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LND150 gyrator for ECC83/12AX7 ???

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#41
Hi.

I have simulated the suggestion, Rod Coleman came up with, and this actually works.

I have used the new "LtSpice LND150" and the DN2540 from supertex.lib , which I know
is working in my 4P1L preamp.

I can adjust the voltage / mA when changing the R12 resistor from 560R to 1K.

Riaa_Gyrator_dn2540_lnd150_new_working_560r_199v.jpg


R12 = 560R gives me 199v and 0.806 mA
R12 = 1K gives me 136v and 0.585 mA

PS! just in case, these are the simulations used in LtSpice for LND150 and DN2540

.MODEL DN2540 NMOS (LEVEL=3 RS=1.05 NSUB=5.0E14
+DELTA=0.1 KAPPA=0.20 TPG=1 CGDO=3.1716E-10
+RD=11 VTO=-1.50 VMAX=1.0E7 ETA=0.0223089
+NFS=6.6E10 TOX=725E-10 LD=1.698E-9 UO=862.425
+XJ=6.4666E-7 THETA=1.0E-5 CGSO=2.50E-9 L=4.0E-6
+W=59E-3)
.ENDS

.MODEL LND150 VDMOS (Rd=450 VTO=-1.35 Kp=2m Cgdmax=1p Cgdmin=0.25p Cgs=7.5p)


Anyone tried to build this ???
 
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#43
Alastair E said:
So--Whats the advantage then of using this scheme--over a single enhancement MOSFET then....?
Much less capacitance issues using a single (easy to get) device rather than using two oddballs....
Click to expand...

Yes, there are many ways to achieve a good current source, or gyrator load.

But for the circuit you are proposing, have you measured the performance in an ECC83 stage - including the considerations and measurements that Merlin gave in post 33?
 
#44
Alastair E said:
What would be the issue by using a normal enhancement-mode MOSFET on top--say IRF820, gate set by potential-divider via high-value resistor, say 10M and a resistor--say 10-15K to plate, plate to gate via a cap, say 0.1uF...
Output taken from MOSFET to plate resistor node, so has low impedance

Plate volts set by pot-divider, to gate.

Ive used it with 12AX7--Works very well....
Click to expand...

The IRF820 has parasitic output capacitance value of 20 to 50 times higher (worse) than the LND150. E.g. 92pF (typ) at the usual data sheet point of Vds=25V. This is NOT an advantage, and the frequency response may even be degraded. If you identify an enhancement FET that can handle the voltages and SOA demand - and has lower capacitance, the performance may be OK. But cascoded stages do offer real improvements in this regard.
 
#45
Hmm, I thought it was the Crss (7pF for IRF830) that was the important one to watch according to many contributors here....

Ive used this scheme with the EEC83 where it was a huge improvement over ECC83 in SRPP.
Frequency-response was flat to over 100KHz, (180KHz -3dB as I recall) so I'm assuming thats OK too--This was in real-life, not a sim.....
 
#46
This is the LND150 model I got from the Spice Models thread (sticky, here):

Code: 
.MODEL LND150 NMOS (LEVEL=3 RS=150.00 NSUB=5.0E13 
+DELTA=0.1 KAPPA=1.O TPG=1 CGDO=2.1716E-12 RD=40.0 
+VTO=-2.0 VMAX=1.0E8 ETA=0.1 NFS=6.6E10 TOX=1.0E-7 
+LD=1.698E-9 UO=862.425 XJ=6.4666E-7 THETA=1.0E-5 
+CGSO=5.09E-10 L=10.0E-6 W=600E-6)
.ENDS

Does that look like a decent one?

--
 
#47
rongon said:
This is the LND150 model I got from the Spice Models thread (sticky, here):

Code: 
.MODEL LND150 NMOS (LEVEL=3 RS=150.00 NSUB=5.0E13 
+DELTA=0.1 KAPPA=1.O TPG=1 CGDO=2.1716E-12 RD=40.0 
+VTO=-2.0 VMAX=1.0E8 ETA=0.1 NFS=6.6E10 TOX=1.0E-7 
+LD=1.698E-9 UO=862.425 XJ=6.4666E-7 THETA=1.0E-5 
+CGSO=5.09E-10 L=10.0E-6 W=600E-6)
.ENDS

Does that look like a decent one?

