Simplistic NJFET RIAA

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You just stack 2 IRFP in the CCS, the one above is shielding the miller of the one below. Have a look in one cascode anode load for a tube preamp that I did, to get the idea. It extends the performance up high a lot.
 

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ikoflexer said:
L=100mH, C=4700u psrr of the above.

I don't know about the peak and roller coaster curve. Although great in dB region. I like soft trends. My guess is that a wee bit of capacitor imperfection, some layout reality, and a few cm of wire, will never let any reg do better than 100-115dB real life magic.
 

iko

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salas said:


I don't know about the peak and roller coaster curve. Although great in dB region. I like soft trends. My guess is that a wee bit of capacitor imperfection, some layout reality, and a few cm of wire, will never let any reg do better than 100-115dB real life magic.

The peak and roller coaster curve has appeared on absolutely all the regulators I have simulated so far, the Jung, yours, all, when the LC filter is inserted in the input. I agree with you that those number don't mean a thing in reality, with all of its imperfections. Ah well, at least it looks good on paper ;)
 
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Better avoid then. It smells interactions. To the contrary, a cascode CCS surely helps on self noise, extending the good region of CCS performance a lot in frequency. But it is more of a hassle to implement. Good for low parts count are DN depletion Mosfets from Supertex.
 

iko

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The cascode doesn't seem to help at all. I might try just go ahead with this version to see what it can do in reality.

By the way, thinking back to your almost perfect scope trace... you got some major filtering before the regulator right? That might explain it, since the regulator does not need to work so hard; I only used an LC filter of about 8000uF and 150uH. In any case, I will report any good news here if I get the time do it.
 
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Hi Salas

Just did the GND mods as per your sugestion and the result is a better stereo image, better stereo integration and much better bass (detail - extension).

There are two issues that I need to deal with:

1 - The hum I am hearing is lower but always present... I can hear it when not playing a disc and the pot is half way up. It seems to me it is related with the regulation because it sounds like a motor running (a little faster than 50Hz).

2 - Everytime I cut the power to the Riaa (to do some mods) and power it up again, I need to wait for 5 - 10 minutes until it stabilizes. During this warm up period, I hear spitting and thunder coming from the speakers. I measured the DC offset in the output and it oscilates between 200mV and -40mV until it reaches 9mV and stays put.... Is this normal ?

Ricardo
 
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Before I replaced all the rsistors in the Riaa, I did not have any of those power up noises.

The shunt is the same as before.

By the way the DMM reads in the output after power on, I believe there is some oscilation in the circuit until it stabilizes completely... The spitting thundering is the same I heard before when I did some mods in the DCP (new psu for the opamps) and latter I found there where some dry joints in the GND connections (now cured).

I believe I need to sit down and search for GND dry joints in the Riaa also.

BTW... The sound is unbelievably good right now.... Of course I miss the bass grip and detail of the CDP, but the high freq is so much better as well as the stereo image and presentation !

This can only be improved by changing the tonearm... I am using a SME 3009 II Improved (fixed headshell with 6.5g effective mass) and it is not the best choice for the MC ACE M Benz.

I would like your oppinion on the Roksam Nima unipivot.

Regards

Ricardo;)
 
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Unipivot arms are great, achieving much with simpler construction, hence having a lower price tag normally too. But I hate the jittery handling when moving them across the vinyl, selecting tracks.

Ricardo, hunt for those noise issues you got after so many substitutions and soldering at your leisure, with clear head. Since they were not there before, they will be taken out again somehow. I still recommend you to try your shielded wire that you use for input, in the same way for output too. It may lower your hum further.

They had a very nice analysis about low noise regs over at the solid state section forum by professional level engineers, me and Iko took part, and an easy to implement suggestion came up for our shunt too. I have it on test. Seems positive for now. Will extend and confirm my listening, and I will let you know if we got an easy shunt mod to adopt or not, soon.
 
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nicoch46 said:

Nima is good ,but your tonearm and cartrigde are good stuff better tweeks

BUILD a Pass amp..... F5 or miniA
Hi nicoch46

Can you suggest some tweeks for my arm/cart combo?

Does any of those preamps have caps in the signal line ?

salas said:

Ricardo, hunt for those noise issues you got after so many substitutions and soldering at your leisure, with clear head. Since they were not there before, they will be taken out again somehow.

Hi Salas

I am sure I will get rid of the noises.... very soon I will get some russian Teflon caps and so I will review all the connections.

Do you mean I can upgrade the existing shunt, or must I build a new one ?

I love these steps forward.....

Ricardo
 
My Salas RIAA is finally finished!
First, it is totally silent through 96 db speakers, without proper connection of tonearm wire shield. The sound as far I can say is excellent! I have not make a proper audition yet, but I it is very promising.
The output caps are temporary 22uF bypassed. Maybe order some auricaps 3.3uF today.
Also I gave the schematic to a friend of mine to built it, he is has no internet and he is amazed too!
Thanks a lot Salas.

George
 

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