Nom Issues..still

[onzlow101]

Hi all-

I posted a while ago about a clear signal coming through the 2015 NomNom. Well I decided to start from scratch and order a new board. I'm having the same issue. I think I've dialed it down to a power supply issue. As I adjust T1, the voltages at the JFET gates do not change. The voltage coming "out" of R28 (the 1M resistor) is the reference (5.1V) voltage, which is applied to the gates. Therefore, the gate voltages are too high for the phase portion of the circuit to function.

I don't have any issues with IC voltages, and I've done all the troubleshooting I can think of. There must either something missing in between the power supply and the FETs or I'm missing/not understanding something entirely. Any input is greatly appreciated.

For reference:
http://www.madbeanpedals.com/projects/NomNom/NomNom2015.pdf

[jimilee]

With what are you powering it? Where do you get your gets? Do you reflow all of your soldering, there are a couple of the square pads that don't look like they have any solder on the pads. Did you check all of your resistors to make sure they weren't mislabeled in the pack in which they came?  Did you use news ICs anyway? Is your LFO working? What are your voltages?


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[onzlow101]

With what are you powering it? Where do you get your gets? Do you reflow all of your soldering, there are a couple of the square pads that don't look like they have any solder on the pads. Did you check all of your resistors to make sure they weren't mislabeled in the pack in which they came?  Did you use news ICs anyway? Is your LFO working? What are your voltages?


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I'm powering with a standard switching? mode ac adapter, something cheap from Amazon but it powers other pedals. My ICs came from Jameco (TI), the dual op amp is from the same batch so I wonder if something was wrong there. Some stuff is from Jameco and some (capacitors mostly) is from beloved Tayda. I believe the square pads with no solder you mentioned are for setting up a pulsing led I believe.

I definitely checked the resistors with my meter as they went in to be sure. The LFO also seems to be sweeping voltages per the ElectroSmash analysis. Here are the voltages: Zener diode: 5.02

                 IC1                                    IC2
1 Vref= 5.0      8 Vref                    1 Vref       5   4.0-5.8 in a square waveform
2 Vref              9 Vref                    2 Vref       6   4.3-5.8 in a sine waveform
3 Vref             10 Vref                   3 4.74       7  8.9-1.3 in a squarish waveform (I think this is the triangular)
4 Vin= 9.79     11   0                     4    0         8  Vin= 9.5
5 Vref             12 Vref
6 Vref             13 Vref                  The drain, source, AND gate voltages across all the FETs are all the 5.0V but
7 Vref             14 Vref                   there is no bridging between them whatsoever.

[gordo]

Silly question but any possibility the trimmers are flipped? 253 where the 254 goes and vice versa?

[jimilee]

Cheap powder supplies play hell on phasers, I don't know why, but I've experienced it myself. And the fets, did you match them yourself?


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[onzlow101]

That's was actually a really good question, but yes both trimpots are in the right place- had to double check though.

I'll look into getting something a little bette for a power supply. Any personal recommendations? And I bought a set of matched Sets from JDsleep (for both attempts).

[jimilee]

That's was actually a really good question, but yes both trimpots are in the right place- had to double check though.

I'll look into getting something a little bette for a power supply. Any personal recommendations? And I bought a set of matched Sets from JDsleep (for both attempts).

One spot is a great inexpensive way to go. Also, a battery snap with a dc plug in the end is one of my favorites. And, if you're going to be playing, a DC Brick power supply like Dunlop works fantastic.


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[onzlow101]

That's was actually a really good question, but yes both trimpots are in the right place- had to double check though.

I'll look into getting something a little bette for a power supply. Any personal recommendations? And I bought a set of matched Sets from JDsleep (for both attempts).

One spot is a great inexpensive way to go. Also, a battery snap with a dc plug in the end is one of my favorites. And, if you're going to be playing, a DC Brick power supply like Dunlop works fantastic.


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Alright I'll get a higher quality power supply and try that out.

[bsoncini]

The power supply is not your problem. Even with the cheapest crappiest power supply you should be able to bias the pedal and have phasing. A good power supply would definitely help to have a quieter pedal though.

Did you make sure that one side of the trimmer is connected to ground. The other to the zener diode. Maybe turn the trimmer all the way down so it is grounded and verify the 1m resistor is touching ground and not 5.1 volts. Maybe pull out the jfets while doing this.

[zgrav]

 If you are getting the same voltage at the output of your zener that you are getting from the middle terminal of T1 regardless of its adjustment, you need to check and make sure that the other side of T1 is connecting to the same ground you are using for the power supply ground. 

[jimilee]

One thing to remember, the trimmer sweet spot is so tiny, it's really easy to miss. Many including myself have done it.


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[bsoncini]

One thing to remember, the trimmer sweet spot is so tiny, it's really easy to miss. Many including myself have done it.


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While this may be true. If turning the trimmer doesn't change the voltage at all he can turn as fast or slow as he wants and will never be able to bias the jfets which in turn means no phasing.

[jimilee]

One thing to remember, the trimmer sweet spot is so tiny, it's really easy to miss. Many including myself have done it.


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While this may be true. If turning the trimmer doesn't change the voltage at all he can turn as fast or slow as he wants and will never be able to bias the jets which in turn means no phasing.

Right.


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