interesting if the circuit could be adapted to use small logic-level mosfets instead of optos ... not jfets.
Quote from: Eb7+9 on February 16, 2019, 09:33:10 AM
So, correct me here if I'm wrong, but neither of these techniques can be used to simulate controlled floating resistors (what's required in a Maggie emulator) ... and the later could only produce very limited phase shift ...
I hesitate to imply correcting you, but it's not clear that the techniques could not produce the ultimate effect of a varying floating resistance, as they were optimized for something else entirely. A solid pass at designing a different end result might be effective. Or not. I think the question is open.
And, if you think about the desired result, it's not clear that only floating resistances are needed. After all the Magnatone stages are just phase shift stages. It's not clear how far from the pure, original circuits one would go to produce the effect.
So one is presented with the dilemma - how much change is allowed by one's own internal "originality meter"? The change being contemplated is already to rip out the varistor setup and replace it with something entirely different. It gets down to some philosophical questions of what, exactly is
required in a Magnatone emulator. Just phasing? No problem. Must use tubes? Again, no problem. Must use tubes as all-pass filters? Trickier, depending on the circuit. Must use tubes in a phase-splitter based phaser with only a cap and a variable resistor as phasing elements? Yep, you probably will need a floating resistor for that. Is it OK if the floating resistor is gyrator based? How about doing the obvious and mechanically hooking up a gang of actual pots wobbled by a motor arrangement? True, that has some mechanical and reliabilitiy issues - but the obvious extension to constant-rotation pots is a whole new wrinkle that's tough to reproduce.
I guess the question is then who is appointed to judge how close to the original circuit is required for a Magnatone emulation?
Isn't what is needed really, after all, that it
sound like the Magnatone? How's that measured?
Quote
so not of any real use here / and not worthy of mention other than vague annectodals
Again, who judges? I actually kind of liked it. It pointed out a different path that exists. Whether it's the only true, correct way to get to the end resuilt depends on who gets to be judge and jury.
And many of us like PRR's references. I would say that it was just fine for PRR's comments to be included, and that it did have worth.
Quote
To get back on topic, adapting the Maggie to SS naturally involves either using optics say Univibr style like I did above /
And as the fellow did in that Marcus compendium I mentioned. I really should go dig that out. I think it's in one of the boxes of books in the workshop. As for naturally, "naturally" has historically meant "what's easiest with the parts at hand".
Quote
ie., bulb and cells or opto-isolators operating differential (using current drive as I did in another couple of projects). or using pwm'd Analogue gates operating in a similar manner - as I'm experimenting with these days using a non-linear CV bender to smooth out the hyper ness of the 1/x transfer function
Again, to recap, there are no other (practical) methods that will provide four or more decades of variable floating redistance // what's necessary for produce a full depth emulation that is plenty adequate speed wise as well
Again, who judges existence of other methods or their practicality? I'm pretty certain that the designers of the Magnatone amps would think that using several hundred million transistors to implement a DSP processor to do a phaser, let alone coding up the application was rediculously impractical. And they were right - from where they stood. Where you stand and what you have experienced has a powerful effect on what is "practical". Others might have a different viewpoint of "practical".
> what's required in a Maggie emulator
Is the True Maggie plan posted in this thread and I missed it?
There's certainly may ways to skin a phase, but without a goal (proven product) it's all just gas.
Surfy Bear used a string of zener diodes in place of the varistors in his new vibrato pedal and results sound pretty good.
First off, I have no idea what's in that pedal. It would be interesting to see what use was made of zeners to get variable resistance.
But let's think about resistance for a minute. That which we call a resistor would smell as sweet by any other name - oh, wait! That's roses, and Shakespeare. A resistor is a thing which is defined by its voltage/current relationship. For any resistor, V= I * R. If we plot that as the value of current against voltage, we get a straight line. Which is good, because if the line was not straight, the current not a linear function of the voltage, there would be distortion of any signal passing through it. As a side light, the slight change of resistance with higher voltages in carbon composition resistors is what gives them a little distortion is likely to be the reason for the "carbon comp is better" myth.
The slope of the I versus V line IS the resistance. For high resistances, the current increases as voltage increases, but very little. The I vs. V line for high resistance is nearly flat. For low resistances, the current increases a lot for only a little voltage, so the I vs V line is much more upright.
