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I recently learned that using guitar with PC is much better if you have an active bypass or buffer in the chain. I dont have any device for that purpose but I do have a guitar combo (laney lg20r) which has its line out (I used that one as headphone output) Is it possible to use this thing as a buffer or active bypass plugging its line out into my PC? If it can be used as bypass, how do I tell if it is active and not passive?

Here is a picture of what inputs and outputs I got on my guitar combo

enter image description here

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    Headphone out is not Line out. Don't even try it.
    – Tetsujin
    Sep 8 at 18:19
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    Electric guitar output is very low level. If it can be used with headphones or line input, there's amplification at some point, i.e. it's not true bypass. The Laney is an amplifier, true bypass wouldn't make much sense there.
    – ojs
    Sep 9 at 6:29
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    @Tetsujin why not? it might be not the same as line out and one may need to be careful about the levels, but it may still work better than connecting guitar directly to line in. Sep 9 at 15:41
  • Could you add something to the question describing the input you're using on the PC? Is it a built-in line or microphone input? Do you have some kind of audio interface? (You can definitely use the headphone out, but how you use it will depend on the nature of the input.)
    – Theodore
    Sep 14 at 13:59
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A buffer is an electronic circuit that presents a near infinite impedance to the input signal, but reproduces that input signal on it's output as a copy of said input signal. It requires power to run and we usually use an op-amp for this purpose. So, a buffered pedal uses an op-amp set up in the buffer configuration rather than 'true-bypass' which means that basically when you switch the pedal off it just connects a wire from the signal input to signal output jacks. True bypass may sound fancy, but to do it electrically it means just deleting any other component and replacing it with a wire.

Buffering has a lot of uses in audio, and is vital for many audio circuits, however it disconnects the guitar, in this case, from any later circuitry and 'interactions' between the guitar pickups and amp are removed, leading guitar players to want true bypass when they want to be sure that when they switch their pedal off then the guitar is connected directly to the amp. Amps are designed primarily to take, and work with, the impedance of guitar pickups, not buffers, though a well designed amp will sound good/same with both. The difference between true bypass and buffered bypass can however be a real thing and can create measurable differences in the audio with either type of circuit, however which is better is really down to the individual, the gear they are working with and what they want/need to do. Buffered bypass can often 'sound better', FWIW, than true bypass, depending on the amp/setup used.

But to your question, the line or headphone output of an amp is almost certainly buffered in some way, and it's going to be an active buffer. In truth, I'm struggling to think of any circuit design which could create a passive buffer.

The thing you are dealing with is that a basic pc audio input is probably designed to take line level audio, line level is the standard way in which audio signals are transferred, distinct from speaker level (much higher voltage and current, saved for the end result), or instrument level (varying standards for level of voltage and current, ideally sent to an amp to be made into near line level for manipulation or recording).

A guitar into a PC input is not ideal. An average guitar can output close to 1v or so in most cases (which is pretty much line level), some more, some less. But impedance is a second problem. A guitar pickup is quite high impedance, a cheap line input generally quite low, meaning most of the output voltage is dropped in the guitar itself and not in the amp you are trying to send the signal to. Add to that that impedance is frequency dependant meaning sending a high impedance signal to a low impedance input will create unpredictable frequency shift, ie the guitar signal will probably be EQ'd in some way, not usually in a good way.

Thats why a buffer is advised, the buffer sorts the impedance problem for the guitar and just gives the entire guitar voltage to the input of the PC, without any frequency shifts. However, it doesn't do anything to boost the guitar signal ready for the PC input, in the case that your guitar is giving out say 0.5v due to the way you are playing, gentle strums in a breakdown etc. (0.5v is less than half of line level voltage). This could be fine, depending on the pc, or could be hissy and noisy.

In this case the line output of a guitar amp is favourable. The pic you posted doesn't have a line out, you could have a look on the back and see if there's one there, that would be the ideal thing to use if so, and it would be active, as a passive buffered line output doesn't exist as far as I know.

The headphone output may work, it solves the buffering and amplification issue as headphone level is near ish line level, will have SOME way of manipulating the gain, and the internal input to the headphone amp will probably be buffered. But the output impedance will be designed to match the impedance of headphones, not a line input. This will probably be ok, but not ideal, though listen out for if it sounds bad connecting it this way. There may also be some stereo / mono issues depending on the cable you use and the type of input your pc has but rather than hypothesize every combo here maybe drop a comment if you try it out and get behaviour you don't understand.

The ultimate fix is to buy a dedicated audio interface that will have line inputs and mic inputs and probably instrument inputs too, these inputs (instrument) will have a good, high, input impedance and an amp to take guitar signals and convert them to line properly.

At the end of the day, it's just the voltages that various instruments give out, and the impedances of each input and output at play. A buffer is simply an input with near infinite impedance, so the guitar's impedance become inconsequential. I had good luck plugging a bass into my pc input direct in my early days, but a pedal with buffered bypass or little bass preamp would have been better, as it correctly controls impedances and gives a bit of gain as well if the way I am playing is giving way less than line level out of the pickups (ie, a very soft section).

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  • "I had good luck plugging a bass into my pc input direct in my early days" - If, like many basses, it had an on-board preamp, that would probably help with both impedance matching and levels.
    – topo morto
    Sep 14 at 13:55
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    @topomorto no, it was passive, but you never really know what sort of design a pc line in is (unless it came with a schematic!) and sometimes it works just about ok. Listening back to that stuff I can hear the bass is a bit odd, but it’s alright, workable with! But yeah an active bass, or some other proper solution, would have been preferable.
    – OwenM
    Sep 14 at 14:03

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