Saturday, April 25, 2015

Echo-Matic (DIY Tape Delay)



I designed my echo-matic panel in the style of the Univox EC model tape delays


Here's my setup:  1/4" instrument input and output, and RCA I/O's to connect to the tape recorder.  I'm using a Marantz PMD221.  I modified this machine slightly by adding a second pitch control.  That's what that little knob at the top right corner of the marantz unit is.  This knob adjusts the pitch drastically for slower delay effects.


This surprisingly simple circuit turns any 3 head tape recorder into an awesome sounding tape delay machine.  The tape recorder has to be a three head unit (erase head, record head, and play head) for it to work.  This type of recorder will have a button or switch that allows you to listen to the source audio, or what has just been recorded to the tape.  The small gap between the record head and the play head creates the delay effect.  I'm a novice when it comes to circuit design, but the schematic just looks like four buffers and some pots to mix the different signals together.

Here's the original literature for the echo-matic:

And here's a layout I redrew from the above article.  It's 600dpi and the image is reversed for photosensitive boards.




Gutz! :]




Per request:

Here's some additional photos and info about the mod I made on my PMD221.


The Pitch knob had a 1.2K resistor in series with it.  All I did was desolder one pin of that resistor and replace it with a 1k pot.  In the picture above you can see the wires running from that circuit board to the 1K pot attached to the battery compartment door.  With this mod, I can get the delay times to somewhere around 500ms before the tape drive stalls out and stops.



A closeup of the solder points




I don't run this unit on batteries so sticking the pot in the battery compartment seemed like the best place to for it.

37 comments:

  1. Do you offer the PCB for sale?

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  2. I hadn't planned on selling any PCB's. I offer all the info and files to make your own if you know how, or if you know someone who knows how.

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  4. How do I make the case and pots though? Do you use a machine?

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  5. How do I make the case and pots though? Do you use a machine?

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  6. The blank case and pots where purchased. I had to machine the holes in the case and make the front panel design. This is not intended to be step-by-step instructions. It's for DIYer's with at least some experience building electronics.

    If your new to this kind of stuff and want to learn more, I recommend you read what you can, learn the fundamentals, start small, experiment (be safe), and have fun.

    cheers

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  7. I'm looking for something like the echomatic that's stereo and pedalboard friendly. Any ideas?

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  8. To clarify, the mixer/send & receive portion, not the tape player/recorder. Thank you

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    1. Hey man.

      Sounds like you just need a simple mixer or feedback looper or something. I'm not sure what your application is but a feedback looper can be really simple and done passively with a single pot.

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  9. Would you mind sharing the modification you did to your PMD221?

    I have a PMD222 that I successfully modded to enable use of the existing pitch control in recording mode. I'd estimate that it now reaches about 250ms delay times. Would like it to go a touch slower though!

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    1. Sure thing.

      I forgot what I did exactly. I think there was a logical reason why I didn't fix the existing pitch control to have a wider sweep. If I remember correctly, the pot I added replaced a resister somewhere in the pitch circuit. The mod is nice tho, and can slow the machine down to a stop practically. When I get a chance, I'll post better details.

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    2. You got me curious :)

      I posted some additional pics of the PMD221 mod. I can get the delay times to roughly 500ms ,I think, before the machine stops. Hope that info helps you out. I don't know how different the 222 is.

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    3. Hey Mihran, can you explain how you modded your 222 to use the actual pitch knob while recording ? I'm very very interested by this feature !

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  10. Nice work!
    Is there a hole between the two cables? it was made by you, desoldering? is that it? soldering the two wires and melting the solder in that hole?
    Thanks in advance

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    1. Sorry, I'm not sure what your referring to in your comment?

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    2. Hello, sorry for the confusion.
      Just wondering if we only need to solder the blue and purple wire to the board or we need to do take out some solder of any point.

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  11. So cool! Questions from a curious mind... First, do you have any recordings? I'd love to hear this thing in action. Also, what did you use for an op-amp? And finally, how do you you do those cool colorful enclosures?

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  13. Great stuff!!! I'm building one of these myself - do you have the PCB files available?

    thanks

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    1. Thanks!! I only have the old school transfer image for making the PCB yourself. The image in this post is the exact image I used to make my board.

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    2. thanks for the reply - I've never done my own PCB before, but it doesn't look to difficult. Do you use the photo-paper & Ferric Chloride method?

      Also, regarding the pot you installed for speed control - can that alter the speed during record or only during playback?

      thanks again ;)

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  14. thanks so much first of all. I have been chasing the idea of a DIY tape delay build for a long time adn this is by so far the most promissing looking one that might actually work adn serve in live shows and recordings!

    only a few things stands in my way. Since there is no schematic diagram is really hard to follow the circuit path from the description 'literature' you attached.
    Usually I would build projects based on tag boards but this one is worth messing around and etching the PCB. Only I dont see where exactly the potentiometers are connecting. Would it be possible for you to upload exact fotos that shows where does the potentiometers lugs connects to on the board ? as well for the In / Out jacks ?... as well for the dc jack ?
    really looking forward to building this as soon as those things gets cleared out I better start looking around for a PMD unit :)
    cheers and thanks!!!

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  15. oops sorry about that
    now i see i missed the second gif link :D
    cheers!

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    1. Yea, no worries. The links are not super obvious.

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  16. This is my first time i visit here. I found so many entertaining stuff in your blog. Keep up the good work.
    Plastic Flow Meter

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  17. what should the dimensions of the PcB be?

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    1. Hi, The PCB should be about 2" x 1.5" Make sure the layout image isn't being resized when you go to print.

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  18. Can't download the PCB image! :(

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  19. Still have one question: how do you get the pitch pot to work during recording?

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    1. Or didn't you bypass the bypass function? If just adding the pot does the trick, I think I might do that as well.

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    2. What's your tape source? Make sure your recorder is on it's monitor setting. The speed of the tape machine (or distance between the record and playback heads) is what determines the pitch/delay time. I don't know if that answers your question. let me know if you get it working :)

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    3. Oh, I get a nice tape delay and everything, it's just that the pitch knob is disabled when recording, and that I'd like to circumvent that somehow.

      My last question was about wether you bypassed the function that disables the pitch control when recording or if you just left it as it is and installed another pot for speed control.

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