Simplistic NJFET RIAA

[cliffforrest]

Originally Posted by Salas

It could be the factory mislabelled or mixed some batches and gave special prices to some vendors?. Don't know, excluding any error during measuring of course. If they are genuine, is not bad that Dual Triode got some strong ones too. DT, can you photo some on macro so we can see the labelling and if it looks genuine? You used the Ameter method with no drop resistor, right? What is the tolerance of those Ameters?

What does happen is:

Given a normal distribution of some test parameter, the premium grade will be sold at the highest price.

If the process is going very well that week, it may be that there are mostly premium grades, so little left for the lower/cheaper specs!

To fill an order, premium parts may be added to the lower grade bins.

I have done this in the past when test manager at a semi-house.

[Salas]

Economy of survival. Understood.

Now lets see how that equivalent circuit to SGregory I built as an upgrade to a friend recently (only with lower IDSS since the PSU was there already and fixed at lower B+ by Tx) goes along on the FFT, so he can compare his graphs.
First graph is open input, nothing attached except than output. Half the output's cable 2m length was twisted crock clips. It has 410R input resistor on board (820//820). Second graph is just the 15R Zo 1 to 200 attenuator cable attached on input. Its other end not attached to the generator's output. The noise floor is lower now. Ooops, 50Hz hum at -90dB and some very little HF hair also. Not possibly an introduced low level gnd loop, the thing isn't closing with something. Its picking it like an antenna. Could catch 6dB more hum if I touched the cable. Third graph is on the gen with 0.5mV input via the attenuator cable. Not bad THD at all for a non loop NFB SE circuit. I have even seen it losing the 50Hz band completely if playing with the cable and the usb card's placing, but I think its standard it will pick up something when connected to a TT cable so I left it there as charactristic hum. Can go worse when on a TT its the norm. So we see that with closed like low Z MC, nearly grounded input its the real low end noise floor, but we will pick up something little inevitably when exposing to the outside of the grounded box. We can close input to ground inside if we want to see it isolated. But a box in box like SG's can possibly also do better.

[RCruz]

Is it possible to minimize the antena effect just by rerouting gnd and +Vin lines in the riaa ?

[Salas]

In my experience no. Its a matter of transmitting sub mV in a real environment over SE connections. They skip that with balanced line measurements in instrumentation. Having just a consumer computer card, and hooking up here and there in the house with cables running around isn't remotely lab grade either, but I am very happy we got that in this modern age. It can basically show what we need to know.

Now stop a little and think of your vinyl dynamic range. Well covered.

[merlin el mago]

Some pics just for fun:

FT-3 vs Mundorfs silver/gold/oil (to have an idea how big they are)


Mundorf alone more near photo


Yes arrived 3,9uF & I have paid 3,3uF

[Salas]

Monsters. Do you have the mounting space?

[merlin el mago]

53mm x 50mm, will see but I believe that I can have enough space.

[RCruz]

Looking good.

Regarding magnetic shielding, I have been reading a lot and that resumed to the following:

Some materials are good to shield the origin of the field (strong field)

Some other materials are better suited to shield the receiving unit (small field)

There is always a compromise !

In my case, I found it easyer to iron shield the origin of the field (IEC inlet) than shielding the complete riaa boards with super materials !

Ricardo

[Joao@AltheaMusica]

Good results here

Is there any other JFET recommendation instead of the SK / LSK 170 with around Gm of 20 ~ 40mS? I'd like to make some listening tests.

[AndrewT]

Hi,
there are a few showing that bf861 & bf862 are good audio High gm Nchannel jFETs.
There are no Pchannel equivalents.