RAT clone problem

[chrisoff]

Hello, sorry for the newbness of this post. I've just started building some DIY FX from kits and have been going OK until I hit a bit of a snag today. Hopefully someone here can help me out.

I bought a RAT clone kit which I finally managed to get working today and it sounded immense. Then I put it in the case and it stopped working

Looked like the problem was the board touching the bottom of the case so I went over the solder points and trimmed any sticking out wires then before I put the bottom back on I had a brainwave to stick a wee poly bag that some screws came in between the board and the case to insulate it (might have been a really stupid idea).  Now that didn't work and when I took the bottom off and plugged it in again all that I get is a horrible constant screeching tone.

I don't have time to dismantle it all tonight and check it so wondering if anyone has an opinion on what's happened in the meantime? Could snipping the solder points have just knocked one of the components or is it more likely that using the wee bag has @#$%ed it (though if something's shorted and fried why didn't it do it with the case)?


Anyone got any tips for what to do if the board is touching the case bottom?

[digi2t]

Anyone got any tips for what to do if the board is touching the case bottom?

Depends on how the board is attached (or not) in the enclosure. Is it screwed in? If so, then longer plastic standoff and screws. If not, I`ve seen adhesive velcro used quite effectively. Use the really sticky stuff, like the stuff they sell for pedalboards.

[chrisoff]

Anyone got any tips for what to do if the board is touching the case bottom?

Depends on how the board is attached (or not) in the enclosure. Is it screwed in? If so, then longer plastic standoff and screws. If not, I`ve seen adhesive velcro used quite effectively. Use the really sticky stuff, like the stuff they sell for pedalboards.

It's not screwed in. Enclosure's quite small so there's not a lot of room for it to move around or to have much choice in how it's positioned.  Are you suggesting the velcro to fix the board in place or just to insulate between the enclosure and the board?

[peterg]

Double sided foam tape works well as an insulator. I leave about 1/8" extra on all sides of the board and leave the peel off covering on the non-board side.



I doubt the bag caused you any problems. The unwanted noise is probably a result of a piece of solder wedged in were it doesn't belong.

[rousejeremy]

+1 on the double sided tape. YOu could also tape a business card to the back of the bottom of the enclosure to stop the shorting out.

[digi2t]

It's not screwed in. Enclosure's quite small so there's not a lot of room for it to move around or to have much choice in how it's positioned.  Are you suggesting the velcro to fix the board in place or just to insulate between the enclosure and the board?

To fix it in place. One side of the velcro on the trace side, the other in the enclosure, and press the board in. As mentioned for the double sided foam tape, leave a bit of a border all around.

BTW, the double sided foam tape is perfect as well. I`ve seen it used between the board, and board mounted pots on the Spaceman Effects units. Glad they brought it up, I hadn`t thought of it. Cheaper than velcro too.

[chrisoff]

YOu could also tape a business card to the back of the bottom of the enclosure to stop the shorting out.

Ah cool, I'll try a bit of card.

More concerned about the screeching noise for now. Had a quick check for any wee bits of solder/clippings stuck on the board but that hasn't helped.  It's switchable between RAT and Turbo RAT and the screeching is present on both diode sets.  Someone on another forum suggested it could be damage to the IC (which is in a socket) when it was shorting on the enclosure, is that likely?

[rousejeremy]

Could be the chip itself. I bought two LM308N's and one of them squealed incessantly. It's probably a good idea to use shielded cable on the inputs and keep wire lengths short, just in case.

[chrisoff]

Thanks for all the help, after a load of poking around tonight I traced the problem to a snapped input wire at the switch.  Had pretty much decided it was the IC that was bust and was measuring voltages to confirm then started wondering why there was no input voltage making it onto the board 

Quick test with a blob of solder got it working again, though it's still temperamental so I'll strip the wire and redo the connection which should hopefully be the end of the problems!

[Kipper4]

Glad it's sorted it's a super effect. I love mine.