--
Click to expand...

Hi.

I can try this instead to see what is happening.

This seems to be the same as in the supertex libs, which we have discussed here.

http://www.diyaudio.com/forums/tubes-valves/278565-lnd150-gyrator-ecc83-12ax7-3.html#post4423982

I have tried it in LtSpice and then my circuit doesn't work at all..
 
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#48
Rod Coleman said:
Hello Michael,

Why not build it and try it for noise? It should be easy to do. The cascoded LND150/DN2540 will provide a good current source without any changes, you can be confident.
Click to expand...

Hi Rod...

I don't have any LND150 yet, but the next time I'm going to order from Mouser, +65 euro for free delivery I'll order some.

In the meantime I'll consider to make a PCB for four, it doesn't cost much, and maybe I'm lucky and it would work. 😀 😀
 
#49
Alastair E said:
Hmm, I thought it was the Crss (7pF for IRF830) that was the important one to watch according to many contributors here....

Ive used this scheme with the EEC83 where it was a huge improvement over ECC83 in SRPP.
Frequency-response was flat to over 100KHz, (180KHz -3dB as I recall) so I'm assuming thats OK too--This was in real-life, not a sim.....
Click to expand...

Crss only accounts for Cgd (which is relevant for source-follower input capacitance considerations); Coss is the real output capacitance, formed of Cgd + Cds. If you have a 100n cap across G -> S then this is definitely the parameter we compare.

Since it is a comparison you're interested in, use the data sheet measurement point (Vds = 25V): Coss = 160pF (typ) for IRF 830; 2pF (typ) for LND150 - so the 830 is worse than the 820 and both are far higher than the LND150.

The actual frequency response also depends on the load of the next stage. If the measured FR was better than 100kHz, then I imagine the load impedance was lower than 500K.

The working value of Coss can be reduced by arranging for a higher voltage Vds.

All this only shows that the circuit as a whole, including its operating conditions, is what counts. Enhancement or depletion mode parts can certainly be made to work; the main advantage of the depleters is minimised number of parts and no real danger to the G -> S oxide because of the low impedances. With higher values of G -> S resistors, a zener may become necessary. A gyrator is also a valid option.
 
#50
michaelvv said:
Hi Rod...

I don't have any LND150 yet, but the next time I'm going to order from Mouser, +65 euro for free delivery I'll order some.

In the meantime I'll consider to make a PCB for four, it doesn't cost much, and maybe I'm lucky and it would work. 😀 😀
Click to expand...

If you like to cover all possibilities, order a few BF862 (NXP) while you are there. If your circuit as a whole is too noisy for your MM cartridge, or you try a moderate output MC, these cheap JFETs might come in handy for your RIAA stage.
 
#51
more on the cascode LND150 CCS

"Keep in mind that you won't be able to get much over .4ma from the cascaded version of the LND150 CCS. The lower LND150 won't have enough voltage to operate.
Looking at the saturation characteristics on the data sheet the LND150 needs ~.3V gate to source to get to 1ma output. But, to be functional, it needs a minimum of 1V drain to source to be active.
As the lower LND150's operating voltage is the gate to source voltage set by the upper LND150, ~.3V, the lower LND150 won't have enough voltage to be operating in a linear zone."

Gary and Rod,
Would using the multiplied bias of Walt Jung's modified cascode with all LND150s allow increasing the current to over (about) 0.4mA?

http://www.waltjung.org/PDFs/Sources_101_Letter_Revisit_0409.pdf

Many thanks
tim
 
#59
What is the pinout for DN2540N3-G (TO-92)?

The data sheet says thats is the same like LND150N3-G ( TO-92)

1 Source 2 Gate 3 Drain

My tester parts are right for LND150 but for DN2540 are 1- Drain 2- Gate 3- Source.

Any notice about this?


Cheers
 
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