Building the tap tempo tremolo

[Les Paul Lover]

Taylor,

I tried to open your web site, but my antivirus blocked it saying:

Location: musicpcb.com
Access has been blocked as the threat Troj/SEO-A has been found on this website.


I thought I'd better let you know!

[Taylor]

Thanks LPL, it's been an ongoing problem, see here for an explanation:

http://www.diystompboxes.com/smfforum/index.php?topic=89687.msg996939#msg996939

[threepwood]

Hi there

I'm just doing a bit of tinkering and wondered if anyone could tell me what the two EXP pads for the optional multiplier switch connect to on the PCB? Looking at the schem it looks like one goes to pin 8 of the TAPLFO and the other to ground. This could be completely wrong though as I am useless at reading schematics.

All help greatly appreciated.

Thanks

[Taylor]

That's right, so a momentary switch across those pads will pull pin 8 of the TAPLFO low, which steps up to the next multiplier. The pin is normally pulled high through the 10k resistor directly above the EXP pads.

[Ultrakd]

Ok so after not working on pedals for a while I've decided to get back into it and I want to fix my tremolo pedal. This was one of my favorites that I made. But right now I'm not getting any sound through the pedal. I have it hardwired without a switch till I get it fixed.

Not only am I not getting any sound what so ever. I've checked the voltages on the tap Lfo and it seems to be within the parameters as everyone else's. So what could be causing it?

[Taylor]

It could be anything in between the audio input and audio output. The audio section is the TL072 and right side of the board. The first step would be to build an audio probe and probe from the input all the way through, using the schematic as your map, until you find the point where you stop getting sound. Checking opamp inputs and outputs is a good place to start to narrow down the area of interest. Also a good idea to put trimpots and wave distort knob to a middle position when testing.

[Joe Dorcia]

Evening all,
Just finished off the circuit and I amp having an issue with the audio side. After a quick probe around I loose my signal at pin 2 of the TL072. I socketed the 072 and if I remove it I can probe and get the signal when pin 2 would be, so it must be something odd with the IC or its biasing. I'm wondering if my Vref is too high?

Here are my voltages:

1 - 3.68      8 - 7.39
2 - 3.68      7 - 3.68
3 - 3.66      6 - 3.67
4 - 0.00      5 - 3.66
Vref - 3.66
This is with a battery hitting 7.5 volts. This figures are the same proportionally using a 9v PSU.

Any ideas?

Also, just to clarify, the NSL32 has the white dot on the negative leg, correct? So it should go into the lower hole on the LED side of the pcb (lower left).

[Taylor]

Evening all,
Just finished off the circuit and I amp having an issue with the audio side. After a quick probe around I loose my signal at pin 2 of the TL072. I socketed the 072 and if I remove it I can probe and get the signal when pin 2 would be, so it must be something odd with the IC or its biasing. I'm wondering if my Vref is too high?

Here are my voltages:

1 - 3.68      8 - 7.39
2 - 3.68      7 - 3.68
3 - 3.66      6 - 3.67
4 - 0.00      5 - 3.66
Vref - 3.66
This is with a battery hitting 7.5 volts. This figures are the same proportionally using a 9v PSU.

Any ideas?

Actually, we expect pin 2 (inverting input of the first opamp) to have no audio signal because that point in an inverting amp is a "virtual ground." Here's a good video that will explain this:

https://www.youtube.com/watch?v=7FYHt5XviKc

So it showing your Vref voltage is correct as the non-inverting input is at Vref and the opamp attempts to make its inputs equal through feedback. Your Vref should be half the supply voltage, which it is so you're good there.

So, the voltages you posted look fine, but they don't tell the story of what's going on with the audio since you presumably were not playing anything into it while measuring, and a multimeter is not a very useful tool for looking at audio anyway. Continue probing - next check the output of this amp (pin 1) for audio, then the output of the output amp (pin 7).

Also, just to clarify, the NSL32 has the white dot on the negative leg, correct? So it should go into the lower hole on the LED side of the pcb (lower left).

Yes, that's right.

[Joe Dorcia]

Evening all,
Just finished off the circuit and I amp having an issue with the audio side. After a quick probe around I loose my signal at pin 2 of the TL072. I socketed the 072 and if I remove it I can probe and get the signal when pin 2 would be, so it must be something odd with the IC or its biasing. I'm wondering if my Vref is too high?

Here are my voltages:

1 - 3.68      8 - 7.39
2 - 3.68      7 - 3.68
3 - 3.66      6 - 3.67
4 - 0.00      5 - 3.66
Vref - 3.66
This is with a battery hitting 7.5 volts. This figures are the same proportionally using a 9v PSU.

Any ideas?

Actually, we expect pin 2 (inverting input of the first opamp) to have no audio signal because that point in an inverting amp is a "virtual ground." Here's a good video that will explain this:

https://www.youtube.com/watch?v=7FYHt5XviKc

So it showing your Vref voltage is correct as the non-inverting input is at Vref and the opamp attempts to make its inputs equal through feedback. Your Vref should be half the supply voltage, which it is so you're good there.

So, the voltages you posted look fine, but they don't tell the story of what's going on with the audio since you presumably were not playing anything into it while measuring, and a multimeter is not a very useful tool for looking at audio anyway. Continue probing - next check the output of this amp (pin 1) for audio, then the output of the output amp (pin 7).

Also, just to clarify, the NSL32 has the white dot on the negative leg, correct? So it should go into the lower hole on the LED side of the pcb (lower left).

