AMZ Mosfet Boost - DEBUG data and pop assistance?

[2x6L6]

Hi all - first post - yah, newbie! First build was a GGG Rangemaster, and loved it! Next I did an AMZ Mosfet boost (using Jack's boards), but have a couple lingering questions.

1. How to get rid of the pop when the pedal is engaged? I have thoroughly searched the forum here and found a number of different suggestions, but no definitive "this is how you fix that pedal's pop." it looks like it has a resistor (R7, 1M) at the output that is designed to eliminate the pop. Yes? I also saw an article by Aron that says put a 1M resistor from tip to sleeve on all jacks - is this worth adding to this pedal? Adding other resistors elsewhere on the board will be difficult, I think... Anything else I should try? I love this pedal - it is exactly what I have been looking for in terms of boost, but the pop is a drag.

2. So far so good on bias - I have completed 2 of the 3 I am building for some guitar-playin' pals of mine - but I would like to know how to solder in a trim pot just in case I get a pesky transistor that doesn't bias with the stock values. What to do with 3 legs of the trim pot on a board with only two holes for the resistor it is replacing? Somehow tie the wiper and the spare leg together? I've searched the web far and wide and can't seem to find a simple "how to wire in a trim pot" tutorial.

3. Final question (for now!) - One of the 3 boosts does not work. It bypasses the signal fine, but produces no signal when engaged; interestingly it also pops when switched on AND off. I have checked and re-checked the wiring. I have checked the BS170. I thought I might have cooked the 3PDT switch (I'm used to soldering amps and have had to learn a lighter touch!) so replaced it and still no signal. In measuring the voltage at the bias test point I get 6.5 vdc even AFTER I removed the bias resistor (I was going to stick a trim pot in to mess with the bias...) - so obviously have some other stuff going on. Is the zener diode a pretty sensitive part as well? I am wondering if maybe I cooked it when I soldered it in... The rest are pretty basic parts that I don't think I damaged nor do I suspect them of being bad (I know, suspect ALL!). Any thougths on what is the most likely part to fail, particularly in this circuit?

Thanks so much - I've been lurking for some time now and have been learning tremendously from folks on this forum.

[d95err]

Hi all - first post - yah, newbie! First build was a GGG Rangemaster, and loved it! Next I did an AMZ Mosfet boost (using Jack's boards), but have a couple lingering questions.

1. How to get rid of the pop when the pedal is engaged?
[...]

2. So far so good on bias [...] I've searched the web far and wide and can't seem to find a simple "how to wire in a trim pot" tutorial.

3. Final question (for now!) - One of the 3 boosts does not work. [...]

1. Yes, try the resistor to ground on the input jack. It's easy to do and easy to remove if it doesn't work.

2. The easiest solution is to socket the resistor. Cut up an IC socket to get two 1-pin sockets. Now you can easily try out different values. It's difficult to insert a trimpot in place of a regular resistor. You could solder two wires where the resistor would go, attach the trimpot in the other end and keep it beside the PCB somewhere (make sure it's isolated so it doesn't touch the chassi).

3. Read the "What to do when it doesn't work" thread and post the corresponding voltage measurements.

[2x6L6]

Thanks for the reply!

2. The easiest solution is to socket the resistor. Cut up an IC socket to get two 1-pin sockets. Now you can easily try out different values. It's difficult to insert a trimpot in place of a regular resistor. You could solder two wires where the resistor would go, attach the trimpot in the other end and keep it beside the PCB somewhere (make sure it's isolated so it doesn't touch the chassi).

Actually, the trimpot fits the board pretty well - I wasn't sure what to do with the 3rd leg - can it just be soldered to the wiper?
I like the socket solution.

3. Read the "What to do when it doesn't work" thread and post the corresponding voltage measurements.

Will do (later today, after work). Meanwhile, for general reference, is the diode the most likely part to be "bad" in a given circuit (particularly as the result of heat exposure?)? I guess I'm trying to ask, "How easy is it to damage the diode when constructing these circuits?"

Thanks for the help!

