Line filtering, X2, Y2, generic "death cap" questions

[Brazen]

Not to be redundant, but I keep finding conflicting info about the proper application of X2 and Y2 type capacitors. Most of the info I've found, both here and abroad, states that while Y2 caps can be safely used for both across-the-line AND line-to-ground situations, I've had a few EE's state that it is perfectly fine to use an X2 rated cap line-to-ground as well on amplifiers. (death caps) There reasoning appears to be that both X and Y caps are hardier and if they do fail, they will fail safely and not explode or burst into flames, etc.

I recently did a 3-wire conversion and snipped the ground cap [C12] on my old Gibson G10 amp. After doing so I introduced some hum, and I suspect that cap was filtering since it was whisper quiet before the mods. I want to replace the snipped cap with a Y2 and see if that quiets it down again, and was having trouble finding a US source that wasn't too $$$ for one little cap, shipped. So I was wondering what's the worse case scenario if I used an appropriately spec'd X2 cap in lieu of a Y2 cap? (.01uF to .04uF 250V... see photos below)

On that note....... the cap I snipped was .01uF. The official OEM Gibson parts list inside the cabinet shows it requires a .04uF. [C12] It was whisper quiet before the mods with the .01uF part, so I'm guessing replacing with that capacitance will be fine. But generally... when it comes to caps... is there any advantage/disadvantage to using a higher capacitance part? ie: if a .033uF or .04uF Y2 is more readily available vs. .01uF Y2, what do you surmise would be the outcome?

Thanks so much again to all of you!
Jimmy

[52 Bill]

I recently did a 3-wire conversion and snipped the ground cap [C12] on my old Gibson G10 amp. After doing so I introduced some hum, and I suspect that cap was filtering since it was whisper quiet before the mods.

Well then test your theory reinstall the cap that you took out and see if the hum goes away. In one of the other threads you posted this problem in, there was a suggestion that switch the two transformer primary leads to see if there was a difference in the hum level. Did you try that? Are you certain that the hot side plug wire is connected to the fuse and the switch?

... the cap I snipped was .01uF. The official OEM Gibson parts list inside the cabinet shows it requires a .04uF. [C12] It was whisper quiet before the mods with the .01uF part, so I'm guessing replacing with that capacitance will be fine.

The value of the ground cap is not that important. They will typically range from 0.01 to 0.05. The original cap was rated for 150VAC, so it was meant for use in line voltage applications, the X cap of its' day. The problem with these caps is if they fail and short the AC line to the chassis, they could present 120 volts to the ground circuit of the amp and also to the person touching any grounded surface. Now if the amp has a three wire cord and the wall outlet is correctly grounded this should cause the fuse to blow or the GFI to trip. Because there are too many variables in the above equation, the usual approach is to just remove the ground cap entirely.

A lot of the circuitry built into computer supplies is to keep RFI that is generated inside the SMPS from getting out into the ac line. If you want to test another theory, try plugging the amp into a filtered power strip and see if that makes any difference.

[Brazen]

Well then test your theory reinstall the cap that you took out and see if the hum goes away. In one of the other threads you posted this problem in, there was a suggestion that switch the two transformer primary leads to see if there was a difference in the hum level. Did you try that? Are you certain that the hot side plug wire is connected to the fuse and the switch?

The original cap was soldered tight to the PCB, so when I snipped it, in lieu of desoldering, there isn't enough leads to salvage, hence wanting to go ahead and install a new, Y2 safety cap of appropriate specifications. Not sure if I missed it or perhaps you are confusing me with another member here, about swapping the transformer's output leads. I never disturbed those connections to the PCB whilst modifying the mains cord. Guess I could try it though.

The value of the ground cap is not that important. They will typically range from 0.01 to 0.05. The original cap was rated for 150VAC, so it was meant for use in line voltage applications, the X cap of its' day. The problem with these caps is if they fail and short the AC line to the chassis, they could present 120 volts to the ground circuit of the amp and also to the person touching any grounded surface. Now if the amp has a three wire cord and the wall outlet is correctly grounded this should cause the fuse to blow or the GFI to trip. Because there are too many variables in the above equation, the usual approach is to just remove the ground cap entirely.

Gotcha! So I'll stick with the .01uF value that I removed. But again..... everything I've read says to ONLY use a Y2 type cap for line-to-ground. Had a guy elsewhere recently ask me why I thought this was so, and that an X2 type cap to ground was just as safe. What are you thoughts on that my friend? Just don't want to go f_cking things up..... I'm just a building contractor and enthusiast so please bare with me! I am an anal sh!t though, so I checked the cord I used for polarity, continuity, as well as the circa 2006 house wiring here. All checked out OK on the electrical input side.

A lot of the circuitry built into computer supplies is to keep RFI that is generated inside the SMPS from getting out into the ac line. If you want to test another theory, try plugging the amp into a filtered power strip and see if that makes any difference.

