Simplistic NJFET RIAA - Page 560

SGregory · 27th December 2010, 10:59 PM

The higher than spec reading may have been an artifact of the coil heating up and glowing like a valve filament

Salas · 27th December 2010, 11:04 PM

Nah, I touched it very fast, only as long as it took to show and I did it at the other end of the leads on the RCAs. 19.16 Ohm but I say 19 Ohm because of the interconnect and arm wires. Then again if it glowed, now I will have tube tone for free, and low noise. I could even manage the No noise spec if I burned it.

But its alive and kicking.

Salas · 27th December 2010, 11:39 PM

The modern DVMs have high internal impedance in resistance mode I trust. Very little current to give. But what about using a known resistor, measured on same DVM, like 2k2 in series and subtracting it from the total resistor+cart measurement. That should protect any

cart from any possibly strong DVM.

But the DVM must reliably show the correct extra Ohm relatively to the 2k2 bulk. Must be a rather good one for tolerance spec.

SGregory · 27th December 2010, 11:47 PM

I need to look up the spec on my Fluke 8840A. I suppose it should be able to measure it.

Salas · 28th December 2010, 12:13 AM

What? A desktop Fluke? Must be crazily accurate.

SGregory · 28th December 2010, 12:24 AM

It is the only calibrated instrument I have. I think I can do a 4 wire measurement with the resistor to buffer the current. However, the 2 wire only passes 1mA and can be offset for lead resistance.

I measure 19.22R on the Right and 17.86R on the left channel. It is repeatable. I did this on the new one fresh out of the bx.

Salas · 28th December 2010, 12:29 AM

Don't do a Kelvin, no need. It surely takes 220R load then. Denon, I come to Japan for Kill Bill 3!

Thanks Scott.

SGregory · 28th December 2010, 12:31 AM

Now I am curious to the sound of it with it properly loaded. I may have to pull the Pheonix out and try it.

AndrewT · 28th December 2010, 12:34 AM

use a 1.5V battery and wire it to a 1k0 resistor in series with the MC/MM coil.
The 1k0 will limit the coil current to <1mA and the power dissipated in a 10r coil would be ~10uW and in a 100r coil ~0.1mW
The coil cannot glow red hot. It might run slightly warm !

Now read the voltage across the coil and across the resistor.

Salas · 28th December 2010, 12:40 AM

No need for protection resistors any more since Scott and I we did not wimp out.

27th December 2010, 10:59 PM	#5591
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	The higher than spec reading may have been an artifact of the coil heating up and glowing like a valve filament __________________ Living Life Doing the Waltz in 4/4 meter.

27th December 2010, 11:47 PM	#5594
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	I need to look up the spec on my Fluke 8840A. I suppose it should be able to measure it. __________________ Living Life Doing the Waltz in 4/4 meter.

28th December 2010, 12:24 AM	#5596
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	It is the only calibrated instrument I have. I think I can do a 4 wire measurement with the resistor to buffer the current. However, the 2 wire only passes 1mA and can be offset for lead resistance. I measure 19.22R on the Right and 17.86R on the left channel. It is repeatable. I did this on the new one fresh out of the bx. __________________ Living Life Doing the Waltz in 4/4 meter.

28th December 2010, 12:31 AM	#5598
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Now I am curious to the sound of it with it properly loaded. I may have to pull the Pheonix out and try it. __________________ Living Life Doing the Waltz in 4/4 meter.

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27th December 2010, 11:04 PM	#5592
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Nah, I touched it very fast, only as long as it took to show and I did it at the other end of the leads on the RCAs. 19.16 Ohm but I say 19 Ohm because of the interconnect and arm wires. Then again if it glowed, now I will have tube tone for free, and low noise. I could even manage the No noise spec if I burned it. But its alive and kicking.

27th December 2010, 11:39 PM	#5593
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	The modern DVMs have high internal impedance in resistance mode I trust. Very little current to give. But what about using a known resistor, measured on same DVM, like 2k2 in series and subtracting it from the total resistor+cart measurement. That should protect any cart from any possibly strong DVM. But the DVM must reliably show the correct extra Ohm relatively to the 2k2 bulk. Must be a rather good one for tolerance spec.

28th December 2010, 12:13 AM	#5595
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	What? A desktop Fluke? Must be crazily accurate.

28th December 2010, 12:29 AM	#5597
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Don't do a Kelvin, no need. It surely takes 220R load then. Denon, I come to Japan for Kill Bill 3! Thanks Scott.

28th December 2010, 12:34 AM	#5599
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	use a 1.5V battery and wire it to a 1k0 resistor in series with the MC/MM coil. The 1k0 will limit the coil current to <1mA and the power dissipated in a 10r coil would be ~10uW and in a 100r coil ~0.1mW The coil cannot glow red hot. It might run slightly warm ! Now read the voltage across the coil and across the resistor.

28th December 2010, 12:40 AM	#5600
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	No need for protection resistors any more since Scott and I we did not wimp out.

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