Let's design a tap tempo tremolo.

[Taylor]

I was looking around and discovered that, as far as I can tell, there are no tap tempo trem projects that have been put together. Seems like there should be. So let's make it happen.

Molten Voltage has a tap tempo LFO chip. It's pricey compared to pretty much any other IC you're likely to find. However, it does a lot, and makes the external component count pretty small. They even have a tremolo schematic already done. However, the audio portion of this circuit is passive. It uses a part I haven't come across before, an optoisolator whose photosensitive part (which would normally be an LDR) is a bilateral switch. So it can only turn down the volume, there can't be any boost. It would, at the very least, need a gain stage at the end IMO.

Can we put together something better? Would the above schem with an opamp amplification stage after it have any drawbacks?

As with the Gristleizer, I'd be up to do a double-sided board layout and get the boards made up. But I don't have the dough to do a group order on the Molten Voltage chips to get a lower price, unfortunately. Still, I think $20's not too bad for what it does.

[anchovie]

Burst Box!

Only problem is that you'd have to keep tapping for as long as you wanted the effect.

[markeebee]

The MoltenVoltage site seems to be down at the moment.  You must have scared them, Taylor.

[earthtonesaudio]

The main problem with the MV tap tempo chip is that the output is an analog voltage.  I know, I know, they tout it as a feature, but if the output was available in PWM or some digital format, you could simply hook up a CMOS analog switch IC and voila: there's your variable resistor.  Total parts count: 2 ICs and a switch.

Since it's a continuous voltage, you're forced to use one of the more standard voltage controlled resistor type circuits (JFET, MOSFET, LED/LDR), not one of which is simple, accurate, and repeatable.



My preference would be just to convert the LFO to PWM.  A high speed comparator and a fast, linear sawtooth oscillator would be required.  That would make a depth control easy (just a voltage divider between MV LFO and comparator).

Then your "variable resistor" would be a CMOS switch, or discrete transistor.

[Nasse]

I wonder if square could be integrated to triangle and somehow make rise & fall times & amplitude adjustable

how would work if I take epfm super tone control and put larger value caps on it so it could "eq" that lo f perfect sine to not so perfect

Last summer I did build Musikding "Das Tremolo" with many knobs and it is difficult to get any ugly sound from it

Today or yesterday I googled simplish midi metronome done with pic or something, it would be nice if a trem could be synced to midi clock

[.Mike]

I built a tremolo earlier this year based on the Tremulus Lune (link), but using Tom from ElectricDruid.com's PIC-based VCLFO 9D. It's output is PWM, and works very well. The LFO is very flexible, easy to use (once burned on the PIC), and offers a wide variety of waveshapes that sound really good in my tremolo.

Tom was working on a tap-tempo version of the VCLFO, and even has a topic here about it (link). I know he had a test version up and running, but I'm not sure if anything has come of it yet.

It may be a good option, though. If he finishes and releases the code, maybe you could design a circuit around his PIC. I know that not everyone has the tools to burn PICs, but if you did a group buy for a board for DIY use, you might be able to get permission to include ready-to-go LFO PICs with the boards.

Just a thought.

Mike

[aziltz]

I had a thought.  Check out this mojohand thingie...  http://www.tonefactor.com/proddetail.php?prod=Ramp

It ramps between two speed settings, and it can be used to drive their flanger, vibrato and vibe.  My first though is that it contains an LFO that takes precedence over the LFO internal to the actual effects.

I think it would really cool to come up with some kind of universal LFO controller or tap tempo device that could be spliced into to any number of modulation effects that we could edit, why stop at tremolo?  Beat sync'd tremolo and delay is very very cool btw!

Maybe we could do Tap Tempo, as well as two speed settings that could be toggled/ramped between.  Design it the right way and you don't have to use all the features in the build necessarily, but the flexibility is nice.

[earthtonesaudio]

I built a tremolo earlier this year based on the Tremulus Lune (link), but using Tom from ElectricDruid.com's PIC-based VCLFO 9D. It's output is PWM, and works very well. The LFO is very flexible, easy to use (once burned on the PIC), and offers a wide variety of waveshapes that sound really good in my tremolo.

Tom was working on a tap-tempo version of the VCLFO, and even has a topic here about it (link). I know he had a test version up and running, but I'm not sure if anything has come of it yet.

It may be a good option, though. If he finishes and releases the code, maybe you could design a circuit around his PIC. I know that not everyone has the tools to burn PICs, but if you did a group buy for a board for DIY use, you might be able to get permission to include ready-to-go LFO PICs with the boards.

Just a thought.

