Simplistic NJFET RIAA

[Doug R]

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?

[Salas]

Very reasonable except what you note for current through R10 must be what goes through R6 also more or less. R6 currents are as expected. What happened, some crock slipped?

[Doug R]

I think my iron touched the Vin alligator clip supplying power to the RIAA board and shorted something. Hard lesson.
When I get it working again I will re-check the currents. I know R10 should equal R6 - I will have to check it again.

[Doug R]

Salas, I am trying some WIMA FKP4 caps. Do you have any experience with them?
It may have been a poor choice, but I will give them a chance. I have read they need 100 hours to break in.

[Doug R]

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

[Salas]

The iron tip is normally grounded...

FKP4...good industrial quality. Nothing extra special.

Your last values table makes sense.

[RCruz]

Hi Doug

What are those yellow caps you are using in the riaa filter ? I must say they really look good !

[Doug R]

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

[The Space Egg Corp]

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 ?

[Salas]

No, use 1Meg.