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Post by mr_sooty on Aug 17, 2008 23:55:05 GMT -5
Two of my pedals hiss like crazy. One of them is a modified Boss CS3 compressor, and one of them is my home brew bluesdriver clone from General Guitar Gadgets (.com).
I know Compressors are known to hiss, but why does my homebrew pedal hiss so much? Is it likely to have been something I've done in the assembly? If so, how do I fix it?
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Post by ashcatlt on Aug 18, 2008 13:02:06 GMT -5
It can only really come from four places.
1) Less than ideal shielding/grounding. Is it in a metal case? Everything grounded correctly?
2) Poorly conditioned power. Are you running it off a battery or a wall-wart. The battery would be about as quiet as you can get. Most of the time the couple of caps added into these types of circuits for filtering of the DC input jack are almost an after-thought, and there are better ways to get quieter, cleaner power.
3) Noisy components within the circuit itself. Different opamps have different noise characteristics. From what I've heard, the TL07x family is not the quietest out there. If you look around you'd ought to be able to find a direct replacement with a lower noise floor. You did socket the opamp, no?
The other big contributor would be resistors. The bigger the resistor, the more noise. Eliminate all which are not essential to the circuit, and reduce the value of any where this is practical. The designer of the circuit probably already did this, though.
4) The hiss is coming from somewhere previous to the pedal in question and being amplified along with the signal. I'd say this is your most likely scenario. Both of the pedals you've mentioned do what they do by adding gain to the signal. The best idea is to start with a well-shielded guitar and a good cable. Then get as much of your gain out of the way as soon as possible in the signal chain to avoid amplifying the noise from later links.
Got an audio probe? If not, make one. All you need is a guitar cable you can afford to cut up and a capacitor (preferable non-polarized, but value isn't particularly important). Some aligator clips can make things easier. Remove one end of the cable. Twist the braided shield together and connect it to a convenient ground point, like the ground lug of the output jack from the pedal. Twist the central conductor of the cable and solder to it one end of the capacitor. Plug the intact end of the cable into an amplifier or other monitoring device.
Now you can touch around inside the pedal with the free end of the capacitor and hear what's happening at any point in the circuit. The capacitor is there to block any DC voltage from being passed on into the amplifier.
I'd try this both with a guitar connected to the input and maybe with the input shorted (tip to ground) to find self noise. Poke around till you find the point where the noise becomes offensive and maybe you can identify something that could be changed. Or not. Either way, it can be a fun and enlightening experience.
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Post by mr_sooty on Aug 18, 2008 16:03:58 GMT -5
Thanks for your exhaustive post, I appreciate your time. It can only really come from four places. 1) Less than ideal shielding/grounding. Is it in a metal case? Everything grounded correctly? Yeah, metal case. I think it's grounded properly, as far as I know anyway. How can I check? 2) Poorly conditioned power. Are you running it off a battery or a wall-wart. Wall wart - Godlyke PA9. I'm pretty sure it hissed when I tested it with a battery too though. I'll check again. You did socket the opamp, no? Huh? Wassat? The other big contributor would be resistors. The bigger the resistor, the more noise. If this was the problem, it would happen in all these MBB kits, which from what I've assertained, it doesn't. 4) The hiss is coming from somewhere previous to the pedal in question and being amplified along with the signal. I don't think this is the case. There is another, louder overdrive directly before it on my pedalboard. This pedal would amplify any hiss more. It doesn't, it's dead quiet. When I had the homebrew pedal before that other OD, the homebrew pedal still hissed. Got an audio probe? If not, make one. No I don't, but maybe I'll give this a go. Other thoughts: The supplier of the kit suggested it could be a faulty chip. What do you reckon about that? He reckons this hiss is not normal. Also I'm not the tidiest pedal builder in the wolrd, and the wires going from the circuit board to the pots are a bit longer than they need to be. Would this have any effect? |
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