Cap outer foil tester build -- Peegoo Custom Special
- Thread starter King Fan
- Start date
Heh, the business was a joke, but we'd be paying wholesale. Fender's Tele switch is probably $4, Hammond box $3.50, etc. We'd be as rich as Croesus, or in modern terms, Elon Musk 'before the fall.'
On the serious side, an accurate, simple, watchable video on the LBL would be awesome. (OK I didn't watch that one -- life is short -- but I may next time a user here needs an LBL reference). I lack the attention span for longer YouTubes, but the big issue is that video doesn't usefully allow for later edits or *helpful* comments. If a video errs, or even just fails to explain a detail, there's no way to correct, amend, or comment *usefully*. Reading YouTube comments is a dog's breakfast at best. So I hitch my ol' stubborn mule to the wagon of the written word, where I can look for sources, hope for corrections, and select among opinions.
But a good vid to recommend to people under my age (~100) would be super-useful in this forum.
joulupukki
Tele-Holic
KF and I had a fun time yesterday afternoon shooting the breeze, plinking on some guitars through our amps, and trying out his fancy PGS box. Turns out, it’s really quite handy in combination with a scope too.
I still get mixed up on which side is which and how to know
KF and I had a fun time yesterday afternoon shooting the breeze, plinking on some guitars through our amps, and trying out his fancy PGS box. Turns out, it’s really quite handy in combination with a scope too.
It *was* fun. See separate post raving about your I was almost as amazed by your skills with the scope as by your awesome guitar talents. The Peegoo Special was really handy for quick switching, and the scope made it quicker and more *obvious* than testing by ear. FWIW, I was relieved to see that the scope didn't correct my 'ear' results, whereas the switch did improve my accuracy compared to crude gator-plug tests.
If it isn't obvious, you can see we just plugged in a ¼" jack to attach the scope's probe; years ago I soldered a red wire to the tip to make it easy to grab.
Thinking about it or describing it in words can be confusing. The Aiken piece is clear enough if you have a scope. The Peegoo switch makes testing by ear pretty easy too, and keeps me from getting confused. I just wired it so the *switch points to the lead that's connected to the plug sleeve = amp chassis = ground.* Switch to front, squeeze cap, switch to back, squeeze cap, mark the end that's quieter.
OK, here's a little demo.
What's most impressive to me is how much quieter this setup is than my alligator clips to a bare plug. The amp here is on 7, and it's not at all loud; in the past I had to have it on 2 or 3 and 3 was pretty loud.
Likewise, you can see the switching is silent -- unclipping is a pop-roar thing unless you kill the volume, which also kinda hinders the A:B thing.
Details:
• Aiken points out several kinds of cap that don't have an outer foil -- nice to know. E-caps are obviously not candidates for this testing, but also silver mica, CD, certain orange drops...
• You don't absolutely need to build a tester. I did this on a number of builds with just the crude clip-plug arrangement in the first pic. Just be very careful to reduce volume, and return it to exactly the same level.
• Don't feel bad if you aren't testing or orienting your outer foil -- thousands of good builds don't. OTOH, any step that can reduce noise is good, plus it's kinda fun. Or of course you can buy nicer caps that have an outer foil mark.
• Aiken discusses the technical factors that tell you which way to orient the outer foil -- they're complex. A nice feature of the plans drawn by maestro @robrob is many of them have outer foil markings.
Cool! But when you are done doing this, how do you know which way to put the cap in the amp? ie: what indicates if the cap is labeled wrong or right?
If by 'labeled,' you mean lettering print direction, that's random. If the cap has an outer foil marker on the label, like Sozo or Jupiter, those have been right IME, but @Peegoo has seen some that aren't; you could test 'em to make sure.
As far as how to orient the cap in the amp using the outer foil mark, the easy way is to copy a Fender original or (slightly better) Rob's drawings -- if you're building one of those amps. Otherwise you gotta read and understand the Aiken article; simple in some places, not so much in others.
No, what I mean is, you've tested the cap using your device. One way it hums, the other way it doesn't hum so much. Now how do you know which end is "outside foil" from your test?
Ach, I shoulda gone ahead and marked the cap in the video. By all means re-read #46 above, cuz I think it overlapped your question in time. But if that isn't clear (words are so lame) let's go back to the crude but simple gator+plug test. The end that's quieter when clipped to the sleeve here is the outer foil end, ie, the one you mark. Does that help?
Think of the outer foil in this test like the shield on your guitar cable. Simple, right? It gets a bit trickier in the circuit, unfortunately. Aiken: "The outside foil will act as a shield against electric field coupling into the capacitor, so you want it to have the lowest impedance return path to ground. For AC signals, the power supply rail is effectively at ground potential, just as the ground rail is. This is why it makes a good point to use as a shield ground." He admits this can be hard to grasp and has fooled experts in the past.
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If you build it like @King Fan has described it, then when you find the side with the switch that makes noticeably less noise, your lead on the same side as the switch knob will be the one connected to the outside foil.
KF and I had a fun time yesterday afternoon shooting the breeze, plinking on some guitars through our amps, and trying out his fancy PGS box. Turns out, it’s really quite handy in combination with a scope too.
I enjoyed it too...even if is was by proxy