What is the resistance of a diode? Its I vs V curve starts flat-ish until we hit about 0.5V, then it suddenly increases, bending upwards until it's almost but not quite vertical. So a diode has a resistance which is very high for low voltages across it, very low for voltages more than about 0.8V. In between, the actual resistance (the SLOPE of the I vs V line) changes smoothly between very high to very low, megohms to tens of ohms.
IT'S A VOLTAGE CONTROLLED RESISTOR!!
Mostly. If you use it for a voltage controlled resistor, you must restrict the signal voltage wobbles to less than about 25mV or distortion gets very big. We know that because we feed diodes a voltage or two to MAKE them distort. But if you will keep the signal levels low, diodes make fine voltage controlled resistors. And they have been used that way. The Thomas Organ Vox amps used four diodes in a "bridge" to capitalize on their variable resistance in exactly this way for a tremolo. They lived with the noise problems from tiny signals.
Magnatone varistors were the opposite. They too vary from a high(ish) resistance at low voltages across them to a low(er) resistance with more voltage across them. In the original varistors' case, the change in resistance was gradual over many volts and you could put a bigger signal through them without distortion.
Modern varistors have been improved by industry to be more abrupt in resistance change, making them nearly useless for the Magnatone application, but more useful for protective devices, which is how they're used.
Zeners, too have a change from essentially non-conducting to low resistance, as they pass their zener threshold and start conducting. This "knee" where the resistance changes is where you'd have to use zeners as variable resistors, and the sharpness of the knee, or lack of it, would in turn affect how big a signal you could use in the "variable resistance" region of their action. Low voltage zeners are known for having sloppy, round conduction knees, so maybe a string of low voltage zeners could be put together to use as a variable resistor.
I've used diodes for variable resistors. It's a tough thing to keep the signal levels small, keep the resulting noise from amplifying the signal back up to an acceptable level, and remove or cancel the necessary much higher voltage (compared to the signal) that you have to use as a "control voltage" to make the resistance change. They're a bit of a pain.
Quote from: R.G. on February 16, 2019, 10:52:35 PM...
Low voltage zeners are known for having sloppy, round conduction knees, so maybe a string of low voltage zeners could be put together to use as a variable resistor.
...
3-volt-ish zeners are usually rounded-knee enough, but have sloppy tolerances so averaging these in a string could be the ticket to having both smooth-enough response curve and repeatability.
Could be. Back when I was designing power supplies, we were flatly told by the Old Grizzled Engineer that reviewed our designs to not use zeners under 4.7V for just the sloppiness/round-knee reasons. Even with a constant current driver, the raw tolerances were horrible, and even with part selection for voltage at a given current, you were probably just picking a point on the knee, not the better-fixed full conduction part of the characteristic.
Using a high-variance part like this probably works for low volume stuff, like boutique pedals. The builder gets to sift through the bin of zeners, stacking up ones to get the best sounding "roundness" and at the same time about the right voltage drop. That would be death on a high volume production line, but works for low volumes and high labor costs.
It would be interesting to see a well done study of knees in 3V zeners versus the roundness of four 1N4148s.
Here's an Ampgarage thread talking about replacing varistors with both MOV & resistor and zener and resistor configurations (with diagrams)
https://ampgarage.com/forum/viewtopic.php?t=23839&postdays=0&postorder=asc&start=0
You want a sloppy zener? If you could pull the one out of a CD4046 pll package. I've never worked out what condition might get it anywhere near the promised 5.1v. I think there's a reason the pin is officially labelled as "ZEN".
For now, I'm happy to have a working Wobbletron with an LED/LDR instead of the FET. I would like to be able to have a little slower speed capability but overall it's a pretty cool sound, like it much better than tremolo which doesn't sound as musical. This video is just testing it before I put my self designed PCB based on this schematic (http://4.bp.blogspot.com/-Ty3MQgwVUrA/TxQZTr8oQYI/AAAAAAAAAkA/o9f18Xyru1k/s1600/Bigfoot_FX_MagnaVibe.jpg) into a box this morning. I changed a few part values but nothing is substantially different.
