Building the tap tempo tremolo

[joinpobob]

So I got around to diming my amp and playing with the gain pot to adjust for bypass / on volume levels. The best combination I found (0-10 scale) was gain at 10, trim in front of TL072 at 10, and trim behind TAPFLO at ~6. With anything less than 10 on the trim in front of the TL072, my led went really dim and the ticking got very loud. Is that typical? I am using a bright blue LED, VAOL-5LSBY2.

Regardless, at those settings I was able to remove almost all of the ticking. With the depth set at full, it wasn't ticking, but could hear is bottom out (if that makes any sense). But it was fine. BUT when I bypass the pedal, I get a loud ticking. This seems very odd to me. I wouldn't think any ticking would get passed on the bypassed path. With the depth down, it wouldn't tick, but with full depth it was very loud. I guess that is bleeding through on the ground path? But I don't understand why it isn't there when the pedal is engaged.

I am going to try the 1n cap that keeps being discussed. But the ticking in bypass perplexes me.

On a similar but different note, I am modding my silverface twin reverb. In doing so I found some interesting info. Of such, I found some info on taming the ticking in the trem circuit. Paul Marossy said, "I had a ticking coming through the speakers from the vibrato. So I installed a .022uF capacitor in parallel with 10M resistor at the optoisolator." http://www.diyguitarist.com/GuitarAmps/TwinReverb.htm

The loop he is referring to has a 1M, to the first lead of the Opto side of the optoisolator, to the second side of the opto, to a 100k, to the other side of the 1M. The Schematic is here: http://www.ampwares.com/schematics/100W_Mast_Vol_SF_Twin_Rev.pdf

I don't know if something like this would help, but I figured that I would throw it out there.

[Taylor]

On a couple of them that I've built, I can hear ticking in bypass at high volume. Pretty faint, but annoying enough, so I came up with an alternate LED bypass scheme. I'll draw up a diagram tomorrow, but basically I ground the PWM signal after the 10k coming from [pin 5 I think] of the taplfo. It will be clearer when I can post the diagram, but this totally does the job.

[thehoj]

This seems very odd to me. I wouldn't think any ticking would get passed on the bypassed path. With the depth down, it wouldn't tick, but with full depth it was very loud. I guess that is bleeding through on the ground path? But I don't understand why it isn't there when the pedal is engaged.

I had the exact same thing. It seemed to be because I had the LED wired through the 3pdt switch.
I got around it with a bit of a different approach. I used 2 LEDs.

Firstly I wired the LED that connects to the PCB, directly, so it's always on if there's power connected to the pedal. Then I wired a second LED to the 3pdt switch which comes on to indicate that the pedal is engaged.
What this means is that I can see the tempo of the pedal even when it's not engaged.

So with the 1st LED being wired directly to the PCB, I have my 3pdt switch wired up as follows (sorry for the crappy pic):

[joinpobob]

Thank you both for your replies. I already had the box drilled for one pedal so I went with Taylors suggestion. Now it works perfectly. Something to take home to mama.

So now my build has all stock, except for an added 1nF in the feedback loop of the TL072 (so a total of 1n33F). Then the LED is soldered straight to the "pos" and "neg" pads. Finally, the 10k resistor coming off of pin 5 on the TAPFLO has one leg lifted (the one towards the "top" of the board) with the to-be-grounded wire coming off of the lifted leg and the the positive side connected to the open pad. Then those wires are soldered to the switch as you would a "regular" 3PDT (so the LED column is positive>>to-be-grounded>>Ground). Hope that makes sense.

Thanks so much for your help, Taylor and thehoj.

[Taylor]

I'm leaning towards trying the VTL5C7, but I am hoping to get some suggestions on what to try. Basically I'd like to try something that will soften any ticking that might occur.

Yes, that looks like a good one to try.

[KazooMan]

I finally found time to finish putting the TTT together.  After resolving an issue with a 9V jack that I had never used before the pedal came to life.  Works great...... with a few caveats (and hence questions). 

I mounted the three pots that go on the board on the same face as the rest of the components with the body of the pots away from the board..  This seems to make them work backwards from my expectations.  Should they be on the other face?  No problem to change them.