That's interesting and good to know. I was assuming this was to provide clean AC power to the PS, as to not introduce noise "to" the computer. Thanks again Bill for the invaluable information. Your opinion is always welcome!

[g1]

If your cap leads are too short, try anything (.01) with a rating of 250V or better. You are just trying it as a test, if it doesn't help you won't need to bother with a class Y or any other.
As far as whether a class X is ok, I won't speculate, but I think it has to do with electrical codes (UL, CSA, etc.) so I would go with what is seen in commercial amps, class Y for line to ground.
As to swapping the primary leads, it's worth a try. When it was 2 prong, you never knew which was going to fuse and switch, hot or neutral? So it may make a difference.

[Brazen]

If your cap leads are too short, try anything (.01) with a rating of 250V or better. You are just trying it as a test, if it doesn't help you won't need to bother with a class Y or any other.

I hear ya. I'm anal but lazy as well (LOL) and have performed all mods with the amp intact so far. If I reintroduce that cap, I'll have to remove the PCB to get to the underside.

As far as whether a class X is ok, I won't speculate, but I think it has to do with electrical codes (UL, CSA, etc.) so I would go with what is seen in commercial amps, class Y for line to ground.

I "imagine" it wouldn't hurt, since they are considered modern safety caps? Any clue as to what the technical difference is between X-type and Y-type caps?

As to swapping the primary leads, it's worth a try. When it was 2 prong, you never knew which was going to fuse and switch, hot or neutral? So it may make a difference.

Everything is correct polarity speaking, according to two DMM's I've used to test with. I was being very careful with the work I had performed, and to not disturb anything OEM that wasn't involved.
Cheers!

[Brazen]

FYI.... here is an email a nice gentleman sent me. He suggests X-type caps CAN be used in a Y-type situation. [to ground]

That sounds like a lot of "vintage" recommendations you see that are based on nothing but what "people have heard." I will see if I can find it but there is a really good article about X2 and Y2 caps written by one of the manufacturers that explains what they are designed for and how they are used.

Essentially, they are simply more robust than standard capacitors. This is due to there intended applications as protection against fire and shock hazards. The Y2 caps are usually used between the ground and each side of the power input and X2 caps are used across the power input. If a Y2 cap fails, it can present a shock hazard but if an X2 cap fails, it can cause a fire. Neither is very likely to cause any damage to the equipment.
If I locate the article, i will send you the link to it or a copy.
Paul

[52 Bill]

If you are that lazy, you should find that the two points where the old cap was connected to are directly connected to ground on one and and to one of the two vertical connectors on the switch at the back of the volume pot. Use your ohmmeter to find out which one. Then temporarily connect a high voltage cap from the switch contact to the circuit ground. I take no responsibility for your safety in doing this, as I cannot control how you hook up the cap and what cap you use for this test. So please use caution if you choose to do this.

As for the other test of switching the transformer primary wires, it was included in a link to another forum that someone posted for you to read. I think you responded to it, but maybe you didn't read it.

The original ac cord may or may not have been polarized. If it wasn't, then depending upon how the amp was plugged in, the ground cap could have been connected to either the hot or the neutral side of the ac line. With the new 3-wire cord the cap will be placed on the hot side to the chassis. This may or may not help with your hum.

[Brazen]

If you are that lazy, you should find that the two points where the old cap was connected to are directly connected to ground on one and and to one of the two vertical connectors on the switch at the back of the volume pot. Use your ohmmeter to find out which one. Then temporarily connect a high voltage cap from the switch contact to the circuit ground. I take no responsibility for your safety in doing this, as I cannot control how you hook up the cap and what cap you use for this test. So please use caution if you choose to do this.

As for the other test of switching the transformer primary wires, it was included in a link to another forum that someone posted for you to read. I think you responded to it, but maybe you didn't read it.

The original ac cord may or may not have been polarized. If it wasn't, then depending upon how the amp was plugged in, the ground cap could have been connected to either the hot or the neutral side of the ac line. With the new 3-wire cord the cap will be placed on the hot side to the chassis. This may or may not help with your hum.

I hear ya Bill, and you have my full attention. I was just jabbing at myself..... I have been lazy, or rather efficient perhaps up to this point. (I "almost" had to pull the board from chassis just to snip that cap, but managed) But I will do it correctly and safely if I decide it's worth it. I'm probably just being "anal" about the hum... it's really not that bad and the amp is only 15w and really not worth much monetarily speaking, so it is tolerable I guess. I just thought since it was literally whisper quiet as I say, after only replacing the large filter cap but before the 3-wire/cap snip, that I might get it back to those conditions by adding back a safer cap. Since I snipped the cap at the same time as upgrading the cord, I can't pinpoint the cause. I'm usually very good at troubleshooting by only do one mod at a time, but I suspected this may have be a safety issue by adding a true earth ground to the ole gal, so the cap was removed.