Building the tap tempo tremolo

[funkgang49]

Hey All,
I'm on my 2nd Tap tempo tremolo build and have run across a problem. I have bypass signal but no signal when the effect is turned on. Checked all my connections and everything is hooked-up correctly. I have the LED hooked-up directly to the board so it should be on all the time w/ an offboard LED that engages & lights up when the effect is turned on. I am measuring 4.68v at both legs of the resistor side of the NSL-32 but no voltage on the + side leg (white dot leg installed in appropriate slot). So I desoldered & installed a 2nd NSL-32 (I have one more on hand) but same result: no voltage on + side leg & no voltage at POS. pad for the LED. Could both NSL-32's be bad?!

[Taylor]

Does the flashing LED flash? If so, trace through the audio portion of the circuit with an audio probe until you find the point where signal stops getting through.

Bad parts exist but in my experience, my own mistakes outnumber bad parts 100 to 1.

[funkgang49]

Hi Taylor!

Does the flashing LED flash?

No, flashing LED does not work - no voltage at positive LED pad.

[Taylor]

OK, so the problem lies (at least) with the LFO section of the board. I'm assuming you've already set the trimpots to different levels while testing, set the knobs to various spots (always start with wave distort in the middle or 50% duty cycle, makes it easier to see things are working). Can you post voltages for the TAPLFO (PIC) IC and the 5v regulator (78L05)? A picture might also help us see something amiss.

[funkgang49]

I set external controls:Depth-2/3,Multiply-3/4,Wave -1/2(50%),Speed-3/4. I then adjusted all 3 internal trim pots (22k as listed in build doc., Board designation lists as 10K?) through entire ranges to no effect.
Here are my voltage readings for Tapflo:(from far left to right bottom row/then top row as in photo)
Pin #1- 5.01v                       #8- 0v
    #2- 2.20v                       #9- 3.45v
    #3- 2.13v                       #10-0v
    #4- 5.01v                       #11-0v
    #5- fluctuating voltage    #12- 2.39v
    #6- 0v                           #13- 2.50v
    #7- fluctuating voltage    #14- 5.01v
Voltages for 78L05:(from bottom to top refer to photo)
Pin #1- 9.34v   #2- 0v    #3- 5.01
Voltages for 2N3904:(from left to right)
Pin #1- .02-.04v (fluctuating)   #2- .2-.46v (fluctuating)   #3- 0v

Here's a gutshot...

[funkgang49]

Just wanted to bump for a response. I tried different 2N3904's and 78L05's & adjusted trim pots to no avail - I'm still getting no voltage at the LED. I am however getting neg. fluctuating voltage at neg. leg of NSL-32 (dotted side). Any ideas would be greatly appreciated 

[Taylor]

Those voltages mostly seem reasonable, though I don't have a built tap trem at this time against which I could check. Since you said you built another one that works you should be able to compare voltages to see where they diverge and get a sense of where to look. The 3904 voltages possibly look suspect, any chance it's not seated firmly in the socket?

[funkgang49]

Since you said you built another one that works you should be able to compare voltages to see where they diverge and get a sense of where to look.

A friend of mine heard that pedal and relentlessly pestered me until I sold it to him. Fortunate for him, unfortunately for me! So I don't have anything to compare voltages to.

I made sure to seat the 3904 properly when I replaced it with another from my stock.

A couple of things I noticed that maybe you could clarify:
1. I am getting 4.68v only on topside leg (resistor side of NSL-32) bottomside leg reads 0v. Is that correct?
2. Dotted side of NSL-32 voltage fluctuates between -(negative).02-.07v. Positive leg reads 0v. Does that seem right?
3. Could voltage to the LED be blocked at the trimmer pot?

New 2N3904 reads (from left to right) : pin#1 neg(-) .01-.06v fluctuating, pin#2 .16-.52v fluctuating, pin#3 0v.

[funkgang49]

Bump for reply - anyone with a working build, some voltage measurements? 

[lwatford]

I would, but it seems like I killed the taplfo somehow. I don't see any voltage out of pin 5, input voltage looks right.

