Simplistic NJFET RIAA - Page 848 - diyAudio
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Old 6th November 2012, 06:23 PM   #8471
Salas is offline Salas  Greece
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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.
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Old 6th November 2012, 07:00 PM   #8472
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Yes... a typo

Anyway, using a 0.22 will increase bass response and you would need to lower the 47k resistor to compensate.
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Old 6th November 2012, 07:46 PM   #8473
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Its all inter related better you stick to the suggested values guys.
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Old 6th November 2012, 08:07 PM   #8474
Doug R is offline Doug R  United States
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Salas,
While I have you here, can the value of the coupling cap be increased without affecting the RIAA?
Thanks
Doug
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Old 6th November 2012, 08:21 PM   #8475
Salas is offline Salas  Greece
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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.
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Old 6th November 2012, 08:23 PM   #8476
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Doug R View Post
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
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Old 6th November 2012, 09:52 PM   #8477
Doug R is offline Doug R  United States
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Thanks again.
I will stick to 0.1uF interstage.
Best wishes,
Doug
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Old 11th November 2012, 03:54 AM   #8478
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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.
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Old 11th November 2012, 07:27 AM   #8479
Salas is offline Salas  Greece
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Cartridge model?
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Old 11th November 2012, 10:24 AM   #8480
RCruz is offline RCruz  Switzerland
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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
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