Three "newbie" concepts I seem to have missed...

[ExpAnonColin]

Somewhere along the line I never got around to figuring these out, and I figure they're sort of important... so anyone who wants to fill me in  a bit, thanks a bunch.

1. The input capacitator-What is it for, is it electrolytic, or non, and what value do people tend to use?
2. The "no-pop" resistor-How come it stops the pop, and where do you put it?
3. The commercial method of using a stereo jack to disengage the battery-How does this work and should I use it or not?
4. The "Ground the ninth 3PDT pin in high gain pedals to prevent leakage"-Why not in all pedals?

Thanks for helping me fill some holes...

-Colin

[Doug H]

Colin,

A good place to start for this kind of info is the DIY FAQ at the top of the page. I know it  covers the cap and stereo jack wiring (for power) questions you have. It is really a rich resource of info and everyone who is starting out should read it. I still find it handy as a reference. There are a lot of good links to other sites with more in-depth info as well.

I would suggest reading that first and if you still have questions, come back and ask again.  You may have a few new items that need to be added to the FAQ.

Doug

[ExpAnonColin]

Colin,

A good place to start for this kind of info is the DIY FAQ at the top of the page. I know it  covers the cap and stereo jack wiring (for power) questions you have. It is really a rich resource of info and everyone who is starting out should read it. I still find it handy as a reference. There are a lot of good links to other sites with more in-depth info as well.

I would suggest reading that first and if you still have questions, come back and ask again.  You may have a few new items that need to be added to the FAQ.

Doug

I also refer to the FAQ pretty often, however, I was looking for more of an explanation of the why rather than a how to do it.

-Colin

[Paul Perry (Frostwave)]

Why does it pop(and how to stop): here's the explanation from the master:
http://www.geofex.com/Article_Folders/box_pop.htm

[Mark Hammer]

The input cap is there to block any stray DC.  You don't want to take a DC offset of 300mv, amplify it by 40 and then try and fit in AC on *top* of that, while using a 9v supply.

Of course, when you can assure that whatever you feed in has absolutely NO stray DC in the signal you can skip the input cap (after all, once it is removed, effects often do that themselves internally).  Commercial manufacturers have no guarantees about where you will stick any of their pedals so they plan around the worst case scenario, which means thatthey will always have an input cap, whether they turn out to need it in your instance or not.

In many of Craig Anderton's projects from the 70's and 80's, he would often include either 2 input jacks or a switch that would permit for a "DC-coupled" input (no cap) or an "AC-coupled" input (DC blocking input cap to assure there was ONLY audio reaching the first semiconductor stage).  This was done to maximize bandwidth where feasible, and reduce any noise stemming from the input cap...assuming you have the luxury.

Pop resistors are there precisely because of the side-effects of those DC-blocking input caps.  Remember that the cap stores charge.  The rather crude analogy I like to use is that of taking a wizz after a long wait.  Wait all day to use the "facilities" and that moment of release is initially agonizing.  With the input cap, the more current is stored, the bigger the rush of current released.  If there is no terminating resistor and one end of the cap is left hanging, there is nowhere for that current to go and it just sits there waiting for the moment it can drain off.  The pop you hear is that sudden current drain.  The terminating resistor allows for a constant bleedoff of current to ground.  If the circuit board itself has no such bleedoff resistor, you can stick one on the switch.

[ExpAnonColin]

Thanks to you all.

-Colin

[Doug H]

Somewhere along the line I never got around to figuring these out, and I figure they're sort of important... so anyone who wants to fill me in  a bit, thanks a bunch.

1. The input capacitator-What is it for, is it electrolytic, or non, and what value do people tend to use?
2. The "no-pop" resistor-How come it stops the pop, and where do you put it?
3. The commercial method of using a stereo jack to disengage the battery-How does this work and should I use it or not?
4. The "Ground the ninth 3PDT pin in high gain pedals to prevent leakage"-Why not in all pedals?

Thanks for helping me fill some holes...

-Colin

The input cap blocks the DC in the circuit from the signal input. Caps essentially pass an AC signal and block DC. The DC in the circuit input is usually used to bias the active device for proper operation. Whether you use electros or not will depend somewhat on the value of the cap. Larger values tend to be electro while smaller values are available in other materials. There is some overlap in the middle (like the .47u-1u range, for example, where you can easily find films and electros available). Different cap materials can sound different, depending on the circuit. Electros can be noisy, and will eventually dry out and need to be replaced. Sometimes their sound is preferable. Tantalums caps can be used in place of larger electros and will not need replacement, but they are expensive. The best thing to do is experiment on the breadboard with different caps with the circuit you are building, then decide what you like the best.

