DIY tape delay from an old cassette deck

[jacobsteel]

I built a tape delay out of a TEAC cassette deck.

Introduction
DIY tape decks from 3-head (erase-rec-play) are common. However, the gap from rec-to-play only gives short delay times, even at very low (and lofi) tape speeds. I wanted longer delay times. Also, 2 head decks are cheaper.

The best candidates are older 2-head decks with separate rec/play switches. Top loaded machines are easier to work with. One section of the rec/play amp becomes record, the other play. You can easily disable one side of the mechanical arm for rec/play - should you ever later want to restore the tape deck.
In my version I also added a small audio transformer in the feedback (play section RCA out to record section in), as there was some direct leakage otherwise.
An extra bonus is I can also add pedals in the feedback loop. I now have a simple Behringer limiter and an EQ for infinite feedback without distortion (well, it's not Hifi, but the distorsion is controlled).

Build
1. Heads: Two mono heads mounted side by side replace the old stereo head. The first (leftmost) head records (soldered to "Left"), the second (rightmost) heads plays back (soldered to "Right")
2. Tape: The Cassette tape is modified to accomodate two heads, add some foam to ensure that the tape stays close to the heads. I tried loops but ended up using a long tape and rewinding it (lasts longer).
3. Speed: The capstan motor speed control is moved to a potentiometer on the front.
4. Input: The tape deck mike amplifier is used for input just as it is.
5. Output: Taken via the headphone jack on the front: Left side direct signal, Right side delayed signal.

Discussion
The first trick was aligning the mono heads properly, not only to each other but to the tape. The second trick was modifying a cassette tape to apply enough pressure to the two heads. I tried modifying the cassette's standard copper-spring, adding a second foam cushion but in the end just cutting coam (from a detergent sponge) worked better.

> Link you Youtube build description
> Longer sound demonstration (piano)

I also added a CV control for tape speed.
> Youtube demonstration of the CV control.

 

[ruffrecords]

Great project. I looked at a few of these on line but they all seemed a but tacky but yours is much better. One question, could you not just replace the erase head with a record head or is that what you did?

Vheers

Ian

 

[Tubetec]

Thats a great idea , being able to tempo match the tape delay gives great depth to the sound .
The mono heads use 1/2 the width of the tape , which gives a performance boost over the 4 track stereo format . The mono heads are also readily available at a cheap price .
I can see how getting proper contact with the heads might take work,
Tricking the mechanical record/play switch into doing both at the same time , thats smart thinking .

Wow CV input too ,

Welcome to the forum Jacob ,

I just checked out the sound clip , thats got a lot of atmosphere to it in a way digtial often lacks ,
can Dolby NR be encoded and decoded simultaneously ?


Hi Ian ,
I guess you could loose the erase head but then youd end up needing to erase the tape before using it next time , definately possible to do it that way though , longer delaytimes is another upshot and you dont need to modify the cassette housing .
Likewise Ive seen a few attempts at cassette based delay units on youtube , mostly with Sony walkman style mechanisms .

 

[Tubetec]

The Watkins copicat Mk1&2 doesnt have an erase head , it uses a magnet to erase the tape ,
depending on the strenght and proximity of the magnet it erases the previous take more or less , but some ghost echo does make it back around .

Two small flat Ndym bar magnets placed in close proximity to the tape , inside the shell , would probably adequately erase the previous dub , the tape having passing twice across the magnets when you flip it over to record on the otherside .
Theres sometimes suitable magnets to be found in retail packaging boxes ,like for instance mobile electronic accessories . Generally not a great idea to be putting strong magnets in the vicinity of the heads ,but you can always demag if the need arrises . there could be other possible issues like the casstte tape not sitting right due to the pull of the magnets ,who knows , but it might be worth a try to avoid the need to modify the basic tape path geometry and each precious cassette tape .

I biterly regret not buying up a bigger supply of blank cassettes when the hifi industry was dumping them for 25 cent a piece , I was the man in the Hifi shop who sold them and I forgot to keep some for myself in the end .
Theres nothing like the sound of fresh tape .....

 

[rock soderstrom]

Interesting project and best project sketch in a long time!

 

[jacobsteel]

Ian, Tubetec, rock soderstrom, Thank you so much everyone!

I've tried several experiments with the erase-functions. The erase head both preps the tape and erases - however, the effect of a switched off erase head varies a quite bit from machine to machine:

• On a few 1/4" machines just taping over the erase head limited the erasing function enough to e.g. record loops of synth notes atop each other forming a chord.
And on the Tandberg I mounted a tiny switch for layer-recording.

• On the Nagras, simply leading the tape away from the erase head is simple - however here the bias is SO intense that the record-head alone erases quite a bit.

• On the TEAC, I did make some loop tapes for the tape echo, and installed a switch to turn off the erase head (green control box).
Turning off the erase head enables some layering but also a bit of erasing. Layer-recording turned out best on an old JVC 1/4" so far.


Tubetec - yes, DOLBY is still working and delay with and without Dolby has various qualities.

 

[jacobsteel]

--- yes, and on quite a few vintage 1/4" machines the capstan speed is fixed to the mains frequency, there I tried attaching a moving head instead.

And as magnetic fields follow the inverse square law (actually in some cases R -3 ), it actually worked having the extra head mounted with magnets (!). Of course they are in the other end of the box, but still...

Youtube demonstration of a broken AKAI turned tape echo with a Moving head, Echoplex (etc) style (still below).