Building the tap tempo tremolo

[EDLK]

I will try again and make sure I have it on the emitter
On the 2nd and 6th waves it flattens the out to where you can nearly tell they are on.

[EDLK]

I will try again and make sure I have it on the emitter
On the 2nd and 6th waves it flattens the out to where you can nearly tell they are on.

[EDLK]

I confirmed I had the cap in the correct position
I did try 10 and22 u they worked about the same
Perhaps I am not getting the same results because my tick is very loud to start with

[Jimi W]

Firstly, thanks to everyone involved in designing this and to Taylor for the pcb and Molten Voltage for the chip.
Just finished building it (pics in pics thread) and I love it!

I used an LM9314 to drive LEDs for the waveform rotary knob. I found a handy calculator to help set it up and I'll post details tomorrow when I'm on my pc and not my phone.

I've had a couple of issues though. Firstly I put the TL072 in backwards (actually soldered the socket in backwards and used that to orientate the chip)....school boy error! Sorted that no probs, had to replace the 10r resistor near the diode and replaced chip.

I then noticed that the pad for the 5v supply on the multiplier pot was only giving out 2.89V. Any idea why? I just piggy backed the 5v from another pot so not really a problem.

The problem that's got me stumped is the multiplier rotary pot. I can't select the last 2 settings using the pot. When I go to the 5th setting I get a 1/4 note (I think) instead of the 8th note triplets and the same for the 16th note setting.
I've checked the voltages going to the chip and they appear fine. They are 0.38, 1.21, 2.04, 2.87, 3.70 and 4.54V.
The strange thing is that I can get the triplets and 16ths if I use the multiplier switch to step through the settings.
Did I damage the chip with the reversed TL072 or something?

Any pointers would be greatly appreciated.

Jimi

[Taylor]

The multiplier's positive pad is supposed to be limited like that. The reason has to do with the code, and I'll explain that below if you're interested. Notice that the multiplier's positive pad is fed not by 5v, but by a resistor connected to 5v. So you thought that was wrong, but it was right, and when you attempted to fix it, you caused the problem you're having with the multiplier.

So nothing's broken, just solder the multiplier pot where it's supposed to go and your problem will be solved.  


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The reason it's like this: in the code, the pot is used as a rotary selector. The code masks off the pot's value until it is a 3-bit number, which gives 8 possible values. Since only 6 were needed, the code is set to give x1 multiplication for the last 2 values, and the resistor is used on the positive lug of the pot to limit the range of the pot to about 0-3v, so you should never get to the last 2 positions.

Awesome build BTW!

[Jimi W]

Oh my god! What an idiot! I looked at the TapLFO datasheet and followed the diagram for the Waveform Rotary and then applied that to the Multiplier. It says 'The top two options are not used for the Multiplier.' but doesn't mention the fact its not being fed by 5V as the Waveform rotary is and needs a 3k6 resistor to drop the voltage. Maybe I should look at the schematic a bit closer next time. I should've really put 2 and 2 together. I'll connect it to its proper pad tomorrow.

Thanks for the help Taylor, its a great pedal and a great PCB. The service you offer is amazing. The time you spend answering questions is unbelievable and I wish there were more people out there offering the kind of customer service/care that you do.

I've got an Echobase PCB waiting to be boxed up, I cant wait!

Thanks again,
Jimi

[Jimi W]

Hi,

Taylor, sorry to bother you again but I've swapped the feeds of the Multiplier roatry pot to their proper places and for some reason I'm now getting 4.64V on the +ve rather than the 2.89V I was getting before. I've checked the 3K6 resistor and swapped it for another. I'm getting 4.93V before the rersistor and then 4.64V after the resistor and on the pot pad. Any ideas whats going on now?

I've been asked to explain how I set up the LM9314 for use with the Waveform Rotary Pot.

I really am still a newb at this electronics lark so I've probably missed something obvious here but it works for me!

After breadboarding a few things whilst looking at the datasheet and app notes I was struggling to get it calibrated right. I turned to google for some help and stumbled across a handy little calculator.

http://www.electro-tech-online.com/blogs/ericgibbs/136-dual-lm3914-v3-0-calculator.html

I still struggled to get it perfect as the calculator didnt seem to like the fact that the voltages on the rotary pot were in steps of 0.6V but the first position was at 0.36V and not 0.6V. Therefore if you calibrated it to 0.6V stages the first LED wouldn't light up because the voltage handn't reached the turn on voltage of 0.6V.

I found that if you swapped the 5k resistors from the 5V and 0V feeds to the pot to 10K it increased the voltage on position 1 to 0.58V. I then used the calculator to calibrate the chip for 0.58V steps and I'd cracked it!

So... on the LM3914 I ended up with pins 2 & 4 connected to ground, pin 3 connected to  9V+, 5 connected to the output of the rotary pot,  6 & 7 tied together, a 4K7 resistor between 7 & 8 and a 13K8 (or 10K + 3K8 in series) from 8 to ground. 9 was left open to keep it in dot mode where just one LED lights at a time. I used 9V to power the LED's with a 4K7 (I think thats what I settled on) resistor to tame them a bit.

I still had a problem because the first LED was always very dimly lit whatever the position. I got a PM from .Mike who suggested placing a 10K resistor across the first LED. Bobs your uncle....problem cured. Apparently it does mention it somewhere in the datasheet but I missed it.

Hope it may help somebody.

Cheers,
Jimi

[.Mike]

Thanks for the info on how you setup the 3914.

Mike

[Taylor]

Hi,

Taylor, sorry to bother you again but I've swapped the feeds of the Multiplier roatry pot to their proper places and for some reason I'm now getting 4.64V on the +ve rather than the 2.89V I was getting before. I've checked the 3K6 resistor and swapped it for another. I'm getting 4.93V before the rersistor and then 4.64V after the resistor and on the pot pad. Any ideas whats going on now?

