My first SHO

[wesman26]

Hey guys, I just finished my first real pedal last night.  It is/was a Z.Vex Super Hard On.  I'm following this wiring diagram to the T.  Everything looks okay, I don't have any cross connections as far as I can tell.  No cold solders either.  However, a problem seems to persist:  it doesn't really work.  As I understand it, the pedal is supposed to be a clean boost, but when it's engaged all I get is a buzz in the background and otherwise a very vague difference in sound that I can tell only when playing high notes (I'm playing my bass through it).

There is no noticeable difference in volume like I feel there should be, the buzzing is something I know shouldn't be there.  I just don't know what's wrong, can anyone help me?


EDIT
The buzzing might just be from using an ac power adapter, but I doubt it, because I don't get a similar buzz when I use it with other pedals.

[deadastronaut]

what pcb/vero  layout did you use?...or is it your own design?...

have you tried it on battery?

have you wired the 3pdt correctly?...does the led come on?...is there a clean bypass/off signal?

pics might help....

[wesman26]

I used my own layout because I figured it wouldn't matter.  It's done on perfboard.  I have not tried it on battery because I didn't buy any battery connectors (I figured I wouldn't use them anyway).  I'm certain the 3pdt is wired correctly.  The LED does come on, and I think the clean bypass is fine, it doesn't sound different enough for me to notice, but I can double check once I'm back home.

EDIT
Yeah the bypass sounds the same to me.  Everything is as it was though.  I follow the wiring diagram exactly as it shows, but I've seen some different ones floating around, maybe my wiring diagram is wrong?

[WGTP]

Mosfets, BS170, are notoriously fragile.  I messed one up the other day changing parts on my breadboard without removing the power first.  Have you tried a different transistor? 

[wesman26]

I haven't tried a different transistor, but I will now.  Do you suggest I put it in a socket instead of just soldering it straight on?

EDIT
Yeah I think I'm going to socket it, but before I go through all that hassle, do you know how to test it?

[Brossman]

As a DIY guy who lacks a good DMM , I find the best way (in theory...?) would be to Plug'n'Chug.  Stick it in that circuit, and use the meter...

- Are the pin voltages correct/reasonable?
- Are the pins oriented correctly??
- check for solder bridging - I've noticed sloppy technique galore on my (early) perf stuff.

BUT, that's just all off the top'o'me 'ead

[WGTP]

Definitely SOCKET Mosfets.  You may want to select for low noise, tone, bias, etc. 

[wesman26]

I've socketed it and the same effect persists.  There is no volume increase and no real notable change in tone.  I reversed the BS170 to see if that would change anything and it did, when reversed from what I think the pinout should be it produces no noise what so ever.  It's as if when the circuit is on the signal just gets grounded. 


Has anyone else had success with the wiring diagram that I'm following?  I don't want to rebuy the parts just to be disappointed again.

[Mike Burgundy]

Test the BS170 for pinout. There's several different ones out there, so make sure everything is connected where it is supposed to.
MOSfets are sensitive to static discharge as said (it can kill them easily), so it might be shot, or it might be in the wrong way round.
MOSfets are easy to test with a DMM luckily. Always handle the MOSfet by its case, don't touch the leads and beware of static discharge.
Touch the negative lead of your DMM firmly across *all* the MOS leads. This clamps them all to the same 0V and shuts the MOS firmly off.
Clip the - lead to the suspected source, and + lead to suspected drain. Should be infinite resistance. Touch the + lead to suspected gate - this, if the pinouts are correct, should turn the device on (puts a + charge on the gate in respect to the source). It will keep this state due to the incredibly high input Z of the gate. Measure SD agan - should be low, device on. Short G to S, device should be off. Keep GS shorted, switch around the + and - leads and verify the internal diode. All this verifies the MOS works, and it's pinout.
If you have the pinout absolutely right and it still doesn't work, measure and post voltages here, etc etc.

