ShortScale.org

A bit of a x-post with the DIYStompbox board, I need some advice here.

I own a old-issue SA Classic and it's a wonderful dirt box, however now it's suddenly acting up with little to no bypass signal (intermittent) and when engaged spews out a high noise somewhat clean signal with some gating. To me it sounds like it's misbiased, to give you an idea. I'm almost sure that the buffer FET is bad, or something in the biasing of it has gone awry.

Does anyone have an actual true schematic of this thing? The one floating around by "unknown japanese guy" isn't really correct, and I did find a cleaned up version from Gila Crisis on DIYStompboxes but I noted he doesn't list where VCC came from on his version, and there's some other odd things from the schem that don't match mine (I'm completely baffled how there's no DC leakage but the input does not connect to any kind of cap at all).

My voltage readings on the pins of the FET are really weird. I'm getting 8.53, 8.57, 8.63 on the FET which really does not seem right to me. I haven't looked up the pinout for this K117 GR 2G FET yet to be certain of the pin out, but those readings do not seem right. I'd expect the gate pin to have about half of the voltage source but it's pretty much all the same.

Ideas?

Welp, I determined with the help of DIYStompers that the buffer FET and/or zener diodes are bad. Unfortunately all I had on hand to swap in was a J201 JFET, and it won't bias right. So, I had to put in an order with Futurlec as they were the only ones that had the diodes, and also the correct JFET, so I have to wait forever for them to ship that out to me.

This is turning out to be so much fun. It's an awesome sounding pedal but an absolute nightmare to work on.

Also, my email to Tech 21 has gone completely unreplied to, so I don't even know if I can send it into them or not. For a $200 pedal it's worth having it repaired, but damn, they won't even reply to me on a pricing inquiry.

I always heard they had excellent customer service. That sucks because i love their stuff. Damn, at least reply with FU or something.

Just got a reply, guess in this day and age of instant communication sometimes we get impatient.

Huh, turns out from the serial mine was made in Dec '94, so it's an old one alright. Either way, the price they quoted for repair is actually really reasonable, unfortunately I need to put the JFET back in since I swapped it with a different one, and I can't since I had to cut the legs off of the old one to get it out through the PCB holes. Oh well, I'll just wait for my shipment, replace the J201 I put in with an exact part, and if it still doesn't work I'll ship it to them to repair. It's gotta be in the buffer board anyway so it shouldn't be the expensive pots/sealed board that's bad. Just gotta wait and see I suppose.

Good news for tech 21 sending you back a fair price and all that.

Pens wrote:Just got a reply, guess in this day and age of instant communication sometimes we get impatient.

You think that's bad? I had to send Pro Co several emails asking for a couple of replacement feet, and it took them about 6 weeks to reply, and the man who replied simply said "You can buy some at Small Bear Electronics." It would have been helpful, if I didn't already try that.

It's so sad too, because the last time I emailed them, it only took a day for a response, and I got a thumbscrew for the back plate by the end of the week.

Just an update, I finally got the FET from Futurlec and put it in, pedal is working fine now once more.

Glad this had a happy ending and thanks for providing detailed info about the process.

I own an original (not Classic) as well, and I had it reworked by Tech 21 in 2004 for a total of $35 after it exhibited similar issues. I had no issue with their customer service and found it a wonderful experience, but it's hard to believe that was nearly as long ago now as 2004 was from the original release. Damn.