I have a question though. When I first put this circuit together I tried using a VTL5C1 and I got nothing out the other side (in other words the LDR section had no action at all). I got nothing with a VTL5C2 either. But I cut a VTL5C7 in half and used the LDR part with a bright amber colored LED and then it worked great. Why is that? I built a Demeter tremolo some years ago and it used a VTL5C1, so I assumed it would work in this scenario as well but that was a total no go.
That's the circuit I used, too.
I have a small handful of sealed optos in the parts drawer, but often prefer to use discrete LEDs and LDRs unless the circuit explicitly calls for a given vactrol, simply because I can actually see if the LED is illuminated, fried, or accidentally installed backwards (remember, it's ME building :icon_rolleyes:). I usually don't know, in advance, what sort of LED efficiency the circuit used, so the LED may be too dim, or too bright.
For my stereo unit, I used a dual-ganged 100k, simply because I had more of them. I reduced the effective value with a parallel fixed resistor, in the manner shown in Briggs' schematic.
One of the nice things about this particular LFO design is that one could implement envelope-control of speed fairly easily, via a second LDR/LED combo in parallel with the speed control. Pick harder and the LDR resistance in parallel with the speed pot goes lower, yielding faster speed.
Quote from: Mark Hammer on February 18, 2019, 07:15:07 AM
That's the circuit I used, too.
I have a small handful of sealed optos in the parts drawer, but often prefer to use discrete LEDs and LDRs unless the circuit explicitly calls for a given vactrol, simply because I can actually see if the LED is illuminated, fried, or accidentally installed backwards (remember, it's ME building :icon_rolleyes:). I usually don't know, in advance, what sort of LED efficiency the circuit used, so the LED may be too dim, or too bright.
I used the other half of my cut up VTL5C7 to see the LED and it was not very intense so I surmise that the LED wasn't bright enough to cause a change in the LDR. Apparently none of the three different ones I have are bright enough.
Quote from: Mark Hammer on February 18, 2019, 07:15:07 AM
For my stereo unit, I used a dual-ganged 100k, simply because I had more of them. I reduced the effective value with a parallel fixed resistor, in the manner shown in Briggs' schematic.
That's exactly how I would do it, with a dual ganged pot. I bet that sounds nice.
Quote from: Mark Hammer on February 18, 2019, 07:15:07 AM
One of the nice things about this particular LFO design is that one could implement envelope-control of speed fairly easily, via a second LDR/LED combo in parallel with the speed control. Pick harder and the LDR resistance in parallel with the speed pot goes lower, yielding faster speed.
There's an effect like that on a Kurt Rosenwinkel CD I have where it speeds and slows down according to how he is playing. I was always intrigued by that and still am. Not sure what he was using to get that effect but it's cool.
It's a feature I enjoy. However, it will take some experimentation to find a set of time constants that give the right feel. It's one thing to make an envelope follower that tracks an individual picked note or chord, and quite another to have an envelope follower track the "arc" of one's picking, such that it feels like you're gradually turning the modulation rate up and then down yourself. And if the envelope-control is implemented by placing an LDR in parallel with the Speed pot, you have to figure out how sensitive you need to make the envelope follower, and what value of LDR resistance you need to use, to have usable changes in speed in response to your picking/strumming. It's not impossible, but compared to the envelope-followers in autowahs, compressors, and gates, that are already worked out for us, it will involve a bit more labor and tinkering on your part. But well worth the effort. You could always do the same thing with a footpedal, I suppose, but then what would you operate your wah with, right? :icon_wink:
Quote from: jubal81 on February 16, 2019, 06:52:15 PM
Surfy Bear used a string of zener diodes in place of the varistors in his new vibrato pedal and results sound pretty good.
Sorry, sounds very limited (at full depth) to my ear ... and proves my point
NSL32-SR3 optos (available at Smallbear) can easily get controlled variations spanning 100r to 10meg using proper drive ckt / that's five decades of large signal resistance variation ... what I used in my opto-vibe pedal to see what it could yield ... way too much for practical use in fact, but at least useful in knowing how much is enough / unlike idle nay-saying
Using diodes as VCRs will give you even less linear range than FETs ... there's only one other technology that can match both range and headroom of optos
Because of how human hearing - and indeed all of human perception in any modality - works, vibrato requires either fast changes, or big changes in pitch, to be detectable. The ideal vibrato sound is really one that just makes the instrument sound more "nervous" rather than boing-ey. I found that, as much as I like nice slow modulation rates, the pitch wobble at slow rates was very hard to detect, even with the intensity turned up full. HOWEVER, with a stereo unit, the pitch wobble was much easier to perceive, even at very slow modulation rates, and even with only a single stage of phase shift. Why? Because one is perceiving the pitch of the guitar not in relation to itself a moment ago, but in relation to the other channel. That difference can be more easily heard, even when the modulation is slow. That's part of why I recommend a stereo build.
