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



8 comments on “Unicord EC-80A Tape Echo: study-repair
  1. Dominik says:

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

  2. jcm says:

    THANK-YOU FOR YOUR NOTE DOMINIK, GLAD TO HEAR THE INFO CAME IN HANDY …

  3. Ryan says:

    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?

  4. jcm says:

    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 …

  5. Ryan says:

    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

  6. jcm says:

    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

  7. Ryan says:

    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.

  8. jcm says:

    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 … :)~

Leave a Reply

Your email address will not be published. Required fields are marked *

*

This site uses Akismet to reduce spam. Learn how your comment data is processed.

360+ Pro Fuzz/Preamp

360+ProButton

360+ DIY Kit

360+diyKitButton

Mu3 DIY Kit

360+ProButton

IFMTA (book)

FWboard-Button

IFMTA (PDF)

FWboard-Button

Champ (PDF)

uChampButton

FORUM MEMBERSHIP

360+diyKitButton