"tape echo machine" ... anybody got a schematic?

[pinkjimiphoton]

picked up one of these
https://www.amazon.com/Tape-Echo-Machine-delay-pedal/dp/B01CI1H6QE
no schematic included. 3pdt.com appears to be either down or neglected, and of course i need to debug something.
does anyone have a schematic for this project by chance they could share with me?
thanks in advance

[Rob Strand]

If no one has it, go down this path:

I first saw this in the product description "The circuit is based on the Mitsubishi 24-pin M65831 delay chip." and was thinking EM5  then I saw this up near the prices:
"Build an Echo Machine Pedal based on the schematic of the EM5 Tape Echo"
You could just trace the board against the EM5 schematic and make small fixes.
I suspect it won't take long to match-up large sections then fill in the difference details.

[pinkjimiphoton]

yeah, thanks rob!
i got the schematics for the em5 but this thing is pretty different. i mean the basic way the delay chip is hooked up is really close, but the rest of it seems a bit different.
when i ordered the board, i ordered all the correct parts for the em5, and other than the digital chip and the 74, its pretty much different, uses two 5532's instead of the proper chip <which i bought a bunch of, silly me> and is using 508/7/8's
its passing audio, but can't get any delay out of it.
i'll give dave at 3pdt.com a few days, hopefully he can hook me up

[Rob Strand]

i got the schematics for the em5 but this thing is pretty different.

That's a pain.  So it's only loosely based on the EM5.

can't get any delay out of it.

If you have an oscilloscope you could check the clock-out line.  If there's no clock then the delay won't work.
The other thing to check is the DC voltages everywhere.

[pinkjimiphoton]

yeah, they left out the in and output buffers, the switching stuff, and modified the damn circuit some.

i DID get it to echo briefly yesterday changing the clock and delay chip.. but i couldn't adjust the delay time at all, tho the repeat/mix were working. the short/long switch didn't work either.

i think i smoked two clock chips now and 2 of the delay chips. my voltage reg 78l05 has been replaced a couple times too, but i think somethings smoking the clocks.. if i replace the delay and clock, my voltages seem right. once it stops working, my 5v output drops down to between 1.4 -3.6 V.

its a black pcb with black traces, so without a schematic i have a hell of a time. not enough contrast for me to be able to follow it with this damn glaucoma shit.

gonna try replacing the delay time pot today and probably reflow most of the board. agravating!
when it DID work, it really did sound nice and very similar to my echoplex with a fresh tape.

[Rob Strand]

i think i smoked two clock chips now and 2 of the delay chips. my voltage reg 78l05 has been replaced a couple times too, but i think somethings smoking the clocks.. if i replace the delay and clock, my voltages seem right. once it stops working, my 5v output drops down to between 1.4 -3.6 V.

Maybe try to get the clock going with the delay chip removed.    From what I can see the clock circuit is very close to the EM5.   First check you can vary the DC voltage on the delay pot wiper with the delay setting.

For IC4, I noticed that circuit uses three gates of the hex inverter.  Make sure the input of the unused gates are grounded.   You get weird problems when there's floating inputs.

[reddesert]

The 74-something chip it uses for the clock cannot tolerate over +5V, unlike CMOS.

I would remove all the ICs (but leave the 5-volt regulator), then measure the voltages on the sockets. Once sure that they are safe, then install the clock chip and measure voltages. If you have an oscilloscope, use the oscilloscope to verify the clock operation and that it is responsive to adjustments. If you don't have an oscilloscope, now would be a great time to buy and build one of those $20 Jye-Tech DSO150 oscilloscope kits (I wrote a detailed build report on the madbean forum for it). Then install the opamps and audio probe to verify that signal is being passed up to the delay chip socket. Finally, install the delay chip and audio probe the path again. Use the scope to test the clock operation into the delay chip (I'm not sure if the delay chip has any output pins that are sync'ed to the clock, but if it does that's also a good thing to check.)

I looked at the archive.org Wayback Machine of the 3pdt.com site, and it has a couple of larger pictures of the built pedal, but no link to a build document.

[pinkjimiphoton]

thanks guys... balls to the walls for the next couple days, the info posted makes a lot of sense.
i will try sunday or monday and report back... thank you!

[pinkjimiphoton]

squashed that fuggin bug GOOD.
i didn't have proper 9mm 100k pots, so i used 16mm pcb mount ones, and used my fiskars to snip down some of the legs to get it to fit. well, the delay time pot couldn't handle the stress of me smoking it i guess and flaked out faster than a flaky guy on corn flakes.
oops. of COURSE i destroyed the traces trying to get the bad pot out and the good pot in..so a little surgery was required here n there, but i got it going.
sounds surprisingly like my echoplex. even the wow and flutter as wall voltage sags with the laundry going. too cool!
so basically <why do i have zappa's "flakes" in my head???> its the em schematic, minus the input and output buffering and the switching stuff. they also separated the dual opamp for two 5532's... i, of course, bought all the shit to build the original one. bugger. i mean, the choke, the jfets, the mosfet, the whole 9 lol..
but that said it was cool, is cool, and now i gotta make one on vero cuz it looks like it should be doable with a little forethought.
got the chips from polida on ebay, have had really good luck with them.
this circuit is worth building, BUT if ya play with the feedback overload too much you may find your delay gets kinda dirty.

thanks guys! will try n post pics/clips etc when i can. peace!

[thermionix]

<why do i have zappa's "flakes" in my head???>

Hand to God, same here, as soon as I read that line.  I was even gonna post "California's got the most of them..."

[pinkjimiphoton]

hahah its not just me then, lol

that said, i got to meet dweezil and band about 3 weeks ago.

i, of course, gave him a monkey balls octave overdrive.

they did flakes, it was funny even without the shrooms

[pinkjimiphoton]

hey, for sure bit off more than i can chew i think with the vero idea. i'm just not that good at it lately, and have gotten lazy and been using circuit boards when/where possible.
ran into a snag trying to figure out the 74hcu04... brain dead. looking at the schematic for the em5, it shows only 3 of the inverters being used... i'm assuming everything else gets tied either to ground or half voltage? is one preferable to the other?
but the big question is it says pin 8 connects to CP1, which looks like a circle in a circle.... i can't seem to find anything else on the schematic that looks like that.
i gotta check the em5 diy thread i guess and try and simplify it, maybe put it on perf. i'd love to throw this circuit in the box to steve hunter to play with but i wanna keep the original for a change
i really appreciate the advice. rock on!!

[diffeq]

i'm assuming everything else gets tied either to ground or half voltage? is one preferable to the other?

Either ground or +V. Half-voltage is where logic chips dissipate most power and can start oscillating (if I remember right).

Regarding CP1, I think it's a test point for checking clock pulse with oscilloscope, as it's buffered by additional inverter stage.

[pinkjimiphoton]

thanks tony!
i guess i gotta do some more reading still