Mike

I have a standalone, analog tap-to-voltage converter that could be used with that:
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/earthtonesgallery/PT2399_tap_tempo.png.html?g2_imageViewsIndex=1
Voltage output from IC1B, everything to the right of it is for converting the voltage to a current and could be omitted.
Obviously this is not as elegant as doing the tempo part digitally... but it doesn't require a clock.

[MattXIV]

I had a thought.  Check out this mojohand thingie...  http://www.tonefactor.com/proddetail.php?prod=Ramp

It ramps between two speed settings, and it can be used to drive their flanger, vibrato and vibe.  My first though is that it contains an LFO that takes precedence over the LFO internal to the actual effects.

I think it would really cool to come up with some kind of universal LFO controller or tap tempo device that could be spliced into to any number of modulation effects that we could edit, why stop at tremolo?  Beat sync'd tremolo and delay is very very cool btw!

Maybe we could do Tap Tempo, as well as two speed settings that could be toggled/ramped between.  Design it the right way and you don't have to use all the features in the build necessarily, but the flexibility is nice.

I've been thinking of something similar - having effects that sweep take a control voltage via a high impedance input (something like a FET controling the current into to the LEDs of LDR/LED pairs)  rather than having the LFO onboard.  In addition to syncing multiple effects from the same control voltage,  you could use the same effects with a envelope follower, sequencer, or expression pedal as well and swap in incrementally more feature rich LFOs without having to alter the primary effect.

[jkokura]

I guess this post is my fault, cause I asked Taylor about a tap tremolo circuit.

Is it wrong to ask questions like "how does the empress unit and the Cusack unit and the Seymour Duncun unit do it?"

I detest Berhinger for their backwards engineering, but I also recognize that we could learn a lot for our own circuit by understanding those.

I know some people don't think tap tempo is helpful, but I want to build one, so nevermind it's helpfulness!

The EA is a tried and true trem, lots like it. Could we base off that and add a tap tempo circuit?

[Taylor]

I guess this post is my fault, cause I asked Taylor about a tap tremolo circuit.

Is it wrong to ask questions like "how does the empress unit and the Cusack unit and the Seymour Duncun unit do it?"

They all have custom digital chips that they designed. Some of them may be digitally controlled but analog signal path, but some may be digital all the way through.

[jkokura]

They all have custom digital chips that they designed. Some of them may be digitally controlled but analog signal path, but some may be digital all the way through.

So then the idea of starting from a common trem like the EA and then adding a digital tap tempo control is possible. It may not be the easiest solution.

I wonder, there's a PTAP for some common delay pedals, how did that come about? I know that circuit works with a micro-controller and digital pot which fits between the 'delay time' pot and it's connection to the board.

Would it then make sense to try and apply that MoltenVoltage circuit in that method (assuming the method hasn't been trademarked and we wouldn't be stealing...)

Just asking questions, I'm a true newbie when it comes to these things, been building for a few months and learning/researching effects circuits for maybe 8 months.

[earthtonesaudio]

PTAP turns tap tempo into a resistance, which means you could use it with basically any of the analog effects which use a pot to set the delay time.

[Taylor]

So then the idea of starting from a common trem like the EA and then adding a digital tap tempo control is possible.

Yep, that's definitely possible, but since much of the circuitry in most trems is for creating and shaping the LFO, we really only need the audio part, which is generally quite simple.

Earthtones, what's your objection to an optocoupler? I think an input buffer, followed by the LDR part of an opto like the NSL-32, into an output gain stage would be good and simple. Is there a problem with it? I know you're a major proponent of PWM, but to me using an opto is a well-proven way to make a nice trem. I guess the only drawback I see is that sometimes optical trems can't get really choppy with a square wave, since the opto smoothes out the waveform a little.

[earthtonesaudio]

I like optocouplers, but they have several drawbacks:
LED brightness nonlinear
LDR response nonlinear and slow
Wide tolerance

Of course you can deal with all of these, but...
CdS cells were recently added to the RoHS blacklist by the EU, so analog optocouplers are probably going the way of germanium.   

With PWM and CMOS or JFET switches, you trade all of those things for a high frequency clock.

[rustypinto]

Hey guys. If i may, let me make an offering.

I have a two PIC, tap controlled, LFO which outputs a 50% duty-cycle square wave that I use it for many applications. It uses a two-tap implementation with a range of 50ms-1000ms. Its been proprietary to my company for a while now, but i'd love to offer burned devices for this project. If there is enough interest, i will make a bulk purchase of the PICs, burn them, and ship them to all the contributors. I'm willing to go $10 on the whole system/ shipped.

