Seeking help with Aion Refractor Build

[OasisMcFly]

Hello everyone. My name is Nathaniel, and I'm stuck. Against my wife's better judgement, I decided it would be fun to build my own effects pedal. I love DIY projects, but this is the first of this type I have ever attempted. I'm an IT software support guy by day, but I play in the band at my church every week, and I gig routinely with a local country/pop artist. I have a basic level of knowledge concerning electronics, but to make this pedal a reality, I gave myself a crash course in the pedal building. I planned on starting with a simple pedal layout to wet my teeth, but I was ultimately drawn into the allure of getting a Klone and thats when I found the Aion Refractor Project and decided to jump in rather than wade in.

To my wife's dismay, I have discovered that pedal building is not just fun, but downright addictive. I will definitely be building more in the future. However, my basic knowledge and experience level have left me clueless on how to troubleshoot the problem I am having with the Aion Refractor.

The build documentation I am using is:  https://aionelectronics.com/wp-content/uploads/2013/09/aion-refractor-centaur-documentation.pdf

I also used the Refractor bypass for the stomp switch as found here: https://aionelectronics.com/wp-content/uploads/2014/09/aion-3pdt-refractor-bypass-documentation.pdf

I did make a few part substitutions to the design, partly out of part availability and partly out of suggested changes I wanted to try. The changes I made are as follows:

C7: I used a .1uf instead of 82n due to availability
C14: I used a 6n8 instead of the 3n9 to achieve the tone mod mentioned in the build documentation
D1 and D2: Russion D9Es
R4 and R25: I used 560R 1/2w instead of 560R 1/4w due to part availability

Everything went great during the build, and I had no issues that I knew of, however, I did not socket anything on the build, which i now know was probably not a wise decision. When I plugged it in for a first full test, I got nothing but a nice bright LED and some extremely loud hum. I went back through everything and couldn't find any obvious mistakes.  I have been at my wits end for over a week trying to figure out what I did wrong. It's clear to me that its time to call in the big guns, a.k.a. You lovely lot. I am be most grateful for any help you can provide.

For reference, here are voltages I am getting:

IC 1:
1:  +4.72
2:  +4.72
3:  +1.27
4:  0.00
5:  +4.6
6:  +4.72
7:  +4.75
8:  +9.41


IC2:
1:  +4.73
2:  +4.72
3:  +4.66
4:  -9.09
5:  +4.66
6:  +4.72
7:  +4.71
8:  +17.09


IC 3:
1:  +9.41
2:  +4.71
3:  0.00
4:  -4.54
5:  -9.09
6:  +5.28
7:  +4.69
8:  +9.41

[mth5044]

Man, I really wonder why they are using +18/-9V supply but still biasing everything around 4.5V. Or why the first stage is running on 9V and the second on a 27V swing.

Anyway, are you getting any signal passing when the effect is off/bypassed?

[aion]

Hey Nathaniel - that's actually a really great looking first build And your voltages look spot on, so it's probably just something really small. The parts substitutions shouldn't affect anything so nothing jumps out yet.

mth5044 is on the right track - what's it like in bypass?

Man, I really wonder why they are using +18/-9V supply but still biasing everything around 4.5V. Or why the first stage is running on 9V and the second on a 27V swing.

I've heard some people theorize that the op-amp clipping in the first stage contributes a little bit to the sound. I don't know how accurate this is, but either way, since the signal gets lopped off to 0.35-0.4v with the diode hard clipping, the headroom of the first stage isn't as critical. As for the 4.5v bias point, this is halfway between both -9V/18V and 0V/9V, so the whole circuit uses a single bias point while staying exactly at the middle point of both voltages that are used.

[aion]

Also... I can't see the pots very well, but are they all insulated from the back of the board somehow? If there's a joint touching the back of a pot case then that might cause what you're hearing. The loud hum makes me wonder if the audio path is being grounded at some point along the way.

[mth5044]

Wow, Im an idiot. 4.5V is the mid point of both  Math!

[idy]

solder on one of the jacks looks light, this has caused a couple of mine to go silent.
Best bet is to make an audio probe (a capacitor on a stick) and plug it into a practice amp with something (a loop, a metronome, an m3 player with the volume turned way down) plugged into the input. Then probe!  Follow the audio. Where does it stop?

It's probably something simple. You may have to take it out of the box and check the back for solder bridges (under a magnifying glass.) Always better to test before boxing....

[OasisMcFly]

Thanks for the help guys. I really appreciate.

The hum is there in bypass as well. And frankly, its such an obnoxious hum that if any signal is getting through from the guitar, I cant hear it over the hum.

I've ordered covers for the pots, but they haven't arrived yet.  At the moment, I have some electrical tape on the back of them as a pseudo insulator, but the pots are soldered far enough out from the back of the board that I don't think they could touch without some serious bending or warping.

I went through and checked all the ground connections, and the cables all seem to get good connection to the jack, but I noticed that the inside of the enclosure where the jack connected had more paint around it than I realized. To be safe, I took everything out of the enclosure this morning and sanded down and cleaned the area where the jacks connect. I'm really hoping that was the issue. I won't be able to test it again with my guitar rig until this afternoon.

Also, looking back over it, I noticed that the 100n Cap in C3 looks to have melted a bit in one corner. I think I may have got to close to it with the soldering iron when I was soldering the volume pot.  You can see it a bit in the picture. It doesn't seem to have affected the Cap at all other than cosmetically, but I don't know enough to be sure. Could that be part of the hum problem as well?

[karbomusic]

The hum is there in bypass as well. And frankly, its such an obnoxious hum that if any signal is getting through from the guitar, I cant hear it over the hum

TLDR but sounds like the main ground for the signal is floating and not connected (as I see you are already checking). A common way for that to occur is to be using the casing for the jack as a ground but it didn't actually make a connection and so on. Can you confirm with a meter if you didn't already say you did, apologies didn't have time to read through it all.

[aion]

Also, looking back over it, I noticed that the 100n Cap in C3 looks to have melted a bit in one corner. I think I may have got to close to it with the soldering iron when I was soldering the volume pot.  You can see it a bit in the picture. It doesn't seem to have affected the Cap at all other than cosmetically, but I don't know enough to be sure. Could that be part of the hum problem as well?

Nope, as long as you only see plastic and not the underlying dielectric you're fine. I've done it many times Same thing can happen with resistors... it melts the paint off but it's fine.

Still thinking it's a ground issue of some sort, whether a floating ground like karbomusic suggested or something else. The multimeter's continuity test will tell a lot!

[OasisMcFly]

Success! It was entirely a ground problem. Once I cleared the paint off the inside of the enclosure where the jacks made contact, everything cleared right up. I tested with the meter and had continuity from all the ground locations and to the case. Plugged it into my rig and it was as clean as can be. No noise at all and it sounds fantastic. I only got to play around with it for a few minutes, but I am very pleased so far.

Thanks for all your help everyone!

[karbomusic]

Glad to hear you got it working. A little something to think about. We always worry about ground loops and many times use the case ground for the jack ground. However, if for any reason that jack comes loose in the future and looses that jack/case connection... BUUUUUUZZZZZZ.