Help Debugging a Weird Analog Echo

[Colonel Angus]

I Know, its not a stomp box. Also it has been a long time since I've posted or even logged in. This is a tricky one and I'm really hoping someone can point me in the right direction.

So I bought a "broken" Univox Echo-Tech EM-200 disc echo. It looks like this :




Looks to be in decent shape overall, but I'm sure its seen quite a bit of use in a touring or studio situation (looks like it was once marked "2" but worked its way down to "5"). Powers on, passes clean signal, no echo. Electronics look sound if a bit dirty, save for one broken input. All the pots seem to work in that they sound scratchy when you turn them. The motor works, as does the speed control . The tape disc is not ideal, but should be good enough to produce some kind of echo (its clean and opaque with no major scratching). Its hard to see but it appears the tape heads are making contact with the disc. One set of heads is reading~ -14VDC the other set is reading~ -0.5VDC

I'm kinda stuck. It was my sincere hope to debug this unit mechanically, getting up close and personal with the electronics will require a good bit more dis-assembly. Any help would be much appreciated. Plus this thing is freaking cool, there's next to nothing on them anywhere. The Tel-Ray forum got me to estecho.com which has pretty much all of the information anywhere on the EM-200

Cheers,
Brian

[Colonel Angus]

Sorry should have brought it to a more concise question. Is there a way to excite a tape head to see if its  passing signal without tape media?

[Mark Hammer]

1) Cool? - Yes.  Freaking? - Yes.

2) So I gather it is using something like the innards of a diskette, recording in spiral fashion to mimic a long piece of tape?

[artifus]

nice. some general tape tips here:

http://www.soundonsound.com/sos/mar10/articles/taperecorderadvice.htm

http://merrenaudio.com/echoplex_repair_and_info

déjà vu:

http://www.diystompboxes.com/smfforum/index.php?topic=97963.0

[Colonel Angus]

Yeah same unit. I figured best to start fresh now that I have the thing. Also the EVO-1 doesn't even power up, so that is for another day.

Thanks for the links. I'll do some more reading.

@ Mark, yes its like a tape loop echo except the heads are fixed and the echo speed is determined by the rotation speed of the tape disc medium. The disc looks like a 5.25" floppy with a drum-head like retaining ring that screws to the rotating platter

[gritz]

Sorry should have brought it to a more concise question. Is there a way to excite a tape head to see if its  passing signal without tape media?

Earbud type earphones will "generally" leak enough magnetic flux to make hemselves self known to coils and such and they're small enough to wriggle into tight spots. Just grab your mp3 player / phone, etc. You will have to get up close and personal with the tape head gap (which will be the bit skimming over the disk) though. Touching the hot pin of each playback head with your multimeter probe would probably be enough to create an audible pop if the playback side of the electronics is doing it's stuff.

BTW it looks amazing! Might be worth starting with a few basics before pulling it apart - checking a few voltages at accessible points and scribbling 'em on the circuit diagram, looking for any previous repairs, etc. I wish it was on my bench!

Edit: added a couple of thoughts.

[wavley]

Try cleaning that rotary switch, I've seen space echoes that had no sound and it's because all the contacts on the rotary switch were black.

[gritz]

duplicate post

[Colonel Angus]

Wow thanks guys! That earbud trick is just the mojo I was looking for. I'll try that in the AM, of course clean the rotary too

Again sorry about the dupe post, I thought this would be better than resurrecting a dead thread.

Oh, yeah and it does "pop" when you connect the MM to the head. So hopefully that means the heads are sending signal to the audio, but i wont hold my breath!

[gritz]

Wow thanks guys! That earbud trick is just the mojo I was looking for. I'll try that in the AM, of course clean the rotary too

Again sorry about the dupe post, I thought this would be better than resurrecting a dead thread.

Oh, yeah and it does "pop" when you connect the MM to the head. So hopefully that means the heads are sending signal to the audio, but i wont hold my breath!

The duplicate post thing was me - I managed to quote my own post when I tried to edit it - I didn't see how to delete it so I just edited it to say "duplicate"

More pictures of this gizmo would be great, Colonel!

Hopefully it's just something minor, like a bad connection within the "record" gubbins. If I interpreted your "~ 14V" correctly then perhaps the heads are getting bias oscillator signal correctly, which would be a good start.

[Colonel Angus]

WWWWW000000000000T!!!!!1!
https://soundcloud.com/brian-moeller/echo-tech-test
She works! I cleaned the rotary, nothing. Held earbuds up to the heads, nothing. Then a thought occurred... Footswitch! I alligator clipped a 3PDT to the leads on the back of the footswitch jack, then tried the earbuds against the heads and voila'! They heads were passing sound! A little "fine tuning" of the head assembly ( not so fine in fact rather coarse) and the disc began writing, playing and erasing!!

Still some more stuff to clean up, broken plastic input jack, scratchy pots but nothing major.

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[gritz]

Yay! 

Thanks for the pics and sound clip. It looks and sounds like something NASA dreamed up between trips to the moon. Good work Colonel, I'd love to hear another clip when you've finished the fefurb.

*jealous"

[mth5044]

That was awesome! Congrats on getting it to work. There is just no way to emulate that kind of sound, it's so unique to tape delays.

[gritz]

gah, what the snot is it with duplicates when I try to modify a post? I'm sure I didn't hit the "Quote" button. Anyway, ignore...

[artifus]

why am i looking at pictures of your crotch?

because that thing is freaking awesome!

glad you got it going.