Commodore Tape Duplicators
35A quick look at a few different duplicators for various Commodore machines: I'm guessing they should work on PET, VIC20, C64 and C128.
The design is quite simple: the read signal (D-4) from the first Datasette is connected to the write signal (E-5) of the second via an inverting buffer (i.e. 7400, 7403, 7404 ... the NAND gate ICs just have the other input pulled high ... so a HI signal is inverted to LO).
As you load the tape via the first Datasette, the second Datasette is saving a copy of the signal. Not sure why inverted ... inverting buffers are more plentiful than non-inverting ... ? I guess we're more interested in transitions rather than absolute bit values ... ?
I didn't have too much luck "backing up" the tape I was using but it could be due to a few factors such as tape quality or the state of the Datasette. But as we're copying a digital signal, I could see that this might be more reliable than traditional dubbing via a twin cassette deck ...