Actually it's the other way around ...
Standard dry/wet or wet only chorus/pitch vibrato gives more of a pitch bendy effect
eg., Roland Chorus pedals, JC120 amps, Rocktron X100 etc.
While perfectly balanced anti-phase (wet-wet) vibrato gives more of an animated effect
I provided examples of this in my second stereo-vibe build page
http://www.lynx.net/~jc/stereoVibe2.html
To really pull this off you need two matched audio channels ...
... a stereo pa set exactly the same in two channels panned hard right/left
... two matched guitar/bass amps and cabs
on a pair of JCM800's it's delicious
Whereas in mono mode (both sides in sync) kinda bland
Not your typical pitch bending effect at all ...
YES!
A tip of the hat (and a jar of salsa if you drop by again) for recognizing what it took me an additional 13 years to stumble onto. The stereo implementation IS more animated. And whether one uses a phase-shift oscillator, like I did, or a more sophisticated LFO, like you did, I think the use of independent LFOs to reduce the periodicity is key to making it more animated than dizzying.
Quote from: Mark Hammer on February 18, 2019, 05:25:12 PM
Because of how human hearing - and indeed all of human perception in any modality - works, vibrato requires either fast changes, or big changes in pitch, to be detectable. The ideal vibrato sound is really one that just makes the instrument sound more "nervous" rather than boing-ey.
A few things I noticed after playing this thing for a few hours:
1. The effect is not so noticeable when doing single note lines unless the speed and/or intensity is at maximum
2. The effect is much more pronounced when playing two or more notes simultaneously
3. It seems that the lower frequencies are easier to hear the wiggling on than the higher frequencies (or it registers in my brain faster)
4. Delay after the vibrato helps to accentuate it
This all works perfectly for my style of playing so I don't see any of those things as a limitation.
Quote from: Mark Hammer on February 18, 2019, 05:25:12 PM
I found that, as much as I like nice slow modulation rates, the pitch wobble at slow rates was very hard to detect, even with the intensity turned up full. HOWEVER, with a stereo unit, the pitch wobble was much easier to perceive, even at very slow modulation rates, and even with only a single stage of phase shift. Why? Because one is perceiving the pitch of the guitar not in relation to itself a moment ago, but in relation to the other channel. That difference can be more easily heard, even when the modulation is slow. That's part of why I recommend a stereo build.
I use primarily a stereo headphone set up, so it sounds kind of like you describe I think. I need to try it with a guitar amp and see how that sounds in comparison.
Quote from: Paul Marossy on February 19, 2019, 09:59:54 AM
A few things I noticed after playing this thing for a few hours:
1. The effect is not so noticeable when doing single note lines unless the speed and/or intensity is at maximum
2. The effect is much more pronounced when playing two or more notes simultaneously
3. It seems that the lower frequencies are easier to hear the wiggling on than the higher frequencies (or it registers in my brain faster)
To make it better suited for higher frequencies try lower cap values for caps that get modulated.
If you have 100nf just like in a wobbletron, try 47nf, it should be right up the alley, or even 22nf.
I guess this is why all those old school designs used buffer before each stage.
Quote from: Danich_ivanov on February 19, 2019, 12:16:43 PM
Quote from: Paul Marossy on February 19, 2019, 09:59:54 AM
A few things I noticed after playing this thing for a few hours:
1. The effect is not so noticeable when doing single note lines unless the speed and/or intensity is at maximum
2. The effect is much more pronounced when playing two or more notes simultaneously
3. It seems that the lower frequencies are easier to hear the wiggling on than the higher frequencies (or it registers in my brain faster)
To make it more suited for higher frequencies try lower cap values for caps that get modulated.
