NomNom and Smoothie Troubleshooting

[rmjlmartin]

Hi, and thanks in advance for your help.

I just finished both a NomNom and a Smoothie. They both seem to work, at least mostly, as in, they both seem to do the phaser thing.

However, they both seem to sweep quickly from one extreme to the other, stay there for a  second, and then sweep quickly back to the other extreme. (Obviously how fast it does it depends on where the speed knob is set.) Almost as if the sweep is using a square wave instead of a sine wave, if that makes any sense.

Both builds went fine, and I used the breadboard layout in the NomNom build document to match the transistors. The Smoothie has exactly matched transistors, and the NomNom has transistors that are within 1% of each other. I used the recommended 2N5457 transistors in both.

I'm also not sure that the Nom switch on the NomNom is really doing much of anything, but I haven't really looked into that yet.

Does this suggest anything in particular that I might have done wrong?

Again, thanks for taking the time to read this, especially if you can offer some helpful advice.

[zgrav]

Does the trimmer adjustment for the nom nom change the effect you are describing?   And can you hear a difference using the second trimmer to adjust the feedback?  I would try playing with those some more to see if you can get a better overall sound to your liking. 

[rmjlmartin]

Thanks!

I've played with the feedback trimmer some, and it doesn't seem to make much, if any difference. To be honest, I'm not completely sure what effect the Nom/feedback switch is supposed to have, and I'm not too concerned about it at this point. I just mentioned it in case it was relevant.

I've adjusted the other trimmer on both, and it seems to balance between the ends of the sweep. In other words, if you turn it one way, it seems to stay at one end of the sweep longer, and if you turn it the other way, it stays at the other end longer. And if you turn it far enough at least one direction, you get no phasing at all.

But the trimmer doesn't seem to change the fact that it seems to sweep quickly and stay at either end of the sweep instead of of having a slower, smooth sweep.

If all that makes sense?

[jimilee]

Thanks!

I've played with the feedback trimmer some, and it doesn't seem to make much, if any difference. To be honest, I'm not completely sure what effect the Nom/feedback switch is supposed to have, and I'm not too concerned about it at this point. I just mentioned it in case it was relevant.

I've adjusted the other trimmer on both, and it seems to balance between the ends of the sweep. In other words, if you turn it one way, it seems to stay at one end of the sweep longer, and if you turn it the other way, it stays at the other end longer. And if you turn it far enough at least one direction, you get no phasing at all.

But the trimmer doesn't seem to change the fact that it seems to sweep quickly and stay at either end of the sweep instead of of having a slower, smooth sweep.

If all that makes sense?

With the second trimmer you mentioned, you have to find the sweet spot in the middle of the sweep. It's a very very narrow window and very easy to miss because it's so small.


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[rmjlmartin]

Thanks!

Do you mean the feedback trimmer, or the other one? The other one does have a very small sweet spot, but that's where I have it set at the moment, at least as best I can determine. I still get the fast sweep that seems like the LFO is putting out a square wave rather than a sine wave.

What pin(s) can I monitor the LFO output at? I do have a lab scope that I can look at it with, if a visual might be better than my ears.

[rmjlmartin]

Here's a picture of the Smoothie.

[rmjlmartin]

And the NomNom.

[rmjlmartin]

Here's a link to a short video clip showing the problem, with an MXR Phase 95 on the Phase 90 setting for comparison. I know they're not set at exactly the same speed, but hopefully you can hear what I mean. Pardon the poor quality, and the weird noise at the beginning. Some sort of electrical interference that came through the amp?

https://youtu.be/foH0_EvydMA

[jimilee]

I hear what you're saying. It isn't a smooth transition. Does it do it even if you lower the speed?

Are all of your resistor values correct?


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[rmjlmartin]

Yes, it does it at any speed. I picked a speed for the video where it was fairly obvious. But the speed doesn't matter.

I haven't had a chance to go back over and double check the NomNom. I was building both at the same time, but I finished the NomNom first. After it sounded odd, I went ahead and finished the Smoothie, thinking I could use it for reference to troubleshoot the NomNom.  But then it did the same thing, too.

I try to be very careful with the assembly- measure each resistor before installing it, that sort of thing, and I was extra careful with the Smoothie after the problem with the NomNom. Which certainly doesn't mean that it's impossible that I made a mistake, but the odds that I made the same mistake on both seems fairly slim. Which is why I went ahead and posted this before I had a chance to go back over it.

Which resistors would affect the LFO? I've built a couple dozen pedals at this point, and repaired a number for other people,  but I have to admit that I don't know nearly as much as I'd like to about how these things work. I'm an automotive technician by trade, and I'm used to using a lab scope to troubleshoot components, communication networks, and such, but you do have to know what you're looking for to be able to find the problem...

[jimilee]

Lemme ask you this, where did you get the fets? So you have any other known good ones you can stick in there?


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[Bio77]

I recently built a Nom Nom.  Mine works great, picture attached.  The resistors look right.  The only differences I notice are R29 and the orientation of the phasing transistors.  R29 is only needed if you want an LED to blink with the LFO.  I noticed you aren't using the LS pad, so maybe removing R29 would help (It is LFO related)?  I used a matched set of 5952s from GuitarPCB for my build.

[rmjlmartin]

Yes, I installed R99, since I was planning to at least see what the flashing led looked like, but I haven't hooked it up yet. I didn't drill the hole for it, since I wanted to see what it was like first, and holes are kinda permanent.

The build document says that the pcb label for the JFETs is oriented for 2N5457s, which is what I used. The 5952s are supposed to be reversed, like you have them, Bio77.

Jimilee, I've bought most of my parts from Tayda, but looking back through my order emails, I don't see any 2N5457s, so I probably got all mine on Ebay. I do have more, and probable a couple more matched sets, but they likely all came from the same place. I've been using them in other pedals, mostly drives of one sort or another, and they've worked fine in everything else I've used them in, but these are the first phasers I've tried.

Where is the best place to get 2N5457s or 2N5952s? GuitarPCB is sold out of the matched sets. Is there a particular spec that I need to make it work correctly? Obviously, as the build document says, JFETs can vary quite a bit.

Are there any other, more readily available JFETs that will work? I do have some other, different ones, too, but I'd have to check my parts box to see exactly what. And I'd obviously have to see what I have that I can sort into matched sets.

[jimilee]

The ones from eBay are most likely fakes the 2n5952s work just fine.  You can post that you're looking in the Buy Sell Trade Lounge. I forget what a good phaser get measured, but it's google searchable.


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[rmjlmartin]

Awesome, thanks! I'll give that a shot.

And this might be a dumb question, but what about J201s? I do have a decent amount of them, though they may be from Ebay, too.