Simplistic NJFET RIAA

[Salas]

I have tried those, so, so, they round the resolution. Avoid PIO there if you can. If you can bypass them with something fast 10nF-22nF they speed up.

 

[Doug R]

Thanks Salas. Will try a cheap ceramic (just kidding!)
Doug

 

[Salas]

FT-1 does a good combo with K40.

 

[Doug R]

Salas,
I am still curious if a 0.22 or 0.47 uF is OK there, or will it mess up the RIAA?
Thanks.
Doug

 

[Doug R]

One more thing, does the output cap need to be so large for a tube preamp?
Thanks
Doug

 

[merlin el mago]

Depends of the input amps, output cap calculator link:

Coupling Capacitor Calculator by V-Cap

Cheers
Felipe

 

[RCruz]

Salas,
I am still curious if a 0.22 or 0.47 uF is OK there, or will it mess up the RIAA?
Thanks.
Doug

Hi Doug

Do not go below 0.47uF because you will loose bass response.

This one forms a frequency dependent voltage divider with th 1M gate resistor in second stage.

It also interacts with the riaa curve response.... Follow Salas advice for a well equilibrated response.

 

[Doug R]

Thanks guys. That's what I thought.
Doug

 

[andyr]

Hi Doug

Do not go below 0.47uF because you will loose bass response.

This one forms a frequency dependent voltage divider with th 1M gate resistor in second stage.

But plugging 1Meg and 0.47uF into the output cap calculator link which merlin posted, gives you 0.34Hz. Which is surely, unnecessarily low?

So why can't you reduce it to 0.1uF ... which produces a result of 1.6Hz - which meets the "x10" rule? 😕

Regards,

Andy

 

[Salas]

0.047uF he surely meant, probably a typo.

 

[Salas]

See post #8453 for plots simulating 100nF and 47nF interstage caps in circuit of the full phono when assuming zero contribution of the output coupling.

 

[RCruz]

Yes... a typo

Anyway, using a 0.22 will increase bass response and you would need to lower the 47k resistor to compensate.

 

[Salas]

Its all inter related better you stick to the suggested values guys.

 

[Doug R]

Salas,
While I have you here, can the value of the coupling cap be increased without affecting the RIAA?
Thanks
Doug

 

[Salas]

Talking the interstage one I believe. Beyond 220nF it will twist it too much. My advice is either 47nF with 2.2uF output cap and 50K up line preamp or 100nF with 2.2-3.3uF output cap and 20K to 50K line preamp.

 

[RCruz]

Salas,
While I have you here, can the value of the coupling cap be increased without affecting the RIAA?
Thanks
Doug

Hi Doug, we have been talking about that in the last posts.... You should not deviate from the spec because the interstage cap is calculated according to the other riaa fiter values.

Rload from first stage + 47k + 6.8k + 47n + 15n + 100n + 1M are all interrelated

 

[Doug R]

Thanks again.
I will stick to 0.1uF interstage.
Best wishes,
Doug

 

[The Space Egg Corp]

Hi phonograph fans !

Still nosing around & getting more components for the NJFET.

Have just been looking at various 'air-caps'.
3 main types have been found.

1. Cheap AM radio type > 100pF
2. Better quality radio type = about 120pF
3. Philips precision teflon - 7 to 100pF

Reason I've been looking mostly...
...is to put one on the cartridge load.
If after figuring out the cable pF and attempting to get 'ZERO' point ideal...
...having a 100pF 'air-cap' set at 50%, I think would give an easy, solder-free way of tweeking the cartridge response.

I have seen various 'DIP switch arrays' used for similar purposes...
...But the R load here ( I think ) only needs to be for 1 cartridge...
...and the 'air-cap' could be used for 'subjective-tone'.
Thus avoiding DIP-switches with resistors altogether.

What you guys think about that...
...anyone tried 'air-cap' front-end tuning ?

Air-cap question #2...
...I had also wondered about 'ZEROing' the RIAA HF cap, with a small value pF or two...
...and then having a 100pF 'air-cap' there too.

100pF, +50 -50, 0.1nF total adjustment here though, doesn't seem much, compared to possible cartridge-load use.
Anyone tried 'air-caps' there in the RIAA HF position ?

How much 'tweeking' of the RIAA HF cap are people doing ?

Also...
...is anyone bothering to 'tweek' the RIAA LF cap at all ?...
...I don't think I have EVER heard anyone talk about this.
( could be wrong though )

Any comments peoples ?

Cheers

Si.

 

[Salas]

Cartridge model?

 

[RCruz]

Si

I usually use a capacitor trimmer (5p to 90pF) to trim the high freq cap. After that I always replace it with a styroflex fixed value cap.... much better.

What do you mean by LF cap ?

As for cartridge loading.... we need cartridge type/model