Wiring Question (Answered)

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DH166
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Re: Wiring Question (Answered)

Post by DH166 »

Ok. Thanks. So now at this point I'm ready to start putting the passives on the turret board. A question on that. How do I find the outside foil end of my caps? I don't have an oscilloscope and I tried the fuzz pedal method and didn't get any difference in hum level. This build is my first tube amp. I just have a Fender modeler and I'm guessing its software is made to eliminate hum from pedals in the first place. Ideas for figuring this out?
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Re: Wiring Question (Answered)

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There are some methods using a disassembled instrument cable.. use Google for the details. But you could buy the sozo caps when you don't have a scope to do this. Sozos have the outside foil side truly marked with a stripe
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Re: Wiring Question (Answered)

Post by TriodeLuvr »

Not all caps have outer foil. Depends on the construction method. Maybe try a few different types to see if any of them respond to the method you're using.

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Re: Wiring Question (Answered)

Post by JMPGuitars »

Jack and Bjorn make good points. If you don't want to invest in an oscilloscope, the easiest thing is to just get SoZo caps. They're great caps, especially after being broken in.
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Re: Wiring Question (Answered)

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Alright. October was a busy month but I'm back at it. Bought a second hand old Tektronix and got the caps figured out. Next question: I'm about to wire up the input jack. I recall reading about how to hook it up with the shielded wire, but I can't find the article I read. Does the shielding get soldered to the ground lug? Does it just get clipped off and heat-shrunk out of the way? On the layout, it just shows the shielded wire going to the tip side lug and a separate wire going from the sleeve side lug to ground. So, the follow-up question would be likewise for the other shielded wire coming off of V1 and V2. How do they hook up? Thanks
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Re: Wiring Question (Answered)

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The shielding of the shielded wire has to be soldered on one side only. The other side should be clipped off and sealed with heat shrink. If you solder the hot wire (core) to the hot/tip side of the input it's best to solder the shielding to another ground reference than input ground. You might add a terminal at V1 where you can solder the other end of that hot wire from input. Connect your 10k grid stopper between that terminal and V1 pin 2. Solder the shielding on the center of that terminal, where it's bolted to the chassis.
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Re: Wiring Question (Answered)

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So, the end of the wire that connects with the input shouldn't have the shielding connected to anything at all? Just clipped and sealed? Connect the shielded portion of the other end to the grounded terminal adjacent to V1? Is that correct?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sat 11/13/21 5:43 pm
So, the end of the wire that connects with the input shouldn't have the shielding connected to anything at all? Just clipped and sealed? Connect the shielded portion of the other end to the grounded terminal adjacent to V1? Is that correct?
Yes, only one end. I don't know if it really matters which end you use. I've read opinions that shielding should have independent connections to ground, and others say it should connect to the preamp ground bus. I've connected either way without issue. 🤷

This is how I wired the input jacks on my latest builds:
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Re: Wiring Question (Answered)

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Ok, thanks. Two more questions:
1. The shielded wire from V2 would probably be similar, since it likewise goes through a grounded terminal, but what about the shielded wires coming from pins 1 and 6 of V1? They go straight from the pins to the board. Does the shielding on those ground anywhere?
2. After wiring up the input and wiring it to the terminal that connects it via the 10k resistor to V1, I tested my connections for continuity. I got a beep when I probed across the core wire and shield wire attached to either of the two lugs on the terminal. Is that right? Shouldn't those be isolated from each other, both by the separation in the wire jackets and by the fact that the terminal is insulated between the lugs? I tested the lugs with the wires removed and they're isolated, and I tested the core wire against the shielding to make sure I didn't tear through the inner jacket when I stripped it but it's also good. The only thing I can think of is that I already wired up all the connections on the input jack, including its ground. Would the signal the multimeter is sending up the core wire go through the input jack and to ground, thereby completing the circuit when I touch the other probe to the grounded lug on the terminal?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sat 11/13/21 6:22 pm
Ok, thanks. Two more questions:
1. The shielded wire from V2 would probably be similar, since it likewise goes through a grounded terminal, but what about the shielded wires coming from pins 1 and 6 of V1? They go straight from the pins to the board. Does the shielding on those ground anywhere?
2. After wiring up the input and wiring it to the terminal that connects it via the 10k resistor to V1, I tested my connections for continuity. I got a beep when I probed across the core wire and shield wire attached to either of the two lugs on the terminal. Is that right? Shouldn't those be isolated from each other, both by the separation in the wire jackets and by the fact that the terminal is insulated between the lugs? I tested the lugs with the wires removed and they're isolated, and I tested the core wire against the shielding to make sure I didn't tear through the inner jacket when I stripped it but it's also good. The only thing I can think of is that I already wired up all the connections on the input jack, including its ground. Would the signal the multimeter is sending up the core wire go through the input jack and to ground, thereby completing the circuit when I touch the other probe to the grounded lug on the terminal?
1. If one end of the shielding isn't connected, it's not shielding. Some people mount a terminal strip or use a ground lead to connect the shielding near the socket. On my Tremolo TMB PCB, I have a shield plane they connect to on the PCB.