[nelson]

The thing most likely to go wrong in this circuit is the BS170, they are prone to fail due to static. The diode is to protect the mosfet when in circuit.

[2x6L6]

The thing most likely to go wrong in this circuit is the BS170, they are prone to fail due to static. The diode is to protect the mosfet when in circuit.

Hmmm - IIRC, I checked the BS170 first - but I'll re-check when I take voltage readings later today. Is it easy to damage the diode when soldering?
Thanks!

[d95err]

Actually, the trimpot fits the board pretty well - I wasn't sure what to do with the 3rd leg - can it just be soldered to the wiper?
I like the socket solution.

You can simply cut off the 3rd leg, but for best reliability tie it to the wiper.

Meanwhile, for general reference, is the diode the most likely part to be "bad" in a given circuit (particularly as the result of heat exposure?)? I guess I'm trying to ask, "How easy is it to damage the diode when constructing these circuits?"

Part failures are quite unusual. Some of the things that most often go wrong for me are:

* Something touching the chassis and accidentally grounding the signal
* Wrong part in the right place (100R instead of 100k resistor...)
* Bad solder joint
* Accidental solder bridge
* Wrong transistor pinout
* Forgot to add a part or a wire (duh!)

The only parts I have had fail were some very cheap plastic pots and a germanium transistor that shattered when I bent the leads. Oh, and an LED burnt after I forgot to add a current limiting resistor. I've never managed to destroy components by solder heat or too high voltages. Start by checking for accidental grounding and resolder any joint that looks even remotely suspicious. I'm no expert, I've only built about 10 stompboxes, so I'm sure more experienced forum members can share more about which parts are likely to fail.

Silicon diodes are usually very robust and I've never heard of one failing. (OK, on the ax84 or 18w forums, people have had rectifier diodes fail in tube amps at very high voltages...)

[2x6L6]

I'm back - and thanks so much for all the input so far.
I went throught the "What to do when it doesn't work" thread and here are the measurements and data:
1. Pedal bypasses signal fine, but produces no signal when stomped on. LED works; pedal 'pops' when stomped on and off. [I have built 2 others of the same circuit that work (except for the pop I can't get rid of!).] This 'dead' one - the bias point (R4) = 9.5 vdc, and does not change bias voltage when I add a trim pot or even remove R2, the bias resistor - this is telling me something obvious but I am having trouble grasping it.
2. AMZ Mosfet Boost
3. Built with Jack's boards and parts from SBE
4. No mods.
5. No substitutions.
6. No PNP/NPN conversion.
7. Battery voltage: 9.51
- Red battery lead at circuit board (red goes to the DC jack = 9.51vdc); the '+9v' lug on the board = 9.51 vdc
- Black battery lead at circuit board (black goes to the input jack ring = 0 vdc); the 'out' lug on the board = 8.31 vdc

Q1 (BS170)
D= 9.52
S= 8.95
G= 9.50

Z1
A= 8.92
K= 9.46
I suspect the Zener, but am not sure why? I don't have a spare 9.1v - too far to Anchorage these days. I do have a 12v and 5.xv I got from the Shack.
-------------------------
Now, regarding the pop - (the two working pedals only pop when kicked on, BTW) again, I have attempted to research this on the forum here and gleaned a few ideas but no definitive solution. I have tried:
- 1 meg resistors from tip to sleeve on both jacks - no help
- 10 meg resistors from tip to sleeve on both jacks - no help
- (1) 10 meg resistor from board input pad to sleeve of input jack - that seemed to eliminate the pop unless you stomp it back on right away, --- progress, though!
- then tried (1) 1 meg from board input pad to sleeve of input jack, thinking the 10 meg was too slow to drain, and it seemed to work perfectly until I turned the amp up, then didn't really seem to work at all ------- in fact seems to pop when kicked off now as well, so I suppose I knocked it out of whack.
So I am not sure where to go next - a 2.2 meg, or back to the 10 (never tried the 10 with a loud amp...) I do really like this pedal but have to solve the pop issue!

Any help on: A) the dead pedal, and B) the 'pop' is of course graciously appreciated.
Thanks,
Jim