Adding LED and PSU filter to DIY Electra Distortion

[Tom9979]

Hi everyone. I am sorry if this is a simple question but I have tried to find the answer and have become quite confused. I have breadboarded an Electra Distortion based on the instructions by Joe Gore of Tonefiend, but before I box it up I want to add an LED. I have read a lot about switch popping caused by LEDs so want to incorporate something to prevent that into my final design. I have found a schematic that seems to do what I am asking at http://www.muzique.com/news/connecting-an-led-to-an-effects-pedal/ by simply adding a diode and a 100uF electrolytic cap after the LED but whilst I have been reading about this, I have also come across people complaining about noise created by radio interence and poor mains PSUs as well as the problem of reverse polarity so I am hoping to also incorporate some sort of noise/interference into the design. The one I have found is at http://www.beavisaudio.com/techpages/Caps/ under 'Power Supply Filtering' although it suggests splitting the voltage at the end which I don't think I need to. I should say that I would prefer to use DC over battery in my pedal due to the cost of replacing batteries and having to remove them from the case.

My question is basically, do I need both circuits and if so, do they literally bolt onto each other. My thinking is LED connected to PSU Filter connected to Electra Distortion. Is this right? Could I simply add a 100R resistor and a 47nF capacitor to the LED circuit (resistor after the diode and 47nF cap to ground after (parallel to) the 100uF? My basic knowledge thinks this would work but I need some clarification.

Thanks

Tom

[Transmogrifox]

This is good for the power supply filtering (your link at beavisaudio) but the LED connection is exactly what Jack says is bad.  In all other regards this is basically the same as the AMZ example.


Connect the LED indicator according to this:


Use AMZ circuit as your example of LED connection and PS filtering.  Then for the RF rejection just add a good ceramic 47 nF cap.

If you want reverse polarity protection I recommend this instead of the beavis example if you're using a DC supply input:



Then just at a 47 nF in parallel to the 100 uF and you're set.

[Tom9979]

Thank you so much. It makes sense when you put it in writing with the images. I will add this to my circuit on the breadboard to test it.

[duck_arse]

that led wiring will indicate power-good, not fx bypass state. was this the intention?

[Tom9979]

I was after an LED that indicated whether or not the distortion was turned on. Would I not be able to wire the LED to the switch to cut power to the circuit when turned off?

[Kipper4]

Sure you could do that just google. Tonepad offboard wiring. I like #5.
Welcome to the forum too.
Beavis audio has some examples of offboard wiring too. I found them both most helpful when i first joined.

[SuzukiScottie]

Several options for led indication of effect on/off status. As mentioned above, Google for off board wiring; you'll get lots of images of examples of how to switch the led on and off. 3pdt switches are pretty much standard, with one of the 3 poles doing the led switching. Also Google millennium bypass for some info on switching using a dpdt switch. Interesting stuff to read up on.

[Tom9979]

Thanks for the info. I've looked at millennium bypass and that might have to wait for another build as it looks quite complicated. I found this image (http://1.bp.blogspot.com/-k5Sh68yVU18/TzGRFKbiALI/AAAAAAAAAlk/CbfaaduUjYQ/s1600/!Offboard+wiring.png) which looks close to what I'm after. I understand how the signal flows when then switch is in both positions however I am unsure how I would add the LED, diode and capacitors that all run to ground and still maintain the function of using the LED to indicate effect on and off. Am I looking at needing a switch that has more poles like a 4pdt for the example by Transmogrifox or can it be achieved using a 3pdt? Thanks.

[Tom9979]

In fact, am I over thinking this? Is the solution to simply add the  additional components in parallel with the resistor and LED and just connect all the grounds to the same pin on the switch? In my mind I am thinking a second small piece of vero with the components connected from +9v to ground and that way I would only need one wire actually connected to the switch pin? Does this sound right? Thanks.

[Kipper4]

You would only need a 3PDT to do true bypass switching with effect on LED indicator.
In the diagram you linked to when the switch is in the upper position the LED is on and so is the effect input and output.
no need for a 4pdt to include an indicator led.

Aron has a handy guide too here

http://www.diystompboxes.com/smfforum/index.php?topic=970.0
Hope it helps

[acehobojoe]

What good is the 47nF in the power supply example Transmogrifox?