It probably has to do with the fact that you're sort of mixing my circuit with Tom's diagram. My advice earlier actually forgot to take into account your rotary wiring, sorry about that.

Tom's diagram shows an 8-position switch, but you should only use a 6-position (the switch can be set for 6p using the inner washer most likely). Forget the 3k6, and put a 25k resistor from the sixth position of the rotary to 5v. It sounds to me like you've got the rotary set up as an 8-position.

[Jimi W]

Cheers Taylor for the quick response.
I am using a 6 position switch and I have a 5k resistor going from 5V to position 6 as shown in Tom's diagram. So should I either take this 5K out and replace with a 25K (or just add a 20K in series) or do I add the 25K to the existing 5K?
I guess the confusion is coming from combining your PCB with Tom's diagram, combined with my lack of knowledge to put 2 and 2 together!
Cheers for the help,
Jimi

[Jimi W]

I'm guessing the 25k is to replace the 5k from the 5V to the rotary switch and the 2 10k's that would be between the extra 2 positions that are missing?
Jimi

[Taylor]

[explanation in black; quick answer in red]

Well, Tom's diagram actually shows what I'm talking about, but it might be confusing.

If you look at the diagram, which is for the waveform switch with 8 waveforms, you see that it says, "the top two options are not used for multiplier". But you should still treat the resistor chain as if those last 2 switch positions were there - you just won't ever select them. So you need to maintain R1, R2, and R3 in order for the resistor chain to form the proper voltage divider. Since they are 3 resistors in series, we can combine them - two 10k's and a 5k equal 25k total. This 25k resistor acts as those three top resistors would if the top two positions were never used. By taking out the two 10k's, you've changed the division ratio of the whole divider (the rotary switch is acting like a pot wired as a voltage divider).

Note that in a voltage divider, the total resistance doesn't matter - only the ratio between what's on one side of the pot's wiper/switch's pole and what's on the other side. That's why, on the board we use 10k pots and a 3k6 resistor, whereas in Tom's diagram, the total resistance is 80k, and it works the same.

Replace your 5k from the top switch position to 5v with a 25k resistor.  

[Jimi W]

Hi Taylor,
Thanks for the reply. I actually understand the long explanation in terms of the voltage divider. Alarm bells did ring when you mentioned a 25K resistor and it dawned on me I would've altered the total resistance of the chain and therefore the voltage divider.

Its working perfectly now and my wife and baby have been out this morning so I've given it a good play through a cranked amp. Great pedal. I really like the multiplier footswitch. I think it would be really useful in a live situation and allow a bit more creativity without needing to tweak knobs. Shame I'm not in a band anymore!

I'd be even better if I could get the status LE D's of the multiplier Rotary switch to change as I stepped through as a visual reference. Is the stepping through done completely within the chip and is there no way to get the voltage and use it to drive a LM3914? I've measured the voltage on the multiplier pin (pin 11 if I remember rightly) and it doesn't change when your step through the multipliers. I'm guessing its not possible.

Cheers,
Jim

[Taylor]

I'd be even better if I could get the status LE D's of the multiplier Rotary switch to change as I stepped through as a visual reference. Is the stepping through done completely within the chip and is there no way to get the voltage and use it to drive a LM3914? I've measured the voltage on the multiplier pin (pin 11 if I remember rightly) and it doesn't change when your step through the multipliers. I'm guessing its not possible.

Cheers,
Jim

Hmm... I don't think it's possible that way, but it's fairly simple logic to have a button press cycle through a set of LEDs. That's not my area, so offhand I'm not sure what logic IC you'd want. I guess a Johnson counter? You'd then need to make the multiplier switch a DPDT momentary, and use the second pole to drive your counter logic.

[Hides-His-Eyes]

You'd need some way of deciding whether the rotary switch or the footswitch controlled the LED counter. You're looking at another PIC there.

[Jimi W]

Hmm, I'm using a DPDT momentary at the minute because thats all I had in the way of momentary switches so thats cool but thats the least of the issues really!
I could add a second set of LED's. I'd then have the original LED showing what the original multiplier position was (as well as the actual knob!) and the second set showing the stepped through multiplier position.....or maybe a Bi-colour LED (depending whether both circuits used the anode as the common source for the LED's) then the LED could light the second colour when the footswitch was used.
Hides-His-Eyes - any idea on what IC would be ideal for such a job, I've had a quick look for Johnson counters but the datasheets dont really show a simple circuit like i'd want where a voltage pulse would trigger the next output (sorry if these terms aren't correct!)
Cheers guys,
Jimi

[slacker]

If you only had the switch, you could probably do it using a CD4017, that will step through up to 10 outputs each time it's clocked. There's no easy way to integrate a logic based method with the pot so that it will start counting from where ever the pot is set.

[Geosh]

Can someone give me a good recommendation for a switch for the tap tempo? The one I have now is very finicky and doesn't seem to lock in well with my taps. It seems to not recognize some and sometimes tapping at 60bpm produces a 6000bpm result (exaggerating... but only a little). Should it be a normally open switch? Supplier and part number would be appreciated.
Thanks!

[Barcode80]

Can someone give me a good recommendation for a switch for the tap tempo? The one I have now is very finicky and doesn't seem to lock in well with my taps. It seems to not recognize some and sometimes tapping at 60bpm produces a 6000bpm result (exaggerating... but only a little). Should it be a normally open switch? Supplier and part number would be appreciated.
Thanks!

Mine does that occasionally. It's a debounce issue I can't seem to track down. It's rare enough it never bothers me though.

[Valoosj]

A big thank you to all those involved in designing this amazing pedal.