Unicord EC-80A Tape Echo: study-repair

An interesting artifact from the 70’s …

The Unicord EC-80A Tape Echo is a pretty rudimentary machine, best suited for old-school regenerated noise effects …

MAIN BOARD COMPONENT LAYOUT AND OFF-BOARD WIRING

unicord-ec-80_a-lyt

SCHEMATIC WITH WITH VOLTAGES

unicord-ec-80_a-voltages

the thing that jumps out is the class-A circuit architecture, and the amount of voltage gain generated there … the following DC-Table results

TINA-TI (OP) SIMULATION OF INPUT PREAMP CIRCUIT
using BC239C models

unicord-ec-80_a-dctest-bc239c

TINA-TI (OP) SIMULATION OF READ-HEAD PREAMP CIRCUIT
using BC239C models

unicord-ec-80a-dctest-bc239cread

50khz bias oscillator voltage, seen at the Collector of Q7

ec-80a-carrier

both tape heads are still working …

ec-80a-heads

final (adjusted) motor speed voltage range:
1.4v – 6.4v

12 Comments on “Unicord EC-80A Tape Echo: study-repair

  1. Thank you so much, you safed me a lot of time for trying to fix a unit that has no wet signal!

  2. Trying to use this delay for studio work, particularly on vocals. Just gave the unit a cap job and replacement the pots as they were filled with white gunk and didn’t sound good. Do you think there is a worthwhile replacement of the audio path transistors? Such as the KSC1845?

  3. YOU CAN ALWAYS TRY A 2N5210 THERE BUT THE IMPROVEMENT WILL LIKELY BE INCREMENTAL … I THINK THE DESIGN IS INHERENTLY NOISY, NOT SO MUCH FROM THE ELECTRONICS SIDE – MORE THE LOW TAPE SPEED, NARROW TAPE WIDTH, HEADS …

  4. Thanks for the info. The cap job and making sure the unit was properly grounded got the noise floor low enough for me. But there is so much low end now and not a lot of high end. Is that 100pf cap on the output a low-pass filter? I’m thinking of messing around with different caps in the 40pf-80pf range to see if I can get a little of the high end back.

    Ryan

  5. RYAN, THE 100PF CAP AT THE OUTPUT IS ACTUALLY 1NF AND IS THERE (I’M STRONGLY ASSUMING) TO SHAVE OFF SOME HIGH-f TAPE HISS … TRY REMOVING IT ALTOGETHER TO SEE IF THAT’S THE CULPRITE // IT MIGHT HAVE DRIFTED IN VALUE ETC … AS THERE IS NO OTHER CAP IN THE WHOLE CIRCUIT DOING THAT SIMILAR (SHUNTING) JOB, IT’S A GOOD GUESS ON YOUR PART … OTHERWISE, IT COULD BE THE TAPE HEAD OSCILLATOR NOT RUNNING FAST ENOUGH // BUT I’M NO TAPE DECK EXPERT SO JUST GUESSING … COULD BE YOUR HEADS NEED TO BE DE-MAG’D AS WELL, MIGHT BE THE TAPE … FIRST, LET’S SEE IF REMOVING THAT CAP DOES ANYTHING

  6. Thank you for your reply. I changed out the cap for a higher quality wima cap. The old one definitely drifted in value and it cleaned up the signal and brought back some of the high-end. The real kicker was changing the 5k input pot to a 500k. It restored the dry signal, as it had lost so much of the high end just going through the pot. There is an annoying mechanical buzz that I’m wondering could be solved with higher value filter caps. Otherwise I’m very happy with this. Your schematic saved me so much time.

  7. YES, THE 5K INPUT POT WOULD KILL HIGHS IN A HIGH Z SOURCE, AND CONVERTING TO 500K INCREASES SENSITIVITY TO SURROUNDING ELECTRICAL NOISES // YOU MAY WANT TO TRY THE 5K POT WITH LOW-NOISE VOLTAGE BUFFER IN FRONT … ALSO, INCREASED FILTER CAP SIZES MIGHT HURT THE PSU AND NOT DO ALL THAT MUCH IN THE END TO HELP DEFEAT THAT (MOTOR ?) NOISE // THAT COULD BE A GROUNDING THING … IT’S A COMPROMISED (ECONOMY) DESIGN I’M AFRAID, ONLY SO MUCH YOU CAN DO HERE OTHER THAN RUN IT ON BATTERIES AND PLAY WITH THE GROUNDING

    GLAD THIS PAGE HELPED YOU SAVE TIME, PLEASE DON’T FORGET THE TIP JAR ON THE WAY OUT … :)~

  8. Hi. Great page!
    Does anyone know of any resources for how to modify an 8-track recorder to do this DIY?
    Specifically looking for details of the 2-head situation. I can handle the speed control circuits and the I/O parts, just looking for further info/ advice before I tear into a working unit.
    Thank you very much.

  9. HI MAX, THANKS FOR YOUR QUESTION … I’M ASSUMING YOU’RE TALKING 8-TRACK WITH PRE-EXISTING HEADS MOUNTED ETC ETC … AS FAR AS ELECTRONICS GOES, USE THE SAME OSCILLATORS AND JUST DO SOME KIND OF NOISE DEFEATING PREAMP/MIXING … KEEP IT SIMPLE, INPUT TO VARIABLE GAIN OP-AMP STAGE WITH PRE-EMPHASIS, TO RECORD-HEAD OSCILLATOR (THIS WAY YOU CAN SATURATE OR EVEN OVERDRIVE TAPE) … FROM PLAYBACK OSCILLATOR OUTPUT TO VARIABLE GAIN OUTPUT AMPLIFIER … THEN TO SOME KIND OF MIXER AND MATCHED DE-EMPHASIZER (DOESN’T HAVE TO BE FANCY) // … DONE!

  10. hello hello;)
    do you have any advice on winding/re-spooling the cassette cartridge that goes with this guy? mine got twisted up inside ,and i’m trying to figure out the best way to go about fixing it, sadly there’s not much info out there;/i came across your page tho and you seem super knowledgeable on all things ec-80,so i figured it couldn’t hurt to ask.. any info or advice would be super super appreciated__🤘
    sincerely,
    _ruby lee

  11. THANKS FOR YOUR QUESTION RUBY, UNFORTUNATELY I’VE NEVER PLAYED WITH THE TAPE ASSEMBLY IN THESE UNITS … WITHOUT WANTING TO SOUND SILLY I WOULD STUDY THE PROBLEM AND FIRST UNDERSTAND HOW THE CASSETTE GOT TANGLED UP TO BEGIN WITH (AN IMPINGEMENT ?!) AND THEN JUST FOLLOW YOUR INTUITION AS TO HOW IT WAS MEANT TO OPERATE PROPERLY … HOPEFULLY YOU CAN REVERSE THE DESTRUCTIVE PROCESS, FIX IT AND THEN MAKE SURE IT DOESN’T HAPPEN AGAIN … GOOD LUCK!

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