POP goes the Mosfet Booster!

[David]

I gave my Mosfet Booster its trial run on Thursday.  It works great for boosting.  Unfortunately, it's popping like a bowl of breakfast cereal when I hit the stomp switch to bypass it or kick it in!  I've done my searching here, and was unable to come up with a definitive answer.  The information I can offer is that I'm using well-regulated 9VDC from an excellent power supply and I do not have a status LED on it yet.  I built it from the GGG component list -- no trim pot substituting for the 62K resistor.  One other piece of information is that the only other DIY pedal I currently use is a Muffer.  It does NOT pop when the footswitch is pressed, and it feeds the MB.  The MB is last in my signal chain.  Thursday, it was feeding a passive DI which connected to the church PA?

Would I be better off using an active DI instead?  I actually am thinking about that because I'm not sending a strong enough signal to the PA at the moment.  I was thinking of using my BlueTube as a final gain boost/active DI.

Are there any other tweaks I can do so this booster can finish its breakfast and stop popping?

[R.G.]

Use your meter to check for DC voltage on the input or output of the effect. You may have an input or output cap reversed and be leaking DC at the input or output, both of which would cause the popping. Or you could have a solder problem leaking DC onto the switching. Did you use pulldown resistors?

[David]

Thanks for the DC tip, R.G.  I had forgotten about that.  I'll definitely be getting the DMM out to check.  The caps are in properly -- especially the big one on the output.  As for the pulldown resistors, if they weren't on the GGG population diagram, they didn't go on the board (meaning I don't know if there are pulldowns or not).

[David]

Here's some additional information:

If I read my DMM correctly, I had fluctuating readings of 0 to 10 mV on the input and output connections of the PCB.  Changing the state of the bypass switch made no difference.  Also, in one switch state (I wasn't playing at the time), I had about 200mV on each bypass wire connector on the 3PDT switch.  I didn't use the GGG connection method, I used the method Aron diagrammed which shows the "bottom" left and right switch connectors bridged with a small wire.

Another note is that I had to replace the 100uF capacitor because one of its leads broke off.  The closest value I had was 10uF.  That's what's in there now.  These tests were made with the PCB and jacks not in an enclosure.

UPDATE:  I ran my guitar through the booster yesterday morning in this exposed condition to key voltage readings to switch pop noises.  I couldn't do it because the switch pops have gone away!  There's no noise at all, even with the PCB hanging naked to the wind.  Things were packed pretty tight in the old enclosure.  I wonder if I somehow created some kind of short when I stuffed everything in there.  I'm going to rehouse it in the old standby RACO box and see what happens.

[David]

Quote from Jack Orman regarding pull-down resistors on MOSFET Booster:

Don't put a pull-down on the front of the pedal.  Period.   Okay, put a 10M if you absolutely are dying to put one there but nothing else.

It is better to change the input cap to a non-leaky one that to put in the input resistor.

There is a drawing on the sheet of instructions that was shipped with the board on how to add the trimpot.  It is the pcb layout in the bottom left corner....  R2, 100k trim.  Just fit the legs of the trimpot in the 3 holes provided.  It doesn't matter which way the trimpot is turned, it's not polarized.

The trimpot has nothing to do with buffering.

regards, Jack

Uhhh, yeah.  I'm confused.  But I'm persistent enough to not let this go -- even though I could.  I'm still having some footswitch "thump"  happening.  It's not bad, but it's there -- and I don't want it to be.

OK, questions:

Could I be having thump occur because I substituted a 10uF capacitor for the 100uF on the output?  I have a 100 ready to pop in there, I just haven't had time yet.
What does the "leaky capacitor" comment mean?  Is there a way to measure this?  What would make a capacitor "leaky"?  Is there a type that I should or should not use?
Should I use the pulldown resistor(s) or should I not?
Finally, I recycled the 5K pot from another project.  It had lugs 3 and 2 already jumpered.  The GGG layout I used ran wires out to these lugs.  Since the booster basically works, I know this can't be a showstopper, but could it influence the popping somehow?  This is a one-second fix with wire cutters.

[rockgardenlove]

Quote from Jack Orman regarding pull-down resistors on MOSFET Booster:

Don't put a pull-down on the front of the pedal.  Period.   Okay, put a 10M if you absolutely are dying to put one there but nothing else.

It is better to change the input cap to a non-leaky one that to put in the input resistor.

