YJM 308 problem

[tungngruv]

I vero'd up Torchy's layout for the 308 and a couple strange things are going on. Only difference to his layout was a dpdt switch added to change clipping diodes instead of mounting them on the vero. I've rechecked for traces, triple checked the board to the layout and still no sound. If I crank the amp up, I can hear the volume control working but no difference in the gain. Also, the battery and op amp got real hot, real fast!! I noticed that the 1n4001 polarity wasn't marked on the layout but I just placed it the same way as the 47uf cap, positive away from the opamp. I'm thinking a ground short? I'll post voltages when I get around to it tomorrow, after I sleep!!!! Thanks for any ideas where to look.

[Prive]

The diode might be connected to prevent mistakes in the power supply polarity, so i bet it's reversed, just take it off and try without any diode.

Saludos, Marcelo.

[NaBo]

:?   yes, that diode IS a polarity protector and should be in BACKWARDS to create a short circuit if the power polarity is ever connected in reverse, ie, the cathode end (with the band) connected as close as possible to 9V+ and the anode as close as possible to ground (battery negative terminal).  When I say as close as possible, I mean connected before any other component's leads to prevent large amounts of current resulting from the potential short circuit from heading anywhere else (a lot of people put them directly on the power jack lugs).  Flip it around and if you dont have any other problems, it should work.  Might need to replace the diode, might need to replace the battery with a fresh one depending how long it was shorted out.  Let us know if it works okay after that... if not something else got killed, and it'll be de-bug time.

[tungngruv]

Thanks guys!!!! I'll get to it tonight and post results. Thanks again!!

[kojjum]

I had exacly the same problem with mine. It was the polarity that was wrong! I rotaded it 180° and it was up and running.

Does anybody experience fedbackproblems when max gain is used? My circuit began to scream so I used shielded wires from the jacks and it went silent. It's a rather loud circuit.

//jens

[dosmun]

Does anybody experience fedbackproblems when max gain is used? My circuit began to scream so I used shielded wires from the jacks and it went silent. It's a rather loud circuit.

Yes it is a loud circuit.  I had the same problems with mine when I first fired it up.

[NaBo]

hmm... not I.  which is weird cuz it was wired up with gator clips and just spawled out on my bed.  some hum and about 10 radio stations, but no squealing...  sound sample in my sig was recorded with gain and volume maxed, and a cranked-but-low-master-volume ruby into a 4x12

[tungngruv]

Thanks guys, reversed the 1n4001, now all is well!! I also get a squeeling when turned up to max but I am going to replace the gain pot with a 500k reverse log pot. I'll post my results. Thanks again for the suggestions!!!!