Build Your Own Clone Message Board

My Mimosa Jr is not working, but in a way that I can't seem to find anyone else having trouble with. Disclaimer: this was my first build ever, so apologies if I'm really dumb.

Bypass works perfectly.
Light comes on when switch is activated.

When engaged, it emits a really loud hum. No crackles or pops, just a consistent tone like a feedback loop. No sound from my bass guitar comes through at all, just the hum.

The volume knob works and raises/lowers the level of the hum, though.

Turning the compression/blend knob or adjusting the trim pot inside seem to have no effect.

I'm GUESSING that I messed up somewhere, but I've reflowed all the joints so many times, the board is starting to get burn marks.

It's easy to miswire the input jacks, and it sounds like a grounding issue. Make sure you have them wired properly, this is a mistake I have made in more than 1 occasion.


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Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box.

+1. The closed-frame jacks can be difficult to wire correctly because of the three connection lugs and the fact that it's not that easy to see what connects to what (tip, ring and and sleeve). Review the jack orientations shown on page 20 of the instructions and make sure your are connected exactly the same way. The explanation and diagrams on page 16 are also very helpful. Even if the two jacks are wired correctly, check the solder joints both at the solder tabs and the connections on the PCB. If any look at all suspect, reflow them with a clean, hot iron.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Hmm, it definitely seems like the jacks are done right. I checked and reflowed those as well, but no change in the issue.

Maybe this will help: http://www.switchcraft.com/Drawings/110 ... ies_cd.pdf
Referring to the diagram in the upper left corner:
SLV = Sleeve = Ground
T = Tip = Input or output (for guitar pedal)
R = Ring = Used on a pedal input jack to turn on the battery power.
TS = Tip Shunt Switch (probably not used for pedal)
RS = Ring Shunt Switch (probably not used for pedal)

I check mine with a multimeter. I use the continuity setting. I still wire them wrong after that, but that's what I do.


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Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box.

Looking more closely at your photo of the back of the PCB, I can see what appear to be solder bridges between a couple of adjacent eyelets that aren't already connected with traces. See marked up photo below. These bridges need to be cleaned up so that the adjacent solder joints are not making contact. Inspect the board carefully, since there could be more than these two. BTW, the bridged eyelets immediately below the right-most ones I circled are OK--they're already connected on the board.

There also seems to be quite a bit of solder "splash" around the board. This stuff is easily removed by gently prying it loose with a small flat-blade screwdriver.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

It can make things a lot easier to see if most of the solder flux is cleaned up too. Commercial flux remover is available, but a little isopropyl alcohol and a soft brush, like a toothbrush, might work well enough.

Ok, so I spent the past couple days cleaning up the solder splash. Good tip! I assumed the burnt looking stuff was the board melting, but it's just solder going everywhere. I got in there really gentle yet firm with a flathead screwdriver, some alcohol, and a toothbrush and spent many painstaking hours on it. I can now confidently say that there's a least a little gap between every joint that I can slide my screwdriver through uninterrupted.

It's still doing the exact same hum/buzz.

I was really hopeful as there seemed to be a lot of splash gathered around the footswitch prongs and a bit around the output jack that I was able to clean off, but still no dice.

Any other thoughts? And also, for going forward, tips on preventing that type of splash when I solder?

I would triple check all your component placement first, including the pots. You could also test the voltages of the IC. If they are way off then you will probably need a signal tester to diagnose what is going on with the signal.

You can just google building your own signal tester. They are relatively simple to build.

I would check the voltages first. The pin layout on the IC is:




I don't have a pedal to check so I got these readings from a post from Steven:

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Math illiteracy affects seven out of every five people.

I can't get enough minimalism.

I'll give this a shot. I have a volt meter, so I can make that work. I assume I'll just set it on like 20v? Also, when you do these pin testings, where do you put the other prong? Sorry, total newb.

Set your DMM to measure DC voltage at whatever range best suits your meter to measure voltages as high as 9V. Connect the black probe to ground. The red probe will be used to take the readings.

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"It’s your soldering."

I checked all my components, every resistor, pot, and pin. All seem to be correct.

My readings are way off.

8.48
8.6
10.1
11.8
8
8.7
7.1

6.9
7
7.2
ground
8.4
7.8
8


Any other suggestions? I'm stumped.

What are you using to power the pedal? You should not get any readings higher than 9V from a 9V power supply. If you're using a garden variety wall wart type power supply throw it in your junk drawer and get a regulated 9V power supply like OneSpot or similar.

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"It’s your soldering."

One would think, right? It's the 9v that came with another pedal I bought some time ago. It's always worked great on the other pedal as well as several other 9v things I've occasionally borrowed it for.

Could be that my multimeter is messed up, because it's claiming an output of 16v from it. That seems pretty far off for something that I use on a daily basis at 9v. Though I also don't know anything.

