Author Topic: Way Huge pcb...  (Read 59397 times)

The Tone God

Way Huge pcb...
« Reply #180 on: November 10, 2004, 06:54:54 PM »
You make the assumption that switching is instantanious which is what most people think of when looking at circuits but in reality during switching there is a moment when the input is not connected to anything thereby giving a chance for some charge to leak. The pulldown prevents that leakage even when switching.

Oh and sorry about your election.

Andrew

Skreddy

Way Huge pcb...
« Reply #181 on: November 10, 2004, 09:30:09 PM »


So you're saying that a charge might build up in the cap while it's switching between ground and input? Would the charge be coming from the input stage of the effect?

I still say that pulldown resistor is superflous. :twisted:

R.G.

Way Huge pcb...
« Reply #182 on: November 10, 2004, 11:26:29 PM »
Quote
So you're saying that a charge might build up in the cap while it's switching between ground and input? Would the charge be coming from the input stage of the effect?

Could well be the cap itself. Look up "dielectric absorption" when you get the chance.

Quote
I still say that pulldown resistor is superflous.

A lot of the time it is. I've paid for insurance on my house for about 27 years now. Never had a fire wipe me out yet. Was I wasting my money? More importantly, should I cancel my insurance now and never pay again?
R.G.

Quick IQ Test: If anyone in a governmental position suspected that YOU had top-secret information on YOUR computer, how many minutes would you remain outside a jail cell?

Tim Escobedo

Way Huge pcb...
« Reply #183 on: November 11, 2004, 01:22:00 AM »
Quote from: R.G.
Quote
importantly, should I cancel my insurance now and never pay again?


I say yes!

 :twisted:

Skreddy

Way Huge pcb...
« Reply #184 on: November 11, 2004, 01:27:04 AM »
:shock:
 :lol:
:x
:?:
:evil:
:P
8)

Damn, R.G.; you tryin to kill me?  Crazy phantom voltages out of nowhere comin to make my bypass pop...


















...still think that resistor don't need to be there...


puretube

Way Huge pcb...
« Reply #185 on: November 11, 2004, 02:58:22 AM »

Skreddy

Way Huge pcb...
« Reply #186 on: November 11, 2004, 11:30:08 AM »
Puretube; you're funny, Man.

Kidding aside, R.G. is the only one who has offered any real reason to use a pulldown resistor, that being the possibility of dielectric absorption building a charge back up in the cap while the switch's throw is traveling between the ground lug and the input lug.

I'm not saying Puretube's reason isn't real; I mean, we can't just amplify the sound of the input cap suddenly going silent while we switch into bypass mode... that could be deafening through a Hiwatt! ;)

But getting back to dielectric absorption... First of all, the standard measurement for d.a. charges a cap with DC for 15 minutes, then discharges the cap for 10 seconds, then tests the cap again for voltage after 15 minutes.  

Compare that to the time it takes a footswitch to break contact and make contact.

Let's assume that was enough time for a charge to build up anyway, arguendo.  Why would this cap have such a propensity to recharge itself?  Because it's been polarized by DC.  So the input has a strong DC offset.  That means that if the cap is totally discharged that it must first get charged with the DC offset before it can start passing the AC signal through.  Which means that a pulldown resistor in this case would actually be a detriment rather than helpful!

:P

(assuming you use the circuit-input-to-ground-during-bypass method of wiring the switch)

moogatroid2000

Way Huge pcb...
« Reply #187 on: November 11, 2004, 11:55:01 AM »
I am assuming the footswitches we use are _break before make_.
Do they have _make before break_ switches?
If they did would this allow for pop free switching or would it cause other problems?
live and learn.

The Tone God

Way Huge pcb...
« Reply #188 on: November 11, 2004, 04:28:30 PM »
Quote from: moogatroid2000
I am assuming the footswitches we use are _break before make_.
Do they have _make before break_ switches?
If they did would this allow for pop free switching or would it cause other problems?


They do make "make before break" switches but I don't think in footswitch form. Even so I think other problems would occur with connecting the bypass and effect modes at the same time which could be worse.

Beyond that leaky caps are but one of the causes of popping in bypass switching. We get caught up with pulldown resistors and leaky caps around here as if it the answer to pop-less switching when in fact it just reduces one of the symptoms, be it one of the most common and easist to solve, so just having non-leaky caps is not going to guaranty pop-less switching. You need to do alot more before you can get/say that.

I agree that in some cases you may not need the pulldown resistor but it is better to put it in just to be safe. Its just good design habit.

Andrew

Skreddy

Way Huge pcb...
« Reply #189 on: November 11, 2004, 06:41:33 PM »
Yeah; a 100uf capacitor across the power rails to 'buffer' the LED current does the trick for me.  :)

puretube

Way Huge pcb...
« Reply #190 on: November 14, 2004, 12:38:25 PM »
that cap is a must even in non-LED pedals... :)