Help troubleshooting issue with AION FX Cerulean Kit

[jrbilodeau]

Hi,

I'm new to the forum and to pedal building. I recently got the Aion Fx Cerulean Amp Overdrive kit and made it through the build, however something doesn't seem to be working quite right. The pedal powers on, and produces sounds, however the pedal sounds really gritty or fizzy even with the drive really low. I have another blues breaker style pedal, and my Cerulean build doesn't sound anywhere near as smooth as that one, or what I see in the video on Aion FX's site https://aionfx.com/project/cerulean-amp-overdrive/

I went over the troubleshooting section in the build document, which includes the schematic https://aionfx.com/app/files/docs/cerulean_kit_documentation.pdf and tested the voltages for Q1 and IC1 with the pedal plugged into my 1 Spot CS12.

Q1

PIN	Aion FX Documentation Voltage	My Voltage
1	7.79V	3.52V
2	1.00V	3.01V
3	0V	0V

IC1

PIN	Aion FX Documentation Voltage	My Voltage
1	4.84V	4.61V
2	4.84V	4.78V
3	4.82V	4.48V
4	0V	0V
5	4.38V	2.26V
6	4.83V	4.58V
7	4.83V	4.58V
8	9.65V	9.14V

After seeing that I have fairly different voltages on pin 1 & 2 for Q1 and Pin 5 for IC1, I took the pedal apart and visually checked to make sure that I didn't accidentally bridge any pins or contacts when soldering. Next I double checked the polarity/directionality of the diodes, LED's, capacitors, IC and transistor and they seemed ok, as best as I can tell. I also when over the documentation again an checked that I had put the correct components all at the right spot and as best as I can tell I did. I also went over all the solder joints again just to make sure and added extra solder if I had any doubt if enough had been applied the first time. I tested the pedal again and got the same results.


Here are some pictures of the build. I'm hoping that someone might be able to help me figure out what's going on so that I can fix it and enjoy using this Pedal.

[antonis]

Hi & Welcome..

Your Vref seems OK (IC pin 3) so for the lower enough measurement on pin 5 the suspect is your meter's low (slightly over 1M, judging from 2.26V instead of 4.48V) impedance..
(it's effectively set in parallel with R1 resulting into significantly lowering equivalent resistance..)

Q1 measurements make no sense..
Check both RX4 (22k) and RX5 (12k) values..

[jrbilodeau]

Sorry if this is a noob questions, but just to make sure, when testing the values for RX4 (22k) and RX5 (12k) I would need to desolder them and test them outside of the circuit right?

Also when you say "so for the lower enough measurement on pin 5 the suspect is your meter's low (slightly over 1M, judging from 2.26V instead of 4.48V) impedance.." what do you mean by my meter's low? like do you mean that my multimeter might be the issue? I'm not 100% sure on the model, but it's a mastercraft one, I picked up at Canadian Tire years ago.

[antonis]

Just lift one leg and measure at 20k range for RX5 and at 200k range for RX4..

All DC voltage measurements (for particular circuit) should be taken with DMM set on 20V range..

[jrbilodeau]

Thanks. I tested those those resistors and I'm getting 22k for RX4 and 11.99K for RX5.
I think I found a typo in the documentation however. Page 4 lists 47pF (marked "470") under the MLCC Caps, but page 14 says C2 47pF MLCC (may also be marked "471")....One says 470 and the other 471...I double checked the one I got with the kit and it says 470, which from my understanding is 47pF

The schematic also lists 47pF for C2.

BTW the part number for Q1 that I got with the kit is PN4303, in case that helps at all, since two possible part numbers where listed.

Any other suggestions for things to test?

[idy]

The thing about "your meter's low impedance:
If your meter had an infinitely high impedance it would not affect the voltage you are measuring. It in real life acts like a big resistor, maybe 1M, in parallel with what ever is there. When you measure the voltage at the input of the opamp, you actually drag it down a bit. If you could measure the other pins at the same time you are doing this, you would see them follow. The other two pins of the opamp are however  "buffered" in that when your meter tries to drag them down, the opamp keeps them up.

So: very common thing. you check voltages on opamp, and the input getting the bias reads low, but the other input and the output all read 4.5 more or less.

[jrbilodeau]

I took some other voltage readings in case it helps.

