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Questions regarding grounding and using LED light in a TT restoration.

T

TWK

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I am restoring a Empire 398 and have a few questions on wiring.

Grounding.

I added an IEC three prong power cord. I can ground this to the motor and add a switch to lift the ground if I have a hum. Is this a good idea or just skip the ground altogether?

The motor is currently grounded on the tonearm. I can omit this and ground as described above. Should I just leave this grounded on the TT arm?

LED Light.

I want to add a blue light and cannot find an incandescent. The hole is 5/8" and I want to add this LED from Amazon. Will the LED add noise to this circuit? I know that the cartridge is very sensitive and if the motor is grounded to the tonearm this light will be too.

Is there anything that I can do to isolate the LED to avoid any potential noise.


Thank you.
 
I'm not an expert but I think it is better to have your turntable grounded to the preamp than to ground itself in case there's a different impedance to ground between the two. You may get good responses from the Vinyl Engine forums. Lots of restorations and mods going on over there.
 
Is this a good idea or just skip the ground altogether?
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If it originally had a ground it's potentially dangerous to omit it. The power ground is a "safety ground" in case something goes-wrong and the chassis gets energized with AC power. If there wasn't originally one there other precautions to keep it safe.

How was the old light powered? The LED says 12 or 24V. How are you going to power it? I wouldn't expect it to make any electrical noise with DC. Higher power LED (1W and up) normally use a switchmode constant-current supply (usually built into "LED lightbulbs" from the home improvement store) and that can generate noise. but "regular little" low-voltage LEDs normally just have a current-limiting resistor and they don't generate noise. "By nature" LEDs are low-voltage devices.

If you add a power supply, that's a potential source of noise.

I found red and green 120V neon indicators which is probably what was there originally.
 
Thanks.

The TT was made in the early 1960s and the motor has a chassis ground wire that goes to the tonearm. Tonearm has the usual ground wire. However, I have other turntables that have the motor separate with a ground. I was thinking to do this here and add a switch to lift the ground if there is a hum.

It has a red lamp that works, I just want blue to match my other gear. The LED says 12-24v but int he pics it shows 6 mA at 110v so it should work, the issue, as you say it might have a little power supply built into it.

6 mA at 110v = 066 watts so maybe it just has the resistors? Even at 120v it is 0.74 watts.
 
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Good idea on the cover. I need something that fit sin a 5/8 hole. I can check if Digikey if they even carry such things.
 
TWK said:
Thanks.

The TT was made in the early 1960s and the motor has a chassis ground wire that goes to the tonearm. Tonearm has the usual ground wire. However, I have other turntables that have the motor separate with a ground. I was thinking to do this here and add a switch to lift the ground if there is a hum.

It has a red lamp that works, I just want blue to match my other gear. The LED says 12-24v but int he pics it shows 6 mA at 110v so it should work, the issue, as you say it might have a little power supply built into it.

6 mA at 110v = 066 watts so maybe it just has the resistors? Even at 120v it is 0.74 watts.
Click to expand...

For lowest noise, frame ground of the motor/chassis should be grounded at the same place as the tonearm. You can do PE with a situation-specific noise penalty, which probably won’t be noticeable anyway. Just don’t do both.
 
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12-24v but int he pics it shows 6 mA at 110v so it should work, the issue
Click to expand...
I'm pretty sure that's a different part number with a bigger internal resistor. (You don't always get good-complete specs from these unknown 3rd-party Amazon suppliers, or eBay, etc.)

as you say it might have a little power supply built into it.
Click to expand...
Not those.

It CAN be done with a resistor, and you can add resistance to whatever is built-in (probably about 500 Ohms). Use the LED voltage from the LED calculator, don't use 12V because that includes the internal resistor.

You may want to buy a small selection of (higher value) resistors in case the LED is too bright.

If you are in the U.S and ordering electronic parts, Mouser doesn't have a minimum order.

With high AC voltage, you'll exceed the reverse-voltage rating for the LED. (The resistor only drops voltage in the forward direction when current is flowing.) The standard solution is to add a reversed diode (or another LED) in parallel with the LED. A bridge rectifier would also work, and you'd get current on both-halves of the AC cycle for more brightness and the AC flicker will be less noticeable.

Most of the voltage is dropped across the resistor so most of the power (wattage) goes to the resistor. By using a higher-value resistor to lower the current (and running the LED dimmer). By running the 120V version at 6mA they can get-away with a lower-power resistor.

It's "good practice" to "derate" the resistor and use a resistor rated for twice the actual power (or more).
 
JP said:
For lowest noise, frame ground of the motor/chassis should be grounded at the same place as the tonearm. You can do PE with a situation-specific noise penalty, which probably won’t be noticeable anyway. Just don’t do both.
Click to expand...
Thanks. The Tonearm will be (should be with a wooden mount plate) completely isolated from the chassis. I will wire a ground from the motor to terminals or a switch where I can swap between either the tonearm or the ground in the IEC.
 
DVDdoug said:
I'm pretty sure that's a different part number with a bigger internal resistor. (You don't always get good-complete specs from these unknown 3rd-party Amazon suppliers, or eBay, etc.)


Not those.

It CAN be done with a resistor, and you can add resistance to whatever is built-in (probably about 500 Ohms). Use the LED voltage from the LED calculator, don't use 12V because that includes the internal resistor.

You may want to buy a small selection of (higher value) resistors in case the LED is too bright.

If you are in the U.S and ordering electronic parts, Mouser doesn't have a minimum order.

With high AC voltage, you'll exceed the reverse-voltage rating for the LED. (The resistor only drops voltage in the forward direction when current is flowing.) The standard solution is to add a reversed diode (or another LED) in parallel with the LED. A bridge rectifier would also work, and you'd get current on both-halves of the AC cycle for more brightness and the AC flicker will be less noticeable.

Most of the voltage is dropped across the resistor so most of the power (wattage) goes to the resistor. By using a higher-value resistor to lower the current (and running the LED dimmer). By running the 120V version at 6mA they can get-away with a lower-power resistor.

It's "good practice" to "derate" the resistor and use a resistor rated for twice the actual power (or more).
Click to expand...

This should be an easier solution. I found these LEDs rated for 110v to 220v.


To derate the resistor do I simply remove the existing resistor, measure its value and find one rated for 2x the power? They rate the LEDs at 0.06 watts and a current rating of 20 mA.
 
FYI you can usually use a regular white/whitish light bulb (or LED) and give it a thin coat of whatever color nail polish you want.
 
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