R28 on Wavelord... Why is it there?????

[danfrank]

R28 (330 ohms) doesn't need to be there... So, why is it there?? I'm getting 5.5 volts at the input of the 5 volt regulator because of R28.
I'm taking it out!
Lol!

[danfrank]

Hey, wow! Wavelord works MUCH better with a jumper in place of R28. I actually get 5.003 volts at the output of the regulator!
This may have been discussed prior but I usually go around with my head up my backside...

[alanp]

My guess would be that it forms a RC filter with the 10uF capacitor just after it, to smooth out any digital hash from the taplfo chip.

[WormBoy]

Yeah, it's probably there to separate the power line of the taplfo from the rest of the circuit. Apparently, 330 Ohm is too big here, given the current draw of the taplfo. 5.5V at the input of a 5V regulator would be insufficient to let it work properly. You could always sub something smaller for R28 (look at the datasheet for the regulator to see what input voltage it's happy with, and use Ohm's law).

[madbean]

Yup, you are absolutely right. Looking at it again that resistor does not need to be so large. It's listed as 330R in the application circuit in the TAPLFO3 datasheet, but there is a note in there saying adjust to taste. I measured 11mA current draw for the entire circuit, but it's fair to say the audio portion is probably drawing less than half that with the remainder going to TAPLFO.

Anyway, dropping it to 100R should be fine. The regulator will work with a supply of 7.5v-8v. Interestingly, I did not seem to have a problem in mine since I measured ~5v off the regulator. But, there's no reason to leave that resistor at that value.

I'll make a note in the doc to change it. Thanks for bringing this up.

[danfrank]

I'm not trying to be difficult, but doesn't the regulator isolate the taplfo from the rest of the circuit?
I have to replace the 8 way switch now. I didn't test the switch before I soldered it in... Big mistake! How I long for the days when you could buy something new and be confident that it would be good! Lol!

One more question about the taplfo IC... I see that with pin 8 on the IC, the output can go from 0-5 volts or be biased at 2.5 volts and have a bipolar output... With reference to ground, either option sounds like it's the same result... So, why is there a bipolar output with 2.5 volt bias option?

The Wavelord has a lot of potential for using it to drive other projects that have a CV input, like the A/DA stuff.

[danfrank]

Wavelord, R.I.P. ...
And small bear can rot in hell for selling me a bad switch!
Lol
Lesson learned, test everything before it goes onto the board... What a costly lesson.

[madbean]

I'm not trying to be difficult, but doesn't the regulator isolate the taplfo from the rest of the circuit?

The regulator and audio portion share a common power rail (VC) so in that sense, no. Does the regulator have to be isolated further from VC? Maybe not. But, it certainly doesn't hurt to put it in either. In a production situation where you are looking at every cent of added cost maybe you wouldn't. I have run into one situation before with a digital device powered by a regulator had to be further separated from the audio power (this was with Function F(x) and it also involved a re-settable fuse so that might have been part of it).

One more question about the taplfo IC... I see that with pin 8 on the IC, the output can go from 0-5 volts or be biased at 2.5 volts and have a bipolar output... With reference to ground, either option sounds like it's the same result... So, why is there a bipolar output with 2.5 volt bias option?

I can't answer that. Maybe the TAPLFO designer had a specific application in mind for that. I don't remember if it's mentioned in the datasheet.

[madbean]

Wavelord, R.I.P. ...
And small bear can rot in hell for selling me a bad switch!
Lol
Lesson learned, test everything before it goes onto the board... What a costly lesson.

What was wrong with the switch? Curious since I've used a lot of these and never had an issue with one.

[WormBoy]

One more question about the taplfo IC... I see that with pin 8 on the IC, the output can go from 0-5 volts or be biased at 2.5 volts and have a bipolar output... With reference to ground, either option sounds like it's the same result... So, why is there a bipolar output with 2.5 volt bias option?

As far as I understand it, at max depth, both options will give you the exact same wave. The options start to differ when you decrease depth. With the offset at 2.5V, the center of the wave will remain at the same spot when you decrease depth, with unipolar, the center of the wave shifts when you decrease depth. What works best depends on the effect you're applying the LFO to. For a modulated filter, you may like the center frequency to stay in place when you decrease depth. For a tremolo, you might like unipolar better: at the right polarity, the perceived output volume will not change much when you tweak depth.

The StompLFO chip has a continuously adjustable offset, by the way. ElectricDruids FilterFX uses that in a very nice way. You can adjust the center frequency of the sweep, and with depth at zero have a foot pedal change the offset for a wah-type effect.

[matmosphere]

One more question about the taplfo IC... I see that with pin 8 on the IC, the output can go from 0-5 volts or be biased at 2.5 volts and have a bipolar output... With reference to ground, either option sounds like it's the same result... So, why is there a bipolar output with 2.5 volt bias option?

As far as I understand it, at max depth, both options will give you the exact same wave. The options start to differ when you decrease depth. With the offset at 2.5V, the center of the wave will remain at the same spot when you decrease depth, with unipolar, the center of the wave shifts when you decrease depth. What works best depends on the effect you're applying the LFO to. For a modulated filter, you may like the center frequency to stay in place when you decrease depth. For a tremolo, you might like unipolar better: at the right polarity, the perceived output volume will not change much when you tweak depth.

The StompLFO chip has a continuously adjustable offset, by the way. ElectricDruids FilterFX uses that in a very nice way. You can adjust the center frequency of the sweep, and with depth at zero have a foot pedal change the offset for a wah-type effect.

Sounds like a good spot to try a trimmer pot

I have a tremolo I really like (and a DigDug2 that I need to finish) so the wave lord hasn't been one I've looked at to closely but...

[WormBoy]

Sounds like a good spot to try a trimmer pot

Well, for using the StompLFO in a tremolo, it would. You would be able to tweak it such that perceived volume stays constant when you change depth. But ... it is a different chip from the TapLFO3 that is used in the Wavelord (and different number of pins). Downside of the StompLFO is that it has less waveforms, and it does not have a multiplier for the tap tempo, which is a problem if you like fast-but-in-sync-with-the-beat tremolo.

I have been daydreaming about this for a while ... and the best option would be to have both chips, with the TapLFO3 as master, with its clock feeding the StompLFO ... Then, on the other hand, maybe I don't need a synced tremolo all that bad. 

[danfrank]

What was wrong with the switch? Curious since I've used a lot of these and never had an issue with one.

The switch didn't switch at all, in fact none of the 8 contacts had continuity with the common lead. Weird, as I never forced it while mounting/ soldering it. I sure wish that I had tested the switch beforehand, it would have saved the day! Lol.
Maybe I should build me one of those neato test rigs...

And thanks to everyone for the informative responses. I was planning on adding a unity buffer to the output of the taplfo IC, to use to plug into the expression/cv pedal jack of several other effects I have. I guess in this case, the bipolar output of the taplfo would serve better than the unipolar one. Does anyone know of any rail to rail single op amps in DIP packaging? I was going to use a CA3130 as it's the only one I could find.

[WormBoy]

I would definitely recommend downloading the TapLFO3 datasheet from electric druid: https://electricdruid.net/product/taplfo3/. It has a lot of good tips and example circuits (including for filtering/buffering the output).

Edit: you probably would like to avoid going for rail-to-rail opamps to buffer a 0-4V LFO, but rather offset the signal to, e.g., 2-7V. But that depends, of course, what you want to drive with the LFO.