I've got a voodoo power I can snag tonight to do some testing. That should isolate this variable once and for all.

By all means, settle the power source question. If that doesn't reveal anything, another possibility is a bad IC. Do me a favor and take one more reading--check the voltage level on the inside lead (closest to the middle of the PCB) of either of the pair of 22K resistors located just above the volume pot connections. This resistor pair is the voltage divider for the circuit, so the reading there should be almost exactly one half of your power source voltage.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

You have an unregulated power supply if it's output is that much higher than it's rating. These types of power supplies are unregulated and have very little if any filtering. They should not be used with audio circuits.

_________________
"It’s your soldering."

Still on the same power supply, I'm getting 5.7 on each of those. Which is just about in line of being half of the 11.8 reading I'm getting as the highest voltage passing through. So that's good? And bad?

I wasn't able to borrow it long enough to do any multimeter testing, but I did get to test my pedal real quick. No more, hum, just a faint crackle, controllable by the volume knob. No sound from the bass comes through, though, when engaged.

So yes, the hum is DEFINITELY a voltage thing, but the pedal not working is yet to be answered.

I'm going to score a better power supply and report back with some more numbers!

All right! Much better power supply purchased, tested and working at 9v. Hum is gone, but engaged still kills all sound output.

I'm getting readings of 4.45 off both of those resistors near the top left of the board.

My IC pin readings are now:

5.25
5.13
6.86
8.53
4.45
5.2
5.25

4.45
4.45
4.45
ground
5.28
4.54
4.84


So it's much closer! Anybody got a suggestion?

Some of your voltages are off. Here are the voltages from my Mimosa Jr. using a 9.47V PS. The voltages above were from my standard Mimosa using a different PS.

1) 5.17
2) 5.16
3) 5.06
4) 9.47 (PS)
5) 4.73
6) 4.75
7) 4.74
8) 4.74
9) 4.74
10) 4.74
11) 0 Ground
12) 4.73
13) 4.74
14) 4.75

Right side of R22 & 23 = 4.74

Pin 4 is connected directly to +9v and should be identical to your PS voltage. Your measurement shows a 1/2V loss at pin 4. This might be due to poor soldering.

Your pin 3 voltage should be lower than pins 1 & 2. Not sure exactly what’s going on there.

Pins 5 & 12 are connected directly to voltage divider resistors R22 & 23. Voltages at these points should be identical. This might be due to poor soldering.

Since you lose signal after actuating the stomp switch I would suggest using a signal probe to track down exactly where the signal is being lost.

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"It’s your soldering."

I've finally had some time to do a little more testing. Realized one thing that was my fault, I put the pin numbers in the wrong order for the second column. Here's a correct readout of my results:

5.25
5.13
6.86
8.53
4.45
5.2
5.25

4.84
4.54
5.28
ground
4.45
4.45
4.45

So pins 5 and 12 ARE the same, I'm just dumb. As far as the power loss, I've noticed an interesting thing. When I test my power supply when nothing is plugged in, I'm reading 9.31 volts on the plug. Once I plug it in to the pedal, it drops to that 8.53v level that I'm reading on pin 4.

I thought maybe I'd soldered the wires from the power jack poorly/backwards or something, but they're correct and it all looks good. If i back the plug up enough that it's still under load but I can get the multimeter prong onto the metal tip of the cord coming from my power supply, it's showing 8.53 there as well.

Did I get screwed? I thought these voodoo power supplies were supposed to be kind of the good ones.

Obviously there's still a few other problems to chase down, but I'm pretty sure that starting a whole volt short at the top is going to be the first problem.

Nah, that's pretty normal. I'd reflow everything and make sure component placement and polarity are correct.


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Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box.

Well, long time no update. But I have still been working on this!

First things first, a buddy and I traced down an error in the schematic. I've attached a markup of the two switched sections.

Next, I noticed that the 4.7u capacitor nearest the footswitch was dead. So I pulled it from the board. Then noticed it tested fine. Then I put in another working one, and sure enough, same issue. I deduced that perhaps it wasn't receiving power to its positive lead, so I replaced the next component up the chain: the transistor between it and the trimpot.

This also has had no effect.

My readings on the pins are pretty close to accurate, except for pin 3. It's a good deal over. If the power isn't getting over to this segment, perhaps that explains the extra power being forced to flow into pin 3? Based on my read of the schematic, it seems like this could be related. It almost seems like maybe the lead inside the board itself is just not connecting. Or anything else. Please. I'm open to ideas.

It also seemed that the 470k resistor right next to the foot switch (R24 I think) was testing as having no resistance. Once again, pulled the component off, tested it, it worked fine, replaced it with another working one anyway, no difference.

The other thing everyone that looks at it says is that the footswitch is cheap and not very good, so maybe I'll try replacing that next.