Cerulean kit troubleshooting (Bluesbreaker/Morning Glory)

[Lenougat]

Hi Everyone,

I'm Alex, 40, from France.
This is my first post here. I'm getting into trouble with a kit...

First of all, I will regard myself as a beginner, even if it's not my first build (I've build a Russian Muff, which worked perfectly at the first try – probably luck ! - , I've modded some of my old pedals, a CE3 and a Cry Baby, and I've modified some of my guitars).
Even if it's painful to go through the troubleshooting process, it a good opportunity for me to LEARN a lot of things. I've collected some knowledge on the internet, especially on this forum, but some of my statements should perhaps appear to be stupid to electronic-wise people, sorry about that ! But I'm sure that I'll learn a lot from your community !!

I've built a cerulean kit (a Bluesbreaker / Morning Glory), from Aion Electronics, bought on Musikding. In the end, I've got some issues :
-   I have to crank both drive and volume knob to get a decent tone (awesome sound by the way... !)
-   The general volume is weak compared to the bypass signal (it needs to be 100% to equal the bypass level). The volume knob has a short usable course : below 75%, the pedal goes totally silent.
-   The drive knob acts like a volume. Below 75%, the pedal goes silent as well. And you can really hear « gain » between 90 and 100%.
-   The « soft clip » options seems to work (but drives down the volume too low, due to the volume issue)
-   The « hard clip » switch seems to have no effects, whether it is engaged or not.

Attached is the schematic of the circuit, coming from Aion documentation, and some pictures of the build.

I've built the morning glory variant, with the output gain stage : I've left C8 and CX5 blank (with no jumpers).
For troubleshooting, I've swapped the stock IC (a TL072P) for a JRC4558 : no change. I've put back the stock IC then.
I've replaced two resistors that seemed to have wrong resistance values : R9, R10. They're good now.
I've replaced R1, because I suspected an issue with it, but the issue is still there after replacement.

Here are the values I've measured :

PCB in : 8,7V

IC1 : 4,34
IC2 : 4,35
IC3 : 4,28
IC4 : 0
IC5 : 2,16
IC6 : 4,34
IC7 : 4,34
IC8 : 8,69

Q1 : E=6,63V, B=1,0V, C=0V

R1 : 2,15V / 4,28V
R2 : 4,34V / 4,34V
R3 : 4,33V / 4,33V
R4 : 4,33V / 4,33V
R5 : 4,34V / 4,34V
R6 : 4,34V / 4,34V
R7 : 3,93V / 3,93V (but I've got a doubt : unstable value shown)
R8 : 3,93V / 4,34V
R9 : 4,29V / 8,70V
R10 : 4,29V / 0V
RX1 : 4,27V / 3,87V
RX2 : 0V / 0V
RX3 : 0V / 0V
RX4 : 8,70V / 6,63V
RX5 : 1,0V / 0V
RX6 : 1V / 1V

D1 : A=8,94 K=8,69
D2 : A=4,32 K=3,98
D3 : A=3,98 K=3,64
D4 : A=3,64 K=3,31
D5 : A=3,31 K=4,33
D6 : A=4,33 K=4,33
D7 : A=4,34 K=4,34
D8 : A=3,90 K=3,60
D9 : A=3,60 K=3,90
D10 : A=3,90 K=unable to get a measure... I suppose to be logically 3,60 (D11A)
D11 : A=3,60 K=3,32
D12 : A=3,01 K=3,92
D13 : A=3,32 K=3,02

C1 : 2,15 / 0V (problem ?)
C2 : 4,34 / 4,34
C3 : 4,32 / 4,33
C4 : 4,32 / 0V (linked to ground)
C5 : 4,34 / 4,31
C6 : 4,28 / 3,94
C7 : 4,28 / 4,26
C8 : omitted (built with the gain stage of the morning glory)
C9 : 8,70 / 0V (linked to ground)
C10 : 4,28 / 0V (linked to ground)
C11 : 8,70 / 0V (linked to ground)
CX1 : 4,34 / 4,34
CX2 : 3,94 / 0V (problem ?)
CX3 : 1V / 0V (linked to ground)
CX4 : 6,63 / 0V (problem ?)
CX5 : omitted (built with the gain stage of the morning glory)

