Help me not screw up.

October 21, 2007 12:01 PM

I'm going to embark on a stompbox-building adventure, and I'd like to know how much one can mess things up.

I'm aiming to make a Fuzz Face (not sure about the specific plan yet, any suggestions welcome). Also, if I can find an incredibly cheap delay pedal (I guess I'll trawl eBay...), I'd like to modify it to produce some good stutter effects. So, as far as experimenting with this... what is the fact that's preventing 9V from running straight into an amp and blowing it up? I'll probably be testing on a Princeton 112 turned way down, but what are the risks and methods of reducing them with this stuff? Are people using tiny amps to test things?

Thanks

posted by tmcw to grab bag (13 comments total)

I made one with my son with some plans off of the internet. It was very simple and it sounds great. Small Bear Electronics is your source of parts, especially the transistors. The exact transistors used in the original are essentially unobtainium these days, but Small Bear can hook you up with acceptable substitutes. I used this paper as a reference.
posted by caddis at 12:17 PM on October 21, 2007

Craig Anderton's Do-It-Yourself Projects for Guitarists has schematics for fuzz boxes and other effects units. Also, Tim Stanley's Build Your Own Effects FAQ seems a little dated but might still be useful.

I guess I'd test it on something like a cheap Pignose-style battery operated beltclip amp, just to be really safe. I used to have an old solid state Fender model that I got in the late 1980's for under $50, and you could probably find one used for $25 these days.
posted by tomwheeler at 12:47 PM on October 21, 2007

As mentioned already, if you're really worried, test it with a battery operated amp first.

I've built a fuzz (but not a fuzz face) from schematics I found online and it's pretty easy. You might want to install posts for capacitors and diodes (I forget the precise name) so you can try switch out and testing different values.

If you get really ambitious, try run off groove projects.
posted by drezdn at 12:57 PM on October 21, 2007

The risk really is not that great. I don't think 9v DC would even really hurt your amp that much (but please, don't take my word for it).

I have built lots of stomp boxes. One of my most recent projects was mounting a bunch of them in a rack-box with a switching network. Anyway, the way I test them is usually with an oscilloscope. You can get an older oscope on ebay for $50. It does kind of help if you know what you're looking for, and generally how to use one.

Also, lots of plans, like the ones at Small Bear and other ones I've seen give expected DC voltages at various places. These are good checks to see if you've got it OK. You can also use this to determine if you're getting a significant DC component in the output.
posted by RustyBrooks at 1:51 PM on October 21, 2007

9v probably won't fry your amp, but to be extra safe you can run the output signal through a small (.1uf or so) capacitor to block any DC charge from reaching amp. There are two wires coming out of your stompbox, once is the shield and the other carries the signal. The shield wire is probably connected to the stompbox enclosure and the negative terminal of the 9v battery, you want to put the capacitor on the other wire, your signal wire. Have the signal wire from the stompbox connected to one end of the capacitor, and the other end of your capacitor connected to the output jack where the signal wire used to be. Pretty much any cap will work, but the fancy plastic ones will sound best, I believe the ones I use are polypropylene.
posted by waxboy at 1:57 PM on October 21, 2007

Check out the Ampage Effects forum.

Effects aren't really very tricky but absolutely use a solderless breadboard for prototyping. 9VDC on the input shouldn't hurt most amps but all you need to do is check the output with your multimeter set on DC with the effect on; if you see 9VDC you know you've got a problem. And you do have a multimeter, right? Adding an extra cap on the output is unnecessary and may adversely affect the sound. Stick to the design until you know a bit more about how these things work.

Component type can be somewhat contentious and much debated issue. I've not built an effect in years but for my tube amps I mostly use polyester caps and metal film resistors in the signal path. For the most part in audio paying more for high end parts, particularly things advertised as such, yields little result beyond a lighter wallet (don't get me started on "audiophiles"). I don't know about effects but some in the amp building circles think carbon composition resistors of the sort that used to be standard are the bees knees and they'll pay a significant premium for resistors that are hissy and drift with time and vary significantly with temperature.

Don't buy carbon comp resistors. Carbon film, the standard cheapest sort, are fine for your purposes, or you can pay a bit more for metal (becomes more of an issue in higher gain circuits).
posted by 6550 at 4:34 PM on October 21, 2007

I have built many pedals, including a handful of Fuzz Faces, and I highly recommend the Axis Face which cleverly makes a FF built with modern components sound more like one built with 60s transistors.

The one thing I would change is to use a 50kA volume pot. The FF circuit gets darker sounding when you use a higher resistance output pot. The downside is that the output level drops a bit, but the tone is better.

In terms of safety, you can't hurt yourself with a 9v battery. However, you can fry your solid state amp if the circuit is putting out a huge amount of gain. I always test my pedals with a crappy amp before I plug them into my real amp. Even computer speakers are better than nothing.

Finally, delays are a whole nother thing. They are inherently complicated. So, building one is probly a bad idea. Modding one is certainly possible and not particularly hard if you can figure out what components you need to change. You might save the delay project til you have a couple builds under your belt.
posted by tcobretti at 7:48 PM on October 21, 2007 [1 favorite has favorites]

I've built a few stomp boxes. The Craig Anderton tube sound fuzz is a great start. It's a pretty good fuzz, it uses relatively few parts and they're all easy to find.
posted by plinth at 8:03 PM on October 21, 2007

Wow, tcobretti, the Axis Face looks awesome, and I hadn't been around that site in a while.
posted by tmcw at 10:56 AM on October 22, 2007

I hope you like the way it sounds! It compares very favorably with my Roger Mayer Classic Fuzz; not identical, but very similar.
posted by tcobretti at 4:18 PM on October 22, 2007

Back to the not-screwing-things-up-category, I think my first little creative endeavor might be to allow swapping of capacitors in the signal path via toggle switches on the enclosure (since that might make the pedal useful for bass). If I wire both capacitors to a switch, will current leak out of the one that isn't in the circuit? Do people do this?
posted by tmcw at 11:30 PM on October 22, 2007

It's worth a try.
posted by drezdn at 6:53 AM on October 23, 2007

Yes, you can make the caps switchable. Depending on the switching, the only current that will flow out of a cap will be the residual energy from when it was still in the signal path, which for these caps will dissipate very quickly - basically don't worry about it.

Switchable caps are pretty common and are useful in some applications. However, I generally just socket that caps that I want to mess with, and that way when I find the one that works best with my rig I stick with it. If you want the pedal to be usable with different rigs, like the bass, then a switch is a good idea. I would probly start by making the output cap switchable. The output cap basically controls how much low end makes it out of the circuit, so a larger value (>1uf, maybe even 10uf) will make the pedal fatter for bass. The input cap has more to do with how fuzzy the pedal is (larger values = more fuzz and denser sounding).
posted by tcobretti at 11:34 PM on October 23, 2007