line level vs signal level

[effbiae]

is signal level the correct term for what comes out of the socket of a guitar?

anyway,... i'm wondering about preamps (newbie)... and i wonder why effects aren't applied at line-level rather than the raw signal? 

ie. why isn't the signal amplified to line-level immediately so that a good, strong signal can go through the effects?

are there effect circuits designed to operate at line-level?

and what is signal-level anyway?  ie. what range do effect circuits operate over?

is there a good page that someone could point me to?

thanks in advance,


jack

[Pushtone]

is signal level the correct term for what comes out of the socket of a guitar?

I think most of us sound reinforcement types only ever refer to line and mic level as that is all we want to see. I use the term instrument level to describe what comes out of a passive guitar.

Using a dBV reference for 0dB = approx 1V
Line level is +4dB
Mic levle is -40dB
so instrument level would be somewhere inbetween, perhaps -20dB.

i wonder why effects aren't applied at line-level rather than the raw signal? 
ie. why isn't the signal amplified to line-level immediately so that a good, strong signal can go through the effects?

I guessing on this one but I would have to think it would be because of the necassary rail voltage required to do line level electronics. Effects use batteries and line level effect pedal would require an AC power source and bulky AC-to-DC transformer. There are lots of effect pedal manufacturers that do this. Lexicon and Morley come to mind.

There are all types of reasons why manufacturers maintain a unity gain instrument level in and out. First of all it has to be compatable with guitar amps and I don't ever remember seeing an amp with a line input. Keyboard amps maybe??. I did once see a guitar amp that allowed the effect loop to be switched from line level to instrument level. I think it might have been a THD or a Fender. Can't remember now.

[d95err]

why isn't the signal amplified to line-level immediately so that a good, strong signal can go through the effects?

All commercial guitar amps are build as cheaply as possible. To have proper line and guitar level inputs would increase the costs. For stompboxes, it would be even more expensive since it would need a more than a 9V supply.

Many guitar amps have a high and low gain input though. On a typical Fender amp, the low input has a voltage divider (68k/68k) that takes the signal level down a bit. That should work make it work better with a line level signal.

[Satch12879]

Actually those resistors are known as "gate stoppers" and are not there for signal attenuation purposes.

Their purpose is threefold:

1. Promote stability in the tube gain stage
2. Act with the input capacitance of the tube (sum of the grid-to-cathode capacitance and Miller capacitance) to create a low pass filter blocking RFI
3. Limits grid current to help prevent "blocking distortion."

Please see the technical article at Aiken Amplification.

[d95err]

Actually those resistors are known as "gate stoppers" and are not there for signal attenuation purposes.

On the low input, the two 68k resistors form a voltage divider. It takes the low input voltage down to about half of the high input. The low input is also lower impedance (about 68k instead of 1M). So, I'd say attenuation is the main purpose of having two resistors. For just grid stopping etc, one would have been enough.

[Gilles C]

From my Fender Hot Rod Deluxe manual



I normally use the Input 2 (with the 68K resistors) when I use preamps or effects for a better signal and impedance matching.

Gilles