Detailed info on the operation of the RE-301 and the RE-501 can be found in the user manuals:
click here for RE-301 manual
click here for RE-501 manual
Unfortunately these do not provide enough details on the interior of these machines. Therefore I connected a guitar to the RE-301 and listened closely to figure out the internal wiring by ear. Below is a simplified schematic of the unit based on what I heard (see attached image).
- In normal echo mode the incoming sound (IN) is recorded on the tape by a record head (R) and read off the tape by three different playback heads (1,2,3). The heads are switchable, so either of those or a combination of two heads or all three heads can be activated.
- repeated echos are generated by looping back the signal from the three playback heads to the record head.
- In Sound-on-Sound mode an additional playback head (SoS) is switched on. It is located right at the end of the tape loop before the erase head (E). The erase head is NOT deactivated in SoS mode. This means everything that is on the tape is played back exactly once. Repeated loops or even layering of several parts is not possible.
(You can layer two parts: Play a first part; Then while this first part is being repeated play a second part live. After this your second part is being repeated once and the first part cannot be heard anymore)
- The loop time depends on the length of the tape loop and on the tape motor speed. In my case with a factory loop this ranges from ca. 12 to 38 seconds. You could achieve longer times by splicing your own extra-long tape loops.
- Everything which is on the tape is also played back in SoS mode. If you have echoes activated, then these are being recorded on the tape and therefore can be heard during replay. The other two effects however (chorus and spring reverb) are not recorded on the tape. These will not be heard at playback time. See the wiring displayed in the schematic..
- Contrary to the RE-301 manual which claims that additional effects can be added during playback in Sound-on-Sound mode the SoS head is routed directly to the output. Chorus and reverb settings do not affect the SoS signal!
- The spring reverb is fed by the input signal as well as by the signals from playback heads 1 to 3. (But not by the SoS signal as mentioned above)
- If you switch off all effects and enable Sound-on-Sound you will hear the dry input signal repeated once after 12 to 38 seconds.
- The spring reverb and the chorus can also be used on their own when tape delays and SoS are switched off. Somebody
wrote that the sound of the reverb can be adjusted via a pot in the mains lead hatch. The pot is there but I couldn't hear any effect on the reverb.
- The tone section (bass and treble control; not displayed in below schematic) affects the signals from replay heads 1,2,3, from the spring reverb and from the chorus. The direct signal and the signal from the SoS head are not affected.
Regarding the RE-501: On harmony central
somebody wrote the following:
The best feature that makes the 301 the best of the bunch is the sound-on-sound function. For those unfamiliar, it is a switch that allows you to listen to the whole of the tape whilst the delay effect is going on, a bit like a giant 15 second delay!! Play delicate chords, then as soon as you hear them start to repeat, harp some high notes. I cannot tell you how much fun you will have in hyperspace building soundscapes! With the other models, including the big brother RE501 the SOS does not cut it. The 501 has the SOS playhead in a different place so you only get a maximum of 5-6 seconds which is a real shame. The 301 is definately the most musical of all the space echos as I have tried all of them out.
Apparently the SoS head of the RE-501 is not at the end of the loop but somewhere after heads 1,2,3.
If you want endlessly repeated Sound-on-Sound the Korg SE-500 seems to be an option. Somebody at gearslutz
But the SE-500 is very interesting indeed, It has this Sound on sound feature which switches off the erasehead so the tape becomes an endless loop. Just put some some nice/calm pattern, piano for example, on a loop and play it thru se SE-500, instant ambient machine!
I think switching off the erase head would be an easy modification of the RE-301 (Cut a cable, install a switch, done). I would expect however that the signal will be heaviliy degraded from one repetition to the next, as with each pass a new signal is recorded on top of the unerased tape.
I hope this provides the info you need
By the way how do you plan to use the Sound-on-Sound? As far as I understand this is mostly useful for solo players. Your nickname implies that you are doing something dubby. However in a typical dub setting these long echoes which are not synced with anything would mess up the timing completely.