Problems with my boost

[firethorn]

There seems to be a problem with my AMZ MOSFET booster.

I followed the schematics on muzique.com to the tee as it was my first pedal with electronics inside. It did not work. I finally decided to rebuild it using tonepad.com's schematics (as they seemed clearer) and also switched out the BS170 in Jack Orman's schematics for a 2N7000 and for a very very short while, there was sound. (I later concluded that the BS170 was indeed in the correct position and was working correctly with my ohmeter but I still do not know why it did not work).

For that period of time, when the pot had no resistance, the sound was loud and obviously vice versa. But after turning off the amp for a bit and then trying again. There was no sound.

So I started fiddling around with the connections on my breadboard and there was still no sound. Till I discovered that by touching the opposite end of the 47pf cap in the schematic on the side opposite the one that connects to ground for a few seconds and then shorting out out the end of the .001 cap that is on the board with the end of the 2k7 resistor opposite that which touches the ground, again with my finger, sound would come out for a short while but it was very soft and would slowly fade out to nothing.

I also discovered that a similar effect could be achieved in the first few seconds of turning on the amp and from the point I switched off the amp to the point, I assume, the power in the amp's caps were depleted.

I assumed this was a problem with my caps but even after changing out all of them, the problem remained.

Does anyone have any idea what is happening?

[geertjacobs]

Check the "What to do when it doesn't work thread".
Probable causes:
- Mosfet orientation wrong: check datasheets and try different possibilities
- Mosfet dead ( they're very sensitive to electrostatic discharge)
- Mosfet not biased right (check and post voltages)
- something else: use audio probe

[firethorn]

Check the "What to do when it doesn't work thread".
Probable causes:
- Mosfet orientation wrong: check datasheets and try different possibilities
- Mosfet dead ( they're very sensitive to electrostatic discharge)
- Mosfet not biased right (check and post voltages)
- something else: use audio probe

Of course I've done that and read that thread. Which is why I've pointed out that I'm sure the MOSFET was oriented correctly and was not dead. It was a recommended alternative so I would think it's biased right.

Which is why I'm wondering what else could be causing the problem.

I've changed out the 2n7000 for a new bs170 again.
Drain source is 9.45V
Gate source is -0 to -0.22V

[petemoore]

  I believe you have an FET, the three leads on an FET are:
  The Drain [Output in the case of a booster]
  The Gate [input]
  and  Source
   And if your drain is at 9.45, and your power supply is 18vdc ok, if the PS is more like 9.65vdc, there's no room for it to swing any much more positive.
  It should probably be sitting at about 1/2v of supply voltage, the only way to make such an equation is by knowing the supply voltage...
  Everything is required, everything shown on the schematic must be represented by the circuit on the board, when that happens the circuit Has to work.
  The debugging thread makes it much easier for us to locate problems on circuit boards.

[firethorn]

oh dear. my PS IS 9v. Well 9.5ish actually (First time trying these roland batts. First time I got a rating above 9.)

1. Tonepad AMZ MOSFET
2. http://www.tonepad.com/project.asp?id=30 (Not the OLD one. the 69.5KB one)
3. It's on a breadboard. Everything is there except the mills bypass which is everything past the 2k7 resistor on the +9V line up till the switch with the output. Also missing is the bottom-most line which connects the output and input signal grounds. the 9.1Zener is reversed biased with the black band facing the transistors source. I believe this is right (even though it doesnt make sense to me on a standardised symbol issue) because of a previous board i built. In this 3rd rebuild (essentially the same but just doubled checked all the wires and resistors and stuff), I removed the 47pf paper cap as I recall Jack Orman's schematic saying it was optional. The .001 cap is single ceramic and the 0.1 is a metalised plastic film cap. -9V and the input's sleeve are shorted directly on a mono plug (the female one).
4. "Yes, I did a google search on that part number and check the pinout against how I soldered it in." haha.
5. It's an NPN.
6. And after rebuilding, NO sound comes out at all. I'm tearing my hair out.

