Wiring Question (Answered)

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DH166
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Re: Wiring Question (Answered)

Post by DH166 »

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)

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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)

Post by Bieworm »

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)

Post by Unit_1 »

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)

Post by DH166 »

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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Re: Wiring Question (Answered)

Post by DH166 »

Got it! Thanks for the response. So, now I'm starting on the turret board. I know that the outside foil end on my caps is meant to face the lower impedance side of the circuit. I have no idea how to identify that on the layout or schematic, though. What do I look for?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Tue 06/14/22 3:28 pm
Got it! Thanks for the response. So, now I'm starting on the turret board. I know that the outside foil end on my caps is meant to face the lower impedance side of the circuit. I have no idea how to identify that on the layout or schematic, though. What do I look for?
Ground or the previous stage's plates, whichever is closer/has less resistance. This schematic is a different circuit, but it should give you an idea: files/JMPGuitars_18_Watt_Tremolo_TMB_Re ... ematic.pdf

Are your caps marked for foils, or did you mark them using a scope?

Thanks,
Josh
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Re: Wiring Question (Answered)

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Awesome, thanks! I used a scope.
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Re: Wiring Question (Answered)

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DH166 wrote:
Tue 06/14/22 3:59 pm
Awesome, thanks! I used a scope.
as odd as it sounds, you can make an audible testing device! It has two alligator clips, an input jack and an on off switch.

You put the device next to a motor or neon light, anything EM noisy. Using the clips you hook up the cap and flip the switch on. Listen. Turn it off, flip the cap and turn it back on. (edited: AFTER plugging into your amp, you do the test)

The side that is the noisiest is not the foil end.

It would have been easier to use if I had a three way switch, but I didn't have one at the time.

fwiw, I have a very large supply of Astron paper in oil caps, they're almost impossible to tell which side is the foil end because they are SO quiet....
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Re: Wiring Question (Answered)

Post by DH166 »

Next question: On the trem TMB layout, there's a 10k resistor between pin 2 on V3 and the .022 cap that leads into the volume pot. That resistor isn't there on the schematic, however. I made my Mouser list off the schematic, so I don't have that 10k (and I don't do enough projects to have bins full of passives). Before I make a new order and pay eight bucks shipping for a seventy eight cent resistor, is that resistor necessary, or is it a mod of some sort? What does it do?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Fri 07/15/22 7:00 pm
Next question: On the trem TMB layout, there's a 10k resistor between pin 2 on V3 and the .022 cap that leads into the volume pot. That resistor isn't there on the schematic, however. I made my Mouser list off the schematic, so I don't have that 10k (and I don't do enough projects to have bins full of passives). Before I make a new order and pay eight bucks shipping for a seventy eight cent resistor, is that resistor necessary, or is it a mod of some sort? What does it do?
That's an optional grid stopper resistor. You might not need it, but I would recommend building with the terminal strip as pictured in the layout, in case you need to add the resistor later.

Thanks,
Josh
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Re: Wiring Question (Answered)

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Got it. Thanks. I ordered it. Learning process. It's getting pretty close to done. Man, it's been a long process. Thanks a ton for all your advice.
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Re: Wiring Question (Answered)

Post by DH166 »

Next question: On the layout, the shielded wires are labeled, but on the notes it says to use shielded wire for the external footswitch. That one isn't labeled as shielded. So, should the wire that's purple in the picture, that goes from pin 7 on V1 through the tip lug on the switch and on to the 2.2M resistor, be shielded wire? If so, can the shielding be grounded at any point or is there a preferred place?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

I'd say it depends on your circumstances whether or not it really needs to be shielded. Shielded is probably safer. Ground the shield only on one side, I would use the ground lug on the terminal strip out of convenience.
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Re: Wiring Question (Answered)

Post by Bieworm »

+1 on shielding those wires. I forgot to use shielded wires once there and ran into trouble. It was fixed when I changed them to a shielded type.
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