Mobius trip looper questions...years later

[vacuumdust]

The tips at GGG call for directly soldering a .1uf cap between pins 12,13 and 28 of the recorder chip...but if you look at the layout, doesn't the .1uf cap between 13 and 16 continue on to 28, therefore functioning as the one between 12,13 and 28?? 
   
If I put in a buffer, does it matter if it's immediately after the input jack, before the switch. OR after the switch, before IN on the board?

In Dean Hazelwanter's picture here http://i179.photobucket.com/albums/w290/extester01/Img010.jpg there seems to be a jumper between pins 5,6 and 12,13 on the recorder chip.  Doesn't seem to be on the schem, layout , or tips. 
THANKS a million if somebody can help me out.

[fpaul]

I think the caps are already there, I built mine without adding any extra and it works.  Looking at the layout I thought they were in there too.  I think the jumper is to tie unused inputs to ground, I never did it on mine.  Mine works but is a little finicky, sometime I have to unplug power and plug back in to get it to work.  Someday I'll add the jumper and see if it helps.  All this has been covered if you do a search for Mobius trip looper.  Hardest part for me was wiring the switches, I used someones idea for one stomp recording and one stomp playback. Recommend doing that but you'll have to search for the info, I built mine several years ago and forget details.  Hope it helps.

[idiot savant]

Heres the full errata for building the GGG Mobius Trip:

PINS 2/3/5/6/26 of the ISD chip need a little jumper to GND(PIN12/13) it was just missed on the PCB. Not doing this may cause issues!

PIN28 on the ISD should have its own 100n decoupling cap. The other one you see is part of the 7805 circuit. Not 100% necessary, but recommended.

The switching is easy but somewhat confusing. Here's my own drawing from a million years ago when I built mine. This is NOT True-Bypass, but makes the unit Stomp-friendly IMHO.



With these notes, you should get it working. You don't need any buffer, seems people just want to throw in buffers everywhere these days!

[vacuumdust]

Thanks for the info!  I am using your switching scheme savant and I don't think it will be a tough build...I'll leave out the buffer too...I have no problem with it not being true bypass and if it doesn't screw with your dry signal what's the point, I agree.
     My only real problem was with the extra cap from pin 13 to 28.  Regardless of what the use of the .1uf cap from 13 to 16 is, it does also contact pin 28.  So if you put another .1 cap from 13 to 28 you are paralleling 2 .1uf caps for the result of a .05uf cap...please correct me if i'm wrong...and maybe it doesn't matter anyway as you have done it with successful results.  THANKS AGAIN

[idiot savant]

Thanks for the info!  I am using your switching scheme savant and I don't think it will be a tough build...I'll leave out the buffer too...I have no problem with it not being true bypass and if it doesn't screw with your dry signal what's the point, I agree.
     My only real problem was with the extra cap from pin 13 to 28.  Regardless of what the use of the .1uf cap from 13 to 16 is, it does also contact pin 28.  So if you put another .1 cap from 13 to 28 you are paralleling 2 .1uf caps for the result of a .05uf cap...please correct me if i'm wrong...and maybe it doesn't matter anyway as you have done it with successful results.  THANKS AGAIN

paralleling caps increases capacitance.

The capacitance isn't the point. You want the cap physically close to the pins of the IC to isolate, and filter the digital noise.

[loves_guitar]

In an effort to ease wiring my Mobius together, I put together this wiring diagram. I had Dean proof it for me, so it should be good to go (I still need to buy the ISD chip for this so I can verify the wiring layout).

http://www.diystompboxes.com/smfforum/index.php?topic=83260.msg692428#msg692428

[vacuumdust]

Savant, yes, me dumb, must have been thinking resistors (in parallel).
And thanks for clearing up my question about the cap in question.
THANKS