AMZ mosfet vero problems

[upspoon12]

Hey guys,

am trying to get the vero layout for the amz boost to work but im having a really rough time with it.

i am using the layout found here:
http://www.diystompboxes.com/smfforum/index.php?topic=75135.0

I had it sounding great in bypass however when i engaged it there was a HUGE pop and then the signal was VERY very very quiet, almost negligible. As read in another topic on this forum, i tried spinning the mosfet (it was oriented correctly to begin with.) when spun, it was louder, however the pot had no effect on volume and there was a very high pitch whine almost up in the 10-13khz range constantly when engaged.

the only deviation i have from the layout above is i do not have the .001 uf Capacitor.  i only have . 047pf, 47pf, .1uf, 10uf and 100 uf  (the ones required for the newer version of the PCB version of the amz mosfet boost) which uses a .047 pf input cap.

A couple voltages to help paint a picture:

Input from batt 9.23v
Mosfet
D: 6.23v
G:4.99v
S:2.99v

But any help with this would be greatly appreciated. My musician friend needs the pedal for a show tonight if i can get it done for him.


Thanks again in advance guys!!!

[upspoon12]

Here are a couple photos.
i realize my solder work isn't the cleanest, but i've tested it with the continuity tester and there are no busses that are connected to each other via a solder bridge and i have gone over the spaces inbetween tracks with an exacto to ensure there is space between legs and that nothing is touching.

At the moment i have a 47pf in the place of c1 which should be a .001uf but i don't have this.

[Kipper4]

The Jelly bean looks back to front according to the vero layout? Could just be my eyes
Did you rock it before you boxed it?
Have you audio probed it?
Why not go to the debugging thread  and go though some of it and report back too mate?

[upspoon12]

if by jelly bean you refer to the transistor, i have tried it both ways, i used the BS170 and the pinout is actually correct the way it is in the board in the photos.
If you look at the pinout on the layout up there its backwards to the pinout of the BS170.

don't have an audio probe put together yet, thats certainly on my to do list.

[Kipper4]

I stand corrected.

[upspoon12]

That was my first mess up in this mess of trying to figure this out, quite frankly i'm suprised i caught it.

Voltages at the zener diode:

Cathode: 5.15v
Anode: 3.15v

[~arph]

Are you sure that you have a 10M resistor there? From the pics it looks like a 10 ohms resistor

[upspoon12]

Yes it is definitely a 5% 10M ohm resistor.  I just double checked it.

[~arph]

Ok good, voltages seem to indicate that as well..

[amz-fx]

Note that in the vero layout linked in the first post, the BS170 pinout is not correct and therefore the mosfet should be rotated 180 degrees.

If you heard a big pop after it was working correctly, then it sounds like maybe a fault in the bypass wiring has blown the mosfet when switched. You probably need to replace the BS170 and double-check the bypass wires.

regards, Jack

[~arph]

And use a socket for the mosfet this time. It can also be damaged by overheating when soldering.

[duck_arse]

you can't use 47pF for C1. C2 is also 47pF, so you have a voltage divider there cutting your signal in half.

i only have . 047pf, 47pf, .1uf, 10uf and 100 uf

if your ". 047pf" is really .047uF/47nF/47000pF, use it until you get a 1nF, otherwise use the 100nF/.01uF to get it working.

and never trust a layout you haven't drawn yourself, becuse when you draw it, you always check the datasheet, so you know the part you have is the right way round (and there is only one right way with the mosfet).

[upspoon12]

Hey guys,

I actually caught the pinout being incorrect on the data sheet and have it the right way around. I noticed that i didn't have a .001 uf cap for the input as duck arse said( i spent a while trying to do the math to make the filter work but just ended up scouring for the proper cap, so i did in fact track down a 1uf cap in an old piece of equipment and swap it out. its electrolytic. I rebuilt the circuit and i did socket the fet this time. Now i still get VERY high pitch noise on the line when the circuit is engaged and the pedal is working the way its supposed to. but the noise is loooud. Any thoughts?

Once again i appreciate your input everyone!