Let's design a tap tempo tremolo.

[ianmgull]

I doubt I'd ever build a tap tempo trem, but I do have an idea to fight the Russian Dragon (rushing or dragging - get it?).

The tempo is set at the start of the song, it's going to be a hassle to tap it in again at regular intervals during the song, and would certainly interfere with your playing. So what about a reset function on a momentary footswitch which wouldn't redefine the tempo, but would at least put the tremolo back on the beat. You could tap it once every so often just to tweak back in.

my line 6 pedals work to this effect.  tap and play, and if it gets off, just tap some more.  Nothing stops or stutters, it just re-averages the tap time.  I know they're digital effects, but maybe we could apply that feature somehow.

This has always been essential to me for any tap effect. I use a lot of tap delays and (as someone else mentioned) after a while the band just treats it as a metronome on those songs where it needs to sync up. This usually works great but we can get sloppy at times and it helps to be able to tap in a few beats to re sync with everyone else. So there's my $.02:

A robust tap tempo tempo chip will average in new changes to the current clock speed.

btw... My hat's off to the digitally inclined people for taking this on.

[ElectricDruid]

Just a note to say that I'm close to finishing my PIC 16F684-based Tap Tempo LFO chip. The final version of the chip produces eight waveforms, and can output a frequency at a multiple of the tempo ( x0.5, x1, x1.5, x2, x3, x4).

I've just got some tweaks to finish off (like getting the Tempo knob and the Tap Tempo input to work together nicely) and then I'm done. I'll post code and a datasheet on my website when it's ready.

I'm thinking of getting a tubeful of chips programmed up, so there'll probably be programmed chips available for people who aren't into PICs.

Thanks,
Tom

[jkokura]

That'd be great Tom.

So to be clear - does your circuit involve a specific trem or could this work with a variety of trem circuits (trem lune, Kay, ea...) Will you be posting a project file with trem and tap layout and offering to sell the preprogrammed chips, or is this going to be an tap tempo add-on that people can include as they design a circuit?

Jacob

[ElectricDruid]

Jacob,

No, this chip doesn't involve a specific tremolo, or necessarily any tremolo at all. It is purely a Tap Tempo LFO, so it could be used to give a tap tempo feature to most circuits that use LFOs. Tremolos are one example, but a tap tempo flanger sounds good to me, or tap tempo chorus, or panning, or etc. etc...you get the idea. Use it wherever you usually use the standard op-amp integrator triangle wave LFO!
I'll put some application circuits in the datasheet, but you could easily use it to drive a vactrol (or homemade LED/LDR combo). This would give you a tap-tempo LFO-controlled variable resistance, which is useful in many circuits. Alternatively, you can get the output as a straightforward LFO voltage output, which might be what other circuits require.
I'm not going to be doing a Tap Tempo Tremolo circuit myself, but  Mike's already done one with my PIC-based VCLFO, and the new Tap Tempo LFO would be a simple replacement. His work is here:
http://www.diystompboxes.com/smfforum/index.php?topic=77471.0

Like I said, I'm hoping to get a tube of chips programmed up, and if anyone was getting a run of boards together, I'd be more than happy to supply a batch of chips for a project. Watch this space.

Thanks,
Tom

[Taylor]

Is it possible to add a tiny slope to the square wave, so that it sounds like a square but alleviates the ticking problem that so many LFOs suffer from?

[ElectricDruid]

Taylor,

Yeah, it's possible. The square wave is generated from a PWM pulse train (PWM DAC) by running it through a filter to recover the average analogue level. So you can smooth the square wave by adding another filter, or by tweaking the one that is there. However, there are many possible causes of ticking, and very sharp edges on the square wave is only one of them. It's possible that the schmitt trigger switching in a typical op-amp LFO causes a voltage spike which could be heard as a tick. That's one problem that this LFO won't suffer from.

Mike might be able to advise us here, since he built a Tremolo with the original PIC VCLFO. I don't remember him saying anything about ticking.

In short, you're right to be cautious, but unless we've got an actual circuit and layout, it's pretty hard to work out ahead of time where the problems will come from. I haven't had any such problem, but I guess your mileage may vary. Please recognise that this is an entirely different design of LFO to most, and so is likely to throw up an entirely different set of 'unexpected features'!

Thanks,
Tom

[Cliff Schecht]

Adequate IC bypassing, careful layout and physical isolation help alleviate ticking. Also some high-pass filtering on the output (something like a 2nd order Sallen-Key filter) at about 30 Hz will usually do without killing your tone.