Yes, that's right.

Thanks Taylor, its all up and running now! As I didn't fully understand how the IC was working I focussed on that instead of just replacing the Vactrol - must have been a dud or I accidentally fried it (unusual, not fried any diodes or trannies before but who knows). Anyway, its sounding great now, a bit of fiddling to do as there is still some ticking on the Ramp Up and Square settings - I also wired my external gain pot backwards so I'll sort that too.

In the build doc you suggest a Ultra Bright Blue LED, I used UV/purple for mine for aesthetic reasons but I know they have a much lower brightness rating than blue. Why did you suggest blue? To allow you to use a lower voltage and it still be bright? Would it be worth me swapping the UV/Purples for something brighter?

[Taylor]

Hmm, I think my thinking at the time had to do with using less current to turn on the LED, since the current spikes when switching the LED are one of the sources for ticking in the audio in trem circuits.

But, there are so many variables in DIY builds that I don't know that it matters too much. If you're unable to trim out the ticking you could try swapping in a high-intensity LED to see if it makes a noticeable difference.

[Joe Dorcia]

Hmm, I think my thinking at the time had to do with using less current to turn on the LED, since the current spikes when switching the LED are one of the sources for ticking in the audio in trem circuits.

But, there are so many variables in DIY builds that I don't know that it matters too much. If you're unable to trim out the ticking you could try swapping in a high-intensity LED to see if it makes a noticeable difference.

Thanks again, I might swap the UV LEDs out for Warm White. Both are Ultra Bright, but the UVs brightness is rated at 3,000mcd, Warm White is 14,000mcd (Blue is 9000mcd) so that may help. Once its all done and looking lovely I'll post a pic.

Big thanks to you and Tom for designing such a great circuit and tap LFO chip, it sounds wonderful!

[acehobojoe]

Anyone got that alternate wiring diagram picture? I believe I just need to Ground the PWM when switched to get rid of that nasty tick.. and somehow make my LED less blinding.

[Taylor]

I redrew the alternate bypass diagram, here's the file, and it's also linked on the tap trem page at the musicpcb site, so you can find it without having to find this particular page of the thread.

http://imgur.com/fi592fn

To make your LED less bright, you just need to turn down its associated trimpot. That's the one in between the ICs, on the right.

[acehobojoe]

Thank you!

[Taylor]

I should add this: the extra LED in that diagram will work like a regular bypass LED - it doesn't show the LFO's activity like the one on the board. But the one on the board will turn off when bypassing anyway, so this second LED is optional. Some people wanted this because in certain settings (square wave, tiny pulse width) the LED is not so visible when flashing. So for anybody using this alternate wiring scheme, if you don't want the second LED just leave it and its resistor off, leave the lug it was connected to on the bypass switch empty.

[acehobojoe]

I just switched that resistor connection to gnd in off mode and it worked great

[lars-musik]

Hi there,
I am using and loving my tap-tremolo very much, but two things I'd really like to change. First thing: I only use the sine and the square waveforms. I think I figured out how to wire a spdt switch to only have these two waveforms. Maybe someone has a better idea?

However, I'd also like to get rid of the triplet settings of the multiplier and here I completely lack ideas. What I have in mind is a switch that switches between half, normal and double tempo compared to the tap. Can anybody help?
Thanks in advance!

[Taylor]

For the sine/square switch, you could wire three resistors in a chain and swap between the nodes between R 1 and 2 and R 2 and 3. After a long Saturday of work my brain's too fried to think of the right resistor values at the moment though. This would only save you a resistor.

A rotary switch with only those three multipliers would be simple - again you'd just wire the resistors in series and connect the throws of the switch to the nodes between resistors. Just pick the right resistor values to only select the values you want. A toggle switch could also be done but most 3-position toggles are center off, so you'd need to pull the center multiplier pad low in the center position with another resistor, and then your toggle would be normal speed, then half speed in the middle, then double speed. You can get 3-position toggles with an actual third throw if having them out of order bugs you, but the only ones I remember seeing have the sort of cylindrical lever which requires an elongated hole drilled through the enclosure, which makes them inconvenient for most DIYers as cutting a slot is tricky to do.

[Unlikekurt]

I am almost certain this has been covered.  I have searched and not found an answer.
1. Is there a way to search an individual thread?
2. Should the momentary switch be NC or NO?
3. When set at 1/4 Notes, what is the longest tempo that can be tapped in?  Can you tap in as slow as the tremolo pot can set?  Is there a point where the last tap is ignored as too much time has passed and a 2nd tap has not occurred?

Thanks

[Taylor]

1. No, and I agree this does make using this thread somewhat difficult. I usually have better results using Google to search this forum rather than the built-in search. So for example something like

"momentary switch" "tap tempo tremolo" site:diystompboxes.com

2. The switch should be normally open.

3. Here's what the TAPLFO chip datasheet has to say:

"The basic range of the TEMPO CV allows the LFO to produce frequencies between 0.05Hz (a 20
second cycle) and 12.8Hz. However, in conjunction with the MULTIPLIER CV, this range is
extended to 0.025Hz (a 40-second cycle) to 100Hz."

There is definitely a timeout on the taps such that after some amount of time the chip stops waiting for a second tap and just goes back to the time defined previously, but I couldn't find how long the timeout is even scanning through the assembly code for a note. Emailing Tom Wiltshire would be the most direct route to an answer. His email is here:

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