Hi Eudoxia, In the early years, 50, 60's, they have to put the echo, tape or drum in front of the amp, because amps had no effectsloop, so, they maybe use stompboxes, ( no compressor, ( stompbox) i think they did'nt excist in that period ) then to the echo unit, and then to the front of the amp, also these echoes on its own have a specific sound in they'r pre-amps, so, maybe line6 modelled these echoes that way, to put them before an HD, or real amp, you can try the dry versions of these echoes, they do not have that virtual echo-pre anp modelled, i hope someone who does know more of this, can confirm this. Huub.