Aion Cerulean kit (Bluesbreaker) Help -

[Spinarette]

I am attempting to build an Aion Cerulean Kit, which is a Bluesbreaker style pedal. I'm having some problems: the pedal turns on but I have very little gain and the Gain knob acts like a volume knob. Basically the pedal works but I have no gain. I have been over my work a dozen times and I'm 99% sure I've done everything correctly. Would a bad IC or JFET cause these symptoms? Here is the link to the instructions:

https://aionelectronics.com/project/cerulean-marshall-bluesbreaker-kit/

https://www.dropbox.com/s/dl/9li9jw6srix580m/cerulean_kit_documentation.pdf

Attached is the schematic.

Here is my pedal:



Here are my voltages:



IC1:
- Pin 1: 4.54
- Pin 2: 4.73
- Pin 3: 4.44
- Pin 4: 0
- Pin 5: 2.25
- Pin 6: 4.55
- Pin 7: 4.55
- Pin 8: 9.08

Q1:
1:7.7
2: .66
3: 0

D1:
A =9.32
K =9.08

D2:
A =4.69
K =4.33

D3:
A =4.33
K =4.54

D4:
A =4.54
K =4.19

D5:
A =4.19
K =4.69

D8: 
A =4.54
K =4.19

D9:
A:4.18
K:4.54

D10:
A:4.54
K:4.18

D11:
A:4.17
K:4.44

D12
A:4.09
K:4.54

D13:
A:4.44
K:4.09

(I can't access D6 or D7, those are the LEDs on the board)

Thanks for your help!

[thermionix]

Is "pin 3" of Q1 the source?  Shouldn't be 0V.

[Spinarette]

According to the instructions Q1 Pin3 should be 0V.

[thermionix]

I looked at the "Project Documentation" pdf in the link, and didn't see voltages listed.  I don't know what "pin 3" refers to on a JFET.

[Spinarette]

I have updated the original post to include the link to the kit instructions. Pin 3 = drain.

[thermionix]

Actually I think pin 3 is the gate.  I would have expected a small voltage there, but then again I'm an idiot.  Or maybe just a JFET noob.  But we should look elsewhere for the source of your trouble.

[thermionix]

Everything that I can see looks correct, including cap and diode orientation.  The soldering looks good, and the overall construction tidy.  There may be some damage to R6, but I doubt that's an issue.  Have you tried a different IC?  Maybe it's just the lighting, but it looks like it doesn't have any printing on it.

[Slowpoke101]

A very interesting fault indeed. Excellent build quality from what can be seen from your pictures.
Having looked at the project doco, can you confirm that C2 is indeed 47pF ?
The doco says that the capacitor should be marked as 470 but I haven't come across a 47pF marked that way that wasn't a 470pF. Got any way to measure it? Just to satisfy my curiosity. 47pF is the correct value for that capacitor. From what I've seen 470pF capacitors (and other values ) marked as 470 or 471 - this can get confusing at times (other values have different numbers of course ).
If it is a 470pF capacitor it would go some way to explaining your troubles.

[Spinarette]

Well, I do have a capacitance meter but I damaged the 47pf cap when trying to remove it - I snapped a leg off. Doh! You'll have to forgive me, this is my first pedal though I have built many amps. I am going to order a new 47pf MLCC, should I get a new IC and/or JFET while I'm at it?

[Spinarette]

I have confirmed my 47pf cap is indeed 47pf.

Is it possible I damaged something via too much heat?

[Spinarette]

I've got the following items in my cart at Small Bear:

- new IC
- new transistor
- new 47pf MLCC
- new 6k8 resistor (R6)

Anything else I should get while I'm at it?

[Spinarette]

So here is what I have determined: everything works on the pedal EXCEPT the clipping switches. I get oscillations when the Hard Clip switch is in the down position. I get no changes from the Soft Clip switch or Hard Clip switch up. Can anyone suggest some debug steps to work out the switches?  Would a bad IC keep my clip switches from working?

[Slowpoke101]

A bad IC could cause what you are experiencing but that would be very odd. Normally they work or they don't. Or they sound terrible. You need to check the diodes. They should be 1N914 (or 1N4148 ) and they can be damaged by excessive heat when soldering but they are tough little things. Hopefully your multimeter has a diode test setting which makes testing a bit easier. Remove power to the pedal and set all pots to mid-range, then set both clipping switches to the centre position. Place the test leads onto D12 - black to the banded end (cathode ) and red to the other end. Your meter should show about 0.7 then reverse the leads and the meter should show 1 Continue to test D10, 11 & 13. They should test similar to above. If you read 0 on the meter that diode may be faulty (short circuit ). Also if you can't read anything other than 1 when measuring a diode then it is probably open circuit (faulty ).
To test D8 & D9 things get a bit tricky. Because they are connected in a reverse parallel manner either one will test as 0.7 regardless of which way you connect the test leads. If they test other than that then one or both are faulty. I do suggest that you get hold of a spare diode and test it with your multimeter so you get the hang of it.
Other test to try on the Hard Clipping switch is to apply power and measure the DC voltage on that switch's centre pin. It should test as 4.5VDC (or so). The Soft Clipping switch will also have about 4.5VDC on its centre pin.
Switches can be damaged by excessive heat when soldering too.

The Gain pot does seem to act as a volume control - this is normal but the pedal should get very loud as it's advanced. Without Soft or Hard Clipping engaged the output of the pedal will sound distorted (but not much) when the Gain pot is fully advanced - the distortion being generated by the OP-Amp itself. The clipping diodes help to make the distortion more acceptable and to occur at lower gain levels.

Getting oscillations when in a hard clipping mode is odd but it is worth checking D8 and D9. I am sorry that you damaged C2 when removing but you did answer my question quite well. I now know that I should be cautious with the below 100pF MLCC capacitors because they may be marked differently from what I've used in the past.

Let us know how you go.