Simplistic NJFET RIAA

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#19,041
Joel Wesseling said:
"21/6/19 The PF5102 JFET became EOL. But GB long term supply is secure. For substituting with J113 see info in post #1559"

Above info is from UBIB thread 33Vdc max. Can J113 sub PF5102 on UFSP? If no, any substitutes? Its the only part I'm don't have for the build. Thank
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Salas said:
It could work here too with proper value source pin resistors if 1.3S's J1 will not see >35V across it. Which is J113's VDS max spec. Asks not to exceed 43V RawDC input to this shunt reg. Approaching but not touching max spec this way. M1 Vgs and LEDs 1,2,3 Vf, drop the difference between those two voltages.
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I have 100 J113's from Digikey. With Atlas DCA75 I measure 12.00ma IDSS on 20 pieces, no variation. I'm assuming all 100 will measure 12.00 ma IDSS
Are they suitable?
 
#19,045
No issue with using J113 in the 1.3S shunt reg regarding its useful output range. Just don't feed it with more than 43V loaded Raw DC input. Antek 0532 50VA 32V transformer gave 42.3V raw dc loaded in glenv6's build yesterday so a 32VAC secondary should be safe for you too.
 
#19,047
Hello Salas - I've built the FSP for MM and a UFSP, which I use for a MC cartridge. The UFSP sounds incredible with an AT-OC9ML/II cartridge, my FSP is used with a Shure V15MRv5 with a JICO SAS NEO needle. I'm using Cardas 35awg wire from the cartridges pins to the RCA's going into the FSP, from what I have found the Caras wire is 140pF. In comparison to the UFSP, the treble is dull and the gain is less, the gain I can increase the volume, the treble I would like to improve.

I have Q1 populated with 91 ohms at R2, Q2 and R3 are empty. C2 is a VISHAY MKP 1837 10nF capacitor and C2y is empty. I was going to install pins for C2y so I can try polystyrene 82pF to 150pF, these I have in several sizes between 82 - 150pF. I'm using Auricap XO in C3 and C4 positions. I have VISHAY Z-foil resistors in R1 & R14.

Am I correct in assuming changes to C2y will improve the treble? ANy suggestions you have?
 
#19,048
I believe changes to input load resistance and total load capacitance would give you more solutions. MM is an electromechanical system with a resonance in the last octave. Rx positions are parallel to R1 and you can utilize all those creatively. Both for creating different R and adding C. Please read this older but informative article: https://www.tnt-audio.com/sorgenti/load_the_magnets_e.html
 
#19,052
BTW you could even install a 100k trimmer instead of R1. Wired as rheostat. To find out best treble balance with the Shure MM. Then measure the settled value and replace with a good resistor. Skipping experiments with Rx combinations. Try with 43dB gain config as well. It should not overload since it's a 3mV cart.
 
#19,053
I like that idea, I soldered in some pins on R2x and R3x to try capacitors and resistor changes. Very interesting article, the trimmer is a great idea instead of buying lots of resistors I may never use.

Can the trimmer be adjusted while playing a record? Or do I need to turn everything off to adjust? Best to ask a dumb question than the unknown.
 
#19,060
I measured IDSS of 100 pcs J113 with13.5v regulated psu.
After settling, the vast majority measure between 19 - 21MA
R4/R7R8 resistors I have 560 and 680 ohms at the moment and non at 750 ohms
Should I pick the lowest IDSS and go with 560 or 680 ohms with Jfets at 20ma IDSS.

Thought I'd ask because I'm right between the two
 
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