Most of my 3PDT pedals pop on one amp, not the other

[disorder]

I don't build pedals too often these days but I whipped up a belton brick reverb the other day and spent some time trying to get rid of the 3PDT pop. I put the usual 1M resistors at input and output, tried another 3PDT switch, tried using the white insulating washer, new input and output caps, etc etc. Nothing would change. Then I remembered I had this problem on my last few builds and that it was only popping on my Fender Champ. Tried the pedal on my girlfriend's solid state Vox and the switching was as quiet as most 3PDT's are. I immediately tried a number of pedals on the Champ and then on the Vox and it was true... the Champ pops like crazy with nearly every true bypass pedal. I should add I tried using a 1-spot power supply as well as battery power on all these pedals, and moved the Champ to different outlets in the house.

The Champ is a mid 70's silverface, all stock, two prong cable. The Vox is also stock but with a three prong cable that I plug into a 3-to-2 prong adapter as all the outlets in our place are still 2 prong.  Any ideas what could be causing this?

[slacker]

It could DC on the input of the Champ, that could cause pops and pull downs on the pedal wouldn't stop it. Try plugging a guitar lead into the Champ and then measure the voltage between tip and sleeve.

[Hatredman]

Even if it doesn't show any voltage, I'd put a pulldown resistor directly on the Champ input jack anyway.

[disorder]

I thought the usual Fender input/grid scheme includes a 1M to ground. Since I'm seeing no coupling cap, can I assume the tube might be bad or on it's way out?

http://www.thevintagesound.com/ffg/schem/champ_aa764_schem.gif

[wavley]

You got a grounded power cord on that Champ?

[disorder]

No like I said, just the stock two prong. Not that it matters my entire apartment is all two prong outlets.

[wavley]

No like I said, just the stock two prong. Not that it matters my entire apartment is all two prong outlets.

Oops. sorry, missed that part.  My guess is that you've got two different grounds because neither of them is actually earth.  Try flipping your power cable around in the socket and see if it changes.

[Gus]

Read Slacker's post

I would change the input tube and test again

[PRR]

> Champ is a mid 70's silverface, all stock

Agree- replace input tube.

Could be damp board. Fender used a treated-paper board material which is damp-resistant but not damp-proof.

When the board gets damp, current can leak. Here it may be sneaking from B+ or Plate to grid.

If it has lived in a damp area, that is another clue.

Replacing the circuit board is a major project.

Since Champs run warm, and running them should not be a big stress, you could try leaving it on for many dozen hours (either when you and your nose are around/awake, or in flame-proof spot) to dry it out.

[disorder]

> Champ is a mid 70's silverface, all stock

Agree- replace input tube.

I will start with this. I've heard of the black paper-y material Fender used becoming conductive. If new 12AX7 doesn't correct this I will measure around the board. Thanks.

[R.G.]

No like I said, just the stock two prong. Not that it matters my entire apartment is all two prong outlets.

It matters.

Maybe not so much for your musical equipment, but for your personal safety. Three-prong outlets are a safety enhancement. There are conditions where a single fault - like a vibration in the refrigerator, for example, wears through the insulation of a hot wire against part of the metallic shell. The shell is then "hot". You won't notice this usually, until you happen to accidentally touch the water faucet and the refrigerator at the same time, and then YOU are the path to ground for the current. If you don't happen to be grasping handles it will shock you. If you have a firm grasp on both, the current will clamp your muscles and you won't be able to let go. It gets worse from there. Much worse.

I know it can be hard to deal with, but you're at risk until you have three-prong outlets, one way or the other.

[tubegeek]

Your two prong to three prong adapter SHOULD have a green wire sticking out of the two-prong part with a spade lug attached to it. That wire is there for a reason - to allow you to get back the safety ground that the two-prong outlet is seemingly denying you.

Loosen the screw in the middle of the outlet and tighten it down on the spade lug. Then plug the two-prong plug into the outlet and the three-prong power cord into the adapter.

This assumes that your two-prong outlets were installed correctly, which is a bit optimistic. You can always try to measure continuity between that screw and a nearby water pipe to see if it is grounded, it is supposed to be.

Then, step two of the electrocution-prevention routine is to replace the two-prong cord in the Champ with a three-prong cord. Remove the "death cap" that connects one side of the AC mains to the chassis and connect the incoming AC as follows:

AC "Hot" must go directly to the mains fuse FIRST, then to the power switch, then to the power transformer
AC "Neutral" goes to the power switch (if a two-pole switch) or the power transformer (if not)
AC "Ground" goes directly to a secure connection to the chassis, typically (and highly recommended) a bolt used only for this purpose with a lock washer. The wire to this point should be longer than the other two so that if the wiring accidentally gets ripped out, the ground will be the last to be torn out.

That about covers it.

Even the worst "vintage gear collector" doofus knows better than to bitch about having the three-wire cord replacement mod done to an amp. I know of one vintage instrument dealer who had to take a customer to the hospital not long ago when he made contact with two amps he was trying out at the same time, everybody was OK but it was quite the shock to everyone concerned.