[Skruffyhound]

Thanks for the offer of programmed chips Tom. I would definitely be interested in one, perhaps a few, dependent on price. This sounds like a n interesting and flexible addition to a lot of circuits. I'm not set up to program as yet, I guess I'm not the only one, so I was kind of hoping you might step in and help us out.

Thanks to Taylor too, for starting this ball rolling.

[jkokura]

I too would be interested in chips, depending on price.

[ElectricDruid]

Okey dokey, I think I've finished. I've put details of my Tap Tempo LFO up online at:

http://www.electricdruid.com/index.php?page=projects.taplfo

There are example circuit diagrams, a datasheet, code, etc. Any questions, please ask.

I'll be trying to sort chips out soon, and if I can persuade Steve Daniels that this is a good idea, you might be able to buy programmed chips from Small Bear.

Thanks,
Tom

[jkokura]

That's a wonderful idea to have the available from steve - that way you don't have to deal with the ordering and mailing process but once, and you still reap the benefits (I'd hope).

I'd buy at least one, perhaps more.

Now the question is, what Trem is this going to work with - does someone think they could design one, or does this drop nicely into some pre-established trems?

Tom, other than a trem, what circuits (specific ones) would you want to try this with?

[Taylor]

I'm still up to design a circuit and PCB for this. Should be pretty simple, just need to decide what kind of control element we should use. Tom has a schem for an optical trem using the tap tempo chip on his page.

http://www.electricdruid.com/images/lfo/TapTremolo.gif

Opticals aren't my favorite trems just because they can't get really choppy at high speed square waves, but for most guitar applications, they sound great. What say you all to an optical tap tempo trem? I can start on the PCB design today if everybody thinks optical's the way to go.

[Skruffyhound]

What other control elements could we successfully use with this doodad. I don't know all the pro's and con's of the different possibilities in terms of musicality in the end result. Anybody care to enlighten me, in broad terms.

[ElectricDruid]

If you're thinking of doing a PCB layout, please be aware that I adapted Mike's circuit diagram for the new tap tempo LFO. Whilst the LFO should be a drop-in replacement, he used a homemade LED/LDR combo, so there might be some tweaks for a given vactrol. I put a VTL5C3 on the schem 'cos that's what I've got in the drawer, but I haven't done the tweaks yet.

The vactrol has the advantage of acting as the PWM filter too, because of the slow response you mentioned. This makes the circuit nice and simple. Other types of VCA will need the op-amp filter stages shown in the other example circuit, which adds more components.

T.

[.Mike]

Great work, Tom. I can't wait to try this. It's so generous of you to go through all the effort to make this for the community.

Just a few notes on the app note circuit that I "designed." I didn't really design anything. It's basically the audio path of the Trem Lune with the LFO replaced by the VCLFO. It works great.

If anyone is wondering about the transistor driving the LEDs, I used that because the PIC is limited at 20mA of PWM current output. So, if you were running two LEDs at full blast, you would be overloading the PIC output. I ended up with some popping when running the LEDs at such high current, so I reduced the current down to something like 3-4 mA. In that case, I'm sure you could omit the transistor that is acting as a current source, and just run the LEDs in parallel right off the PIC.

Taylor, I'm wondering if this will do the choppy square wave like you mentioned, at least a bit better than the standard LED/LDR tremolo. I am able to get a very good chop on mine by setting the waveform to square, and then using the wave distort to alter the on/off time of the LED. Basically, make the dark period much longer than the light period so there was more recovery time allowance for the LDR to catch up. On mine (using the original VCLFO9D), I can get it very choppy. The more choppy I let it get, however, the more gain I need to add to compensate for volume losses. Still, it works pretty good, and I would be happy to make a sound sample for you.



Mike

[Taylor]

Hmm, that sounds good, I had considered something like that. I admit I haven't had the time to really read up on all the capabilities and controls of this chip, but I have in other designs used a shorter "on" period to create a choppier wave.

I'd love to hear some sound clips if you have that capability.

The only thing that's worth some pause is that I don't know the legal/ethical/licensing issues with using a snippet of the Trem Lune to make PCBs. I could run it by Dann Green, though. I don't want to step on any toes, but at the same time I don't know that I could afford a licensing fee. Does anyone know the provenance of the Trem Lune's design? Is it from a manufacturer's app note by chance? I guess it's pretty much exactly what anyone would come up with when using an optocoupler to create series resistance, but I'm never sure how much ownership people can claim of ideas like that, and again I've always liked Dann, so I don't want to be disrespectful.