IC Pin 1 4.58V
R7 4.58V
R8 4.58V (with tone knob set all the way to the right)
RX2 0V

Measuring with the pcb's mounted in the enclosure and the input/output/DC jacks facing up/top
RX4 9.17V on the left of the resistor and 3.54V on the right side of the resistor
RX5 0V top side of the resistor and 3.01V on the bottom side of the resistor
RX6 2.98V on the left of the resistor and 3.01V on the right side of the resistor

@idy thanks for the explanation. Just so I know, if I where to get a better multimeter with a bigger resistor, would this difference be lessened in order to get better readings? Just wondering since the Aion FX documentation shows 4.38V for IC1 Pin 5, so i'm just curious how they got that result? Or would simply opening up my multimeter and putting a larger resistor in place of the 1M ohm resistor be another option?

[idy]

I mean the meter has a quality called impedance, which is "like a resistor."
You can't change your meter to improve this, It is likely good enough.

I was just saying, it is normal for the + input of an opamp to read a bit low. If the other two pins  (- input and output) are correct, we know to take that other reading in context. We know that, when we aren't measuring it, the + input is the same as the others. (Also when we are measuring it, and "loading" it or drawing it lower, the other two pins follow it down.)

I'm getting 22k for RX4 and 11.99K for RX5.

You know those should be 10k and 220k? Are the color codes right? I can't see how those numbers could be. You are turning power off before testing resistors? You should. Any reason for the x's? RX4? You mean R4, right?

No, you can't be measuring 0v on one side of R5, unless it is not attached. It goes between - input and output of opamp, pins 1 and 2, both are mid voltage. how can it read 0? did you remove it from the board? Is it soldered in?

[antonis]

You know those should be 10k and 220k?

Drain resistor (RX4) should be 22k and Source resistor (RX) should be 12k, so they measure right..
Also, 0V at Q1 Gate (at any leg of RX2) is fine..

Still can't get the reason for Q1 particular measurements..

@jrbilodeau: Try to jumper (via an aligator clip) Tone pot lug 3 to OUT (Volume pot wiper) while disconnecting HARD switch middle lug from VR..
(you should have a loud distorted signal..)
Then connect again HARD switch middle lug to VR..
(you should have a more distorted signal of lower level..)

[idy]

Sorry, now I see the RXs. "Never mind."

Now that I am looking at the right end of the horse..
It looks like the schematic shows two options, but I see in the docs they don't explain this to you, just say leave CX5 off.

The PCB allow two options:
either you populate C8 and CX5 to get a "stockfish" blues breaker
or you populate C2 and Q1 and you get a morning glory-is thing.

Trouble if you do both maybe? a big feedback loop...

About the 47p cap: 47p is the correct value, and that would be written either "47" or confusingly "470". Yes, "471" means 470, and it looks like the docs have a typo where they list the part both ways...

[anotherjim]

Q1 seems the big bug to me. Either you have the JFET gate where the drain should be or it's a fake (not unknown) and probably actually a PNP transistor or it's just faulty.
I guess it's also possible that CX4 is shorted letting DC from the preceding stage into the JFET gate.

[duck_arse]

I think I found a typo in the documentation however. Page 4 lists 47pF (marked "470") under the MLCC Caps, but page 14 says C2 47pF MLCC (may also be marked "471")....One says 470 and the other 471...I double checked the one I got with the kit and it says 470, which from my understanding is 47pF

The schematic also lists 47pF for C2.

I'm not entirely sure this is 100% correct. find the spec sheet for the manufacturor of your part, see what standards are in use for the markings. 47pF should be marked as 47 or 47pF [or 47R0 in some cases] but I think 470 is illegal. 47K would include the tolerance. 470pF should be marked either 470p or 470pF, or 471. 0r n47.

if you get the thing working, but sounding "dark" or low gain, you can test-lift this cap, see what it effects.

[jrbilodeau]

The PCB allow two options:
either you populate C8 and CX5 to get a "stockfish" blues breaker
or you populate C2 and Q1 and you get a morning glory-is thing.

Trouble if you do both maybe? a big feedback loop...

About the 47p cap: 47p is the correct value, and that would be written either "47" or confusingly "470". Yes, "471" means 470, and it looks like the docs have a typo where they list the part both ways...

I went with the morning glory-is option and can confirm that nothing is hooked up to C8 or C5. Also thanks for confirming about the typo.  I reported it through the Aion Fx contact form, so hopefully they'll fix that in their documentation.

