Simplistic NJFET RIAA

[stajo]

Aha now I see. I can forget those values since I use only one FET?

 

[Salas]

In the 43dB & 40dB versions forget that incremental IDSS and resistors chart.

 

[stajo]

In the 43dB & 40dB versions forget that incremental IDSS and resistors chart.

Thank you. Ive been matching 369s for 5,5 hrs and just now read that note thoroughly

 

[stajo]

So, now a little further...

First; Salas warned me to go much over 7,75 on the quad LED string cause the FETs starts to bleed gate current. And with my new Brymen DMM to compare with I think my UNI-T is showing some half to one percent to low values, and since I hade matched them up to exactly 7,75 with the UNI-T I had to redo them. Now they both start at 7,74 and goes down to 7,71 after warm up.

And today I have measured 369 Idss. Phew. I hope they are the real McCoy. At least the Idss ranges seems to make sence. The also look stored cause the pins are sligtly different shade where the bandings were and the banding was stone hard.

Heres my batch of 100. I made a new test-jig with super-short connections and matched up a 100,0 resistor with the Brymen. They all sat fired up a couple of minutes each. Pretty good BL spread. What should I pick, mid 11s?

 

[nezbleu]

I'll defer to Salas, but my instinct would be to use the high end of the recommended range. The guide says 10.5-12.5; I would use high 11.x (like 11.90/11.93) or low 12.x (like 12.37/12.38, there is another one next to 12.30 but I can't read the last digit). At this gain level the source degeneration is really swamping the Idss I think.

 

[Turbon]

I'll defer to Salas, but my instinct would be to use the high end of the recommended range. The guide says 10.5-12.5; I would use high 11.x (like 11.90/11.93) or low 12.x (like 12.37/12.38, there is another one next to 12.30 but I can't read the last digit). At this gain level the source degeneration is really swamping the Idss I think.

I think that tempco follows the gain. But they are so close anyway so go with nezbleus suggestion would be good.

Regards

 

[stajo]

there is another one next to 12.30 but I can't read the last digit). At this gain level the source degeneration is really swamping the Idss I think.

Thank you. 12,35 it was. I tried to measure Idss in my Caltek but it just blinked something like 17-1800 then it said 1. To high to be allowed there maybe?

 

[stajo]

The plot thickens

 

[nezbleu]

That looks great. I take it you are integrating the DCB1 and FSP into an integrated preamp?

I assume that when you mount the FSP boards on stand-offs you will be able to shorten the legs of the MOSFETs a bit.

 

[stajo]

That looks great. I take it you are integrating the DCB1 and FSP into an integrated preamp?

I assume that when you mount the FSP boards on stand-offs you will be able to shorten the legs of the MOSFETs a bit.

Thank you. Indeed it is to be a DCB1 buffer preamp with the FSP as integrated RIAA. Akouo select & volume with a Muses 72320 chip.

It doesnt show at the pic but the boards are actually piled up to the final height so the legs are about right. Ill solder them when its fixated.

I am to fodder the alubox with thin ply and fodder the heatsinks even more so they only radiate to the outside.

The DCB1 will have its own foddered compartment with heatsinks with the same principle.

Plus a separate PSU box with a lot of different voltages in the umbilical cord connecting the two.

 

[chat72]

Got the board running just now. I have to change Q3x to higher Idss value to get the correct bias. Sound big, warm and a little bit polite, but I'll wait a little longer before come to any conclusion. My set up is Thorens Jubilee with sme3009 sII imp and audio technica atf7.

Some pictures here.

 

[Salas]

Congrats. Looking good. Using PIO for C3? Input load & C2Y values, also the arm's VTA, are your handy tone tuning friends before thinking components. But let it settle and play many records to get intimate with the average replay quality regarding your vinyl collection so to cover most without exaggerations if to tweak a bit. Its responsive anyway.

 

[chat72]

It's not PIO it's polycarbonate cap. After a few hours sound open up a bit and changing input load seem to be giving a good result. I will keep FSP this way for a while because I'm thinking of changing my cartridge to denon dl304.

 

[Salas]

An excellent cart, but low output, it would take +10dB line preamp (at least) to have a proper result dynamically speaking vs a 0.5mV cart in the same total system.

 

[Marra]

Try with one channel PSU on the transformer only. Check if the hum is there on the active channel still. If gone, then you need double mono or separate secondaries Tx as expected by the Raw PCB design. If the hum is there still then its something about the cart grounding.

Thank you Salas it turns out that that is the problem.Time to order a new transformer.

 

[Salas]

Thank you Salas it turns out that that is the problem.Time to order a new transformer.

 

[bucurb]

most appreciate electrolytic capacitor brands

Hello,
What would be, in your opinion, most appropriate brand (brands) of electrolytic capacitors (C1, C2, C4, C5 and C6 ) for Salas Simplistic NJFET RIAA circuit, please?

 

[nezbleu]

C1, C2, C4 are film caps. Suggested types are in the build guide. C5 and C6 are electrolytics, and the build guide suggests Nichicon KZ or Elna Silmic II. Of course you can feel free to use whatever is your favourite.

 

[bucurb]

2N5457 alternative

J105, J107 and J109 (Fairchild Semi) are proposed as 2N5457 alternative. Did you tried, please?
Thank you.

 

[Salas]

They aren't, they got too much IDSS. Don't use those instead of K117GR. No 2N5457 or BF245A with VGS (off) higher than 0.6V in the Q3X position either.