[PRR]

> vibration in the refrigerator... wears through the insulation of a hot wire

Not even that. An ALL 2-prong house is an OLD wiring job. Much of the stuff we used in the 1940s-1960s didn't last well. My parents learned not to touch their light fixtures, because every time some more old crumbly rubber fell off. (In the nick of time, a developer bought them out to knock-down for a mall.)

I know what a huge job a total re-wire is. (I'm midway in my second.) I agree it isn't practical (unless you have time to do it clever and anticipate eventual return).

An additional problem: there are 2 equal slots and 2 different slots. Nearly all modern 2-pin expect the type with one slot bigger. If you have the 2 equal slots, even 2-pin plugs (other than old amps) is A Problem.

I sure would use the 2/3 dingus WITH GREEN TAIL TO SCREW and use a 3-light tester to see what it shows. If Open Ground, then you don't even have grounding. If no Open Ground light, it may be correct, it may be a box-white jumper or short (bad!), it may be a loose clamp which will power the LED but let-go in a real fault. No way to be sure until you open and inspect every junction and the main box.

But knowing you have one maybe-ground, I would use a 3-pin power-strip from the one outlet for the WHOLE audio set-up (so you can't have different ground potentials), and stay away from sink(*), radiators, dirt/concrete, and other outlets and fixtures.

(Pay no attention to alleged "hot/neutral swap". First: this is not serious in properly wired equipment. Second: your 2/3 pin dingus can go in either way, and the other way "fixes" this non-problem.)

(*) One interesting trend in newer housing. We have less "metallic systems". I now have all plastic water plumbing, can't get a shock at the sink. Huge iron radiators are rare. Hot-water baseboard is the same risk but harder to lean-on or brush against. But I would think if you still have 2-pin outlets, you have the "good" copper or iron water pipes.

The flip-side of that: there is no solid DIRT ground unless someone has done it right. But a dirt ground only matters outside or in cellar.

Hot air heat registers can be ground. Here it is hit-or-miss, but in a good job the registers are screwed to metal ducts to furnace to electric or gas or oil grounding.

While you have the mechanical chops to fix some of this, you do NOT open-up electrical without extensive experience. You can NOT learn this on the internet. You can't even learn it from books, even my collection back to 1915. There have been too many variations in "proper" wiring. That's before you get into IMproper wiring which is perhaps more common. (My last house, I seriously think they let the kids re-wire from 1910 loom to 1972, and they did things wrong in the most unlikely ways in the worst possible places. But some adults, even adults with trucks, are little better.)

[cmdrfun]

HA! I have had the exact same problem! My late 70s Silverface Champ pops, while my late 60s SF Vibro Champ does not. Both have 3-prong cords. Eager to hear what you find out.

[tubegeek]

(*) One interesting trend in newer housing. We have less "metallic systems". I now have all plastic water plumbing, can't get a shock at the sink. Huge iron radiators are rare. Hot-water baseboard is the same risk but harder to lean-on or brush against. But I would think if you still have 2-pin outlets, you have the "good" copper or iron water pipes.

Yeah, I forgot to cover some worser case scenarios - I'm coming from a New York City perspective, where we have had a very tough electrical code for a very long time. I've seen some crazy stuff inside my 120-year-old walls and the walls of others, but not nearly as crazy as what you get outside the city. And PVC pipe is - I think? - still illegal here for residential water. Of course, that doesn't stop them from selling it at Home Deep.

[PRR]

> New York City ...we have had a very tough electrical code for a very long time.

Gas too, I assume.

Yet didn't a NYC building just blow-up, because the landlord paid a licensed gas-pipe guy to sign for work really done by guys who did not have a clue? Who jumpered one pipe to another, then disconnected for Company Inspection? And then when the gas company flunked the work they could see, the fools re-connected the jumper with valves wide-open, smelled their mistake, and ran? Then BOOM.

You never know what is REALLY in the walls until you LOOK at EVERY joint.

And especially in electric, there has been enough history to confound any simple understanding. Some things have been wrong for about a century. Some things were right once upon a time, are frowned-on now, but may be left if in good condition and not causing trouble. Many specific devices can look OK today and start a fire tonight, due to unsuspected manufacturing mistakes plus age.

[tubegeek]

> New York City ...we have had a very tough electrical code for a very long time.

Gas too, I assume.

Yet didn't a NYC building just blow-up

You mean the lot full of rubble in the East Village? Yeah, not too often code violations have such disastrous consequences, but there's the reason why densely populated urban areas really need them. This one was not just a simple negligence, though, this was flat-out criminal. More murder than manslaughter in my book.

There was another building only 3/4 of a mile from my house, another gas explosion, State Street, killed an elderly couple and a neighbor in their home. About 15 years ago.

http://www.nydailynews.com/archives/news/explosion-victim-found-clutching-cordless-phone-article-1.877259