2. If the jack is fully wired, then the hot will be grounded out without a plug connected. Insert an instrument cable, and you should no longer get continuity between the shield and the hot lead.

Thanks,
Josh
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Re: Wiring Question (Answered)

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Cool, thanks. So then, I will need to add a ground lug or grounded terminal for both of the other shielded wires coming from V1?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sun 11/14/21 8:17 am
Cool, thanks. So then, I will need to add a ground lug or grounded terminal for both of the other shielded wires coming from V1?
You can connect them to the same point. Cover the shielding wire in heat shrink tubing so it can't short out on anything.
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Re: Wiring Question (Answered)

Post by DH166 »

Great. Next question. As I re-tested all my passives before building the board, I've got a couple resistors out of tolerance, so I'm going to put in a new Mouser order, which leads to my question. When I ordered the two carbon comp 100k resistors called for in the TMB build (at least shown to be carbon comp on the layout diagram), I chose my resistors under the suggestion of an article I read on the Aiken site that argued that the only time to use carbon comp was to induce signal distortion and that, if that was the aim, then you should accentuate that distortion by choosing the lowest wattage that your application could effectively handle. So, I've got 1/4W resistors that I believe are rated at 250V, whereas everywhere else, I went for 1W or higher metal film where possible, again influenced by that opinion from Aiken. What wattage do you use for those carbon comp resistors?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

I use 1W if I have them, otherwise, 1/2W. I would never use 1/4W in an amp.
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Re: Wiring Question (Answered)

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I think the .25W type applies only for small Electronic devices. And come on.. those tiny resistors look pretty sh#tty in an amp...😄
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Re: Wiring Question (Answered)

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So, opening this thread back up. About a week after my last post, I broke my wrist and the project got put on the shelf. Back at it now, though, and hoping to finish it once and for all over the next couple weeks. My question now is about the shielded wire from the input to V1. A couple of posts up the thread, you said to ground one end of the shielding, preferably near V1, and just heat shrink the other end. I put a terminal strip near V1 with one isolated lug and one grounded lug and wired up the hot wire through the isolated lug to the 10K resistor on pin 2. Then, I soldered the shielding to the grounded lug on the terminal. Problem is that I now have continuity between the two. Obvious answer is that I have a short in the wire itself, that I did a poor job stripping and separating it. However, before I start over with a new strand of wire, I just want to make sure that I wired it up correctly. Picture is below.
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Re: Wiring Question (Answered)

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It's kinda blurry, and my old eyes have a hard time seeing blurry, but it does look ok. I usually ground at the input jack side since there's already a ground available, never any problems whatsoever.

You can't even tell my Hiwatt DR504 is on until you hit a string and then everyone in the room jumps a foot off the ground 'cuz it's so loud and unexpected.

I also use a very short length of shielding, only about 3/8" and I twist green insulated wire to this and solder before shrink wrapping it. Then I run the green wire to ground. Much easier and you're not stripping away a large amount of shielded wiring just to make a longer ground. Plus everything is now insulated, no chances of it ever touching anything.

You can see the green wire running out of the bottom of the blue shrink wrap, and can you imagine as crowded as this is how hard it would be to keep from touching something else?

https://postimg.cc/Ff6XqDss

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Re: Wiring Question (Answered)

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Thanks for the reply. I started over with a new length of wire and was extra careful stripping it to make sure I didn't puncture it anywhere and that no strands of braid were left touching anything. Problem is, I'm still grounded from the hot side that connects to V1. Now, I do also have a ground at the input jack. Not from the shielded wire, but just a length of wire between the outside most lug (tip, sleeve?). See pics (sorry, they attached upside down and I don't know how to flip them). Is that right? That ground should be there regardless of which end you ground the shielded wire, right? So, if you ground the shielding at the input, there'd be two connections to ground up there and none at the V1 end and if you did it like I did, there'd be one connection to ground at each end? Confused.
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Re: Wiring Question (Answered)

Post by JMPGuitars »

Without a cable connected to the input jack, the input will be grounded if it's wired correctly. Insert a cable in the input jack and test again.

Sorry to hear about your wrist, I hope you're all healed up now!

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by Unit_1 »

Are you maybe measuring 68K or 1M across that resistor to ground?

When checking for continuity you should have your ohms set to the lowest setting. Then touch both of the probes together. You should get a very low reading like .1 ohms. If you get more than that when you connect to a circuit, then a resistor in the circuit somewhere is involved.

Try inserting a 1/4" plug into the input jack and see if it changes, this should separate the leads of the switch on the jack.

I can't really see how everything is hooked up on the jack. But on my DR504 with no plug in the jack I measure 68k from pin 2 to ground, which is as it should be.
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