If sub is properly grounded, it only can damage outputs of preamp, even if it is defective. The only case when cartridge can potentially be damaged is if there is no reliable grounding and sub sent line voltage to ground connection common with phono preamp. In all other cases preamp will die first before cartridge.
Loud POP, Dead new cartridge.
- Thread starter SPEC2man
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restorer-john
Addicted Member
We have no idea of the input topology of the Jolida. It may be a design where the front end latched up under a transient (acoustic via the speakers and overloaded, or electrical via the lack of an effective common ground on the RCA shields) and if it is direct coupled through its front end- it could have destroyed the cartridge. There's plenty of multi (tr and fet) paralleled direct coupled phono front ends that cook cartridges when they oscillate or latch up.
The fact we had a floating earth somewhere in that system, valves (HT) and a DC transient is a recipe for destruction.
The fact we had a floating earth somewhere in that system, valves (HT) and a DC transient is a recipe for destruction.
restorer-john
Addicted Member
With all due respect, you are mistaken, many subwoofers generate a significant DC offset (on the input RCA) when they are turned off and their front end (filter stage) PSU rails internally collapse.
Many, many subwoofers will trip the DC protect on amplifiers during that turn off condition. Amplifiers without DC protection or slow acting protection will amplify that transient or collapsing voltage and I've seen plenty of damaged woofers from that situation.
Amplifiers can also have their output stages blown.
There are also subwoofers that have a constant DC offset on their RCA input- enough to trigger some DC-daylight amps' DC protection.
Many, many subwoofers will trip the DC protect on amplifiers during that turn off condition. Amplifiers without DC protection or slow acting protection will amplify that transient or collapsing voltage and I've seen plenty of damaged woofers from that situation.
Amplifiers can also have their output stages blown.
There are also subwoofers that have a constant DC offset on their RCA input- enough to trigger some DC-daylight amps' DC protection.
restorer-john
Addicted Member
I think this situation is very unusual and stems from several issues as highlighted above, combining to destroy the cartridge.
Terrible to lose a brand new cartridge that way.
Terrible to lose a brand new cartridge that way.
WaynerN is mistaken about the resultant reading using an ohmmeter to determine the condition of a magnetic cartridge coil. An open coil will show a reading of INFINITY, NOT zero ohms (which indicates a shorted coil). It is extremely unlikely that a cartridge coil will fail shorted when subjected to a large transient.
INCORRECT :nono:
0 Ohms= 0 resistance= 100% conductivity or dead short
No reading or over-range = infinite resistance = open circuit
woodj
Super Member
I feel we are getting into the vagaries of different meters here. Both open and dead short should both read 0.
In reality, infinite should indicate that the measurement exceeds the bounds of measurability, but I guess that could be indicative of some meter builders trying to differentiate between open and short.
So the reading would depend on the particular digital meter used. An analog meter would read 0 in both cases, but could be dangerous to use on cartridges, especially MC's.
In reality, infinite should indicate that the measurement exceeds the bounds of measurability, but I guess that could be indicative of some meter builders trying to differentiate between open and short.
So the reading would depend on the particular digital meter used. An analog meter would read 0 in both cases, but could be dangerous to use on cartridges, especially MC's.
If you're lucky.
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JBL GUY
Addicted Member
If your DMM indicates 0 for both a short and a open circuit, how can one tell the difference.
If I build a set of interconnects and measure from the center conductor to the shield and my meter is going to indicate 0 for both a short circuit and an open circuit, how do I know which is which?
Because on most DMM the indication for open circuit is not 0.
And the meter scale on an analog Ohm meter will say 0 on one end and infinity on the other end (the indication for an open circuit).
Note on the Simpson 260 meter scale, the top scale which is the resistance scale calibrated in Ohms, the far right is 0 Ohms, such as you would have if you connected the test leads together (ignoring the resistance of the test leads).
On the far left side is the symbol for infinity or an open circuit. The meter pointer will be on one end or the other depending on whether it is a short circuit or an open circuit, it will not be in the same place for an open circuit and a short circuit, that is how one can tell the difference. BTW, for higher resistance ranges as selected on the meter, one multiplies the scale by a factor of 10 or 100 and so on.
The same with a DMM, the indication has to be different so on can tell the difference between a short circuit and an open circuit.
To be clear, I mean no disrespect to anyone here.
If I build a set of interconnects and measure from the center conductor to the shield and my meter is going to indicate 0 for both a short circuit and an open circuit, how do I know which is which?
Because on most DMM the indication for open circuit is not 0.
And the meter scale on an analog Ohm meter will say 0 on one end and infinity on the other end (the indication for an open circuit).
Note on the Simpson 260 meter scale, the top scale which is the resistance scale calibrated in Ohms, the far right is 0 Ohms, such as you would have if you connected the test leads together (ignoring the resistance of the test leads).
On the far left side is the symbol for infinity or an open circuit. The meter pointer will be on one end or the other depending on whether it is a short circuit or an open circuit, it will not be in the same place for an open circuit and a short circuit, that is how one can tell the difference. BTW, for higher resistance ranges as selected on the meter, one multiplies the scale by a factor of 10 or 100 and so on.
The same with a DMM, the indication has to be different so on can tell the difference between a short circuit and an open circuit.
To be clear, I mean no disrespect to anyone here.
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JBL GUY
Addicted Member
That is the way most of my DMMs work, although my Fluke 8050A bench DMM indicates an open circuit by displaying a 1 as the left most digit and the rest of the display is blank and some of my off brand DMMs indicate an open circuit by displaying dashes across the display instead of numbers.
The point is, there must be a difference in order for the meter to be useful.
BTW, if it has not been posted already, the internal resistance of the cartridge being discussed is IIRC 475 Ohms. Any large deviation would indicate a issue.
None of my meters read zero for open circuit and if they did they'd be in the trash barrel.
To overload a cartridge winding, current would have to pass through it. If the schematic I found for the preamp is correct, it's a conventional cap coupled phono input to an opamp, 4.7 uF. That means DC is blocked, but I can still imagine a transient of good size going through the cap. Unfortunately, it also has to go through the input circuitry of the opamp, as the only other path is the loading resistor. Those are protected with diodes, so it's conceivable the cart was blown that way, but it would be incredibly unusual and not terribly beneficial to the opamp. There's also a higher level input, but I'd assume that isn't being used- it isn't cap coupled. I'd be having a look at the cables and grounding to see if anything is amiss, and make sure the input caps are present. Does the table have a separate ground wire? I did have an open Grado one time right out of the box, but it's too much coincidence to have it fail when the sub was switched.
edit- Wait, I was wrong! A conductance meter will read zero on open circuit. Of course, if you go to Digikey and try buying resistors using the conductance value, you won't find much.
To overload a cartridge winding, current would have to pass through it. If the schematic I found for the preamp is correct, it's a conventional cap coupled phono input to an opamp, 4.7 uF. That means DC is blocked, but I can still imagine a transient of good size going through the cap. Unfortunately, it also has to go through the input circuitry of the opamp, as the only other path is the loading resistor. Those are protected with diodes, so it's conceivable the cart was blown that way, but it would be incredibly unusual and not terribly beneficial to the opamp. There's also a higher level input, but I'd assume that isn't being used- it isn't cap coupled. I'd be having a look at the cables and grounding to see if anything is amiss, and make sure the input caps are present. Does the table have a separate ground wire? I did have an open Grado one time right out of the box, but it's too much coincidence to have it fail when the sub was switched.
edit- Wait, I was wrong! A conductance meter will read zero on open circuit. Of course, if you go to Digikey and try buying resistors using the conductance value, you won't find much.
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