JFET phono stage (Boozehound) help!

[MagnumOpus]

Ummm...DC has polarity. Did you change anything with how the power supply is hooked up to the board right before you had this issue?

You have 2 power in holes on the PCB. Find the one that shows continuity with the one labelled "ground" or the negative lead of one of the caps. This is your negative pcb connection. The other is positive. Now take your meter and hook the red lead to the positive pcb connection and the black to the neg. pcb connection (you can use the solder pad if there is no bare wire).

Do you get negative or positive voltage? If it's negative then you are hooked up to the PCB backwards and your electrolytics caps are fried. If it's positive you are OK.

Negative voltage...Some one told me when I got started with diy that polarity on dc didnt matter..guess they were wrong

There was a schematic on the back of the plug, but I did'nt understand from it which of the wires from the inlet was + or -

Well I know now. Surprised it worked this long..Allthough it was terribly noisy, almost like a motorboat speeding...

So only the electrolytics are fried, my fets should be fine?

 

[Hikari1]

Did the wire that "snapped" and you fix have anything to do with the power supply?

If you indeed had the PS hooked up backwards it would not have passed a signal. Maybe some noise but definately not any music.

Be sure to hook up the PS correctly. Make sure you know which hole is neg/ground on the board and which is pos. Use your meter to find pos/neg on the PS wires. Your caps are burned up and may even explode if hooked up backwards (dont get your face close). In my case the Jfets were fine. Really, the only things that can go bad are the Jfets and the electrolytic caps.

You can use any electrolytic caps rated 35V or greater (even 25V but that's pretty close). They do not need to be the same UF value...just in the same ballpark. Actually, you don't need the caps at all...if you are using a regulated SMPS. But I would put some in there.

You may get the "motrboating" even w/the SMPS hooked up right. Some are just noisy. I am using batteries (16 AA) which you may want to try.

 

[Hikari1]

And whoever told you DC has no polarity is either really misinformed or you misunderstood. It's possible that the discussion was about resistors or non-electrolytic caps which don't care which end is positive or which end is negative. In this case, polarity doesn't matter. But DC is by nature, polarized.

 

[MagnumOpus]

No, the wire that broke was one of the inputs. I resoldered it. But if I measured like stated in a couple of posts back, with the black on ground and red on positive, how did it play before? I read minus voltage that way...

Thanks for helping

You know, thos caps arent expensive, I think I'll redo all the wires, install new caps and then test it again. Or is there some other measurements I can do before taking it apart?

You know, I consider this a good thing. I learn more when things break I have a simple circuit to tinker with

 

[Hikari1]

Something bad is going on.

On the board, the hole closest to the edge is POSITIVE. The hole next to the PWR text is NEGATIVE.

Take the power wires off the board. Use the red lead of your meter to find which is positive. Make sure the leads are plugged into your meter correctly.

Attach one lead to each wire if the value is +ve then the red lead is connected to the +ve terminal if the displayed voltage is -ve its the black one (assuming you have connected the leads to the meter correctly).

Then put the positive lead in the right place on the board.

 

[harperrc]

if you look at the circuit board and find the C6 caps, the + side connects to resistors and the + side of the supply, the - side goes to ground. i don't have access to my board but it appears that the PWR label would be the - or ground side just looking at the picture in post 25 (r6 & r7 go to +)

sorry post #25 is correct i misread (guess i should only work when i am at work )