Cardinal Tremolo (Vactrol-base Harmonic Tremolo) - schematic & discussion

[midwayfair]

I had never heard of Pedal Geeks United until now! Thanks for mentioning it, I'm going to have to check it out. As far as the taplfo version, I've worked with electric druid's lfo a few times before, so I've got that part down, I just wanted to make sure the schematic on the first page was still the most up to date. I noticed you mentioned some updates throughout the thread, but I'm not sure if that first schematic reflects them or not. Thanks!

The schematic on the first page is currently "my" schematic for the basic project. The forthcoming PCB project has one or two small changes, but nothing substantial. When I get home tonight, I can try to remember to send you the Eagle files for the TAPLFO version, if you want to save yourself the trouble of drawing the schematic. There's a couple weird, specific things that needed to be done with it compared to Taylor's TTT, because you have to drive two LEDs. I'll tell you that one of them is the transistor after the LFO output pin is backwards ...

[mth5044]

Interesting! Sure I'd love to see your schematic, I'll PM my email.

[Jazznoise]

Cardinal with Tap Tempo LFO?  I'd be very curious to see this too. I'd already abandoned the idea of buying a tremolo over building this or a Blue Warbler

Is it o.k to send you my email?

[midwayfair]

Cardinal with Tap Tempo LFO?  I'd be very curious to see this too. I'd already abandoned the idea of buying a tremolo over building this or a Blue Warbler

Is it o.k to send you my email?

I'll just post it here, as soon as I have time to actually turn my home computer on ...

[midwayfair]

The Eagle .brd file is on Pedal Geeks United.

Despite some funny looking stuff (yes, Q4 really is collector to ground -- it worked better that way), this is verified. R16 and R17 may actually need to be socketted -- I ended up with 22K for R16. I had one heck of a time with the LEDs: Two superbrights is pretty much the absolute max the chip can drive, so I had to find some other way of referencing the LED. Turned out to be simply a matter of sending it to ground. R18 is to make sure it stays in sync with the vactrols. Incidentally, if anyone's interested in making a tap tempo univibe type thing, that right there is an easy way to get the oscillation of one vactrol out of sync with another to create a loping effect.

It does tick in triangle and "ramp up" wave settings in Harmonic mode above 12:00 on the depth, which seems unavoidable. But to be honest, settings like that have basically no harmonic effect anyway because there's no frequency crossover, and there's no noticeable ticking in the same settings when in full-range mode. The sine wave and "humps" setting are exceptional in Harmonic mode, and all the full-range stuff from the TTT is there in good working order (including all the glitch settings). There's a ton of depth. Most of the time I'm not above noon.

I built one on the last round of prototyping boards, before I made one or two fixes ...

[samhay]

Looks great.
Do you get any ticking with the non-TAPFLO version?
I was about to build this and decided I should try an op-amp work-a-like first (I seem to be shying away from discrete transistors these days). However, I am not sure I'm having fun anymore. It works beautifully, but I can hear the LFO in the audio pathd depsite quite brutal power filtering. It is probably the dodgy grounding you get on a breadboard, but I am not sure I want to pull the trigger and build it lest it continues to tick/whine.
Also, have you found that are there any LFO waveshapes that are particulalry good or bad for harmonic tremolo?

[midwayfair]

Do you get any ticking with the non-TAPFLO version?

I get some line noise with single coils, which modulates, so there's some swooshing (it's not really noticeable in a mix or while playing), but no ticking.

I was about to build this and decided I should try an op-amp work-a-like first (I seem to be shying away from discrete transistors these days). However, I am not sure I'm having fun anymore. It works beautifully, but I can hear the LFO in the audio pathd depsite quite brutal power filtering. It is probably the dodgy grounding you get on a breadboard, but I am not sure I want to pull the trigger and build it lest it continues to tick/whine.

Okay, the WHINE you're getting is something different. I used FETs because the treble side had a high pitched whine that was noticeable when using transistors BJTs. I also had some whine in the tap tempo version, but that was related to the TAPLFO chip, and it got filtered out with the right sized resistors on Q4. If it's the same thing in yours, it can be filtered out in the audio path. You should be able to get rid of it with a PF cap in the feedback loop of the treble side, counterintuitive as that may be. Keep it really small, though - 10pF is probably enough. If that filters out too much, you can also put it across the volume pot or something. You could also try some series resistance in front of the output volume control, to get an output impedance closer to a FET's. Like just a 1K or something.

