[sdiy] Delays: how?

[Seb Francis]

Thanks for the info, Harry.  Seems like I should look out for a model with continuously variable speed (presumably one like this might have variable pre/post emphasis EQ to match?).  Or perhaps I should get my mechanical head on and build a sliding head mechanism which tries to keep the head aligned at the same time!

And I though it would be so easy ....

Seb


harrybissell wrote:

> 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]