[LaceSensor]

Here is my fourth take on the MusicPCB Tap Tempo Tremolo / Gigatrem

This was a bitch to get rid of the tick, dont think ive totally managed it to be frank.
It only affects the ramp, which you can avoid by selecting triangle and wave distort it for the same sound, the square wave and random

I decided this time to do the "resistor string on rotary dial"
If I were to do this again Id probably skip a few modes with the correct resistor values for convenience sake.
I have no plans for this other than to probably pass it to my cousins husband who was asking me about trems a while ago.
He likes classic sine wave trem, so the tick on teh square and ramps wouldnt bother him as I doubt he would use those modes

The other thing I did new for this build was add a small momentary multiplier step switch which skips the rate set by the tap tempo through various subdivisions. neat!

Enjoy pics

[jmasciswannabe]

Building this for a bass player. In/Out caps need any adjustment. They are fairly large at 1uf, but thought I'd ask.

[Taylor]

I just simulated it with the Falstad Filter App, with the values in the schematic it's flat to way below bass's lowest fundamental, so no need for bigger caps. In fact, it could be 100n and wouldn't be rolling off any appreciable bass.

[jmasciswannabe]

Thanks, Taylor. Hard to believe this thread started 4.5 years ago with our posts! HA! Lace, did you use the NSL32 or roll your own? I ordered a slew of ldrs with the specs you use in the doppel and was going to give it a shot.

[Taylor]

Thanks, Taylor. Hard to believe this thread started 4.5 years ago with our posts! HA!

Yeah, that is crazy, and even though I know a lot now that I didn't know then, I'm glad my posts on the first page don't seem dumb to me now. There's stuff still up on the internet that I wrote last millennium when I was 13, ranting about Ralph Nader. Now that is too embarrassing to link. 

[jmasciswannabe]

Thanks, Taylor. Hard to believe this thread started 4.5 years ago with our posts! HA! Lace, did you use the NSL32 or roll your own? I ordered a slew of ldrs with the specs you use in the doppel and was going to give it a shot.

Guess I could have answered my own question by taking a look at the pic closely! 

[Unlikekurt]

Hey guys.  I read through a great deal of this thread and didn't see anything jump out at me with respect to my issue.

I built the unit and tried out a few different vactrols.  A little bit of ticking, mostly only in the ramp up/down and square settings.  But it's really only noticeable when no music is being played.  I'm currently using about 4.3nF to try to buck the ticking.

Sure I'd love to kill the ticking entirely, but that's not the meat of my main issue.

If I tap a tempo in.  All is well.
Then if i adjust depth or waveform, the tempo immediately reverts back to that of the tempo potentiometer setting.

-in fact, sometimes i'll tap in the tempo using very slow and deliberate taps.  and then within say 2 or 3 seconds it'll automatically revert back to the pot setting as well.

Any help or pointing to other post would be greatly appreciated.

Thanks all!

[Taylor]

Try measuring the voltage at pin 13 of the TAPLFO chip - the tempo pot ADC input - while moving the other knobs that cause this problem. Seems like maybe there's a bridge from those other pots leaking into the tempo pot. When the tempo pot is moved, the chip is designed to snap to the knob value, so I suspect there's some noise or bleed there that causes enough change in the tempo CV to make the chip think you're moving the pot.

[Unlikekurt]

Thanks Taylor.  I'll measure it up.  When you suggest a possible bridge are you meaning in the chip itself?
There certainly isnt any physical bridge seen during inspection between any of the pots / rotaries or any of the pads.

I actually did measure this earlier today.  Pin 13 seems to stay stable throughout the process.
It is almost as if the PIC is deciding that there is not a tap switch connected.  ie: if you were to hook the switch up with jumper clips tap in a tempo and then remove the jumpers the unit would revert back to wherever the tempo pot was set.  

This is an intermittent thing but without fail it will happen each time i turn it on.  almost immediately.  I have tried different switches as well.  same issue.

If it were bleed or cross talk from the other controls how would i troubleshoot / confirm?

[Taylor]

The tap switch is a normally open momentary type, so when you aren't pressing it down, as far as the TAPLFO is concerned the switch could be gone. I didn't write the code but I don't know of any other input condition that makes the chip switch to the tempo pot's value, other than when it thinks you've moved the pot. You could try emailing Tom Wiltshire (electricdruid.net) to see if there's another reason it would do that, which would give you an idea of where to look.

One other direction to look from: it's not clever about averaging the last few taps. It wants to measure between two taps only. If you tap thrice, on the third tap you've just re-initiated the time measurement. It will only listen for some period (I think ~10 or 20 seconds but it should be in the datasheet at Tom's site) before reverting to the tempo pot value. Maybe this is happening when you tap in an odd number of taps?