Author Topic: NPN Boost switch popping wont go away  (Read 8625 times)

zeestar

NPN Boost switch popping wont go away
« on: March 01, 2010, 04:51:11 PM »
Hi, Ive successfully built the NPN boost pedal , apart from one problem. The pedal 'pops' when it is switched on. Ive searched through this forum, and tried many things, but i cant seem to get anything to work. As soon as i remove the LED the problem is solved ??
I really want to use a LED on this project. Ive tried the pulldown resistors, as described in the wiki, on the input and output of the circuit board (1M), no luck , Ive swapped out the input cap, tried 3 different makes !! no luck,, tried pulldown resistors on the input and output sockets, no luck.
Any idea where I'm going wrong ??


aron

Re: NPN Boost switch popping wont go away
« Reply #1 on: March 01, 2010, 05:57:37 PM »
Are you wiring the switch the same was as on the pictures in this forum? Can I see a picture? What type of LED and what resistor value?

zeestar

Re: NPN Boost switch popping wont go away
« Reply #2 on: March 02, 2010, 08:50:18 AM »
Hi Aron

Ive wired the switch as per the picture here on the forum , the LED Ive used is here :
https://www.rapidonline.com/productinfo.aspx?&tier1=Electronic+Components&tier2=Optoelectronics&tier3=5mm+LEDs&tier4=5mm+Oval+high+power+LEDs&moduleno=82709&catref=55-2194

Ive tried various resistors from 1k to 6.7k , the popping is always the same in either case. The pedal is running from battery , I'm still waiting for my DC sockets to turn up. But like i said, as soon as the LED is taken out, the popping disappears.

aron

Re: NPN Boost switch popping wont go away
« Reply #3 on: March 02, 2010, 11:28:41 AM »
Very strange. Do you have a multimeter? With the LED in, try measuring the DC voltage from ground to the signal input and the signal output and see if you have DC on either one.

zeestar

Re: NPN Boost switch popping wont go away
« Reply #4 on: March 02, 2010, 03:39:56 PM »
Tested with a multimeter, there is no voltage across the input or output ... I tested voltages on the circuit compared to the picture on the forum ... these seem to be  OK .. would the LED and resistor used alter these voltages ?? I seem to have less voltage on the collector side of the transistor, about 5.4v and more on the emitter side, about 2.3v.. Would this make a difference?
Would a different value input cap make a difference ?

aron

Re: NPN Boost switch popping wont go away
« Reply #5 on: March 02, 2010, 05:42:40 PM »
I don't know what it is. I have built several of these units and none of them exhibit loud pops. Usually the culprit is DC on the output, but in your case it's not. So it is the current from the LED that seems to be causing it. Here are R.G.'s comments on this matter (from the Wiki).

http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ#POPS

zeestar

Re: NPN Boost switch popping wont go away
« Reply #6 on: March 02, 2010, 06:26:25 PM »
Thanks Aron, when he mentions 'cold switching' using a PNP .. is that the millenium bypass ???

aron

Re: NPN Boost switch popping wont go away
« Reply #7 on: March 02, 2010, 10:28:35 PM »
I think he's referring to this schematic and how it's handled:

http://geofex.com/FX_images/oaspltr.gif

zeestar

Re: NPN Boost switch popping wont go away
« Reply #8 on: March 03, 2010, 06:12:17 AM »
Are you referring to this part of the circuit ?



aron

Re: NPN Boost switch popping wont go away
« Reply #9 on: March 03, 2010, 11:41:31 AM »
Yes, from what I read, I believe so. I have to point out that I have never had this bad pop with this circuit which leads me to think that maybe something else is wrong. Do you have a picture of your circuit?

zeestar

Re: NPN Boost switch popping wont go away
« Reply #10 on: March 03, 2010, 04:33:30 PM »
Hi Aron

I think ive solved it ... i rewired the switch like this
https://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_battery.gif
and it seemed to solve the problem... strange lol .

aron

Re: NPN Boost switch popping wont go away
« Reply #11 on: March 03, 2010, 09:39:11 PM »
Hey thanks for the tip. I did momentarily think about rewiring the switch, but I have never had to do that.

zeestar

Re: NPN Boost switch popping wont go away
« Reply #12 on: March 04, 2010, 05:17:16 AM »
Thanks for the help Aron, very much appreciated. :)

aron

Re: NPN Boost switch popping wont go away
« Reply #13 on: March 04, 2010, 03:12:45 PM »
Thank you for building the beginner kit.

aron

Re: NPN Boost switch popping wont go away
« Reply #14 on: March 11, 2010, 12:58:46 AM »
More on this. I've been checking some things out. If you run DC only then try connecting the ground wires from the LED to the output jack instead of input. Try using a pull down resistor at the front of this circuit. Clean your input jacks, it does make a difference. If you use an active preamp in your guitar, you can add 10K series resistance to the input  of the effect and this seems to reduce popping even further.
« Last Edit: March 25, 2010, 06:57:33 PM by aron »