Simplistic NJFET RIAA

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Thank you Felipe

Only one shinkoh on the riaa filter (6k8) because I could not find a 43k also.

All other are kiwame apart from R5 1M carbon takman.

You got the caps right ! (The big BG N cap is the 2200u bypass on r2.)

I am waiting for the tuning caps to arrive..... I will get it running this week (I guess)

Ricardo
(Never say never)
 
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I am now listening to the 57dB riaa with only one shunt.

After 1 hour the sound is already very good.

I was afraid it would lack the BG bite but it seems Silmic produce a very well balanced sound.

I hear a very faint hum (equal in both channels)... will need to try new tX positions ....
 
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well, I have a BG N 2200u 6.3v for bypass first stage R but did not try it yet...(did not switch the dip) I am experimenting the 57dB riaa with a ACE Benz mid output (0.8mV) so it is already too loud.

The r core came from France :)

I guess I might bypass the silmic on the shunt vref.... I miss the BG "bite" a little.
 
I got 2 rcores 4x18VAC 50VA, few years ago from a GB. I think they must be from HK. I series - parallel the primaries to get 36VAC. In reality more like 41VAC even under load. When I used one for two shunts it was getting a little warm so I used the other one I had too. Doing this I also got a couple more volts after rectification. Also used 12Ohm resistors to drop voltage to 45V before the shunts. I know I am a little bit on the edge, but I tested for one day with around 47V and didn' t burn anything!
I can tell that there is a worthwile difference from my previous toroid I was using. Less grunt going through the power supply. Music seems slower with more definition betewen the notes.
Also there is a ground wire coming out from the primaries. Should I connect this and at which place? AC ground or central power ground? However, I have no problems keeping it unconnected.
 
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As is, switching on the 2200u gain caps there is no alteration in tone but bass becomes slightly fat and lacking control..... I must wait for the BG to settle.

Regarding the faint hum, it is not field related because I can turn and move the tx without any alteration. (These r core are really silent).

I am studying my GND setup .....

Linking output GND RCA to Star produces loud hum
Linking input GND RCA to star does nothing
Linking shunt input GND to star does nothing
:confused:
 

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  • 57dB GND setup r.pdf
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Basically you up the 2nd harmonic with a 0.8mV cart on a 61dB switch setting. Since the most gain is in the lows due to RIAA filtering, its likely to translate in ''thicker'' lows. The 57dB setting is for 0.5mV carts, the high one for 0.25mV in this phono as its second stage best performs. Its good that it does not completely breakdown subjectively, but you push it with the mid out ACE. Thats best on the 48dB, the ACES normally hit more than nominal output.

Put the final caps you like in the shunts, and when with 2 that you have on your configuration pdf schematic, check if you still get any harmonic noise from GND. Now its early to think and act on something you will soon change anyway.
 
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Confused with the different sonic results from bypassing riaa caps in my three riaa, I decided to buy a decent LCR.

I got a TENMA 72-8150 that states an average precision of 0.5% in capacitance reading.

After that I desoldered the 47n caps in the 48dB unit and measured 47.6 R 47.1L.

No wonder the sound lost magic when I added 680p //

In this design we should not overshoot 47n :)