Building the tap tempo tremolo

[spargo]

More questions...about the expression pedal jack.  I assume I use a stereo jack?  How exactly do I wire it to the pot?  You mentioned every expression pedal is different...I have a Boss FV-500L, but am making this for a friend and I'm not sure what he may end up using.  Is there one way that is most common?  How does the Boss one get wired?

Also, the direction of the pot wiring?  The board is not labeled, so I'm a bit mixed up.

[Taylor]

I don't know how the Boss is wired, but what makes being a DIYer great is that you can easily pop it open and see for yourself since you have one. I use Moog EP-2s and wire my expression pedals for that.

Here's a diagram I drew a while ago to show how to do it. Use a stereo switched jack (one that has 6 contacts).

http://img689.imageshack.us/img689/8049/gizerspeedexp.png

This is done in accordance with the Moog exp. jack, which connects the tip to the wiper. Other expression pedals are different, so figure out how yours is set up before copying this diagram.

[spargo]

So, just got it all wired up...bypass works.  When I engage the pedal the LED stays steady on and I get no sound.  Any trouble shooting tips?  Tried tweaking all the trimpots.

Both the IC and TAPFLO chip appear to be getting power just fine. I could post voltages if necessary.

[Taylor]

Did you wire the wave distort as a pot or fixed resistors? If you used a pot, make sure you have it set to the center while testing.

The audio path is really simple, so it will be easy to probe through the circuit with an audio probe and see where your audio dies. Set the trimpots all to the center while testing.

[spargo]

Sweet, adjusted the pots and set the wave distort knob to middle and it works great now! Except the tap switch seems to be pretty spasmatic?  Like I'll tap it to a tempo and it just kind of randomly seems to pick a tempo...

[Taylor]

What kind of switch did you use?

[spargo]

This one: http://www.smallbearelec.com/Detail.bok?no=672

[Taylor]

Hmm, that's what I'm using too. It may just be that you need to get the hang of how to tap with this particular circuit/PIC program. I had some problems too at first. I think the debounce part of the program could stand to be beefed up, but for the most part you'll figure out how to tap to get it to work. You need to hold the switch for just a bit longer than you think for each tap.

[spargo]

Got one more question...after I built this pedal I gave it to a friend and he said: "I tried messing around with the internal pots but I wasnt able to get the volume up enough to compensate for the drop."

Any ideas?

[.Mike]

Did you experience the volume drop when you were testing it?

There are three trimpots. The two that are side-by-side control the current going to the LED and the photocoupler LED. Once set for minimum clicking or popping, they should be pretty much left alone. The other trimpot is for adjusting the gain, and if your friend doesn't quite know what he's doing, it is probably the only one they should mess with.

Also, make sure you have explained that the wave distort feature should be set in the middle. It alters the on time verses the off time. If it's up too high (or is it too low-- I haven't built mine off this board yet) so that there is a longer quiet period compared to the audible period, then the perception is that the overall volume has decreased.

Maybe Taylor has some other ideas.

Mike

[spargo]

Ya, I had the volume drop when I was testing it but I didn't try to adjust it so much because I thought that it would be different on every pedal board, depending on how your pedals are all set.  I figured he'd have to adjust it anyway.

And the other trimpots shouldn't affect volume at all should they?  Only the ticking?  I don't think I set those well enough either.

[Taylor]

The trimpot right next to the PIC controls the optocoupler, as Mike said. It definitely does affect the volume. More resistance means that the optocoupler doesn't light up as bright when on, which equals a lower max volume. If the gain pot doesn't allow unity gain even at max, it means that you don't have the optocoupler trim set right. It should be possible to adjust the gain trim to the point of getting huge distortion.

So you'll need to readjust the optocoupler trim, and possibly up the cap marked 330p if you need to have the trim dialed so far down to get rid of ticking.

[spargo]

Thanks!  So the optocoupler trimpot that may affect the volume is the one directly next to the TAPFLO chip, correct?

[mth5044]

Just ordered parts from Taylor. Excited!

Anyone have any finished pics for layout ideas?

[tictac]

Hello,

Sounds like a great build!

I can't see the PDF build instructions when I go into the galley; am I doing something wrong?

TT

[Taylor]

Click on "no thumbnail", then on the next page, click on "download document".

[karter2000]

Hi all,

I have a tremolo that needs a debug, and I'm afraid it's beyond my abilities!  The issue is that it doesn't pass sound, only ticks.  It appears the LFO is working properly, as the LED works, and changes when the pots are moved.  I've poked around with an audio probe, but nothing really stands out.  I'm getting clean signal at pin 1 of the TL072, but quiet ticking everywhere else.  I'm getting loud ticking at the photocoupler.

Kinda frustrating as the audio part of the circuit isn't that complicated!

[karter2000]

Just an update.

Been messing with it this morning.  After it dawned on my that I should have signal at pin 2 of the TL072 (which I didn't), I resoldering the two 220ks and the TL072.  The good new is I'm now getting signal through with tremolo.  However, it's very weak and I got the gain trim maxed.  I'm also getting ticking, but I also have the optocoupler trimmer quite high as that's the only way I get a strong signal.  Not sure if the ticking is 100% related to that, or I have another problem.

[mth5044]

Quick question about pot orientation - I typed out a long confusing thing, but pictures are much easier. 1, 2, 3 or 4 



Now that I think about it, 1 and 4 are the same, as are 2 and 3. Oh well. Also, will 16mm pots fit next to each other? I don't have the board with me now, so I thought I'd ask. Thanks!

I also want to say, great board Taylor. I really like the size of the pads and the layout!

[Taylor]

You can use either 1 or 4 - I use 4. This allows to trim the trims once the pedal is all built. 16mm pots do fit all next to each other - I use the angled PC mount ones.

Thanks for the comments!