Simplistic NJFET RIAA

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andyr

Member
Joined 2003
Golana said:
Yes thanks!

I'm trying to read up the Quasimodo thread. Wish there was more time in the day. I honestly don't know how most of you do it.

Salas, I asked earlier about a very low outout cart. What about 3.2mV? Would I be correct at 43dB.
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Yes, you should be. 43db gain gives you 710mV output for the standard 5mV in ... so 450mV output for 3.2mV in.

450mV should be enough input to your preamp, unless it has very low gain.


Regards,

Andy
 
M

Mas Penk

Member
Joined 2003
Finally... After having trouble with matching the led (the one from GB somehow didn't lit).
I can play the Tp1 and Tp2 in between 3.6 and 3.7.

But the drifting of Tp1 and TP2 is quite high (3.55 ~ 3.73) and It keep drifting on those value... is that normal??

I also have to increase the R3X to 11K (with 9K1 I always get 7.6V)
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Mas Penk said:
I did measure it after 30 minutes... it seems that that the variation is started to steady (smaller drifting)...

BTW is it OK using R3X up to 11K? I can't adjust it if I follow the manual... everything is stable. I tried to connect it without case and got alot of hummm :D
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If the mean average IDSS of K117GR fell lower in the kits then 11K is valid.

Drift will be there in MC two JFET builds. When just hovering around target center fairly when warmed up means good to go. Hum is a buid and wiring issue. Many said they could get very low hum with FSP even when naked but this does not apply to all environments and system groundings. Are the raw PSUs wired as the PDF's generic model?
 
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Offie

Member
Joined 2014
I'm stil strugling wether or not leaving the gate stoppers away...I read a lot of differences in feedback.

I will follow classic Le pacific...with a 6,2mV cartridge output volume. Due to lowering the drain resistors (for a better output impedance)..I will losse some gain...but I don't see a problem. But what do you think is the best to do with the gate resistors?
 
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Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
In my layout and gain structure missing them did not present problems. They are very detrimental regarding SNR of the head amp when entering MC area builds. If you can, do without. If its MM they are more tolerable. It takes practical research in every different preamp. It can tune in radio even.
 
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Mas Penk

Member
Joined 2003
Salas said:
If the mean average IDSS of K117GR fell lower in the kits then 11K is valid.

Drift will be there in MC two JFET builds. When just hovering around target center fairly when warmed up means good to go. Hum is a buid and wiring issue. Many said they could get very low hum with FSP even when naked but this does not apply to all environments and system groundings. Are the raw PSUs wired as the PDF's generic model?
Click to expand...

Yes.. I use two JFET 369...

I'm got a quite stable Vrail at 30V (Tp1 & Tp2 3,5XX to 3,7XX)....

Still looking for decent chassis before upload the pic....
 
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Offie

Member
Joined 2014
I'm gonna put my Jfet phono in the same case as my DCB1....hope this will work fine. So two toriods...and I really hope the "envirement" is quiet enough. In the pas I buided a opamp circuit (with good OPA-types)....even in a wooden enclusere....the result was "doable"....but these days we wouls like to build everything more decent :)
 
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