Clear/clean signal coming through (as opposed to phased signal) Nom Nom

[onzlow101]

Hi all-

Pretty new to building pedals and circuitry, but I've built a few simple fuzz/distortion/overdrive circuits with no issues. I just finished populating and wiring the Madbean NomNom and was testing before getting it into an enclosure. I'm getting a regular signal through the amp, but there is no phaser effect. I can include a picture if requested, but since it's wired up with alligator clips, it'll be hard to look at (I have't built a testing rig yet). All voltages across the ICs matched with Madbean's project doc, and I'm trying to think if this is just a rookie mistake and I'm missing something super obvious.

I appreciate the help.

Dan

[onzlow101]

Alright so I had more time to write down voltages and do some research:

IC1     1        2        3        4        5        6        7        8
       5.08    5.08   3.45      0          (5-7 oscillate)     9.51   (This seems to be okay, but pin 3 seems a little low)

IC2    Same voltages (5.08V) for pins 1-3, 5-10, and 12-14. Pin 11 is 0 and pin 4 is 9.51

Here's the funky part: JFET (I used four matched 2N5952) are as follows: G      S      D
                                                                                                        5.08   5.08  4.97-5.09
I'm still pretty new to this, but something tells me that's not right.

Q1 voltages are: E       B       C                                        The 5.1 Zener diode voltage is 5.08
                       5.08  4.50   3.33

Any ideas regarding those JFETS?

Uploading a picture; yes T1 is soldered on the other side because I ordered the wrong size for now.

[jimilee]

When you calibrate it with T1, you have to turn it in very minute turns. The sweet spot is microscopic, it's easy to miss.


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[onzlow101]

When you calibrate it with T1, you have to turn it in very minute turns. The sweet spot is microscopic, it's easy to miss.


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So I just spent about 30 minutes doing this with no change; could there be something else I'm missing?

[jimilee]

Got any pictures of the solder side?


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[onzlow101]

Got any pictures of the solder side?


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I haven't cleaned it up yet and I'm hoping to get the right size trimmer today (not sure if that'll make a difference).

[jimilee]

Looks like several solder joints are starved. I'd go through and reflow and add solder to the ones where the pad is covered with solder.


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[onzlow101]

Looks like several solder joints are starved. I'd go through and reflow and add solder to the ones where the pad is covered with solder.


Sent from my iPhone using Tapatalk

Alrighty. Went through and checked everything out, replaced T1 with the correct size trimmer, and now I get a slightly distorted signal which varies with adjustment of T1. I ordered a 4.7V Zener which MadBean suggests in the build doc as a possible solution.

Does it make sense that I get the same voltages across all the pins of the JFETs?

[jimilee]

Looks like several solder joints are starved. I'd go through and reflow and add solder to the ones where the pad is covered with solder.


Sent from my iPhone using Tapatalk

Alrighty. Went through and checked everything out, replaced T1 with the correct size trimmer, and now I get a slightly distorted signal which varies with adjustment of T1. I ordered a 4.7V Zener which MadBean suggests in the build doc as a possible solution.

Does it make sense that I get the same voltages across all the pins of the JFETs?

Did you reflow and add solder to the starved joints? The zener won't effect the sound in this regard.


Sent from my iPhone using Tapatalk

[onzlow101]

Looks like several solder joints are starved. I'd go through and reflow and add solder to the ones where the pad is covered with solder.


Sent from my iPhone using Tapatalk

Alrighty. Went through and checked everything out, replaced T1 with the correct size trimmer, and now I get a slightly distorted signal which varies with adjustment of T1. I ordered a 4.7V Zener which MadBean suggests in the build doc as a possible solution.

Does it make sense that I get the same voltages across all the pins of the JFETs?

Did you reflow and add solder to the starved joints? The zener won't effect the sound in this regard.


Sent from my iPhone using Tapatalk

I did, I held the board up to a light to check for bridges/poor soldering and it seemed pretty decent. I'm no solder god but I feel as if the connections are pretty good...

[bsoncini]

Yes. The voltages at all the jfets should be roughly the same. As in all d/s and all g should be the samevv

Your gate voltages are way too high. It must be lower than the source to act as a variable resistor. It depends on the jfets but somewhere around 3v.

A few questions. Does turning t1 change the voltage at the gate? If not check all parts between the gates and lfo. Make sure there is no bridge between the source/drains and the gates. Maybe also check with continuity the one side of t1 is connected to the zener diode. The other to ground and the middle to the 1m resistor. Then the other side of the 1m to the gates.

Is the voltage at the gate moving? Should be wiggling by .5 to a voltage. Put the lfo speed slow to be able read with a meter.

[onzlow101]

Yes. The voltages at all the jfets should be roughly the same. As in all d/s and all g should be the samevv

Your gate voltages are way too high. It must be lower than the source to act as a véritable resistor. It depends on the jfets but somewhere around 3v.

A few questions. Does turning t1 change the voltage at the gate? If not check all parts between the gates and lfo. Make sure there is no bridge between the source/drains and the gates. Maybe also check with continuity the one side of t1 is connected to the owner diode. The others to ground and the middle to the 1m resistor. Then the other side of the 1m to the gates.

Is the voltage at the gate moving? Should be wiggling by .5 to a voltage. Put the lfo speed slow to be able read with a meter.

So no, turning T1 doesn't change the gate voltage, nor does the gate voltage move (I've tried about every position with T1). I did check for continuity for all of the pins of T1 with the diode/resistor and it all checked out. There isn't any bridging between gate/source/drain on any of the FETs either. I checked continuity between the 3M9 resistor and the gates, and the emitter of the regular old transistor to the resistor where the signal hits the LFO circuit. One thing I did notice was the emitter of the regular transistor did not have continuity with the gates, which it seems like it should per the diagram:

(http://www.madbeanpedals.com/projects/NomNom/NomNom2015.pdf

Could that be the issue?

Thanks all for your continued input!!

[bsoncini]

The emitter of the transistor should be connected to the source on the jfets. Not the gate.

If you put the speed slow what are the voltages on pin 5, 6 and 7 of the lfo?

[onzlow101]

The emitter of the transistor should be connected to the source on the jfets. Not the gate.

If you put the speed slow what are the voltages on pin 5, 6 and 7 of the lfo?

You're right, I totally misread the diagram. Here are voltages:

5: jumps between 4.13 and 5.94
6: rises and falls between 4.40 and 5.82
7: starts at 1.3, rises to 1.5, jumps very briefly to 13.1 and then drops to 9.59 and holds steady (then repeats)

[bsoncini]

are you sure the lfo jumps to 13v?

I'm reaching the end of my abilities  to help.  Hopefully  someone smarter can chime in. 

I would  check with continuity all comnections around the trimmer. Make sure there is no short or non connections from desoldering by following the schematic 

In the mean time https://www.electrosmash.com/mxr-phase90