Building the tap tempo tremolo

[KyleLaster]

Okay so i finally got around to building my tap tremolo last night.  bypass works fine, but when the effect is engaged i just get an ossilating sound.  all the knobs work because the oscilating pulses and the led flashes but no guitar signal is passing through with it.  Any Idea at all what this could be?  I'm still pretty new to the pedal building game, I've built 5 or 6 BYOC kits so I thought I could take the leap to this.  Appartently I suck at it.  Help me!

[.Mike]

Hi Kyle,

If you've got the LFO going, you have the most complex part of the circuit working, so that's good.

The first thing to do is to make sure there isn't a simple mistake. Make sure the vactrol is mounted the right way. Make sure the opamp is inserted in the right direction. Make sure you used the right component values in the right places. Make sure the trimpot for the vactrol is set somewhere in the middle. Otherwise, it might be that the LED side of the vactrol is turned all the way off.

If that doesn't work (and it probably won't), it's time to take some voltages.  Here is the debugging topic, which will walk you through it. Since the opamp is the only active component in the signal path, the voltages for it are the most important.

If the problem isn't obvious after posting voltages, the next step will probably be to make an audio probe. You can then figure out where the signal stops, and debug whatever problem exists after that point.



Mike

[KyleLaster]

How do i go about making an audio probe?

[Taylor]

http://www.diystompboxes.com/pedals/debug.html
http://www.geofex.com/FX_images/audioprb.gif

[Ultrakd]

Ok I have a couple questions. Im still new to pedal building so they are sorta noobish. Some that have probably already been asked but I didnt really see the so Ill ask again .

1) If I wanted to add the multiplier spst switch what exactly does it do? Is it the same as the multiplier pot? (I feel really dumb for askin this one lol)
2) For the waveform and multiplier pots, how many people use a rotary switch? Is using a rotary switch better than using a pot? If it is better to use how do I go about doing it? I was a little confused as to how to do it when I was looking at the diagram.
3) How can I add a second LED so that I have one for showing when it is bypassed and one that stays on that blinks with the tempo?

Thanks for helping and sorry for the noobish probably really obvious questions...

[.Mike]

1) If I wanted to add the multiplier spst switch what exactly does it do? Is it the same as the multiplier pot? (I feel really dumb for askin this one lol)

It cycles through the multiplier, overriding the value set by the pot.

2) For the waveform and multiplier pots, how many people use a rotary switch? Is using a rotary switch better than using a pot? If it is better to use how do I go about doing it? I was a little confused as to how to do it when I was looking at the diagram.

Most people use pots because they are cheap and easy. That makes it slightly less obvious which waveform you have selected, but it's still pretty obvious when you have switched waveforms. Wiring up a rotary switch is more complicated, since you have to basically solder 2 resistors to every lug on the switch. The rotary switch setup is covered briefly in the Taplfo's datasheet.

3) How can I add a second LED so that I have one for showing when it is bypassed and one that stays on that blinks with the tempo?

Basically, the board has a spot to hook up an LED for indication. If you want that LED to always be flashing, regardless of whether the pedal is in bypass, then just hook up an LED. Your status indicator LED would hook up to your 3PDT just like any other pedal. If, however, you want the flashing LED to only appear when the effect is engaged, I think there is certain technique that works best. It is covered earlier in this topic (sorry, I don't know where).



Mike

[Ultrakd]

3) How can I add a second LED so that I have one for showing when it is bypassed and one that stays on that blinks with the tempo?

Basically, the board has a spot to hook up an LED for indication. If you want that LED to always be flashing, regardless of whether the pedal is in bypass, then just hook up an LED. Your status indicator LED would hook up to your 3PDT just like any other pedal. If, however, you want the flashing LED to only appear when the effect is engaged, I think there is certain technique that works best. It is covered earlier in this topic (sorry, I don't know where).



Mike

Ok so just stick the one led in the area on the PCB where it says LED Negative  & Positive and the setup the other led the way the off board wiring shows on Tonepad? Oh and the other question I had was what is the control voltage?