I have NO ticking but, then again, I have no LED.  I do have voltage at the LED pads (bouncing all over the place around 3V) and it does respond to the trimpot on the right.  However, I have yet to see even a glimmer of light from my LED.  I have explored several LEDS, and checked (even reversed) the polarity without success. I have attached the LED directly to the board to avoid issues with the stomp switch and still no luck.  I can live without the LED, but I would like to resolve the issue if possible.  Any suggestions?

PS:  I have to make a confession.  While trying to figure out the different 9V jack I was getting voltage readings well below what I should have seen.  I did note that the schematic calls for a 9 - 12V supply, so I unplugged my regulated 9V supply (Small Bear) and hooked up my regulated 12V supply (same design as SB, different transformer and resistors to control the output - it works just fine to run my Vibratone Amp based on Rick Holt's design).  Well.... I let the smoke out of the 10 ohm resistor just on-board from the PS.  Replaced the resistor and neighboring dioide just in case, pulled out the 9V jack and put in one I have used before and the tremolo worked fine.  No harm, no foul.

[Taylor]

Your LED situation is pretty weird. If the trem is working, then the transistor that grounds the LED is working. If you have voltage at the POS pad, that means that what's on the other side of the LED is working. So assuming you're using a regular LED that works and you have it in right and your soldering on those pads is good, I can't think of any other reason that it wouldn't work. I guess all I can say is: double check that you have 9v going into the board, and reflow your solder connecting the LED to the board. And try a new LED.

The pots should be the other way, yes. I need to add a photo to the PDF to show this, just haven't gotten around to it yet.

[KazooMan]

Thanks for the reply.  I pondered the pots before installing them.  I had already populated the rest of the components and it was difficult to follow traces to determine the correct orientation.  I chose wrong.  Easy to fix.

I'll work on the LED some more.  The pedal does work exactly as it should, and as I mentioned, I do have voltage at the pads.  I tried three different LEDS without success.  The ones I had in the bin were unlabelled, so I do not know their exact voltage requirements.  I'll get some new LEDs and see if that fixes things. 

[KazooMan]

I pulled the pots and put them on the proper side of the board, rewired the power input since the leads were now too short when the board was flipped, and installed a new LED (a nice 8mm high-brightness blue LED from Smallbear).

Everything works just fine

I may have to tweak the trimmer for the LED brightness a bit.  There is little adjustment and then at the end of the travel the LED is full on.  An appropriate resistor in parallel should do the trick.  I am still dumbfounded as to why it was not working yesterday.  Perhaps it has to do with the small amount of adjustment I am getting for this particular LED and maybe the one I had installed was just over the limit.

The tremolo sound is very nice.  I haven't played much with the different waveforms, but it is easy to tell when the chip switches modes as you rotate the pot.  I may still decide to go for a rotary switch although I am concerned that this may introduce a pop when changing modes.  The pot is silent.

I still have not heard any ticking, but I have only tried this at low volume levels.  Perhaps I got a good optocoupler (thanks Smallbear  ).

I put this is a pretty big box (Hammond DD) since I wanted to include both the tap tempo and multiplier switches without creating problems for clumsy feet.  Not the most aesthetically pleasing when you see how much room there is left in the box, but it will do the job nicely.

Thanks again to Taylor and all of the others who contributed to the design of this pedal and for providing a source for the boards and chips. 

[Taylor]

Glad you got it sorted. 

[KazooMan]

An update:

I tried to tweak the LED brightness, but never had much success getting a better range from the trimmer.  What I did find is that my "no ticks here" observation had some limitations along with it.  Very strange!  My trimmer was varying the LED brightness below a good level and then came full on.  At the full on setting I had very little (or no) ticking as I reported.  As I tried to tame the LED I realized that at lowere brightness levels there was ticking, especially in bypass. 

I had read the other comments about modifying the cap and I did that.  I did notice that the lead dress had a lot to do with the LED ticking.  I had unfortunately mounted my LED close to the input jack and the lines were talking to each other.

I decided to go with the two LED solution and added an "on/off" LED that is controlled by the stomp switch, moving the tempo LED to the other end of the box.  The tempo LED stays on (I am not certain that I needed to do this with the other mods I did - I may play around with the pedal to see if I can get away with the close proximity of the LED signal near the in/out signals at the switch). 

I replaced the wiring for the input and output signals as well as the tempo LED (and the short bridge on the switch) with shielded cable and made a star ground around the switch.  There is NO ticking with this setup.  Probably overkill, but it is one quiet pedal!

