Simplistic NJFET RIAA

Success (Alas, Temporary)

OK, hooked things up, and it actually played music. Only listened for a minute or so, then put it back on the bench. I was waving my soldering iron around and heard ZIP and something fried. Dumb!!! I will look at it tomorrow.

Anyway made some measurements across resistors, as shown below. Some differences between channels in a couple places, even though most of the JFETS were pretty well matched, except the LED part and the output buffer.

Do they seem reasonable?
 

Attachments

  • RIAA-Board.jpg
    RIAA-Board.jpg
    318 KB · Views: 230
  • Annotated RIAA Circuit.jpg
    Annotated RIAA Circuit.jpg
    91.8 KB · Views: 232
  • Shunt-Photo.jpg
    Shunt-Photo.jpg
    20.3 KB · Views: 222
HOORAY!

I went back and reconnected things, and everything lights up and looks OK.
Darn lucky!

Re-checked some voltage drops:

R2 (below Q1) - 2.3 mA
R9 (above Q5) - 6.7 mA
R7 (below Q5) - 7.3 mA
R10 (above Q2) - 4.2 mA
R6 (below Q2) - 4.0 mA
R12 (above Q6) - 7.2 mA

Look OK Salas?
Thanks!
Doug
 
Thanks Salas,
RC, they are some "vintage" RelCaps.
I think I will get some more. I just wanted to get something working before ordering a bunch of "audiophile" parts. Right now I have a Multicap and a WIMA for coupling. I will see which I like better. I have some russian k40's, but they are .47 uF. The output caps are Angela tin foil.
Also, fortunately I had some Rikens left over for resistors.

Thanks for your encouragement and help.
I will keep you posted on things as they burn in.

Doug
 
Hi Salas

Still on the parts hunt !

Don't want to use any 'Unauthorised Parts'...
...but...
I found some 'nice' high-stability 1.6megs today.

Should be OK in the 1meg positions ?
Yes ?

Cheers

Si.

P.S. cap-pickers...
...what USSR silver-mica's do people like around here ?
I read the larger ones in the 'metal-cans' are good for bigger values, like 47nF & 15.5nF...
...anyone tried them ?
 
I haven't really listened to it yet Salas. I just plugged it in to see if it worked. I need to re-check it after my boo-boo, but wasn't planning on listening to it until it has burned in some more. It did not sound very good after one minute of playing. :)

Thinking about capacitor options now. You use the Russian siver mica for RIAA, right? What about the 0.1 coupling cap?

I have an AR "The Turntable" with a new base and with Marc Morin's mass loading (using Linn springs and then adding weight (about 1.5 kg !) to the sub-chassis to get all three springs equally compressed.) Really settles the suspension down. Looks fugly though. :)

Currently have a Grado gold in Linn Basik LVX. Want to try a DIY tonearm. Got some nice spruce, since I build violins as another hobby. Marc also suggest getting a Grado MCZ stylus, which he says makes a HUGE improvement. It costs about $175 I think.