SHO Debuggin

kurtlives · May 11, 2008, 05:28:05 PM

Damn it, such an easy circuit and I fudged it up.

Layout:

R1 and R2 are 3.3M....Is the layout saying saying I need 1M?

R3 is a pot to bias...10K.

I think I might have killed my transistor with static.

Voltages:
D: 8.26V
G: 6.81V then starts dropping, as it drops longer it slows down.
S: 6.81V then starts dropping, as it drops longer it slows down.

Thanks...

ambulancevoice · May 12, 2008, 01:56:50 AM

Quote from: kurtlives on May 11, 2008, 05:28:05 PM
Damn it, such an easy circuit and I fudged it up.

R1 and R2 are 3.3M....Is the layout saying saying I need 1M?

R3 is a pot to bias...10K.

I think I might have killed my transistor with static.

Voltages:
D: 8.26V
G: 6.81V then starts dropping, as it drops longer it slows down.
S: 6.81V then starts dropping, as it drops longer it slows down.

Thanks...

r1 and r2 can be either 1M or 10M (both r1 and r2 being the same value, not "one is 1M and the other 10M")
the 3.3 you used has probably mis-biased the fet
most of the schematics ive seen have the 10M resistors
i dont know what differences they have but yeah

also, the bs170 is very static sensitive, so if its not handled properly, you will fry it

Jered · May 12, 2008, 02:39:30 AM

Swap out your BS170, I think yours is toast. If memory serves, you should be getting 2-3 volts at the gate, .7 - 1.7 at the source depending on gain knob setting, and at the drain about 7.5 volts at minimum gain setting and around 4.5 volts with the gain maxed.
Jered

flo · May 12, 2008, 08:26:38 AM

Try the following thread for some more voltages and such:
http://freestompboxes.org/viewtopic.php?f=7&t=8

kurtlives · May 12, 2008, 11:38:31 AM

Ok thanks guys...any tips for handling the BS170 without destroying it?

There are all in a zip lock bag,

ya I know.

flo · May 12, 2008, 05:44:55 PM

I always try to get rid of any static voltage buildup by touching a radiator or other earth point near my workbench.

Jered · May 12, 2008, 05:54:14 PM

If your just going to swap one for another, just touch something metal that's grounded before you handle the BS170. If your going to be tweaking a circuit for any amount of time, get yourself a grounding wrist strap. They're cheap.
Jered

kurtlives · May 12, 2008, 11:37:05 PM

Ok thanks guys...I replaced the 3.3M with 10M today and still no sound.

I will try this static removal trick.

Thanks

ambulancevoice · May 13, 2008, 01:40:23 AM

Quote from: kurtlives on May 12, 2008, 11:37:05 PM
Ok thanks guys...I replaced the 3.3M with 10M today and still no sound.

I will try this static removal trick.

Thanks

keep the 10M in there
you can buy anti static wrist bands which usually connect to a anti static mat or some kind of earth connection

dxm1 · May 13, 2008, 10:51:00 PM

And while your body is electrically connected to earth, you'll want to be weddddyyyy wedddddyyy kehfole touching anything connects to your mains - light switch, soldering iron, anything plugged in. ESD prevention is a beautiful thing, but opens you up to many more chances to get zapped.

earthtonesaudio · May 13, 2008, 11:07:08 PM

Touch some plumbing to ground yourself. Shuffle across carpet to build up charge again.

kurtlives · May 13, 2008, 11:10:37 PM

I do wear slippers and the floor is carpet hehe

zachary vex · May 14, 2008, 05:08:07 AM

Go barefoot.

gez · May 14, 2008, 07:19:15 AM

...in the park...

R.G. · May 14, 2008, 10:09:07 AM

It's almost impossible to get static electricity when the humidity in the air is high.

So make it high. Go into your bathroom, turn on the shower with hot water. When the air starts feeling steamy, you can solder in MOS parts without problems.

MikeH · May 14, 2008, 10:46:10 AM

I don't know if it's just that I don't carry much static, but I've handled about a trillion BS170s with my bare hands, without grounding myself, and all the while keeping them in a plastic bag. I guess I'm just lucky. I've even found one that had been kicking around on the floor and it still worked. Ooops! I forgot, nobody likes a braggart.

earthtonesaudio · May 14, 2008, 06:48:49 PM

Quote from: MikeH on May 14, 2008, 10:46:10 AM
I don't know if it's just that I don't carry much static, but I've handled about a trillion BS170s with my bare hands, without grounding myself, and all the while keeping them in a plastic bag. I guess I'm just lucky. I've even found one that had been kicking around on the floor and it still worked. Ooops! I forgot, nobody likes a braggart.

Same here! That is, until recently when I fried one inverter out of a 4069. First time ever (even in winter), and I'm always shuffling across the carpet in wool/acrylic socks!

I guess us Midwesterners are blessed/cursed with high humidity. $:-\$

kurtlives · May 17, 2008, 11:22:08 AM

Ok...I tried a J201 cause they are less sensitive to static. I got audio now but it was very low volume, it was also bassy and farty.

Also I get continuity between lugs 3 and 2 of the "PCB" mounted pot. I cut the trace and it looks fine. Is that soposed to happen?

jayp5150 · May 17, 2008, 12:43:36 PM

Quote from: kurtlives on May 17, 2008, 11:22:08 AM
Ok...I tried a J201 cause they are less sensitive to static. I got audio now but it was very low volume, it was also bassy and farty.

Also I get continuity between lugs 3 and 2 of the "PCB" mounted pot. I cut the trace and it looks fine. Is that soposed to happen?

You mean 0 ohms? If the pot is all the way up, then that's correct, as lugs 3 and 2 are connected. If it's all the way down, you should have 5k of resistance between them.

Also, keep in mind that the J201 and BS170 have different pinouts.

Flat side up, the J201 is DSG, and the BS170 is DGS. Double check your datasheets, but the ones I have are those pinouts.

kurtlives · May 17, 2008, 12:45:14 PM

I wasn't measuring resistance I was seeing if their was continuity.

I check the datasheets but I will try flipping theJ201.

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