[wesman26]

Okay I've tested the BS170 and indeed, the pinout I was using was incorrect.  I've put the transistor in appropriately now and I still get the same problem as before when I reversed it which is no sound comes out what so ever.  What voltage measurements do you need?  I measured from the drain to the source and got about 0.6 volts...  I'm not sure if that's low or not.

[wesman26]

Nevermind, my original pinout was correct after a close second look.  Has anyone built this effect following the diagram I'm using and had any success?  Particularly when playing a bass through it?  The effect I get is nothing like what I expect.

With the transistor back the way it was I'm remeasuring voltages and get 6.23 Volts from Drain to Source on the transistor.

[Mike Burgundy]

Okay, the MOS works, and apparently opens and closes. Next step is bias and supply conditions - so measure voltages (against ground) as stated in the "what to do when it doesn't work" sticky/FAQ. Oh, and the rest of the info mentioned there.
Schem looks okay to me.
My guess would still be a shot MOS, but that tested ok, so...
You can get it to turn on (DS low) and off (DS high) by shorting GSD (for off) and touching G (for on) with your DMM lead right?

[wesman26]

Okay so here are some voltages I measured with the negative lead grounded.  (see the wiring diagram for numbering)

Q1: BS170
D: 7.81V
G: 0.74V
S: 1.59V

D1: 1N4148
A: 0V (it's grounded)
K: 0.75V

D2: 1N4148
A: 0.75V (it's connected to the cathode of D1)
K: 9.47V (it's connected to the power directly)

I'm not sure what else to check.  from the hot to the ground on the power supply the voltage reads 9.47V just as the cathode of D2.  Let me know if there's anymore you need.

Also thank you for being patient, I'm pretty new.

[Mike Burgundy]

Gate is way off. What does that measure without the MOS in the socket?
Gate should be at 1/2 Vdrain through the 2x 10M voltage devider.
If it measures Vd arund 9V, Vg 0.5Vd, Vs 0v without the MOS in there the MOSfet is not okay/wrong way etc.  Otherwise check for solder bridges (again), make absolutely sure you have the right value resistors and the diodes are both facing the *right* way.

[deadastronaut]

out of curiosity do you have a pic of 'your' layout design....it may be more helpful to the guys helping you with this.....?...

[wesman26]

My circuit is nothing special, it looks a lot like the wiring diagram I posted, even placement is pretty much the same.
My diodes are going the right way as is my electrolytic cap.  The resistor values have been triple checked again as well.  Vg reads 0.74V, Vd reads just above 9V, and Vs is 0V.

I've tried a brand new BS170 and yet again the same problem persists; the voltages are the same.

[Mike Burgundy]

And voltages without a MOSfet installed?
I think the question for the picture is very valid - often a tiny error will jump right out for a new set of eyes, while you have been looking at it for so long it's invisible. I've done that a lot....
Probably best to try and take several pics of both sides of the board, overview of connections, all in the sharpest detail you can get it.

*IF* the voltages are normal without the MOS in there, your pinout is definitely wrong.
The diode-drop between "g" and "s" also suggests that.

[wesman26]

And voltages without a MOSfet installed?

Vg reads 0.74V, Vd reads just above 9V, and Vs is 0V.

I'll post pics as soon as I can.

[Mike Burgundy]

Okay, without the MOS in there, Vg is solely determined by the voltage devider formed by R1 and R2 and can *only* be 1/2 Vd. This means it has to be either R1/2 value, D1/2 orientation or failure or wiring/soldering/shorts around those bits. Very slight chance one of the caps might be shorted. More inspection to do... if visual inspection doesn't help, move to measuring, for a start lift the diodes (one end is enough) and see what happens, etc etc. First get Vg sorted without the MOS in there.

[wesman26]

My DMM can't measure the resistance of the resistors (10M is about 8M too high for me to be able to measure), but I've checked the colored bands on them multiple times (Brown, Black, Blue, Gold, 5% carbon film, going off of this).  I also used the 2k Ohm / diode test mode to test the diodes.  With the positive lead on the anode and the negative lead on the cathode each diode reads about 670 Ohms.  With the leads reversed there is no reading.