If you have 100nf just like in a wobbletron, try 47nf, it should be right up the alley, or even 22nf.
I guess this is why all those old school designs used buffer before each stage.
OK, I'll try the .047uF instead and see what that does.
To correct myself a little bit, i said "capS", thinking about two of these stages, but given that there's only one, i meant cap that's just after collector, and just before "varistor" thingy. I like to think of that circuit as a filter, and that cap is what sets the range of frequencies you're modulating, and given that 100nf covers most of the spectrum guitar sits in, and you mixing that cap with out of phase signal, you're just a hint from phase cancelation, "tremolo", which is why you have to go lower in value than 100nf, untill you will really start loosing low frequencies, below 22nf (47nf seems about right), to get pronounced effect.
Quote from: Danich_ivanov on February 19, 2019, 02:04:42 PM
To correct myself a little bit, i said "capS", thinking about two of these stages, but given that there's only one, i meant cap that's just after collector, and just before "varistor" thingy. I like to think of that circuit as a filter, and that cap is what sets the range of frequencies you're modulating, and given that 100nf covers most of the spectrum guitar sits in, and you mixing that cap with out of phase signal, you're just a hint from phase cancelation, "tremolo", which is why you have to go lower in value than 100nf, untill you will really start loosing low frequencies, below 22nf (47nf seems about right), to get pronounced effect.
Yeah, I know which one you meant. But good to clarify that for anyone else following this thread.
Quote from: R.G. on February 17, 2019, 10:05:19 AM
It would be interesting to see a well done study of knees in 3V zeners versus the roundness of four 1N4148s.
I hear you. I don't have any zeners on me right now (I'll get a couple tomorrow), but here are some V-I plots for 1-4x silicon and 1-4x germanium D9E diodes.
X: 0.5V per divison, right-most border is zero volts
Y: ~2mA per division
Here's a closeup of the two diodes:
(https://i.postimg.cc/xXNJ2Mbg/WP-20181029-22-48-34-Pro-LI.jpg) (https://postimg.cc/xXNJ2Mbg)
The diodes are vintage, I think. They came from a pack that looks like this:
(https://i.postimg.cc/Hczj2tfW/WP-20190219-23-16-32-Pro-LI.jpg) (https://postimg.cc/Hczj2tfW)
germ x1:
(https://i.postimg.cc/fkkMpZdf/WP-20190219-23-18-08-Pro-LI.jpg) (https://postimg.cc/fkkMpZdf)
germ x2:
(https://i.postimg.cc/crn01mXK/WP-20190219-23-18-20-Pro-LI.jpg) (https://postimg.cc/crn01mXK)
germ x3:
(https://i.postimg.cc/JsCmsk2p/WP-20190219-23-18-32-Pro-LI.jpg) (https://postimg.cc/JsCmsk2p)
germ x4:
(https://i.postimg.cc/tZJGKts4/WP-20190219-23-18-44-Pro-LI.jpg) (https://postimg.cc/tZJGKts4)
silicon x1:
(https://i.postimg.cc/BjCWtwDv/WP-20190219-23-19-07-Pro-LI.jpg) (https://postimg.cc/BjCWtwDv)
silicon x2:
(https://i.postimg.cc/ygttwqqL/WP-20190219-23-19-20-Pro-LI.jpg) (https://postimg.cc/ygttwqqL)
silicon x3:
(https://i.postimg.cc/0bghnq0Q/WP-20190219-23-19-33-Pro-LI.jpg) (https://postimg.cc/0bghnq0Q)
silicon x4:
(https://i.postimg.cc/bsQWFFmR/WP-20190219-23-19-49-Pro-LI.jpg) (https://postimg.cc/bsQWFFmR)
Conclusion:
Germanium has a 2x softer transition.
So it turns out that if I use this vibrato with speed and intensity set to the lowest setting along with my Boss Tone "Trombetta" it sounds really cool. It's kind of like adding some synth LFO modulation to it, livens up the sound a bit.
Well now you've made us curious.
Quote from: Mark Hammer on February 20, 2019, 07:33:59 PM
Well now you've made us curious.
I'll have to do some kind of recording in the near future
Quote from: Mark Hammer on February 19, 2019, 08:51:12 AM
I think the use of independent LFOs to reduce the periodicity is key to making it more animated than dizzying.