For the ticking, I want make sure it's actual ticking and not just WOOSH sounds happening very quickly. If I knew more about how you've done the tremolo on both sides, I might have other suggestions -- but there are some ways of producing tremolo on an IC that would be modulating bias and that, when it happens very quickly, could sound like ticking. If it's just the general LED wup wup wup (yeah, I'm full of really specific sounds, eh?), then yeah, it's probably the grounding. If you do an etch of your version, be sure to separate the ground planes or just avoid a ground plane altogether.

Also, have you found that are there any LFO waveshapes that are particulalry good or bad for harmonic tremolo?

The harmonic phasy effect occurs when the frequencies cross over between the treble and full-range sides. Unlike in a phase 45, there's no "permanent" dry signal here, so you're relying on the two sides to have a point where they are of similar amplitude. (This, incidentally, is why you hear more "gloop" when bass and treble strings are played together, rather than just in a midrange note by itself.) This can't happen with a really hard waveform, like a true square wave, because there just won't be any point where the frequencies line up.

But wait a minute, you say. The output of the LFO I used is a triangle, and that's a pretty hard waveform. And you're absolutely right. In fact, I have seen the scope images to prove it. But the vactrols have a sluggish response, and this makes the triangle come out sounding more like a sine wave.

[artifus]

But wait a minute, you say. The output of the LFO I used is a triangle, and that's a pretty hard waveform. And you're absolutely right. In fact, I have seen the scope images to prove it. But the vactrols have a sluggish response, and this makes the triangle come out sounding more like a sine wave.

could this be due to human logarithmic perception vs linear reality? (genuinely curiosity driven question badly phrased so as to appear rude - this is not intentional, i'm tired)

[midwayfair]

But wait a minute, you say. The output of the LFO I used is a triangle, and that's a pretty hard waveform. And you're absolutely right. In fact, I have seen the scope images to prove it. But the vactrols have a sluggish response, and this makes the triangle come out sounding more like a sine wave.

could this be due to human logarithmic perception vs linear reality? (genuinely curiosity driven question badly phrased so as to appear rude - this is not intentional, i'm tired)

It absolutely could be. And this doesn't sound rude at all to me. I mean, falible human ears are why pitch vibrato happens in a Magnatone amp, for instance, even though that's just another example of phase cancellation. Similar physical phenomena producing completely different effects.

[samhay]

But wait a minute, you say. The output of the LFO I used is a triangle, and that's a pretty hard waveform. And you're absolutely right. In fact, I have seen the scope images to prove it. But the vactrols have a sluggish response, and this makes the triangle come out sounding more like a sine wave.

could this be due to human logarithmic perception vs linear reality? (genuinely curiosity driven question badly phrased so as to appear rude - this is not intentional, i'm tired)

It absolutely could be. And this doesn't sound rude at all to me. I mean, falible human ears are why pitch vibrato happens in a Magnatone amp, for instance, even though that's just another example of phase cancellation. Similar physical phenomena producing completely different effects.

I suspect it has a lot more to do with the blessfully slow response of both the LED and LDR, which smooths out any sharp bits in the LFO.

Jon - Thanks for the suggestions. I guess the noise might be similar to yours - it's not ticking, but rather moaning/swooshing/whining; I don't really know how to describe it either. i think it is probably the current through the LEDs causing ground weirdess, but need to get the scope out.
The audio side of the tremolo I currently have on the breadboard is very different to yours. The only real similarities are the LFO, a vactrol and the end effect. It was inspired by the same comments that Jimi made to you, but got off the ground when I started thinking about a dual band compressor - so I have you, Jimi and Merlin B to thank for the impetus. I will post it once I have convinced myself it is worth sharing, and will try not to derail your thread in the meantime.

