Shaka Express Gating Issue

Cliff Schecht · July 24, 2005, 10:19:48 PM

I've searched through the forums and realized that it is a JFET that isn't biased properly, or so I think. I am using the GEOFEX layout (the notorious one, yes) and could use a few clarifications:

1) Are jumpers required in the two places (to the right of c2 and c6; to the right of r15)

2) Should I use 9v or 18v?

3) What should I be getting in the way of voltage readings?

aron · July 25, 2005, 03:06:36 AM

wait... voltages are listed in the schematic (PDF). Try those first.

Cliff Schecht · July 25, 2005, 04:01:56 AM

:shock: Oops forgot about thems there.

aron · July 25, 2005, 06:05:53 AM

No problem. I had to re-check too! :lol:

Paul Marossy · July 25, 2005, 10:46:46 AM

QuoteShould I use 9v or 18v?

18V.

Cliff Schecht · July 27, 2005, 12:34:01 AM

It's still gating, just not as severly... Would tweaking the trimpots help or is something else the culprit? Should I run it off of a wall wart or can I use batteries?

Paul Marossy · July 27, 2005, 10:14:38 AM

Quote from: Cliff SchechtIt's still gating, just not as severly... Would tweaking the trimpots help or is something else the culprit? Should I run it off of a wall wart or can I use batteries?

You could use either to power it up. As far as the gating is concerned, read the note regarding R12 and the other trimpots on this page: http://www.diystompboxes.com/pedals/ShakaExpress.pdf
I did as it instructs, and that was my starting point. I didn't deviate much from those recommended settings.

syzygy · July 27, 2005, 10:27:07 AM

I didn't have any gating issues using the GeoFX layout.. But there are jumpers that are needed that aren't drawn or talked about in the pdf. (I believe there are two of them, if memory serves me)

I don't know if the following would lead to gating, but :
The layout is also wrong (not a big deal I guess) where you have to cut the trace to utilize one of the resistors for a mod. If you look at the mod schematic at the bottom you'll see that two resistors are drawn there, tied together at one end. I just drilled another hole into an existing trace and soldered the extra resistor in. Like I said, I don't know how much difference it makes.

The labelling is also wrong on some of the caps, and I think one label is duplicated and one label is undefined. Do a search to find that discussion we had recently.

Paul Marossy · July 27, 2005, 10:41:46 AM

QuoteThe labelling is also wrong on some of the caps, and I think one label is duplicated and one label is undefined.

Yep, this is true. I don't remember having to add jumpers not shown on the layout, but I built mine over a year ago. Anyhow, RG said he would get that layout fixed, but I think he never got around to it...

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Shaka Express Gating Issue