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 Post subject: Mimosa - no wet signal
PostPosted: Sun Jun 20, 2021 7:41 am 
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Posts: 2
First post, thankful for any input! I have been putting together a couple of DIY stompbox kits recently and have been enjoying myself and learned a lot. Up until now everything has worked, but my lucky streak seems to have ended with the BYOC Mimosa kit. I get no wet signal when the blend knob is fully turned up. I have about zero prior knowledge in electronics, so I´m quickly running out of troubleshooting ideas after trying to reflow the solder.

- Bypass works
- LED comes on when pedal is active
- Sound comes through when pedal is on, except there seems to be no wet signal. When the blend knob is at 100 % the pedal is muted. The level knob acts like a boost.
- I set the trim pot to 1.67 V, according to the building instructions, but the sound does not change at all when I turn the trim pot except for some almost inaudible hums and buzzes in some spots.

From reading on this forum, I understand that soldering quality is the usual suspect. I have tried reflowing all of the solder, and I am fairly confident I got to all connections. Nothing had changed when I tried the pedal after reflowing, though. However, I am well aware that my soldering is poor at best. Should I maybe try to get some fresh solder on the connections? I would be very happy to get some pointers on particularly problematic spots!

Also, one of the 47n capacitors has a crack in its hull. I am unsure if it was broken when I started, but I´m guessing I casued it somehow. Could that cause this kind of issue?

I measured the voltages on the IC pins and as far as I can tell from voltages given in other Mimosa threads, the values seem OK:

1: 4.18V
2: 4.19 V
3: 4:19 V
4: 8.37 V
5: 4.15 V
6: 4.34 V
7: 4.19 V

8: 4.57 V
9: 4.57 V
10: 3.77 V
11: 0.0 V
12: 4.15 V
13: 4.19 V
14: 4.19 V

Realised that my power supply (Riot Black box) seems to be putting out only around 8.35 V (as measured on the pedals + power inlet), but I assume that this is no major problem since it works for my other 9V pedals. At first, I tried the pedal with a 9V battery that turned out to be old. This caused the pedal to produce a fart-like fuzz sound for a minute before the battery died completely. Could this somehow have damaged the circuit? I havent tried with a fresh battery yet as I don´t have one at home.

Thanks in advance!


Attachments:
File comment: Cracked capacitor
Kondensator spricka.JPG
Kondensator spricka.JPG [ 370.54 KiB | Viewed 901 times ]
File comment: PCB soldering side
Undersida PCB.JPG
Undersida PCB.JPG [ 194.55 KiB | Viewed 901 times ]
File comment: PCB Parts side
Översida PCB.JPG
Översida PCB.JPG [ 479.42 KiB | Viewed 901 times ]
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PostPosted: Mon Jun 21, 2021 10:16 am 
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Location: Moses Lake, WA
That cracked 473 cap is the first thing in the wet signal path, so I would assume that's your problem.

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PostPosted: Tue Jun 22, 2021 4:56 am 
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Joined: Sun Jun 20, 2021 6:04 am
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Thanks for the reply!

Then that capacitor is the primary suspect for now, so I will have to replace it. On that note, I have two questions that I´m hoping someone here could help me with!

First, could I use one of the 334 caps that are included in the kit as a bass mod? I will use the pedal primarily for guitar.

Second, when looking to order a replacement for the capacitor I found that the kind of capacitor (I think) I need are sold out at both BYOC and my Swedish reseller (Moody sounds), and they seem to go by slightly different names in different shops. At BYOC they are called polyester film capacitor, and at Moody sounds they are called SMF capacitors. Looking at Mouser right now, but they have about a gazillion different types of capacitors with different voltage ratings, which is making my head spin. So my question is: is the type of cap crucial or could I use any type, as long at it has the same capacitance (0.047 uF) and about the same voltage rating (63 V?). And if the type is important, what kind of cap am I really looking for and what would they call it at Mouser?

Thanks in advance!


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PostPosted: Tue Jun 22, 2021 10:23 am 
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Yes, you can use the 334 caps that came with your kit. It will just allow more low frequencies through, so you won't even notice a difference.

Please provide a link to the cap(s) in question and we'll let you know if that's what you're looking for.

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PostPosted: Tue Jun 22, 2021 10:49 am 
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quercus wrote:
...Second, when looking to order a replacement for the capacitor I found that the kind of capacitor (I think) I need are sold out at both BYOC and my Swedish reseller (Moody sounds), and they seem to go by slightly different names in different shops. At BYOC they are called polyester film capacitor, and at Moody sounds they are called SMF capacitors. Looking at Mouser right now, but they have about a gazillion different types of capacitors with different voltage ratings, which is making my head spin. So my question is: is the type of cap crucial or could I use any type, as long at it has the same capacitance (0.047 uF) and about the same voltage rating (63 V?). And if the type is important, what kind of cap am I really looking for and what would they call it at Mouser?

In the capacitance range you're talking about (1nf - 1 uf), you generally want to be using some kind of film cap, of which there are several types. In addition to the capacitance value, you want to be matching the lead spacing of the PCB cap eyelets (5 mm). The lead spacing of the caps can be a bit larger than that (just bend them inward a bit), but be careful not to order caps with high voltage ratings (>100V), since the physical size and lead spacing quickly gets too big. Polyester film box caps like these are pretty much ideal for DIY pedal applications: https://www.taydaelectronics.com/capaci ... itors.html

BYOC has regularly supplied this type of capacitor in their kits for years. I've had good luck ordering from Tayda and they ship quickly worldwide.

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