Can I fry my guitar/amp/speakers by pluging in a homemade effect with problems?

[malephik]

I recently made an effect (5th gear overdrive) but I don't want to try it yet because I'm not sure how well it's made. It may have not-so-good soldering or stuff like that.
Is there any chance of me frying something and if there is, what would I most probably fry? I'm most worried for my guitar .

[teemuk]

Yes, there is a chance of frying something. However, with only 9V it is only slight. I hope you realize that you can test if the circuit is built/functions correctly without plugging it into anything. (Plugging things in and listening should be the last tests anyway). Basically I would worry about

a) Oscillation
b) DC offset
c) Very high output signal

a) Oscillation may damage your amp, speakers or ears if you keep the "volume" setting at a high level when you test the FX pedal. I recommend everyone to start the initial tests with volume set to zero, which is then gradually increased if there is no sign of oscillation.

b) Likely the most important test: Check if the circuit's input or output has any excessive DC offset (there should be max a few mV). That, I guess, would be the fist candidate of causing damage to your guitar because amps are generally AC coupled while guitars are not. Excessive DC may cause damage to pickup coils (although 9V is not much) and (in a long run) it definitely will  harm typical potentiometers, which become noisy and scratchy. In some rare cases the offset might damage your amp as well - i.e. by reversing the polarity of the input electrolytic capacitor, saturating stuff in a wrong place etc.

c) A too high output signal may cause damage to some circuits/opamps. Usually guitar amp input stages have protections against this (and again, 9V is not much) but as a rule of thumb assume there aren't. Output signals less than 2 - 3 V should be OK but hardly useful: Anything above 1 - 2 V (sometimes less) will likely just overdrive your preamp and (usually at least in SS designs) cause very nasty distortion.

Basically, I would say that after the initial test for excessive DC offset it should be fairly safe to plug any of those DIY 9V pedals into your guitar and amp and test them. Remember: Set volume to "0" before you turn on the amp, this will help against problems a) and c).

[malephik]

I'm guessing that I would need a voltmeter (or at least a multi-meter) to find out the DC offset, which I don't have. Is there any other way of finding out what the DC offset is or should I just buy a multi-meter?

I don't currently have an amp, i've been doing all my playing using the AUX in on my CD player/audio system-thing. Having that in mind I doubt that the volume could be loud enough to cause any harm(to my ears anyway), although I allways gradually turn up the volume, starting with 0.

[teemuk]

Just buy the multimeter. A basic DMM with voltage, current and resistance meters (and usually even a test slot for transistor Hfe and diode) is extremely cheap (about 10 $) and helpful in many situations, whether it's fixing house wiring or building low-voltage electronic stuff. You see, you can't live without one.

[malephik]

I will , thanks!
If it's not too much of a bother, pls tell me what do you think about using an audio system to play a guitar? Is it ok? (should I try to avoid doing it because of long-term problems or is it perfectly safe) - without taking into account the quality of the sound, which obviously isn't very good 

[teemuk]

If it's not too much of a bother, pls tell me what do you think about using an audio system to play a guitar?

Your amp likely won't care a bit but for several reasons consumer HiFi-quality speakers usually aren't too happy about that: Their voice coils can't handle much of abuse (heat) without deforming and tweeters can't take the overtones of clipping. Dedicated instrument or PA speakers usually "softly" restrict the excessive cone excursion while HiFi speakers do not, as this kind of limiting would seriously impact the linearity of sound reproduction.

To make matters worse, HiFi speakers are usually very inefficient, when compared to PA or instrument speakers, so you have to feed them with higher power to achieve the same sound pressure levels that a dedicated instrument speaker might provide. This increases the severity of aforementioned problems and also stresses your amp causing more distortion. And like we all know, guitar amps aren't usually played on a very "quiet" setting. If you play on low volume level you might get away with that type of setup of yours - but increase the volume and distortion and be prepared to kiss your speakers goodbye.

[malephik]

Hi, again.
I finished the effect and luckily I have a new guitar amp to try iy out on (Laney Linebacker 65). I found that there was hardly any distortion and I did turn the pots around, discovering that the 100k pot was the volume and the 2k pot didn't do much so I supposed it was the gain.
The samples on the wiki don't work, perhaps someone can fix the links. I'd like to compare the sound I get with the sound I probably don't get, but should.

[joecool85]

Hi, again.
I finished the effect and luckily I have a new guitar amp to try iy out on (Laney Linebacker 65). I found that there was hardly any distortion and I did turn the pots around, discovering that the 100k pot was the volume and the 2k pot didn't do much so I supposed it was the gain.
The samples on the wiki don't work, perhaps someone can fix the links. I'd like to compare the sound I get with the sound I probably don't get, but should.

Sorry about the links not working.  The university web server is down for right now and I haven't gotten any answers as to why/for how long.  For now go here: http://thatraymond.com/mediadl.html