Over the last couple of years, I’ve spent a few evenings building DIY guitar effects. It's fun to build things that you can use. If you want to get started, one of the hardest things is buying components. Try to buy a 10Ω resistor from Farnell, and you’re faced with a choice of 345 items. So, starting out buying a kit is a good idea. At least you’ll know the parts are right, even if when your soldering isn’t.
However, not many people sell kits. Despite the potential markup on a handful of bulk components, the customer service is - presumably - a nightmare. Here are 23 companies who will sell you complete component kits for guitar effects - many more people produce PCBs, or sell finished pedals. Stay tuned for similar lists on synths/noise boxes and tube amplifiers.
US
1. Build Your Own Clone Probably the best known company in the business, BYOC have a huge range of kits
From the Confidence Booster, a $15 booster kit with no box or switch to the $150 analog delay that they describe as extremely difficult’. They have a very good reputation on the forums for selling reliable, easy to build kits. Their UK Distributor is Vibe-O-Tronic and Moody Sounds (below) sell them in Sweden.
Price: $15-$150
2. General Guitar Gadgets
The other big player in US kits, GGG seem slightly less ambitious than BYOC, but still offer a good range of familiar sound-alike pedals in complete kits, including switches and pre-drilled boxes.
Prices $38 - $80
3. OL Circuits
Officially Licensed Circuits have an interesting collection of kits developed on various online communities. They sell the runoffgroove.com collection of famous guitar amps converted into pedals, plus various interesting valve circuits including the Beavis Tube Cricket amplifier.
Prices: $65-$135
4. 4ms pedals
Big range of exotic and interesting pedals, stand alone noise boxes and modular synth gear, including the knob-tacular Tremulus Lune. Kits and finished products available.
Prices: $90-$140
5. Small Bear
Small range of kits (boost, fuzz, tremolo) from the company who specialise in components for DIY pedal builders.
Prices: $36-$85
6. PAIA
Grandaddies of DIY audio kits. They don’t sell any real stompboxes, but have a few interesting guitar projects like the QuadraFuzz, and an entire modular synth range.
Prices: $25 - $200+
7. Mod Kits
Small range of boost and distortion pedals, plus a reverb built around the Belton Brick.
Prices: $25-$100
8. Fuzz Box World
Sells one simple fuzz kit for $39
9. Get LoFi
An interesting range of simple circuits including a fuzz, an amp and (coming soon) a lo-fi delay. They don’t sell enclosures or switches, just the boards and components.
Prices: $18-$25
10. Synthrotek
A few interesting noisy kits, including a Lo-Fi delay unit and various fuzzes.
Prices: $35 for the delay kit.
11. Devi Ever
Devi Ever is a Portland-based boutique builder who makes endless varieties of Fuzz. She sometimes sells kits through her Etsy shop, but is currently out of action.
12. Triode Electronics
Among their huge range of tube amp gear is one Germanium boost kit for $75.
Global
13. MEK Electronic (Germany)
A big and varied range of kits including a Klon clone, a delay, a reverb and four (!) varieties of Muff Pi. They’re fairly cheap. The Fuzz Factory clone they sold me worked first time, and had a very neat layout.
Prices: €22 - €56
14. Musikding (Germany)
Fairly wide range of surprisingly cheap kits from a German supplier with a vast range of DIY effect parts.
Prices: €21-€35
15. Moody Sounds (Sweden)
Good range of pedals including the the interesting Moody Echo, which comes with a light sensitive option for extreme crazy. They also resell BYOC pedals in Sweden.
Prices: €45-€75
16. Pigeon FX (UK)
Small range of nice mojo-ish kits: Fuzz Faces and Rangemasters with carbon comp resistors, dark brown PCBs and big ol’ capacitors.
Prices: £15 for the boards and components.
17. DIY Stompboxes (Germany)
Big range of curiously translated but familiar-looking circuits, including clones of almost the full Zvex range.
Prices: €25-€85
18. DIY Pedal Kits (UK)
Small range of loopers and fuzzes. Despite pictures of Boss-style pedals all over the site, these all come in the more normal Hammond-style enclosures (Like MXR effect pedals)
Prices: £35-£60
19. Boutique Techniguitarre (France)
A small range of distortions and boosters, available in pre-drilled boxes with appropriate stickers.
Prices €38-€59
20. Ess_7Stores (China)
An Ebay Store from Hong Kong selling an interesting-looking point-to-point wired (that’s putting it very politely) FET Fender Blackface preamp kit.
Price: $32 inc shipping
21. Quasar Electronics (UK)
A handful of guitar circuit kits from this old-school Velleman-ish educational company. I tried to build their trem and managed to mess it up, which is no reflection on them.
Prices: £12-25
Meta-Kits:
22. Beavis Board
$250 gets you a breadboard, specially made audio/power connectors and a complete kit of parts to build numerous projects. I thought about buying this when I first got started. I wish I had.
23. Tone Crafter
A breadboard in a stompbox for $150 with parts for 7 effects
If you are one of these companies and I’ve got something wrong, do get in touch. Main image: BYOC kit by Terekhova.
Over the last couple of years, I’ve spent a few evenings building DIY guitar effects. It's fun to build things that you can use. If you want to get started, one of the hardest things is buying components. Try to buy a 10Ω resistor from Farnell, and you’re faced with a choice of 345 items. So, starting out buying a kit is a good idea. At least you’ll know the parts are right, even if when your soldering isn’t. 
9. Get LoFi
An interesting range of simple circuits including a fuzz, an amp and (coming soon) a lo-fi delay. They don’t sell enclosures or switches, just the boards and components. 
16. Pigeon FX (UK)
Small range of nice mojo-ish kits: Fuzz Faces and Rangemasters with carbon comp resistors, dark brown PCBs and big ol’ capacitors.
: 8:32 pm