[Tom9979]

Thanks Kipper, there's some really good info in there. So, using a 3pdt switch with the input connected to ground when the switch is "off" is the best way of connecting a switch and effect on/off LED to minimise pedal pop or would a pull down resistor still be a good idea? Am I being overally cautious or would a simple LED and resistor in series be adequate? Thanks.

[Kipper4]

Kind of.
The capacitor in the power supply are there to reduce ripple from the wall wart. Especially when using an unregulated wall wart.
The smaller cap 47nf does something similar but for the higher freqaucies. I believe it's called a Miller cap. They are even sometime pico farad values too.
Correct me if I'm wrong fellas. Im here to learn too.
The series resistor between the +9v and led is a currant limiting resistor. Commonly referred to here as a CLR.
It's role is in the name and will stop the LED burning out your eye balls and burning out. Does nothing for switch pop as far as I remember.
The LED should not make the pedal pop if you are wiring as in the tonepad diagram 5 off board wiring.
You will probably be wise to put a 1m resistor (R pop) on the input to reduce switching pop.  As close to the input as possible.
I do it as a matter of course now.
I hope I got most of this right and it helps

[Transmogrifox]

What good is the 47nF in the power supply example Transmogrifox?

Large-valued electrolytic capacitors don't have very good high-frequency performance.  They usually have a self-resonant frequency from several MHz to 30 MHz.  Above 30 MHz they look like an inductor and aren't of much use for filtering RF noise coupled in from antennas and power lines and any other high frequency noise (like switching power supplies parasitic ringing and other high-order effects sometimes can produce transients up into the >30 MHz range).  

The 47 nF capacitor hopefully will be of a type with low impedance up past 100 MHz.

Why do we care about RF Noise in audio circutis?  Most of our circuits contain many nonlinear elements and functions along with filters wonderfully tuned at radio frequencies -- things hiding in PCB layout, off-board wiring, and inside IC's and transistor packages that you don't see in the schematic.

The combination of all of these non-obvious circuits constitute a receiver and demodulator for high frequency noise and then it becomes audible in some form or another.  

That is the reason for a 47nF cap in parallel with a 100 uF cap.  It extends the high frequency rejection range because real capacitors aren't ideal capacitors.

[acehobojoe]

That's great to know.

[Tom9979]

Thanks again guys. I had no idea how complicated this could become! Tonepad offboard wiring 5 looks like the kind of set up I am after although I won't be using the battery snap.

Kipper, you mention using a 1M resistor as close to the input as possible. Would connecting this between the tip and sleeve of the input jack achieve this or is it better between the in and ground on the circuit board?

Following that, can I include a diode from the DC input before reaching the circuit board +ve input to prevent reverse polarity damage and add the 100uF and 47nF capacitors between the +ve and ground of the DC input to reduce ripple from the power adapter?

I am assuming the rest of the setup will then remain as in the diagram?

Thanks

[duck_arse]

tom - what kipper meant to say was put the 1M anti-pop on the outside-world side of the input cap and ground. it goes between the footswitch and the in-cap, as it is meant to stop that cap putting volts onto that switch. at the jack defeats the purpose.

as for the series diode, put it after the +DC input, and before anything you want protected. so your electros come after the diode, to get some protection. IF you have a ripple dirty supply, you can inclue a series resistor, anything around 100R or so, between the protection diode and your first of the cleaning caps. this forms an RC filter, cuts lots a supply carp. if you have a regulated supply, the resistor is not necessary.

[Kipper4]

I think you have it now.
Personally I wouldnt put the resistor on the input jack. I'd keep it on the board less likely to be damaged.
Try  it out. Let us know how you get on.

[Kipper4]

Duck is right. Notice the 47ohm resistor in the first diagram in his first post. any value up to and around 100ohms would be good here.
For the series diode Duck talks about I normally use 1N5187 IIRC

[Tom9979]

Thanks guys. I got round to soldering the leads to the 3pdt switch tonight and connected it to my breadboard along with an LED. I haven't got the pop resistor or filter caps yet as I'm going to have to order them (there's nowhere local that supplies electronics components without over charging) but having said that, there were no pops when switching the effect on and off and all worked brilliantly once I noticed a resistor across the base and emitter on my transistor instead of the base and collector but I managed to trouble shoot that with no real fuss. If I have no popping now, am I pretty safe to assume there won't be any pops when fitted into the enclosure or would it be best to fit the pop resistor anyway to be on the safe side?

Thanks, Tom.