[sdiy] Delays: how?

[harrybissell]

Some snipping and more inline...


>
> <thinking mode on>
> makes sense!  some kind of processing (e.g. EQ) in the feedback path would also be interesting
>
> I've had it in the back of my mind to build a tape delay for a while, but not really started to seriously think about it yet.  I've got an Eventide which does all kinds of delay+pitch shifter stuff, but I just plain like the sound of analog stuff .. I've always wanted a Roland Space Echo.  The Schober Reverbatape looks pretty cool too!
>
> > Three head reel to reel machines can usually do echo with no modification
> > ... as is. Feedback from the play head to the record head and you're there.
> >
>
> yeah, seems like the more playback heads the better for multi tap delays.  perhaps 12 would be a nice musical number to have :)
>
> BTW, how easy is it to vary the speed of the tape transport?

That depends on how the motor works. There are syncronous AC motors
which are very hard to change speeds on (have to vary the line frequency...
make a sine-wave inverter ???). There are DC motors with internal governors
(basically a switch with a counterweight) these are hard to reguate. There are servo motors which can be varied over a small range, easily. There are SOME machines with variable speed as a built-in feature...

One old design used an 8 track chassis with three casette heads in the holes for the
normal two heads of an 8 track.  This one did the speed by using the normal motor
winding for slow speed... and a rheostat to provide more and more DC to the fast-forward winding.

The big problem is tape EQ  (usually a NAB standard in the USA).  There is
a pre-emphasis and de-emphasis curve for different tape speeds. See some old Nat Semi books like the Audio handbook for circuit examples and data.  Gist is...
there is a BIG adavantage to using a fixed tape speed...and multiple heads... or
fixed speed - sliding head (a'la Echoplex)... or varying the speed only slightly (to reach the next fixed head in delay...) and that is the EQ does not have to vary.

That cheap 8-track unit I mentioned just picked ONE EQ and that's that. It didn't
work very well for faster speeds... but who cared. It was my first 'reel' echo
(sorry ;^)

There was ONE old sony reel to reel... I forget the number maybe TC-780 ???
that had a servo drive that would run the machine from 1 7/8ips to 15ips in ONE
range. Sweet.  Look carefully and you can find some nice stuff.

FWIW:  The Guitar solo in Queen's "Brighton Rock" with the three echoes
panned in stereo... was done with a modified Sony reel to reel.  There was one additional playback head added to the unit on the takeup reel side of the capstan.
The original signal... and the two equally spaced echoes were sent to the console from the normal playback head and the added head.  Got to see it very close up
in concert... a long time ago in a far distant galaxy.  (I was a Sony tech in a past life ;^)

Tape head alignment is VERY hard... plan on doing a really good mechanical job that allows all the normal adjustments... or just use a BBD fergodssake...
(woah did i say that outloud ???)

H^) harry

>
>
> Seb [feeling inspired to go searching in some junk shops for old tape decks]