Post by pablogilberto on Oct 28, 2020 19:47:55 GMT -5
I have an old Strat SSS pickup set. (Ceramic Magnets)
The Neck pickup sounds too thin and the volume level is low. (No bass, more on treble only) The Mid pickup sounds good. (but suspicious because of the electrical readings) The Bridge pickup sounds good.
Upon checking using a multimeter, The Neck and Mid pickups reads a very high resistance (1 to 2 Meg ohms) The Bridge pickup reading is good at 8k ohms.
I think the Neck and Mid pickup coil wires are somewhat broken that's why I'm getting a very high resistance reading. Using an LCR meter, the DCR for Neck and Mid have no reading which suggests that it is open or the wire is cut. The Inductance is also very high (1 Meg Henry) The Bridge pickup has the same good DCR at 8k.
My questions are: 1. If the Neck pickup coil wire is broken, why does it still produces a sound (more on trebly sound and low output)? 2. I'm confused with the middle pickup because based on the readings, it is bad. But based on sound, it is pretty normal. Same volume level with the Bridge.
Post by blademaster2 on Oct 29, 2020 20:21:10 GMT -5
That 1-2 Mohm reading must mean that a pickup coil or external connection to it is broken (open-circuited) and you are reading whatever else is in the circuit in parallel (likely volume knobs) depending where you are probing to make your measurement.
The mysterious aspect appears to be still hearing a signal from something that is supposed to be "broken", but perhaps if you traced the circuit you could discover that you are getting the signal from a good pickup feeding through the circuitry when you have it switched to the 'broken' pickup. Some people call that a 'sneak circuit'.
For sure, any pickup truly reading such a high dc resistance must be dead.
Post by pablogilberto on Oct 31, 2020 20:15:43 GMT -5
Just to clarify, I removed the pickup from the circuit before making all the readings. That means, the readings are directly from a pickup with nothing connected to it.
When assembled in the guitar, the weird thing is that, I can confirm that the sound really comes from the Neck and Mid (for positions 3, 4 and 5) because when I use a screwdriver to touch the polepieces of Neck and Mid, they produce sound!
You might have some capacitive coupling across the break. This would work better at high frequencies.
Can you show me an equivalent pickup circuit when this happens? I want to understand it better.
A guitar pickup is an inductor with series resistance, with a sum of parasitic capacitances that are parallel, and a simple pickup model just lumps all of the parasitic capacitances into a single parallel capacitance.
To simulate a wire break with an LCR pickup model, you can put a break the trace connecting the inductance, resistance and the lumped capacitance, or, instead of delete the trace, put a very high value resistor there that can be "switched" on and off, in order to plot the difference between continuity and broken wire.
In other words, the parasitic capacitance of a guitar pickup is usually too small and trivial to matter, but once the wire breaks, that capacitance becomes the only means by which the current can cross the pickup. With the wire broken, the capacitance is no longer in parallel, but instead it's not in series, and if you put a capacitor in series with the pickup, it will attenuate low frequencies, and all you hear are high frequencies emerging from the guitar pickup.
I have another case here. This time it's a Humbucker pickup.
This is a dead pickup. No output / movement using the screwdriver test.
The Inductance is very high at 40.8H (@100hz) The Capacitance (PAR) is 510pF (@100khz)
The weird measurement is the DCR. It reads 0.3Meg and then it increases every second. It reached 0.9Meg after 1 minute or two and then I stopped the measurement.
What do you think is the problem here?
The Inductance and Capacitance reading doesn't change in reading.
I'm was expecting to get a zero DCR reading if the coil wire is broken.
The inductance value is wrong because the LCR meter is guessing that you have a functioning inductor, but since it has a break in the wire, it's not a functioning inductor and the LCR meter is fooled. The capacitance is probably more accurate, since a broken inductor is still very capacitive.
I think for the resistance, you might be measuring "AC resistance", which distinct from "DC resistance". If you measure with AC, then the capacitive aspect of the pickup allows current to pass through, but if you measure DC resistance, than the pickup will read open. Are you using a DE-5000? Is so, DCR is the fourth and very last mode, it goes "L" "C" "R" then "DCR".
I'm in the DCR mode not AC resistance. That's why I'm confused with what's happening with the reading.
Upon opening the Humbucker pickup (it uses a braided shielded wire), I was able to identify that 1 coil is good and the other is dead.
I did rewind the dead coil and now the pickup is perfectly fine.
Still, I'm not sure what's happening with those weird readings and I want to understand it more.
Thanks for your response!
Needless to say, I don't think the DC resistance reading is demonstrating anything fundamental about the pickup. If it's supposed to be an open circuit, but nevertheless there is a reading across the circuit, then it would appear there is a short, but a lot of resistance across the short. Check the DCR of the individual coils and see if they are as you would expect.