[ianmgull]

Okey dokey, I think I've finished. I've put details of my Tap Tempo LFO up online at:

http://www.electricdruid.com/index.php?page=projects.taplfo

There are example circuit diagrams, a datasheet, code, etc. Any questions, please ask.

I'll be trying to sort chips out soon, and if I can persuade Steve Daniels that this is a good idea, you might be able to buy programmed chips from Small Bear.

Thanks,
Tom

I would definitely buy a couple if you offered pre programmed PICs. I'm sure there's quite a few of us here that would love to give this a try but aren't set up for PIC programming.

[danngreen]

The only thing that's worth some pause is that I don't know the legal/ethical/licensing issues with using a snippet of the Trem Lune to make PCBs. I could run it by Dann Green, though. I don't want to step on any toes, but at the same time I don't know that I could afford a licensing fee. Does anyone know the provenance of the Trem Lune's design? Is it from a manufacturer's app note by chance? I guess it's pretty much exactly what anyone would come up with when using an optocoupler to create series resistance, but I'm never sure how much ownership people can claim of ideas like that, and again I've always liked Dann, so I don't want to be disrespectful.

This sounds like a great project! Of course I don't mind anyone using a series-resistance photocell circuit for a tremolo effect-- as long as no one minds me making my own tap-tempo devices! I've developed a tap tempo on a curious little bass synth project, using an AVR chip with code written in C:
http://4ms.org/projects/?p=49

It has a similar tap tempo subroutine (measure time between taps, ramp a PWM output to get an analogue output, which drives an LED, which shines on a photocell, which controls a resonant analogue filter), but it only does triangle wave. An interesting feature is a mode where you can tap a complex tempo (daaahh dit dit daaahh dit dit) and it will play that rhythm.... Tom, I'd be happy to help unearth that section of the code if you (or any coders) are interested. Basically, instead of keeping track of time as a single variable (FREQ_INC) I use an array of values for tempo, and the code steps to the next element in the tempo array each time it completes a waveform.

HTH

[Taylor]

Awesome! Dann, you're a cool guy as always. I was checking out that Autonomous Bassline the other day and it's extremely neat and clever - especially the IR communication between circuits. And this is coming from a bass player - soon to be obsolete. 

It has a similar tap tempo subroutine (measure time between taps, ramp a PWM output to get an analogue output, which drives an LED, which shines on a photocell, which controls a resonant analogue filter), but it only does triangle wave. An interesting feature is a mode where you can tap a complex tempo (daaahh dit dit daaahh dit dit) and it will play that rhythm.... Tom, I'd be happy to help unearth that section of the code if you (or any coders) are interested. Basically, instead of keeping track of time as a single variable (FREQ_INC) I use an array of values for tempo, and the code steps to the next element in the tempo array each time it completes a waveform.

This is very intriguing...

[jkokura]

Awesome! Dann, you're a cool guy as always. I was checking out that Autonomous Bassline the other day and it's extremely neat and clever - especially the IR communication between circuits. And this is coming from a bass player - soon to be obsolete. 

It has a similar tap tempo subroutine (measure time between taps, ramp a PWM output to get an analogue output, which drives an LED, which shines on a photocell, which controls a resonant analogue filter), but it only does triangle wave. An interesting feature is a mode where you can tap a complex tempo (daaahh dit dit daaahh dit dit) and it will play that rhythm.... Tom, I'd be happy to help unearth that section of the code if you (or any coders) are interested. Basically, instead of keeping track of time as a single variable (FREQ_INC) I use an array of values for tempo, and the code steps to the next element in the tempo array each time it completes a waveform.

This is very intriguing...

Most interesting if it were a switchable option, like in one mode we could get a patterned tap to influence the speed, but if we could also have an option where we could use the switch to measure the time between 3 taps to get the speed of the trem (or whatever LFO).

I like the potential of Tom's chip a lot though. I'd love to see what other kinds of implementation we can come up with down the road. Taylor, are you making progress on a circuit? Is this an add-on type feature like the PTAP, or is this an integrated feature (you can't seperate the tap function from the tremolo)? With my very limited knowledge, resources and skills, is there any way I can help out at all?

Jacob