Debugging Easy Vibe (Half-works) Voltages listed

[Kevin Mitchell]

I've put together another Easy Vibe for a friend and I've been trying to figure out the issue all night but I'm pretty clueless when it comes to debugging. Compared to working Easy Vibes I can tell this one is missing the swoosh of the vibrato setting. At first I thought maybe the switch got damaged but I'm not sure if that's likely to be the case. When switching from chorus to vibe there is absolutely no change.

Before I have to gather voltages I was hoping someone could tell me where the issue would logically be. I'm a bit lost due to my lack of understanding how a circuit works.

I've populated my own etch board using the classic layout and -mostly- recommended parts;
http://www.geofex.com/PCB_layouts/Layouts/easyvibe.pdf

-I should mention I ran out of red LEDs so I used yellow out of curiosity. The depth is there but I'm considering using a 50k pot instead of 100k because it's depth hits minimum at about 9-o'clock(3/4 rolled down) But this isn't part of the issue as far as I know.-

[Kevin Mitchell]

After viewing the schematic I believe the issue could most likely be a bad ldr or bad solder relative to that rail. Assuming the vibrato setting is the one coming off the ldrs to the switch?

I'm pretty sure I'm only hearing the chorus setting. I've switch out the spdt with a different one but as I suspected, that was not the issue. Maybe you guys have had this kind of issue or helped debug one with a similar problems. Any help (preferably before Christmas) would be really appreciated.

Schematic;
http://www.hollis.co.uk/john/easyvibe.jpg

[slacker]

The chorus setting is the one that sounds like a phaser, it's the setting with the switch in the down position on the schematic, it mixes the vibe signal coming from the last opamp stage with the dry signal from the first opamp stage. If chorus is working then you must be getting the vibe signal, so i would start by checking the wiring and the connections to the switch. If you disconnect the switch do you get the vibe effect? 

[Kevin Mitchell]

If you disconnect the switch do you get the vibe effect?  

I was just looking at the layout and thought to try this.

The chorus setting is the one that sounds like a phaser, it's the setting with the switch in the down position on the schematic, it mixes the vibe signal coming from the last opamp stage with the dry signal from the first opamp stage. If chorus is working then you must be getting the vibe signal, so i would start by checking the wiring and the connections to the switch.

Thank you I really appreciate the knowledge.
I've traced what I believe to be the vibrato and the chorus rails to get me started debugging.


Since the chorus is working, would that mean that the issue is most likely to be a wiring issue (which I doubt) or some traces perhaps have been joined on accident (also doubt, I've spent allot of time checking the traces)

It must be bad solder on a component on the bottom part of the opamps(according to the layout) but idk why the circuit would work at all if that were the case. What a pain...  

Once I'm home tonight I'll collect the voltages and hopefully get to the bottom of this.

[slacker]

What you've marked in green is the dry signal, which is the output of the left most opamp on the schematic, if you have an audio probe you could check that you are getting this signal on the pad going to the left hand lug of the switch, you should get a clean signal a bit louder than the input.

The traces you've marked in orange aren't the vibrato path, they are the bias voltage, all the bits connected to the top of the 1N914 and the two LEDs on the left hand side of the schematic. The vibrato path is through the four opamps with the LDRs attached to them, this comes out of pin 7 of U4 on the layout then through R13 and R14. If you audio probe pin 7 of U4 you should get the vibe signal, it should wobble up and down in pitch, more noticeable at high speeds.

I can't see anywhere where the dry and vibe signals could get accidentally mixed, the dry signal is only present on the left hand side of the layout and the vibe on the right, the only way they can really get mixed is through the chorus/vibe switch. I suppose in theory if you had the stomp switch wired wrong or had a short there the guitar signal could get mixed with the output with might sound like the chorus setting, that's pretty unlikely though. Having only the vibe effect would be a more likely than only the chorus, that could happen if the dry signal wasn't getting to the chorus/vibe switch.

[Kevin Mitchell]

I can't thank you enough for the information you've provided. So if I am hearing the vibrato perhaps it sounds different from what I'm used to because I'm using yellow LEDs instead of red. I plugged in a strat (to get a little more noise) to see if I can hear any difference when switching the spdt. I can barely make out a difference.

I'm in the process of boxing it but I'll post the opamp voltages momentarily and let you know if it sounds any better sealed up. (no light shielding, didn't use it for other vibes, didn't pose an issue)

[Kevin Mitchell]

Okay here are the op amp voltages;
I tried to read the high and low voltages of ones that fluctuated "3.87-3.97"
U1
1-4.12
2-4.12
3-0.36 (4.12 on other side of R2 resistor) -I would guess this is suspicious but I really wouldn't know
4-0
5-3.96
6-4.12
7-4.12
8-9.23

U2
1-3.87-3.97
2-4.12
3-4.12
4-0
5-3.96
6-4.12
7-4.11
8-9.23

U3
1-4-4.06
2-4-4.06
3-3.96-4.02
4-0
5-3.89
6-4.12
7-4.12
8-9.23

U4
1-3.95-4.28
2-4.12
3-3.93-4.05
4-0
5-3.88
6-4.12
7-4.11
8-9.23

I'd greatly appreciate if someone where to review this and tell me if anything seems funky as soon as possible.

[Kevin Mitchell]

The deed is done.

While boxing it I check the traces and components and noticed the top part of the R14 resistor was missing it's pad and was not connected to the trace. I've just fixed it up and there's that  woosh I was looking for. I was hoping it wouldn't be something as simple as that and I apologize for any trouble.

Thank you very much slacker for your information it definitely helped me source where to check.

[slacker]

No need for apologies, good to hear you got it working, it's a great pedal.

[PRR]

> a wiring issue (which I doubt)

If you live long enough, you learn that, no-doubt, 98% of problems involve "wiring issues".

It has ALWAYS been this way. I found a story about this. It is from 1959, and he uses a colored pencil where we might use yellow hi-lighter, but some things stay the same.

http://www.diystompboxes.com/smfforum/index.php?topic=109351.0

> resistor was missing its pad and was not connected to the trace.

His #2 problem is a solder-joint that didn't "take". I would class this as "wiring issue" but it is a separate step on the bench. Full daylight and a magnifier finds many flaws.

[Kevin Mitchell]

Full daylight and a magnifier finds many flaws.

This flaw was pretty hard to spot. Only at a certain angle I could see the problem. With my knowledge, lack of tools on hand and the fact I work during the day makes debugging a little difficult. But so far a multimeter and an audio probe helps where they can.

This is my first 100% complete stompbox. I did a beautiful paint swirl (enamel dip method) on an aluminum box and threw in a pulse LED. Holding up like a champ so far. Sounds magnificent. Better than i was expecting with the yellow LEDs on the board.

[Kevin Mitchell]

Here's a picture. Happy holidays.

[tubegeek]

I did a beautiful paint swirl

Truth!

[Kevin Mitchell]

I did a beautiful paint swirl

Truth!

Thank you! I was surprised how it all came out.