There is a drawing on the sheet of instructions that was shipped with the board on how to add the trimpot.  It is the pcb layout in the bottom left corner....  R2, 100k trim.  Just fit the legs of the trimpot in the 3 holes provided.  It doesn't matter which way the trimpot is turned, it's not polarized.

The trimpot has nothing to do with buffering.

regards, Jack

Uhhh, yeah.  I'm confused.  But I'm persistent enough to not let this go -- even though I could.  I'm still having some footswitch "thump"  happening.  It's not bad, but it's there -- and I don't want it to be.

OK, questions:

Could I be having thump occur because I substituted a 10uF capacitor for the 100uF on the output?  I have a 100 ready to pop in there, I just haven't had time yet.
What does the "leaky capacitor" comment mean?  Is there a way to measure this?  What would make a capacitor "leaky"?  Is there a type that I should or should not use?
Should I use the pulldown resistor(s) or should I not?
Finally, I recycled the 5K pot from another project.  It had lugs 3 and 2 already jumpered.  The GGG layout I used ran wires out to these lugs.  Since the booster basically works, I know this can't be a showstopper, but could it influence the popping somehow?  This is a one-second fix with wire cutters.

Leaky means that DC is leaking through the capacitor.  It shouldn't.
Yes, use pulldown resistors.  I use them on both the input and the output.  On the input I usually use a 1m or 4.7m (better choice) and on the output a 1m most always.
The pot won't be an issue.

[David]

Leaky means that DC is leaking through the capacitor.  It shouldn't.
Yes, use pulldown resistors.  I use them on both the input and the output.  On the input I usually use a 1m or 4.7m (better choice) and on the output a 1m most always.

OK, I've built enough stuff to see that makes sense.  Then Jack's comment is tongue-in-cheek?  I was taken aback to discover this circuit didn't look like it had pulldowns.  That seems surprising since Jack has probably forgotten more about audio than I'll ever know...

[Processaurus]

 

OK, I've built enough stuff to see that makes sense.  Then Jack's comment is tongue-in-cheek?  I was taken aback to discover this circuit didn't look like it had pulldowns.  That seems surprising since Jack has probably forgotten more about audio than I'll ever know...

Jack's trying to keep the input impedance as high as possible (~10M).  Even putting a 10M pulldown resistor halves that. 

If you want to keep the input impedance high, but drain DC off the input cap, I think the volume pot on the guitar does that when its engaged, you could always ground the input when its bypassed, so the cap is only floating for the ms when the switch contacts are in the middle of getting switched.

Though it doesn't seem like it matters because guitars have a 250K-1M volume pot which is exactly the same thing electrically as the Mosfet boosters input impedance, a resistive load on the pickups.  So the guitar pot is making up 10 to 40 times the load on the pickups than the mosfet booster.

Another solution to popping is to leave the circuit on all the time, and use the footswitch to switch between boost and unity gain, that adds the benefit of the pedal acting as a buffer when the boost is off.

[burningwater]

dont mean to derail the thread but does anyone know of a BS170 with an internal zener from gate to source?

[amz-fx]

The pc boards that I sell have a place for the output pulldown resistor.

You can use a 10M pulldown on the input but it reduces the input impedance...   still quite high but it does have some impact. 

Maybe the LED current is causing the pop when it switches on?  http://www.muzique.com/lab/led.htm

-Jack

[David]

The pc boards that I sell have a place for the output pulldown resistor.

You can use a 10M pulldown on the input but it reduces the input impedance...   still quite high but it does have some impact. 

Maybe the LED current is causing the pop when it switches on?  http://www.muzique.com/lab/led.htm

-Jack

Jack, if I were to do this again, I'd just buy your board.  As it is, though, I have a completed effect that's functioning at about 97%.  I'd just like to get it the rest of the way, if I could.  I'm not using an LED right now because I wanted to get this popping stuff resolved before I introduced another variable.  As to the impedance, I'm not too worried about that.  Five meg input impedance is PLENTY.  Besides, the booster is at the end of my effects chain.  The signal it gets is probably nice and low impedance.

OK, now for the repairs.  I use Aron's 3PDT switching configuration.  Can I just put the pulldown resistors right on the switch poles?  If I were to power the booster from a 9VDC jack, would it be possible to just connect the pulldowns right to the (-) connector on the jack to ground them, or do they have to go to board ground?

Thanks!