Randall RRed vs Pre Amp From Hell

BuddytheReow

Breadboard Baker
Hey all,

Going to build a Randall RRed soon, but first I want to compare it to a separate stripboard layout called the Preamp From Hell

This layout calls for 2n5484s and I think they’re obsolete now. Is there an equivalent JFET I can use? I’m not too good on comparing datasheets. Any help would be appreciated. I’ve got j201s, 2n5457, and 2n5485s lying around. Could these work as well as direct substitutes?
 
I'm not 100% sure, but when used as an amplifier, it's probably the "Forward Transfer Admittance" (Yfs) and "Forward Transconductance" (gfs) that would be most critical to look at:

From what I could find:

Yfs / Gfs (uMhos)

2n5484: 3000 to 6000 / 2500
J201: 500 / 500
2n5457: 1000 to 5000 / 1000 to 5000
2n5485: 3500 to 7000 / 3000

The 2n5485 seems pretty darned close. And otherwise very similar (in/out capacitance, etc.) IDSS is different but that's mainly important when used as a switch.

 
Look for smd version - MMBF5484.
I took some measurements of various smd MMBFxxxx today.
So...
model - Vp - Idss

MMBF5484 - 1.4V - 2.6mA
MMBF5484 - 1.75V - 3.8mA
MMBF5484 - 1.54V - 3mA
MMBF5484 - 1.99V - 4.4mA

MMBF5485 - 2.5V - 6.16mA
MMBF5485 - 2.3V - 5.4mA

MMBF5458 - 1.96V - 4.45mA
MMBF5458 - 2.3V - 5.3mA
MMBF5458 - 2.1V - 5.12mA

MMBF5457 - 2.0V - 3.14mA
MMBF5457 - 1.97V - 3mA
MMBF5457 - 1.41V - 2.97mA
MMBF5457 - 1.37V - 2.85mA

MMBF5484 - Aliexpress
MMBF5457 - Aliexpress (with Vp close to 2V) and Tayda (with Vp around 1.4V)

I'd try 5457 with higher Vp and Idss then maybe 5458.

ps. Banzai Music has 2N5484 in stock. Price is quite high, almost 2.5 EUR for a piece.
 
Hey all,

Going to build a Randall RRed soon, but first I want to compare it to a separate stripboard layout called the Preamp From Hell

This layout calls for 2n5484s and I think they’re obsolete now. Is there an equivalent JFET I can use? I’m not too good on comparing datasheets. Any help would be appreciated. I’ve got j201s, 2n5457, and 2n5485s lying around. Could these work as well as direct substitutes?
Did you end up making it?
 
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