Pots :
3 pots have correct resistance values and behavior regarding their specs (linear vs audio). BUT : Drive and tone show some voltage when testing (drive = 4,34V on three legs, tone = 3,90V on two legs and slightly less on the third), volume shows 0 on its three legs, when the effect is in operation (but something goes out from the pedal when the effect is engaged, and volume pot is effectively decreasing the output volume between 100 and 75%, pedal is silent below that).

Some toughts regarding the measures, that I assume to be issues (but I'm perhaps wrong...) :
-   Volume pot shows 0 voltage on the three legs
-   C1, CX2, CX4 show 0V on one side, but are not linked to ground
-   IC5 gets only 2,15V instead of something around 4+V (according to Aion doc value)
-   R1 shows these 2,15V on one side, but I can't figure out why... I've changed R1, the new one still shows exactly 2,15V
-   Q1 emitter legs seems to be slightly weak compared to Aion doc.

I will continue to brainstorm on that schematic, and collect information on how the different components should behave, but if some wise people can show me the light, it would be wonderful !!

Thanks for your help on my case, I'll be around if someone needs more information !!
Rock on !!

[willienillie]

Q1 is supposed to be a JFET, and will have Source, Gate, and Drain pins.  What did you use?  If it is a JFET, are you sure of the pinout?  Are you sure it's real?  Did you buy it from a reputable supplier?

[11-90-an]

First of all.. welcome to the forum

A agree with willienillie on this... have you tried swapping it out for another one?

[antonis]

Welcome also..

I don't like IC1 pin 5 measurement, unless your DMM has an impedance of about 1M..

P.S. No need for DC measurements across resistors of one leg connected to a capacitor..
(you'll get no voltage difference..)

[11-90-an]

P.S. No need for DC measurements across resistors of one leg connected to a capacitor..
(you'll get no voltage difference..)

We need more people like Alex who are more than happy to give voltages 

[antonis]

We need more people like Alex who are more than happy to give voltages 

Totally agree, as long as there are voltages to be given..

[Marcos - Munky]

We need more people like Alex who are more than happy to give voltages 

And also post photos at first post of a topic

First, welcome, Alex!

As asked, what did you used for Q1? And also, do you know how to do an audio probe?

[Lenougat]

Hi guys ! Thanks for your replies !

My bad on that one : it is a JFET (I dont' know how to verify that, but it's been supplied with the kit by Musikding, I've got a total confidence in those guys). I've used EBC as an "habit"...
Values are : Drain 6,63, Source 1,0V, Gate 0V.
I've swapped it for a regular transistor, values were E=3,19, B=2,93, C=0. I don't know if that can help...

I've seen some tutos to make an audio probe (I don't have one yet), but will it be useful in my case ? The signal is going from the jack in to the jack out, there seems to be no signal disruption.

For IC5, I don't know the impedence of my DMM. Is there a mean to see that (it is a cheap model, I've thrown the manual a long time ago...)

[11-90-an]

I've seen some tutos to make an audio probe (I don't have one yet), but will it be useful in my case ? The signal is going from the jack in to the jack out, there seems to be no signal disruption.

With an audio probe, you can test where the good sounds end and the bad sounds begin...
It helps to diagnose which section of the circuit is broken/defective so our suspicions will be narrowed down to whatever component...

Do you happen to have an extra audio jack, alligator clips and hookup wire? A quick and dirty audio probe can be made with this...

[willienillie]

R7 is supposed to be 1K, you have 1M installed.  1000x difference!  Also, can you confirm the value of the giant pulldown resistor (RPD)?  I can't make out the stripes on that one, but maybe see a gold multiplier band.