[good air]

I got the wrong sized 330nf cap from mouser.  Its the big block 334J100.  Atleast I think thats the code for 330nf.  Anyway, the pdf says cap values are just suggestions and I'm trying to get this working for this weekend.  Any recommendations on a substitute?  I have a lot of ceramics that would fit in there but not 330nf.

Edit: Also, I was reading the post above and saw the problem about the ticking.  is 1n going to be the new 330pf or should I use something else?

[Taylor]

The PDF says "cap types are just suggestions". This is because, I wanted to note the standard cap type to use in that position for beginners who don't know anything about different cap types and are overwhelmed trying to buy parts for projects. I thought it would make it easier if they could type in "ceramic 10pf capacitor" or whatever to Mouser so they didn't have to be baffled my the endless different cap types. But then I got a bunch of emails asking "can I use film caps instead of ceramic?", "I heard film caps sound better than ceramic, why did you spec crappy parts in this project???" So I added that little disclaimer, hoping people would get the idea that, you can use these cap types, but if you think you know something that will work better, use whatever makes you happy. Maybe I should have just written that.   But cap values are not merely suggestions: you should stick to them unless told otherwise or if you know better than I do.

For the record, the 22p caps that I recommended ceramic for are part of the digital LFO, so no matter what you might think about film caps sounding better than ceramic, I can say unequivocally that in this spot, it will make absolutely no difference. Crystal oscillators will not sound any more like Hendrix with a film cap to ground.  

Ok, that rant out of the way:

Yes, I'd use 1N instead of 330p.

The 330n is power bypass on the input of the voltage regulator. I think you'd be fine with something a little bigger.

[good air]

Haha ok thanks for the clarification.. and the rant.  If someone can tell the difference between a ceramic and a film, they should stop what they're doing and go on a gameshow or something cause thats pretty ridiculous.  Anyway,  1n it is.  If 330n is supposed to be there, I can bend the big one I have so it lays sideways off the end of the board and everything will be exactly like the list.

Just have those 2 caps then the led and wiring left to do.  Am I doing the led like in the pdf or should I wire it to the board and lift that 10k above the chip and grounding it thing?  (Still gotta read that dudes explanation a couple more times to get it).  Just trying to get it done and introduce it to the rest of the board without any debugging.

[Taylor]

Just to clarify, there could be some truth to different cap types sounding different when they are in the signal path. I still don't think it matters enough to care about, but there is at least a reasonable explanation for why it could matter. But the 22p ceramics are part of the digital section of this circuit, and not at all a part of the signal path, so they can have no influence over the sound.

Also for clarity, I'm wondering if you're getting confused about 330n and 330p. The 330N is on the far left of the board and is part of the digital LFO. You can use something a little bigger than 330N here.

The 330P is on the right of the board and is part of the audio section. Here you can use anything around 1N.

Regarding the LED, I have to draw a diagram to better explain that. I'll try to do it tonight.

[.Mike]

If 330n is supposed to be there, I can bend the big one I have so it lays sideways off the end of the board and everything will be exactly like the list.

330n is not an absolutely essential value for C14. It's taken right from the datasheet for the regulator-- 330n on the input, 100n on the output. I've seen values all the way up to 100u on the input on some schematics. In fact, the 330n cap might not even be necessary. The datasheet says it is "required if the regulator is located more than 3" from the power supply filter."

Mike

[Taylor]

I can't remember now what it was, but I have seen a lack of bypass cap on a regulator input cause a problem before. I was going to say he could leave it off too, but to be safe you may as well put something there, and you may as well make it bigger as Mike says.

[.Mike]

Yeah, I can't figure out any rhyme or reason as to how people pick the value for the capacitor on the input. I'd love to know, though... heh.

[good air]

I put the 1n in there in place of the 330p (next to the trimmer), I'll leave the 330n off for now to see how it works without it.  I have a 1uf that will fit in there too. 

Thanks in advance for the led diagram, I'll save that and the 3pdt for last.  Almost done, glass is getting empty.

[Taylor]

Here you go. I'll also add this to the PDF. Note that my way is a little different from joinpobob's suggestion. His leaves the PWM output of the TAPLFO floating when the circuit is bypassed, and while this seems to work for him, it's suppose to be bad practice to do this. In my diagram, I ground the PWM output in bypass through a 10k resistor instead of just disconnecting it.