Debugging DIY Klon Circuit (Sounds like a fuzz)

[markypizz]

Hey guys, great to meet you all. I've been lurking around for a while and finally made an account. I've been making a handful of Klons using the Aion Refractor PCB. I got two working, but this third one has given me some issues, was wondering if you guys could help point me in the right direction. I have it wired for buffered bypass (standard Klon Centaur style). Here's what I notice:

1. In bypass mode with all the knobs down, works just fine without issues. Turning up the volume knob (while in bypass) causes the signal to morph into a spitty gated fuzz tone
2. With the pedal engaged, the volume seems hyper sensitive, and similarly when turned up goes into a spitty gated fuzz. The knobs appear to be doing what they should, volume, gain, tone.
3. I've confirmed the ICs are working fine. I've swapped them out individually in my other working Klon and they are performing as they should.
4. I have not been able to identify any bad solder joint or solder bridge. Regardless, i re-flowed the majority of joints that could have been suspect. No change
5. Removing IC2 entirely removes the issue (resulting in just a buffer pedal), so I am certain the issue is isolated to around IC2 and beyond.

I thought I'd take voltage measurements at each of the ICs for both my good and bad klon. IC1 (TL072) and IC3 (TC1044) matched at each pin, but not IC2 (TL072) after the clipping stage. See the attached screenshot. In green are the voltages I read from the good klon, in red is any voltage I read from the bad one that does not match. So it is just the two op amp outputs, both of which are way out of sorts. It sure seems to me that at least the first one is saturated, hence the fuzz.

I have taken resistance measurements across components around IC2, and can't find anything on this bad klon that doesn't match my good one. Capacitors from what I can tell are not shorted, though I haven't desoldered anything yet. Unfortunately I have no tools to measure capacitance, other than checking if they're fully shorted.



Good Klon (Bad Klon) Pins:
1- 4.2V (15.2V)
2 - 4.32V (4.32V)
3 - 4.5V (4.5V)
4 - -8.66V (-8.66V)
5 - 4.5V (4.5V)
6 - 4.5V (4.5V)
7 - 3.99V (-6.25V)
8 - 16.31V (16.31V)

I hope this is appropriate for the forums and I hope I've posted this in the right place, if not let me know! Happy to be here :-)

[bluebunny]

Welcome, markypizz.  Thanks for all the information and sticking rigidly to the rules!     You can still post a link to Kevin's documentation, which is here.

[duck_arse]

also welcome, and also PHOTOS, please.

I think we allow Aion schems being posted, as it's been done a million times already. and posting it makes it easier for us to get interested in the fixing.

[markypizz]

Thanks all! I attached my annotated Aion schematic in the original post.

[MikeA]

You have slightly less than VB (pin 8's 18V nominal) on Pin 1, and it has to be coming from somewhere between the cathode side of D4 and Pin 8 of IC2.   Look for a solder bridge on the solder side or a wire scrap on component side on that path from D4 to IC2 pin 8, maybe around C13.

[markypizz]

So far no dice, cant see anything visibly wrong, and can't find any shorts using my multimeter between the D4 cathode and pin 1, tracing through and around that feedback loop (C13, R20). Will keep looking around. I should also add that I'm comparing any measurements I take to my good klon, and things have matched perfectly so far. (though I can't reliably test for exact capacitance)

[idy]

Welcome!

One thing with new people, no one knows how much or little you know, so it is common for things to be totally elementary or over some ones head. That being said, problems are usually something totally elementary...

Mike A has a point. there are only a few places in the circuit with a voltage near 15 or 16 volts. One of those places is pin 8. Pin 8 and 1 are close together. I would power down and remove ICs (you did socket?) and then check for resistance between 1 and 8 on that IC. It should be... too high to measure.

If that isn't doing it, I would reinsert maybe only the charge pump and begin hunting for other places nearby that have that voltage. It should only be on C22+, diode 4, and pin 8.

The other possibility is DC gain...

[antonis]

The other possibility is DC gain...

Ahaaa..!! 

[duck_arse]

elementary...