Here is the momentary switch i use:

http://www.smallbearelec.com/Detail.bok?no=27

(One half is Normally Open, the other half is Normally Closed. The middle terminal is common to both. My chipset uses N.O.)

Here is the basic schematic:


This is very easy to add a depth and "shape" control (with an RC filter). I've used this to make an LDR trem like the Lune.

Of course you can deal with all of these, but...
CdS cells were recently added to the RoHS blacklist by the EU, so analog optocouplers are probably going the way of germanium.

LDRs are still being manufactured, even the infamous VTL5C1:
http://www.alliedelec.com/search/productdetail.aspx?SKU=9800700

with availability on Ebay, SmallBear, and who knows where else.

Let me know what you think!

[rustypinto]

One more note on clarity: the 10k pot shown is for the rate, same 55ms-1000ms range. You can use the tap or the pot at any time. I added the pot because nobody (that i know) can tap a 55ms tempo, so the pot lets you get at the vibe-like settings.

[jkokura]

While I'm thinking about it, I need somewhere to read and understand LFO - I'm lost in some of the conversation here. If I'm not mistaken, it stands for Low Frequency Oscillation, but Taylor made me think I need to understand it better, cause I'm planning on mounting a Phase, Trem and Flanger all in one DD box, and he said something about making their LFO's match and I thought to myself, "I don't know what that means, but sure - especially if it's good for my sound.

If we can get a tap tempo mod from this that will apply to the trem, I'd love to get it so we can externally mount it (or I just have to think hard about where to mount the other switches for the phase and flange) and then add it to this project. If not, then I may just build a separate EA Trem with the tap function (or whatever trem we come up with here). Yes I will be posting pics of this build. I plan on making it freaking perfect, with a spiffy paint job and labeling, so I can enter it into any future contests (here and/or at BYOC).

Boy am I realizing how much I like this stuff, but that I feel like there's a mountain of info in front of me.

[.Mike]

While I'm thinking about it, I need somewhere to read and understand LFO - I'm lost in some of the conversation here. If I'm not mistaken, it stands for Low Frequency Oscillation, but Taylor made me think I need to understand it better, cause I'm planning on mounting a Phase, Trem and Flanger all in one DD box, and he said something about making their LFO's match and I thought to myself, "I don't know what that means, but sure - especially if it's good for my sound.

According to my best understanding, a Low Frequency Oscillator is used in modulation effects to create a sweep. For example, a tremolo modulates volume from loud to soft. If you imagine a square wave, in terms of a tremolo, when the wave is high (or on, or however it would be described), the volume put out by the tremolo would be as loud as it goes. When the wave is low (or off, however it would be described), the volume put out by the tremolo would be as quiet as it gets. The LFO oscillates between high and low.

In other effects, like a phaser, the LFO modulates the phase shift. In regard to a delay, LFO modulation usually describes a slight raising or lowering of the pitch of the repeats, usually by slightly raising and then lowering of the delay time, which causes the repeats to sound, um, more spacial and, I suppose, liquidy-- kind of chorus-like.

You can use many shapes. Square waves, which are on-off, sine waves, which smoothly ramp up and back down again, "ramp up," which slowly ramps up and then quickly cuts off, "ramp-down," which quickly ramps up and the slowly cuts off, etc. Maybe this graphic will help you visualize it a bit.

Syncing LFOs could open up a whole bunch of interesting combinations-- like a phaser whose sweep is in sync with the repeats of a delay, or a tremolo whose volume changes are in sync with the repeats of a delay. You could even us a ratio, so, for example, the sweep of a phaser could be twice as fast as the repeats of the delay, but still proportional. There are many possibilities.

Shifting gears, I emailed Tom from ElectricDruid to see if he's made any progress on his tap tempo VCLFO. I'll post here if I hear back.

Mike

[Processaurus]

The molten voltage chip might have scared people off by having lots of options, but I think if you cut those down (by not hooking up the crazy sequencer section), it would be rudimentary to hook up the molten voltage LFO chip to the signal path part of any existing analog tremolo design, just a matter of getting the amplitude and DC bias right, and then feeding that into the tremolo's gain control element (LED/LDR, FET, VCA).  Like take their odd passive tremolo, and shine the LED on the photocell in the signal path part of a tremulous lune, or run the LFO through a cap into the FET on an EA trem (or better, the rEAgenerated trem spinoff, with more depth).

I'll try to draw something up that fits the bill, I got a couple of their chips to experiment with, and an extra EA trem board I made for some reason.   That or a design using a modern VCA, like national's stereo voltage controlled level/pan/treble/bass chip, the LM1036.