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PostPosted: Wed Jan 10, 2024 12:06 pm 
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Hi all,

First post ever here. I need help to figure out what is going on with my latest build. It's a Parametric OD. The signal passes though with the pedal bypassed. When turned on (with battery and power-supply), the tone is very weak, and thin. The volume and gain knobs react, but the faint tone we hear is like a very dirty fuzz tone, and the volume level fluctuates if I strum the guitar harder. The LED light comes on when the pedal is on.

I took lots of pictures. I also already tried to reflow my solder joints that looked suspicious, but no luck there. Also, I am unsure if this could cause the problem, but when I was assembling it, I noticed that I was missing two resistors (22k - labeled 223), and I went to my local electronics shop and got the equivalent. The ones that are in the kit are 0.25w resistors, correct? The ones they sold me were just a bit bigger in size, but the value was the same (22k - 0.25W). I wondered if that could be the problem, but I doubt it.

I was careful with my soldering techniques, and not to leave any long leads after soldering parts. I am at loss. Any help is welcome. Here are the pictures. If you need any more, I can gladly send them over.

Image

Image

Image

Image

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PostPosted: Wed Jan 10, 2024 12:48 pm 
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Please take voltage readings of the op amps and transistors.

Image
Image

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PostPosted: Wed Jan 10, 2024 4:04 pm 
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Ok. Will do this tonight. And do I need to unsolder the transistors before taking the reading? I am a rookie at those things!


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PostPosted: Wed Jan 10, 2024 4:12 pm 
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jetstobrazil wrote:
...do I need to unsolder the transistors before taking the reading?

No, leave them in the circuit. You should be able to touch each of the three legs with the red probe of your multimeter. You can gently bend the body of the transistor to one side or the other to get the angle needed to do this.

Here's how to take DC voltage measurements of transistor legs: Set your multimeter to the DC voltage mode, indicated by a straight line above a dotted line; use the 20VDC range setting if it's not an auto-ranging meter. Your power source needs to be connected and there needs to be a cable in the pedal's input jack. If the pedal is assembled into the metal enclosure, put the black probe into one of the corner screw bosses of the enclosure--this is your ground connection. If the "guts" are out of the enclosure, use the sleeve tab of the input jack for the ground connection. Then touch the red probe to the test point that you want to measure and hold it there until the reading is stable within a couple of hundredths of a volt. Repeat the process for each of the three legs of the transistor. The voltage on the pins of the two op amps are measured the same way.

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PostPosted: Wed Jan 10, 2024 8:24 pm 
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Wow, thanks so much for the explanation and directions. It is very helpful. Here is what I can find.

Transistor reading (They are all 2N5088)
E: 4.52
B: 4.93
C: 8.12

E: 3.595
B: 3.895
C: 8.12

E: 5.14
B: 5.75
C: 7.36

E: 1.527
B: 2.037
C: 5.75

OP AMP #1
1: 4.91
2: 4.91
3: 4.91
4: 0
5:4.91
6: 4.91
7: 4.92
8: 8.12

OP AMP #2
1: 4.91
2: 4.91
3: 4.91
4: 0
5:4.49
6: 4.94
7: 4.94
8: 8.12


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PostPosted: Thu Jan 11, 2024 1:26 pm 
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Your voltages all look perfect. It's possible to isolate the EQ and overdrive sections. This may be helpful in isolating the problem. If you remove the jumper, then disconnect the foot switch wire from the #7 eyelet of the PCB and reinsert it into the empty jumper eyelet closest to the foot of the PCB, this will turn it into just a single band parametric EQ. You won't have any volume control, but the signal level should be relatively unity gain (with the boost/cut knob at noon).

You can do the same with the overdrive section, but you will need a spare capacitor. Leave the jumper out, but return the foot switch wire to eyelet #7. Remove the end of the wire that connects eyelet #5. Use a capacitor (something between .01uF and 1uF) to connect the wire to the empty jumper eyelet furthest from the foot of the PCB.

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PostPosted: Thu Jan 11, 2024 1:36 pm 
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Your supply voltage seems a bit low. Is there any chance you are using a dying battery or have too many pedals connected to a daisy chain?

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PostPosted: Thu Jan 11, 2024 1:38 pm 
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byoc wrote:
Your supply voltage seems a bit low. Is there any chance you are using a dying battery or have too many pedals connected to a daisy chain?


I took the readings with only a guitar cable plugged into the input jack and with a regular 9V power supply. Nothing daisy chained...

I'll try what you recommended in the previous post to isolate the problem.

Thanks for the help, again!