Mike A has a point. there are only a few places in the circuit with a voltage near 15 or 16 volts. One of those places is pin 8. Pin 8 and 1 are close together. I would power down and remove ICs (you did socket?) and then check for resistance between 1 and 8 on that IC. It should be... too high to measure.

it's also worthwhile to pull just IC2 and then power up and measure the voltages on each empty socket leg.

[markypizz]

Thanks all for the replies. I tried all your suggestions:

1. Pulled all ICs and measured the resistance across pins 1 and 8 of IC2. I observe the resistance rise quickly (3 secs) from 0 up to +2M and beyond. I see this same behavior on my good klon.

2. Measured the voltages on the IC2 socket with IC2 removed. Here's what I found on each pin
<EDIT> Had the pins mis-numbered, these are the correct ones:

Good Klon:
1: Starts around 3.7V and drops to 2.8V over the course of 1 second
2: 5V
3: 4V
4: -9V
5: 4.04V
6: Same as pin 1
7: Same as pin 1
8: 17V

Bad Klon:
1: 0V
2: 4.39V
3: 4.45V
4: -9V
5: 4.45V
6: 0V
7: 0V
8: 17V

The behavior of pins 0,6,7 is interesting. Implies potentially a busted cap? Going to peek around C14. I think this is getting us closer. Thanks all for the help so far. Was suspicious of just massive DC gain but now I'm more skeptical of something shorted. Will try to get these voltages up in an annotated schematic after work. Thanks guys!

[markypizz]

Sorry for the double post, another interesting find. I went and measured the resistance across C14 on a hunch (no power applied, IC2 removed), found an interesting difference.

Good klon - 54k
Bad klon - 104k

Tone knob was all the way down in this test. But signs are pointing to something about this feedback area. Hopefully more discoveries to follow...

NVM. Found a tone pot wire had snapped off. Not related to the fuzz issue, that's still present.

[antonis]

Bad Klon:
1: 0V
2: 4.39V
3: 4.45V
4: -9V
5: 4.45V
6: 0V
7: 0V
8: 17V

Are you sure for 0V indication conserning pins 1, 6 & 7..??
Your readings should indicate "open" instead of "short"..
(just after respective caps dis/charge fluctuation)

[duck_arse]

as antonis always sezz - your circuit diagram is incomplete, as it does not show how VR is generated or derived, and also, still no photos of what you've built.

[markypizz]

Very sorry guys, my mistake. I can't seem to edit my original post now, so here's the full schematic from the Aion Refractor page https://aionfx.com/app/files/docs/refractor_documentation.pdf. This is what I'm working with:



I have skipped the switch and hardwired it to buffered bypass. I am confident in this area of the circuit.

<edit>
Here's the images of the board and such. A bit messy at the moment (couple long leads to snip). Got as clear of shots as I could on the front and back. Also, yes I'm going to clip the diodes, just comparing with others at the moment.







There is the one pin on the socket towards the middle that looks like a bad solder joint, which is an artifact of the lighting. That joint looks solid, double checked it, just an artifact in the photo.
Also R30 seems to have popped up a bit when reflowing :-) will fix that. (it's still soldered fine). Double checked the pots and they are not shorted to the enclosure. Although, I put some tape under the gain pot which was a bit suspect.

Let me know if I can explain the madness of the switch assembly. Using a DPDT instead of 3PDT, center column is the LED control, right column is swapping the buffer out and FX out connecting to the output jack.

Thanks for your patience all, I really appreciate all the help and support so far.

[markypizz]

Fixed!!!! Thanks all for the help - the debugging tips helped a lot in pointing me in the right direction, and will definitely help me a lot going forwards.

So the issue turned out to be a bad trace between C13 and pin 2 of IC2. I couldn't find any physical damage at all, traces looked fine, solder joints looked fine (tried reflowing anyway), so go figure. Put a jumper between those two pads and viola!! Working great! At least now I know how to make a klon-style fuzz circuit!!

Here's a video! Excuse the bad playing, I'm definitely more of an electronics guy than I am a great guitar player. Hope you all dig the KTR style enclosure

https://www.youtube.com/watch?v=4iCJD6mlzD8