Orange Drop "polarity" ?

[Krinkle]

Not trying to hijack the thread but Ampdoc1, I am in the middle of an Express clone build and I have been thinking about building one using pcbs after I get this one working. I used to lay out pcbs at my last job and since then I've read all of the TUT books and feel that I could do a much better job than having all of these wires stringing about everywhere. I have access to a cnc machine at work and I make prototype pcbs all the time so I could do a few iterations if need be.

I would love to find some of those pots that Fulltone uses on the new Fulldrive. The leads bend up towards the shaft so you can use the nut on the pot to mechanically secure the pcb, and not have to depend on the solder joint only. Then you could lay out the pcb until there were no "lead dress" or in this case "trace dress" issues. I think that it would be nice to have 2 pcbs for an Express (main one and one behind the pots) that would almost allow you to snap the amp together. That wouldn't be any fun for most people BUT would allow some of the less experienced builders to get an amp that sounds great without worrying about investing hundreds of dollars into something that may not work very well, depending on their build experieince and technical skill and knowledge. Just thinking out loud.

Darrin

[ampdoc1]

Krinkle,

I also don't mean to get off topic, but Krinkle has a good idea about the potentiometer board (although I didn't put the pots on my TW boards).

Instead of using "special" pots though, a simpler method would be to bend the pot leads upwards toward the shaft and install them and the tone stack components on the "rear" of the PCB. With the Alpha 24mm pots like this, you could cut off the terminal "rings", and have a perfect PCB mount pot. I'm sure other types would work pretty easily also.
I designed (but never produced) a board in this style for a Dumble design I laid out.

ampdoc

[BobW]

Using the 'foil test' method similar to Weber's suggestion, may show better results if you use a capacitance meter to measure from foil to each lead. The highest reading (closer plates) will be the outside foil. This assumes the foil is even spaced between the leads.

[Krinkle]

Ampdoc1,

That's exactly what I was thinking. I'm going to start this topic over at technical discussion to see where it goes.

Darrin

[Johnhenry]

I've been useing my amp to find the polarity of my O/D's or any tubular type cap, I took a guitar cord that i had chopped up and put a on/off/on toggle switch on the cord leads, and 2 short wires with aligator clips out of the other end of the switch for latching on to the Cap with, the switch is for changeing the polarity of the cord lead's to the amp, when you turn the amp on and turn up the volume just enough to hear the hum while i hold the cap between my thumb and forfinger, then i hit the switch and change the polarity, the loud hum will be the outside foil and the lower hum will be the inner foil, there is a quite a difference between the two so decideing which one's loudest is very easy.
hope this help's those that have no scope for testing polarity.
Johnhenry

[nickt]

I've been useing my amp to find the polarity of my O/D's or any tubular type cap, I took a guitar cord that i had chopped up and put a on/off/on toggle switch on the cord leads, and 2 short wires with aligator clips out of the other end of the switch for latching on to the Cap with, the switch is for changeing the polarity of the cord lead's to the amp, when you turn the amp on and turn up the volume just enough to hear the hum while i hold the cap between my thumb and forfinger, then i hit the switch and change the polarity, the loud hum will be the outside foil and the lower hum will be the inner foil, there is a quite a difference between the two so decideing which one's loudest is very easy.
hope this help's those that have no scope for testing polarity.
Johnhenry

Hey cool idea! I'm going to have a go at this - Thanks for posting!

[Johnhenry]

Works Great for me Nick, Let me know what you think of it !
[IMG768]http://i199.photobucket.com/albums/aa33 ... ure005.jpg[/img]
here's a pic of the way i wired my switch, i did put a bracket on a small piece of plywood for mounting the switch, made it very easy to use, and i noticed my thumb was interducing hum into the switch's toggle so i put a rubber sleeve over the toggle.
Johnhenry

[Karl]

I imported pictures from my oscillioscope of both waveforms when the ground is connected to the outer and when the ground is connected to the inner foil . The polarity obviously makes a difference.

[paulster]

That's about the difference I see on the scope too.

I'd love to know how much difference it makes in the real world, i.e. the effect of swapping round each of the caps, but I really can't be bothered to try it! It's not likely to be quite as marked a change in the real world because the impedance difference won't be as marked unless it's a cap connected at one end to a plate or to ground.

I like the switch trick though. That makes it practical for everyone without a scope to try it if so inclined.

[Johnhenry]

Karl, That's what I saw on my scope and when useing the Amp test i see that when the tip of the cord is connected to the outer shield i got the loud hum, I tested about 20 or so cap's and i noticed that on all the Sprague's i tested, if you can read the writing on the cap the outer foil lead was on the right end of the cap,
Paul, I agree with you, what diff swapping them would do is Beyound my intelligence !
But i did read this somewhere from Sprague, that oreinted correctly it would help reject EMI, and crosstalk in the amp.
Johnhenry

[Karl]

Karl, That's what I saw on my scope and when useing the Amp test i see that when the tip of the cord is connected to the outer shield i got the loud hum, I tested about 20 or so cap's and i noticed that on all the Sprague's i tested, if you can read the writing on the cap the outer foil lead was on the right end of the cap

I took 2 0.22uF OD715 caps with me to school and tested both. I got a different result. On one cap the outer side was on the left and on the other the outer side was on the right of the writing.

[paulster]

I tested about 20 or so cap's and i noticed that on all the Sprague's i tested, if you can read the writing on the cap the outer foil lead was on the right end of the cap,
Paul, I agree with you, what diff swapping them would do is Beyound my intelligence !
But i did read this somewhere from Sprague, that oreinted correctly it would help reject EMI, and crosstalk in the amp.

I found that with the Cornell Dubilier PVC series, the writing was random so you had to test them. Same with Mallory M150s. I've gone to the effort of putting them round the 'right' way, so I'm loathe now to try them round the 'wrong' way to see how much noisier my amp gets or how different it sounds.

My hunch is that the sound won't be any different but the susceptibility to EMI and potentially noise will be lower.

[nickt]

Works Great for me Nick, Let me know what you think of it !
here's a pic of the way i wired my switch, i did put a bracket on a small piece of plywood for mounting the switch, made it very easy to use, and i noticed my thumb was interducing hum into the switch's toggle so i put a rubber sleeve over the toggle.
Johnhenry

Ok not to be outdone I've mounted a switch a jack and two terminal posts on a plastic box
and hey! it works like a beauty!

One design flaw - needs a switch to short the terminals while you're changing caps

Just polarity checked a bag of orange drops (and can confirm the labeling has NO relation to the polarity).

Thanks JH

[gearhead]

when you turn the amp on and turn up the volume just enough to hear the hum while i hold the cap between my thumb and forfinger, Johnhenry

Just stumbled across this thread ending Are you holding it with your thumb/forefinger as a way to introduce outside interference to the outer foil, or just to hold it?

[Johnhenry]

Good idea on the grd sw Nik, I put my Sw. in a plastic box also, work's so well i'll be keeping this homemade tool on my bench, and after testing a bunch of caps with it i also find that the writing does not alway's tell all,
Gearhead, Yes, I'm holding it to introduce the Hum, without my fingers on the cap I hear very little hum.
Johnhenry