Simplistic NJFET RIAA

diyAudio Chief Moderator
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Another one up and running.

4 x k170 input fets
K72-6 Teflon 15n caps
K71-4 Polystyrene 47n caps
Full on second stage buffer (with fet ccs)

Now listening with a DL160.... no clipping... super silent... dynamic... Tone seems correct, must let it settle for a while, then retrim voltages and serious listenning ahead.

What are those little coils? Anti resonance gate measures? 4xK170 is ~63dB gain, using a HOMC is hardly a way to listen to it correctly, still not clipping is noteworthy though.
 
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I got some ft1 to try as RIAA caps. As matter of fact, I think I got every kind. Can't remember. Get used to it as you will need to listen for difference in sound(if any) in tx2575 resistor.

Beware of FT-1... The thin wires do not help and tend to come loose.... I had trouble with drifting values also.... IMO no go.

The best are FT-3 with alu casing... but no values for the riaa. The K72-6 are bulky but the insides are +- ok (I opened one to see :) )

The K71-4 polystyrenes are really good.... nice mids, fluid....

What are those little coils? Anti resonance gate measures? 4xK170 is ~63dB gain, using a HOMC is hardly a way to listen to it correctly, still not clipping is noteworthy though.

The coils are the placements for the input / output wires and also he output cap..... Really better than trying to solder those directly on the boards.

I use the DL160 just for the initial burning... I will soon change to the Benz and start serious listening.

Anyway, after an hour, the sound is now very powerfull (I agree that the buffer is better... just need some riaa trimming)... Spatial presentation is awesome, bass is deep and controlled and the highs are becoming sweet.
 
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*A friend tried with single k170 in lieu of 369 for the base circuit the other day although I warned him it is designed around the 369 and then he told me it was bit weird until he found 4 proper ones I had given to him a long ago and used two for stereo. Then all fell into place and he had some audio epiphany moments with some bass galore etc. :) Conclusion is just follow the tested circuits, they work correctly.
 
Salas,
Do you know of a good adapter that would allow for easy changing of caps? I haev looked for somthing simple, like the coils, but have not fonud anything. I was considering just doing multiple daughter boards with different caps on them that will fit PCB holes, but still not plug and play.

Thanks RCruz. Ill have to get some of the K71's to try. I have some seimens KS coming. ALso ordered some modern PPS. This is goign to be fun. Just got to talk brother into letting me remove his long enough to listen to newer versions.

Salas,
If we buiilt them as spec'd, what would you do with yourself:rofl:
 
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Salas,
Do you know of a good adapter that would allow for easy changing of caps? I haev looked for somthing simple, like the coils, but have not fonud anything. I was considering just doing multiple daughter boards with different caps on them that will fit PCB holes, but still not plug and play.

Thanks RCruz. Ill have to get some of the K71's to try. I have some seimens KS coming. ALso ordered some modern PPS. This is goign to be fun. Just got to talk brother into letting me remove his long enough to listen to newer versions.

I use golden inserts like those found in older meridians

PS:
Looking forward to try those resistors have you sent them yet ?:)
 
diyAudio Chief Moderator
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Help me think this out guys.
In RIAA,
We are looking at 15nf caps, plus - a 150pf or 300pf I guess. Total 15.15-15.3nf
I assume this is important. Would a silver mica or polystyrene work best?
PCX has 150pf polystyrenes. (Silver mica too).

Its important to have the right value in this design, and yes, silver mica and polystyrene are great trim caps. As it is matching the semis well between channels. *Two K369BL of 11mA IDSS when tracing curves are pictured in the attachment.
 

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After some more hours listening I am glad to report the tone is really good. No stridency no bass blurring, sweet mids and that magical super wide soundstage.

I read on the papers of Allen Right that matching riaa components between channels is really important to preserve a very tight gain/phase relationship so as not to corrupt the stereo image.... totally agree.

In this case I was not able to follow the prescribed cap / resistors values due to stock shortage but am getting really good at simulating riaa components.... This time it was a total hit from the start... no need for further trimming.

Please bear in mind that 15.15nF are meant to be 15.15nF any deviation will blurr everything. If you can no get the exact values, trimming must be done in "all" riaa components.

I am willing to help of course.