The "anti-pop" resistor grounds the coupling cap to ensure that there is no DC voltage on the "blocked" side of the cap. Caps are imperfect and will leak small amounts of DC. This DC difference between the effect (input or output) and the bypass circuit (0VDC) can cause a "pop" when the effect is switched in or out of the signal path.

The stereo pwr jack is explained in the faq. The stereo lug of the jack shorts to ground on a mono plug. This is used to allow the plug ground to serve as a switch, to switch the battery in and out of the circuit. The battery ground is connected to the stereo lug instead of the ground lug of the jack. When the mono plug is plugged in, the stereo lug gets shorted to ground and the battery is then grounded and current from it flows into the circuit. You should use this if you find it useful. All my stuff is battery powered so I need a switch on the box somewhere for shutting off the battery so it doesn't get drained when I'm not using it. Using the stereo jack saves me from having to install another switch on the box somewhere (which I may forget to turn off). I simply remember to unplug all my input cables when I'm finished and it's easy. If you don't use battery power at all, you don't really need this, but some people like this feature anyway because it is somewhat of a defacto standard in the way commercial pedals work as well and they are used to it.

I'm not really sure what the "ground the 9th 3pdt pin" deal is. My guess is that it is grounding the input of a high gain circuit when it is bypassed.  Because of the large amt of gain, high-gain circuits have very sensitive inputs. Sometimes, when the effect is bypassed, leaving the input "floating" can cause oscillation (squealing) which you can hear in the background when the effect is in bypass. What happens is that the input stage picks up any amount of noise and amplifies it, then somewhere the output stage is feeding that back into the input stage. Someone else may be able to explain this better but I believe the input stage is more vulnerable to noise pickup when there is nothing connected to it or driving it with a signal. This can be aggravated by a noisy input stage, and the feedback can be caused by poor layout, but that's not always the case. Grounding the input stage essentially "turns it off" and nothing can get picked up and amplified by it. This keeps everything quiet when the circuit is bypassed.

Doug

[ExpAnonColin]

Hey now, just because I have newbie questions doesn't mean I'm a newbie.... but thanks for all the info anyways.  I'm pretty sure I have the 9th pin on the 3pdt figured out... if you ground the positive side of the battery it turns "off" the active components that are causing the high gain.  The signal is leaking between the effect pins and the bypass pins, making you able to hear the hiss and whatnot that occurs in high gain circuits.  Just need a way to switch all of the actives off.

-Colin

[Doug H]

Hey now, just because I have newbie questions doesn't mean I'm a newbie.... but thanks for all the info anyways.  

OK, I'm officially confused at this point... I pointed you to the FAQ in response to your original question. Your response (in a nutshell) was that you had read it and wanted to understand more of the "why". So I responded with some of the "why" and now you imply that somehow I treated you condescendingly or something. You either wanted to know the "why" or you didn't... I didn't know what flavor you wanted so I guess you'll have to be more specific next time. In any case, I don't like playing "go get a rock" so I'm done with this thread (part of the reason I rarely respond to these kinds of threads anymore).

I'm pretty sure I have the 9th pin on the 3pdt figured out... if you ground the positive side of the battery it turns "off" the active components that are causing the high gain.  The signal is leaking between the effect pins and the bypass pins, making you able to hear the hiss and whatnot that occurs in high gain circuits.  Just need a way to switch all of the actives off.

-Colin

Dead-shorting the hot side of the battery to ground is never a good idea.

Doug

[drew]

Yeeeeow. Indeed.

My vote is that if you call a cap a "capacitator" that you should be more gracious when people expend several paragraphs trying to help you


drew
toothpastefordinner.com

[Peter Snowberg]

It takes a lot of time and effort to type up long, thoughtful responses such as those from Mark and Doug.

[ExpAnonColin]

Sorry, I've had a terrible day and haven't been in the greatest mood... thanks to both of you for taking your time.  The reason I was asking about the grounding of the 3pdt is because I heard someone recommend it in a previous post about someone complaining about their high gain pedal making noise when it was off.

And drew-I typed that when it was about 6:15 in the morning and I had been awake for maybe 5 minutes, it was just a mistake...

-Colin