Depending on what type of equipment you're plugging into this instrument-level amplifier, you are likely to get a distorted signal. Line level input is NOT like instrument level.Both might have similar input impedances (but not likely) but one is designed for signals under 1 volt (typically 200mV) and the other is designed for signals over one volt (typically 1,4V RMS).
what are you trying to do?
what are you trying to do?
Those differences are miniscule, and don't make any difference, particularly as instrument inputs have enough gain for far lower input levels.
Impedances don't matter either, as you're feeding a lowish impedance line source in to a high impedance instrument input (you don't use impedance matching, that's the worst possible scenario for almost all occasions).
Always nice to know
Although I trust you I have difficulty accepting the facts. And what I know is this (I've tried it before) : if you take any headphone output audio device (walkman, dscplayer, mp3 player) and plug it into an instrument level amplifier, you will, eventually, distort the signal. Is this due to the higher output voltage these devices put out? I'd say yes. Maybe not so much, the output impedance (which is orders of magnitude lower, around 16 to 32 ohms, I've read) but I know what I've seen and heard.
Headphone outputs aren't line level, they are headphone level - which is usually considerably higher.
Either line out or headphone outputs are going to have impedances below maybe 200 ohms. If for some reason you wanted to increase that impedance a series resistor would probably work. Far as the level goes, what makes it into the first stage depends on whether it has an attenuator or a gain control, or both. If all you have is gain control it may be easy to overdrive the grid circuit (usual tube job insturment amp), unless you make an attenuator, which could easily be just an L pad. If it has an attenuator, or volume control, your L pad is already there. Just keep it turned down so the first stage isn't overdriven, unless you want that.
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But why would you want to?.
Adding a LARGE series resistor will make an attenuator with the input impedance of the stage, but is increasing the chances of hum and noise for no advantage at all.
If you DO need to attenuate it, then use a lowish imedance L pad, which will maintain low hum and noise levels.
However, the output from a loudly played passive guitar is going to be well above line levels anyway, so line levels aren't a problem.
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