In Out, Shake it All About, or Return to Sender

[stewblack 1,909]

So, what's the difference between line in / line out, and send / return? 

[paul_c2 496]

There are variations amongst amps, but normally:

1) send and return are instrument level. Line in and line out should be line level.

2) plugging something into send, should reroute 100% of the signal (so if nothing were plugged into the return, there would be no output from the amplifier). A line out should normally tap off the signal so that 100% still goes to the output of the amplifier.

3) a line in combines the signal with the instrument input. I am not sure what happens if you plug something into the return without anything plugged into the send but it certainly isn't blended with the instrument input.

Obviously it depends on the amp, there's loads of variations and possibilities ie pre- or post- EQ, with/without effects loop, whether it mutes the amp's output if the line out is used (I don't think it should at all; but some amps do this). Also, line out is normally presented as a balanced signal, you'd hope male XLR but maybe 1/4" TRS.

[stewblack 1,909]

10 minutes ago, paul_c2 said:

There are variations amongst amps, but normally:

1) send and return are instrument level. Line in and line out should be line level.

2) plugging something into send, should reroute 100% of the signal (so if nothing were plugged into the return, there would be no output from the amplifier). A line out should normally tap off the signal so that 100% still goes to the output of the amplifier.

3) a line in combines the signal with the instrument input. I am not sure what happens if you plug something into the return without anything plugged into the send but it certainly isn't blended with the instrument input.

Obviously it depends on the amp, there's loads of variations and possibilities ie pre- or post- EQ, with/without effects loop, whether it mutes the amp's output if the line out is used (I don't think it should at all; but some amps do this). Also, line out is normally presented as a balanced signal, you'd hope male XLR but maybe 1/4" TRS.

Fantastic reply, thank you. 

[jrixn1 440]

Send/return might be in parallel to allow you to blend your external effects with the dry signal.

Edited August 15 by jrixn1

[G-Dog 16]

In my experience an amp's Send only duplicates the preamp section's EQ'd signal to some external destination.  But, if nothing is plugged in to that amp's Return, then the original preamp signal goes on to the amp's power section for amplification and out to the speaker(s).

The originally intended use was to Send the preamp signal to some effects box(es) then Return that effected signal to the amp's power section, and out to the speaker(s).

But if any signal is plugged into the amp's Return, regardless if it originated from the amp's Send or not, that signal goes to the power section and speaker(s).

So, you can Send one amp's preamp signal, via instrument cable, to the Return of another amp and they both amplify the first preamp's signal and the second amp's EQ has no effect!  Use of the Return on the second amp seems to turn it into just a powered speaker!  That's because the Return has a switch that cuts off the normal flow from preamp to power amp when in use. 

If that switch gets corroded an amp's preamp may not seem to work.  An instrument cable directly from Send to Return that restores function indicates a corroded switch that can be corrected by plugging & unplugging the Return several times, or direct (non-spray) cleaning of the switch.

Hope this helps.

Edited August 20 by G-Dog
Clarification

[G-Dog 16]

On 15/08/2019 at 15:09, jrixn1 said:

Send/return might be in parallel to allow you to blend your external effects with the dry signal.

I don't think that is usually the case.  See my explanation above.

The external effect needs to have the blend, or level, function.

[jrixn1 440]

I don't think there is a standard approach.  For example, a Genz Benz works in exactly the way you have described; but a Markbass effects loop is in parallel, with a fixed 50/50 blend.

[songofthewind 325]

And and and you can open up a Markbass and fiddle with the send return config. Sounds exactly the same to me.

[paul_c2 496]

11 minutes ago, songofthewind said:

And and and you can open up a Markbass and fiddle with the send return config. Sounds exactly the same to me.

Do you mean a 50/50 wet/dry blend sounds exactly the same to you as a 100% wet signal?

Or that a Markbass can be internally changed so it has the same behaviour as other amps, in its send/return?

[agedhorse 73]

On 15/08/2019 at 12:57, paul_c2 said:

There are variations amongst amps, but normally:

1) send and return are instrument level. Line in and line out should be line level.

2) plugging something into send, should reroute 100% of the signal (so if nothing were plugged into the return, there would be no output from the amplifier). A line out should normally tap off the signal so that 100% still goes to the output of the amplifier.

3) a line in combines the signal with the instrument input. I am not sure what happens if you plug something into the return without anything plugged into the send but it certainly isn't blended with the instrument input.

Obviously it depends on the amp, there's loads of variations and possibilities ie pre- or post- EQ, with/without effects loop, whether it mutes the amp's output if the line out is used (I don't think it should at all; but some amps do this). Also, line out is normally presented as a balanced signal, you'd hope male XLR but maybe 1/4" TRS.

There are indeed more variations than there are what you have suggested.

As a generalization, most effects loops (also called insert loops) are serial and operate at line level. Most are post eq, but there are some that are pre-eq also. The normal routing switching is almost always done within the effects return jack.

There are line in jacks that are usually called 'AUX IN", they provide a line level input sums with the main signal path. Line outputs are usually the same as the effects send as described above. 

Most XLR outputs start out as pre eq, balanced, mic level and add switched options such as mic-line level, pre-post eq routing and pin 1 ground lift. 

Of course there are exceptions, but the above is by far and away the norm.