With the black lead on the battery's neg end (ground):
-) +9V of circuit board is +9.5V and on neg end of the circuit board end it's 0V
-) This schematic that I'm following does not label the resistors and stuff.
-) +9V end of the 62k reads +9.5, opp end reads 5.65V. This end splits into the 10uF cap and the 100k resistor. The opp end of the cap reads 0 and the opp end of the 100k resistor reads 0v.
-) All points on ground read 0V.
-) The other resistor on the +9V line on the schematic reads +9.5V on the +9v side and +9.49V on the other end.
-) On the drain end of the transistor, it reads +9.49V and also obviously the end of the 0.1 cap that connects these resistor and the transistor also reads 9.49.
-) Everything else reads 0V.

There is no DC voltage on the electrolytic caps so I don't know if the debug thread is asking me to measure in AC.

[ayayay!]

Time to build an audio probe then, even if it is on a breadboard. 

http://www.storm-software.co.yu/diy/index.php?project=audio_probe

[firethorn]

I left out the 100nF because I don't have it and I assume it's only for the popping sound.

One end of the probe is connected to the output tip and the other end is the probe. Sounds comes out only immediately after the 0.001 cap. There is no sound anywhere else. That seems pretty bad.

[geertjacobs]

It's better to replace the 100nF capacitor by a different value (47nF,220nF,...) than omitting it.
The ground of your probe needs to be the ground of your effect pedal.
With the other side of the probe, you start at the input plug to find the signal and then you move your probe further down the schematic to find a place/node where you expect a good signal and find something else.

ps. you probably have already read it, but there are biasing instructions for the Mosfet booster over here.

[plankspank]

     From your description, it appears the MOSFET is either dead or not biased correctly. Are you sure you have the zener polarity installed correctly? check it with an ohmmeter, (or take it out of the circuit temporarily, it's only for static protection). 
     As a previous post correctly states, MOSFET gates are extremely sensitive to static charges and are easily blown. Always leave them in their protective anti-static bag prior to installing them; right before handling them for install, always discharge yourself by touching a grounded water pipe or similar earth ground....

[firethorn]

It's better to replace the 100nF capacitor by a different value (47nF,220nF,...) than omitting it.
The ground of your probe needs to be the ground of your effect pedal.
With the other side of the probe, you start at the input plug to find the signal and then you move your probe further down the schematic to find a place/node where you expect a good signal and find something else.

ps. you probably have already read it, but there are biasing instructions for the Mosfet booster over here.

Yep. That was where I originally got the schematics from. But if the audio probe is connected to the ground at one end, how will probing close the circuit in a manner it links with the audio output?

     From your description, it appears the MOSFET is either dead or not biased correctly. Are you sure you have the zener polarity installed correctly? check it with an ohmmeter, (or take it out of the circuit temporarily, it's only for static protection). 
     As a previous post correctly states, MOSFET gates are extremely sensitive to static charges and are easily blown. Always leave them in their protective anti-static bag prior to installing them; right before handling them for install, always discharge yourself by touching a grounded water pipe or similar earth ground....

I removed it entirely in my second rebuild but still did not work.


I've just removed the zener again and replaced the transistor with a new one and finally it worked. The pot had a very bad curve but it worked and aside from bad audio quality which i'm attributing to the breadboard, I just can't believe my chances in that I now have 7 possibly dead transistors. I'm pretty sure I handled them right.

Thanks again for all your help guys.

Will post up something if I can find out anymore.

[firethorn]

The Zener was shorting!!!

>.<

But so far at least 2 of them are working. Horrible horrible.

Thanks guy for all the help. Case closed. =D

[rogeryu_ph]

Is there a hiss sound when you volume up your AMP? Mine is terrible
I already built the pedal and found out later, that is why I breadboard it again but  still have the same result

Roger

[petemoore]

It's an NPN.
Is this an answer to '#5'?
  If the question is about 'what transistor', NPN isn't a mosfet...

[firethorn]

Is there a hiss sound when you volume up your AMP? Mine is terrible
I already built the pedal and found out later, that is why I breadboard it again but  still have the same result

Roger

Currently yes.

I'll double check it when I rebuild it again with proper stuff.

[rogeryu_ph]

Thanks I'll wait for your feedback
Roger