[Taylor]

Ok so just stick the one led in the area on the PCB where it says LED Negative  & Positive and the setup the other led the way the off board wiring shows on Tonepad?

Yes, that's right.

Oh and the other question I had was what is the control voltage?

I don't understand this question - could you say it in a different way? Are you just wondering what control voltage is in a general sense, or something to do with this project?

[Ultrakd]

Oh and the other question I had was what is the control voltage?

I don't understand this question - could you say it in a different way? Are you just wondering what control voltage is in a general sense, or something to do with this project?

Yes pretty much in general. But also in this project, under the modifications section. It says "Any pot can be modded for CV (control voltage) input easily."

[Taylor]

Well, Google can find you all you'd need to know about CV, but the basic idea is that you have a varying voltage, and that voltage controls some parameter. In this pedal, all five standard controls are changed by a varying voltage between 0v and 3.3v (actually less than that for the multiplier knob).

This isn't generally of much interest within a standard effects pedal setup because you need other CV circuits to do anything with it. But it's useful for synth people who have other modules that create varying voltages based on a variety of factors. It's really only useful when you have multiple separate units which can either create or accept or modify control voltages. Read up on modular synthesizers to get an idea.

For somebody with only pedals, most of which they didn't build, CV isn't something that's of much use.

But for example, if you had an envelope follower CV module, you could plug your guitar in there, and get a CV that changes with the playing dynamics, so you could change the speed of the tremolo by playing harder or softer for example.

[Ultrakd]

oh ok I under stand some better now...thanks

Is there a way to make stereo output so I can plug it into 2 amps?

[Taylor]

If you just want to split your mono signal to two amps, you'd want to build a buffered splitter - plenty of schematics for that online. If you want to pan back and forth or apply tremolo to a stereo signal, you'd need to add another the optocoupler and duplicate the whole audio path of the circuit.

For panning, you'd also need to invert the control signal - this is tricky since the the control signal enters the optocoupler as a PWM signal, not an analog voltage. You'd need to filter the PWM into analog CV. So this is somewhat more advanced, and the relevant info is in the datasheet for the TAPLFO on electricdruid.net if you want to dive into it.

[.Mike]

For panning, you'd also need to invert the control signal - this is tricky since the the control signal enters the optocoupler as a PWM signal, not an analog voltage.

If I remember right, it is really easy to invert the action of the LED with no extra components. I just don't remember exactly how.

I think that instead of connecting the LED anode to +5V and letting the LFO vary the voltage above ground where the cathode sits, you connect the cathode directly to ground, and let the LFO vary the voltage to the anode. Something like what is shown here.

I'd have to breadboard it to be sure, but it's really simple.

Mike

[Taylor]

D'oh, you're right Mike. I did that in my fake phaser project a while ago; don't know why that slipped my mind.

I suppose there's a possibility that this could make the trimmers harder to set w.r.t. ticking, but that may not be an issue at all.

[Ultrakd]

Ok this is what I was meaning something like this pedal does. http://www.youtube.com/watch?v=73K-9ErZroQ

[Jamforthelamb]

Just ordered my TTT board and chip from Taylor  . I have quite a few projects to finish before I start on it (that is if I can keep myself on track lol). I'll update my progress once I get there.

-Kevin

[Ultrakd]

What would be the best size enclosure for putting this pedal in? Having 3 footswitches...

[dfine22]

Question,  Getting ready to build a TTT. The BOM indicates 22K trim pots and the board looks like it should have 10K trimmers. Please help?

[.Mike]

They're used as the current limiting resistors for adjusting the maximum brightness for the LED and the vactrol. Anything from probably 5k on up will work well. It's not going to change the sound at all.

The bigger the value, the dimmer you will be able to get the LED. By dimming the LED, you decrease the chance of ticking. For most LEDs, 10k will work. I suspect Taylor suggests  22k because some really high efficiency LEDs might still able to be dimmed further than 10k.

Mike

[Ultrakd]

What would be the best size enclosure for putting this pedal in? Having 3 footswitches...