[artifus]

I suspect it has a lot more to do with the blessfully slow response of both the LED and LDR, which smooths out any sharp bits in the LFO.

and how did you, as a human being, perceive that phenomena?

i had recently been reading about pwm, led brightness, lfo's and human perception/cognition. hence my question. it is an interesting subject. also look up: psychoacoustics. my! it's a big universe! 

[midwayfair]

when I started thinking about a dual band compressor

If you keep posting phrases like this, derail away ... I tried getting one of those to work recently and the results weren't exactly pretty. Really want to see what you came up with.

I'm intrigued by how much design space there is in simple signal split mechanisms, stuff that goes way beyond a harmonic tremolo or stereo splitting. Like someone 's recent request for an effect that oscillated between a clean and dirty signal.

[samhay]

I suspect it has a lot more to do with the blessfully slow response of both the LED and LDR, which smooths out any sharp bits in the LFO.

and how did you, as a human being, perceive that phenomena?

i had recently been reading about pwm, led brightness, lfo's and human perception/cognition. hence my question. it is an interesting subject. also look up: psychoacoustics. my! it's a big universe! 

No doubt. PWM works with LEDs, at least in part, because our eyes have a pretty poor time resolution and we use on-the-fly averaging. One big question is to what extent we are digital (use quantum mechanics), which is what I do for a day job.

[samhay]

when I started thinking about a dual band compressor

If you keep posting phrases like this, derail away ... I tried getting one of those to work recently and the results weren't exactly pretty. Really want to see what you came up with.

I'm intrigued by how much design space there is in simple signal split mechanisms, stuff that goes way beyond a harmonic tremolo or stereo splitting. Like someone 's recent request for an effect that oscillated between a clean and dirty signal.

Yeah, the circuitry certainly mounts up pretty fast. Once I have the tremolo off the breadboard (or buy another breadboard), I will try the compressor out. I am pretty sure I now know how to do it, but have to work out a few kinks.

[Jazznoise]

I suspect it has a lot more to do with the blessfully slow response of both the LED and LDR, which smooths out any sharp bits in the LFO.

and how did you, as a human being, perceive that phenomena?

i had recently been reading about pwm, led brightness, lfo's and human perception/cognition. hence my question. it is an interesting subject. also look up: psychoacoustics. my! it's a big universe! 

We hear sound in a logarithmic way, so actually a triangle wave sounds kind of exagerated to is. The smoothness of a triangle in an vactrol controlled scenario is really due to their poor response to chance. The higher order harmonics are really what dictate how abrupt the rate of change is.

Thanks for posting that schem, MWF! You didn't happen to try filtering the LFO to prevent the ticking? I'll have to dig around for our PIC Coder.

In response to the multiband thing, it's a peculiar type of processing that is often very context reliant. Things like Vocoders would be a classic example. Any type of filtering requires energy in desired bands. Multi band compression is messy and even things such as makeup gain can be a total pain - I rarely used it when mixing, something would have to be pretty broken to require that solution.

[pinkjimiphoton]

hoping to finally be able to start on this this week jon... really looking forward to it!!
just so i'm clear, what is the easiest/best version you've come up with?
remember, homie here is a hack.

[midwayfair]

hoping to finally be able to start on this this week jon... really looking forward to it!!
just so i'm clear, what is the easiest/best version you've come up with?
remember, homie here is a hack.

The one on page 1 is correct, except that C14 is redundant with C13.

[pinkjimiphoton]

thanks jon, gonna start working up a vero tonite hopefully..

dear god, the addiction is kicking in again...

[drolo]

Hi Jon,

First of all I would like to say Brovo as I think your trem sounds amazing. I had completely lost interrest in tremoloes since i sold my big box Pulsar but this one sounds really interresting and much more useful, musically.

I have a question about your demo on this clip:

http://www.youtube.com/watch?feature=player_embedded&v=SyFoTRWPq_A

It's not clear to me which LFO you are using in this one.
It sounds really deep and a lot better than your first demo.

[midwayfair]

I have a question about your demo on this clip:

http://www.youtube.com/watch?feature=player_embedded&v=SyFoTRWPq_A

It's not clear to me which LFO you are using in this one.
It sounds really deep and a lot better than your first demo.

That demo is with the TL072 IC-based LFO, the one shown in the schematic on the first page.