Nothing to do with topic at hand Mark (re., Maggie emulation)
Running two independent LFOs would be the same as running two separate chorus pedals into two different amps ... producing a confused effect /not what Don Bonham's idea is about at all
To make his idea shine you need a well balanced phase/anti-phase LFO (not hard to do) and equal modulation amounts in parallel channels heading in opposite direction .. requiring careful matched variable resistance sets, not a big all around favourite perhaps
I'm saying that the phase/anti-phase arrangement is not as aurally pleasing as the aperiodic "two separate" arrangement.
That said, because a single-stage (or even two-stage) vibrato circuit doesn't produce a strong pitch shift, a phase/anti-phase arrangement would not be awful, but would produce a jiggly "nervous" quality to the sound, rather than any sort of "roller-coaster" up-and-down, going from side to side.
For me, the poster child for why an aperiodic (unsynced LFOs) arrangement is better is the old Ibanez Flying Pan. An intriguing sound...for about 20 seconds, and then an instant source of migraines. The idea for a panned phaser sound isn't/wasn't a bad one, in principle. The problem was that the high-contrast movement of the output - now-it's-here-now-it's-there - in tandem with the sweep of the phaser, was like trying to keep track of two rambunctious untethered toddlers in a crowded shopping mall. Just waaaay too much to attend to. A gentler phasing effect, or a gentler pan, would have improved the product, and transformed it from two toddlers loose to two toddler fidgiting in a stroller. In the case of Don Bonham's idea, the gentleness of the pitch-wobble makes it manageable.
Why do I think aperiodic is better, from a perceptual perspective? Because its unpredictable nature means one can, and does, direct attention away from the side-to-side modulation, and simply pay attention to the overall effect.
Quote from: Mark Hammer on February 21, 2019, 11:39:23 AM
a single-stage (or even two-stage) vibrato circuit doesn't produce a strong pitch shift, a phase/anti-phase arrangement would not be awful, but would produce a jiggly "nervous" quality to the sound, rather than any sort of "roller-coaster" up-and-down, going from side to side.
Just a side note about my build. I noticed that when I have the intensity all the way up I get kind of a combo of slight tremolo and the side to side movement too. It's interesting to watch on the scope. I need to try this thing on my amp(s) this weekend to see how it works outside of my headphone only environment.
http://moosapotamus.net/files/stompboxology-vibrato-rama.pdf
I've been down this rabbit hole before:
https://www.diystompboxes.com/smfforum/index.php?topic=111802.0
There is an analogue version and sound clip in post 12.
I then built a PIC to do an LFO with 2 outputs that vary in phase between 0-180 degrees. I also played around with one where the phase varied via another slower LFO. Sounded interesting, but also somewhat nauseating.
Ultimately, a 2 stage phase shifter with stereo outputs modulated 180o out of phase sounds good and is worth building if you like that sort of thing. If you built 2x 2 stages as per the Magnatone, I imagine it would be lovely. Must put that back on the list.
Interesting, I had a self-buit 2x2 stage "phaser" in 80's, with metal-can 741s...
Quote from: Rob Strand on February 23, 2019, 04:33:19 PM
http://moosapotamus.net/files/stompboxology-vibrato-rama.pdf
That's interesting... looks like a good read
EDIT: That looks like it's from Boscorelli's Stompbox Cookbook. I have that in PDF form. Or it looks very similar anyway.
If you want other than 180deg phase shift in the LFO's, you can, if it's a form of phase shift oscillator, pick an intermediate point along the RC-RC-RC network and buffer it so it don't load the oscillator out of whack. This is how some 3 phase ensemble choruses work. An alternative is a quadrature LFO.
180deg shift can be a bit unpleasant, especially over headphones.
QuoteThat's interesting... looks like a good read
It's a while since I've read over it but I remember reading about the Magnatone somewhere.
Has anyone got data on the Magnatone VDR's?
Quote from: Rob Strand on February 24, 2019, 04:08:17 PM
Has anyone got data on the Magnatone VDR's?
I've heard from some reliable sources that the specs on those are unknown. I think about 10,000 other people would also like to know that! :icon_lol:
QuoteI think about 10,000 other people would also like to know that!