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PostPosted: Thu Jan 11, 2024 8:16 pm 
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byoc wrote:
Your voltages all look perfect. It's possible to isolate the EQ and overdrive sections. This may be helpful in isolating the problem. If you remove the jumper, then disconnect the foot switch wire from the #7 eyelet of the PCB and reinsert it into the empty jumper eyelet closest to the foot of the PCB, this will turn it into just a single band parametric EQ. You won't have any volume control, but the signal level should be relatively unity gain (with the boost/cut knob at noon).

You can do the same with the overdrive section, but you will need a spare capacitor. Leave the jumper out, but return the foot switch wire to eyelet #7. Remove the end of the wire that connects eyelet #5. Use a capacitor (something between .01uF and 1uF) to connect the wire to the empty jumper eyelet furthest from the foot of the PCB.


OK, so I tried what you first recommended, by removing the jumper wire, and soldered the #7 wire to the bottom pad, and indeed, I was getting a full tone, but I was getting ground noise. It might be normal, but I'm not sure. That should be easier to fix (later!).

As for the other test I could do for the overdrive section, I did that with a 0.1 uF disk capacitor (Bc104 is written on it). This is where the problem is! The same thin farty sound is back. The volume and gain pots are reacting, but with that low volume fuzzy/thin sound.

SO! What now? :)


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PostPosted: Fri Jan 12, 2024 11:52 am 
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Are you sure you have the B100k in the drive pot space and not the B10k?

Try swapping the 4558 chips and see if that makes a difference.

It's hard to say if it's just glare in the pic, but it looks like you have some unwanted solder around the 1k resistors and clipping diodes on the under side of the PCB. Double check for anything that may be causing a short.

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PostPosted: Fri Jan 12, 2024 4:16 pm 
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Ok, will do. I'll keep you posted what I come up with! Sometimes, the solder pads are so close together that it's hard to minimize those shorts. I'll try to suck some of that solder out and do those joints again.


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PostPosted: Sun Jan 14, 2024 8:05 pm 
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byoc wrote:
Are you sure you have the B100k in the drive pot space and not the B10k?

Try swapping the 4558 chips and see if that makes a difference.

It's hard to say if it's just glare in the pic, but it looks like you have some unwanted solder around the 1k resistors and clipping diodes on the under side of the PCB. Double check for anything that may be causing a short.


OK, here are the results of my latest tests.

I do have the correct pots in their respective spots. Nothing wrong there.

I tried switching the chips, and nothing changed.

I tried to see if there was a bad solder joint, and nothing changed. I reflowed some joints just to be sure, and no luck.

Now... About shorts in the circuit: Some spots, I can detect continuity between two solder pads, but I am too much of a newbie to understand what is the signal route in the circuit and how to understand properly the schematic. I circled a few spots where I was getting "shorts" or continuity, and you can tell me if it's normal or not. I circled where I was getting a continuity on my multimeter when touching the 2 pads (and there was a spot on the left hand side of the PCB where the 3 pads seemed to connect. Normal? I also sent you a clearer picture of what the board looks like now, maybe you have other ideas of what I could try. I wish we could find a way to put a finger on the problem...

Here are the pics:

Image

Image

Image


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PostPosted: Tue Jan 16, 2024 1:56 pm 
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Those are all locations that should have continuity. Can you please test your power supply ala carte and see what it reads?

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PostPosted: Tue Jan 16, 2024 7:46 pm 
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byoc wrote:
Those are all locations that should have continuity. Can you please test your power supply ala carte and see what it reads?


I'm not sure of what you mean by ala carte. English isn't my first language, so I might be missing something :?


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PostPosted: Wed Jan 17, 2024 4:30 pm 
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Test the power supply by itself (not plugged into the pedal). How many volts is it producing?

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PostPosted: Wed Jan 17, 2024 9:29 pm 
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byoc wrote:
Test the power supply by itself (not plugged into the pedal). How many volts is it producing?


I tried two different power supplies, and one indicated 9.19V and the other 9.3V. Both give the same bad tone when I plug it to the pedal.


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PostPosted: Thu Jan 18, 2024 1:19 pm 
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I'm not really sure what to tell you at this point. Your voltages look good, so there's not a likelihood of a faulty semiconductor. I cannot really make out the color bands on the resistors from your pics, but if you're certain that you haven't misplaced any components and your soldering isn't faulty, there aren't a lot of other trouble shooting suggestions.

I'm looking over out previous posts and I don't see that you've tried reflowing your solder joints. Am I missing that? If you haven't, you should definitely do that. It usually solves most problems.

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PostPosted: Thu Jan 18, 2024 8:26 pm 
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byoc wrote:
I'm looking over out previous posts and I don't see that you've tried reflowing your solder joints. Am I missing that? If you haven't, you should definitely do that. It usually solves most problems.

It only takes one bad solder joint to render a pedal defective, so this process is well worth working through: viewtopic.php?f=9&t=52188

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