Simplistic NJFET RIAA

[guglielmope]

Hello ,
Salas I belive that in the next days we'll see an NJFet RIAA optimized for Denon DL103R?
Ciao
Guglielmo

[Salas]

For the time being I set it up a bit roughly late today so to find its buttons and let it run a bit. Interestingly the Mission 774 gave 8.5Hz Fs on test disc monitored on FFT with it. Tracks very well. I bypassed the 1st stage source degeneration resistor of the normal 0.5mV MC version Simplistic with Chemicon 1000uF 25V KY type (gel jokes OK) and got beautiful gain and tone. Hiss is naturally somewhat more but not what you can call obvious even on my 95dB speakers. I have in mind a 4 parallel 2SK170 45V B+ first cascode stage revision at a point for low MC so we can avoid cap bypass. On the other hand, this thing went so smoothly with bandaid gain solution and same basic from the previous DL-160 set up geometry from the very first minute, that it is a blessing. Don't be afraid to bypass the 56dB, the tone is golden. It can go back normal MC fast if you change cart, so its a good Low and normal MC solution in one package. I found that 260-280R loading sounds good for now. Its an obviously high quality, much musical, gentle cart. Excellent piano, things are happening much more with jazz bass players, satin mids n' highs, no stress nowhere, natural stage and depth. Reminds me of a Supex but with little more natural freshness. Here is its initial response on the 774 at 2.5G VTF and 265R load. No VTA experiments yet. 30 mins run in time. OK I listened to it more, something like two hours, but the graph has been taken early.

[Tham]

Hi Salas, another question about resistor choice...Takman was mentioned as one of the recommended type. Are they needed throughout the build or only at specific locations (ie only at RIAA stage)?

[Salas]

Takman pink are good enough for all places. Shinkoh I prefer for the cart load one and the one which connects the first stage to the Riaa (43k or 47k depending on version).

[Tham]

Thanks. My current built has a 1K Rload + 1000uF cap across R2 for a 61dB gain for a Supex 909 mc cartdridge at 0.2mV output. Had enough gain in my small listening room. Can the low output mc version be tweaked further for higher gain (say up to 75dB)?

[Salas]

Firstly, is your Supex a 2 or 5 Ohm? Get your load down at 100 -200 Ohm if so.
Also try a 2200uF R2 bypass. It will flesh out with both those moves.
Very high in gain it can go with large B+ and more 2nd harmonic, but I don't know of a cart needing more than 63dB in a sane total system gain structure, plus I don't know of an input stage that it will not hiss a lot beyond that.

[ikoflexer]

Originally Posted by Salas

Firstly, is your Supex a 2 or 5 Ohm? Get your load down at 100 Ohm if so.
Also try a 2200uF R2 bypass. It will flesh out with both those moves.
Very high in gain it can go with large B+ and more 2nd harmonic, but I don't know of a cart needing more than 63dB in a sane total system gain structure, plus I don't know of an input stage that it will not hiss a lot beyond that.

IMHO, syn08 uses the proper parts in the input stage of his latest phono stage, Hitachi 2SC2547/2SA1085. Because of the low source resistance that the MC poses, that bjt makes more sense than the jfet. The noise figure puts together the current and voltage noise; for the 2sc2546/7 the NF is 2.455 dB, while for the 2sk170 the NF is 5.025 dB. Signal to noise ratio is 71 and 68.43 dB respectively. Just found this in that chapter told you about. This seems to be a significant difference. For MM the case is different, no problem using 2sk170 in the first stage.

I don't know much about this stuff, just came across this info and thought I'd pass it along.

[Tham]

It is 2 ohm. Do I go for 100ohm Rload?

[Salas]

I will use 4 2SK in parallel like in the Pearl for genuine low MC input stage when I will make next. Will not be going back easy to normal MC though since the B+ and the load resistors will be different. But the funny thing is that even with this MC 56dB one with just one SK and boosting it with Rsource bypass the hiss is not something to notice on 95dB speakers when not looking for it. I would miss the sound of the Jfet if I would have to go bjts though. Could be most silent for say 67dB gain for a 0.1mV Ortofon, but would have different signature.

[Salas]

Originally Posted by Tham

It is 2 ohm. Do I go for 100ohm Rload?

Go fast.