[jrbilodeau]

I'm not entirely sure this is 100% correct. find the spec sheet for the manufacturor of your part, see what standards are in use for the markings. 47pF should be marked as 47 or 47pF [or 47R0 in some cases] but I think 470 is illegal. 47K would include the tolerance. 470pF should be marked either 470p or 470pF, or 471. 0r n47.

if you get the thing working, but sounding "dark" or low gain, you can test-lift this cap, see what it effects.

I got this as a kit through aion fx's site, and from what i've see with various forums they seem pretty legit and use quality components. When first looking into the possible typo, I looked up how to read the values on capacitor, as is seemed that there were a few standards. From what I read on various site and video's the ones that use 3 numbers, the first two are the capacitor value in PF and the 3rd number is the multiplier or number of additional 0's to add to the value. So 47pF and add 0 0's = 47pF, where as if the value was 471 the capacitor value would be 470pF.... at least that's how I understood it.

[jrbilodeau]

Q1 seems the big bug to me. Either you have the JFET gate where the drain should be or it's a fake (not unknown) and probably actually a PNP transistor or it's just faulty.
I guess it's also possible that CX4 is shorted letting DC from the preceding stage into the JFET gate.

To check if CX4 is shorted would I do a continuity test between the two legs of the capacitor? If so I set my meter to 200K ohms and got a reading that fluctuated around 100-111K

The Transistor came with the kit ordered directly from Aion FX and has the following numbers on it FB426 PN4303

After work i'll do the test that @antonis suggested and let you guys know the result. If we don't get anywhere I can always order another transistor...or is there some way that I can take it out of the circuit and test if it's good?

[anotherjim]

Pn4303 is obsolete but is the right kind and should be pinned DSG. If your meter has a diode test, Red on 3 (G) should give a reading with Black on either 1 or 2. Black on 3 should not read with Red on 1 or 2. This ought to work with the transistor in the board.
Don't do any diode or resistance checks with power on the board!

[antonis]

What Jim said but with resistance measurement..
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/meter-check-transistor-jfet/

[jrbilodeau]

Still can't get the reason for Q1 particular measurements..

@jrbilodeau: Try to jumper (via an aligator clip) Tone pot lug 3 to OUT (Volume pot wiper) while disconnecting HARD switch middle lug from VR..
(you should have a loud distorted signal..)
Then connect again HARD switch middle lug to VR..
(you should have a more distorted signal of lower level..)

I unsoldered the middle pin for the HARD switch and hooked up the aligator clip from pin 3 on the tone pot  to pin 2 on the volume pot, and I had a loud signal with some distortion, but way less then before. Next I resoldered the middle pin on the switch and did the test again with the aligator clips still on, and it was more distorted then the previous test, but less than without the clip. The volume sounded similar, maybe a bit less.

I also tested the JFET with red on the gate and black on pin 1 and then pin 2 and it seemed ok. I tried the reverse and got nothing which i believe is a good thing. I also did a test shoring source and gate with the red lead and black on the drain and got 278 ohms.

[anotherjim]

It looks like the JFET is ok, so you need to find out why there is other than 0v on its gate pin. The 1M RX3 is the only thing supplying 0v to the gate (yes, 0v ground is a voltage!). Cap CX2 is the only thing blocking any other DC voltage from interfering with the gate voltage.
As RX3 is very high resistance, it doesn't take much for leakage from parts nearby to interfere with it. Even an unsuitable soldering flux can conduct enough to interfere. An idea is to scrub the area with IPA (alcohol, not beer).

Normally, you would trace this kind of fault by selective disconnection of nearby parts and see if the voltage then corrects. If you have a double-sided PCB this can cause damage as it needs more heat to flow the solder and you can disturb the thru ferrule in the hole that is there to connect both sides of the traces.

[jrbilodeau]

I tried cleaning the board with 99% isopropyl alcohol, but i'm still getting the same results.

Regarding the 0V on the gate. If the JEFT is DSG, than I thought I was already getting 0V on the Gate, based on my original readings. It was more the voltages on the drain and source that seemed off.

Q1
PIN   Aion FX Documentation Voltage   My Voltage
1   7.79V                                        3.52V
2   1.00V                                        3.01V
3   0V                                             0V

Not sure if I'm misunderstanding something, as I'm a bit new at this and learning...but I appreciate the help

Also just so I know, is it usually a good practice when building a circuit to go over and clean the pcb with rubbing alcohol afterward soldering to clean off the flux?