[Lenougat]

I didn't catch that one about R7, thanks ! I've checked the value of all the resistors beforehand, and was pretty confident about that.
I've been reading 1000, but on the 2000k range... so 1000K, you're right. That's a good lesson for me !

I'm changing that right now, and I'll tell you the result !

The pulldown resistor is 2M2. I had to change the stock one, but the only one I had was a 1W, pretty big...

[antonis]

it is a JFET..Values are : Drain 6,63, Source 1,0V, Gate 0V...

Pretty good for a healthy & working JFET..

I've swapped it for a regular transistor..

BJTs don't like their Bases grounded when they are fed from single supply..

P.S.
Don't bother too much about pulldown resistor value, unless it's significantly lower than 1M..
To be precise, the lower the resistor value the more effective the input cap "grounding" (by lowering the RC time constant) but also the lower the input impedance..
(which input impedance is the parallel combination of RPD & R1, ignoring C1 capacitive reactance..)

[Lenougat]

BJTs don't like their Bases grounded when they are fed from single supply

After a double check, it's been swapped for another JFET, labelled as J109. I don't have his specs, but it showed the values I gave, different from the right ones.

R7 is supposed to be 1K, you have 1M installed.

Willienillie, you rock !! This swap solved all the problems immediately !

My pedal is now working perfectly ! It has now suitable volume/gain ranges, and every pot/switch is working as expected ! No noise or hum, and a great tone ! I never had a BB previously, so I can't establish a comparison, but it sounds great ! I'm about to put it in place of my good old and beloved SD-1, too bad for him...

Thanks a lot guys for the time you spent to help me !! I owe you a beer or two...

The lessons I've learn :
- troubleshooting can lead to long personal brainstorming sessions, but you can miss something hidden in plain sight
- even after two or three checks : check again more carefully, before assuming you did it right ! 

[11-90-an]

Yessir this is what this amazing forum is for..
Actually this thread about troubleshooting  isn't really that long.. sometimes they are 2-5 pages long with loads of learining and nosebleed to some of us
May you have more builds to come!

[Marcos - Munky]

It's pretty common to build something, it doesn't work, you recheck your parts and everything seems right, until you (or somebody else) finds it's a wrong resistor value.

Just wait until you build something that doesn't work, you spend an hour trying to find the problem, then you notice you didn't connected a power supply or didn't put an IC into it's socket. Or even better, you plugged the cables on the circuit but forgot to plug in the cable on the amp/guitar.

[antonis]

Not to mention reverse IN-OUT plugging..

[GibsonGM]

Lenougat, welcome.

It gets easier 

[Lenougat]

Hi Everyone !

I'm back with another problem with the same pedal...
After two week of use (it worked perfectly , thanks to your help guys !), I've decided to try the "high gain mod" described in the kit documentation : you just need to replace the 100k gain pot by a 250k. That's the only thing I've changed.

After that, I've got the following symptoms :
- the bypass works correctly
- the LED lights up when the effect is engaged, but no sound is coming out from the effect, even with gain and volume fully crancked.

I did some check with a DMM all across the board, and I've found these things, which are different than previously :
- IC6 shows 0,5V, IC7 shows 0V (all the other legs have consistent value with the "pre-mod" state)
- R2, R3, C2, C3, C4 show 0,5V
- leg 1 of the new gain pot shows 0,5V, the two others 0.

I've tried to swap the IC (a TL072) with a JRC4558, and got the same values.

I've been forced to heat the 100k solder joints for a long time, since it was pretty tough to desolder. Can it cause some other components to fail, somewhere else on the PCB ?

Thanks for your ideas on that subject !
Alex

Here's a screenshot of the circuit as a reminder.

[11-90-an]

changing pot values don't usually break anything... (especially increasing value..)

you could have toasted some of your components... do you happen to have a pic of the area where you soldered your pot? and have you tried to reflow the pot solder joints? (basically heating the soldered area again, but just enough to make it melt, to make sure that it really made contact with the pot)

[Lenougat]

Yes I did reflow the joint, just in case...
Here are some pics :