Modify a Space echo for layering sounds ?

[Haible Juergen]

 > I also used the sound on sound capabilities of the 301 by first
> recording the tape loop at high speed then reducing the rate when it
> began to loop giving a dual speed layering.

My RE-201 does not do this, unfortunately. What do I have to change,
if I want this feature? 
Simply switch off the erease head current?
The HF bias in the recording head as well?
Maybe just disabling the HF oscillator for both?

Someone with a 301 manual can tell how Roland implemented it?

Thanks,

JH.