:icon_mrgreen: Ah, it's one of *those* issues.
Interesting,
https://dalmura.com.au/static/Magnatone%20vibrato%20design.pdf
page 4, info on Varistors.
Cool, full data,
https://www.datasheetarchive.com/233BNR-32-datasheet.html
https://datasheet.datasheetarchive.com/originals/scans/Scans-94/DSAIHSC0006535.pdf
Some general info,
https://ia600105.us.archive.org/19/items/TNM_Thyrite_varistors_quick_catalog_1963_-_Genera_20180115_0183/TNM_Thyrite_varistors_quick_catalog_1963_-_Genera_20180115_0183.pdf
Quote from: Rob Strand on February 25, 2019, 06:19:38 PM
Interesting,
https://dalmura.com.au/static/Magnatone%20vibrato%20design.pdf
page 4, info on Varistors.
Cool, full data,
https://www.datasheetarchive.com/233BNR-32-datasheet.html
https://datasheet.datasheetarchive.com/originals/scans/Scans-94/DSAIHSC0006535.pdf
Huh, you must have spent a fair amount of time researching to come up with that. That is indeed very cool. That seems to be everything we ever wanted to know about the Magnatone vibrato varistors. :icon_eek:
QuoteHuh, you must have spent a fair amount of time researching to come up with that.
Hard to believe but I found that first doc fairly quickly (maybe Varistor was the keyword). The document is hot off the press in 2019. Couldn't believe my eyes that someone had written it all up like that. A big thanks to the author Tim Robbins!
Quote from: Rob Strand on February 25, 2019, 06:43:08 PM
QuoteHuh, you must have spent a fair amount of time researching to come up with that.
Hard to believe but I found that first doc fairly quickly (maybe Varistor was the keyword). The document is hot off the press in 2019. Couldn't believe my eyes that someone had written it all up like that. A big thanks to the author Tim Robbins!
Huh that must've been published right after my failed attempt at a Maganatone-esque vibrato which prompted this whole thread. I waited a few weeks before admitting defeat and asking questions here. IIRC I started messing with it last December.
QuoteHuh that must've been published right after my failed attempt at a Maganatone-esque vibrato which prompted this whole thread. I waited a few weeks before admitting defeat and asking questions here. IIRC I started messing with it last December.
Pretty bizarre. The internet is fluid place. I've had the opposite where I found some stuff but I didn't have time to look at it. Come back the next week and bzzzt completely it's vaporized. That's happened to me more than once.
Quote from: Rob Strand on February 25, 2019, 07:05:57 PM
QuoteHuh that must've been published right after my failed attempt at a Maganatone-esque vibrato which prompted this whole thread. I waited a few weeks before admitting defeat and asking questions here. IIRC I started messing with it last December.
Pretty bizarre. The internet is fluid place. I've had the opposite where I found some stuff but I didn't have time to look at it. Come back the next week and bzzzt completely it's vaporized. That's happened to me more than once.
That happened to me several times early on so that's why I save stuff onto hard drive (and back that up) or print it out. I have one whole bookshelf of various categorized 3-ring binders of printed stuff... schematics, articles, etc. and a lot of MS Word docs too (most of which is printed out but is also backed up in several places). Coming from the time when CAD first started being in widespread use, I learned to back up the back ups because things got accidentally deleted, or a hard drive crashed, a floppy disk failed or whatever.
Up above my bench right now.
(https://i.imgur.com/K5MEcFK.jpg)
Quote from: Mark Hammer on February 26, 2019, 11:14:33 AM
Up above my bench right now.
(https://i.imgur.com/K5MEcFK.jpg)
Dude, you've got me beat for sure.
I probably had a head start a few years before you, Paul, plus I'm sure there are duplicates in there that haven't been weeded out.
Quote from: Mark Hammer on February 26, 2019, 11:39:07 AM
I probably had a head start a few years before you, Paul, plus I'm sure there are duplicates in there that haven't been weeded out.
I'd guess you have 15-20 years on me in the electronics dept. I completed my first pedal in 2001 on my firstborn's birthday. Before that, in early 2001, I fixed a broken optoisolator in a '74 Twin Reverb. Before that nothing. :icon_lol: