Simplistic NJFET RIAA

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#8,201
buzzforb said:
THanks,,
Ill go ahead then.
Click to expand...

The mezmerize like routing and switch system was the main pig for p2p, I am done with it at least. Phono tweak time starting from next week probably.
 

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#8,203
That pic is from the mate's line pre. I put single supply b1 in the ones we are going to check out already, a couple of 1uF simple supreme caps I got, the pot to the 6v6 buffer is 50k, no need I go symmetric supply and dcb1.
 
#8,205
Rush said:
159155
Divide your resistance then your uF into the above number and you have the 3 BD down roll off frequency. Multiply the 3 DB down frequency by 10 and that is how far the phase shift effects the frequency response.
So, 159155/1000000/.1 = 1.59 Hz x 10 = 15.9 Hz. All good, below 20 Hz
If, 159155/500000/.1 = 3.18 Hz x 10 = 31.8 Hz.

As the resistance goes down, the cap size goes up for the same roll off.

Rush
Click to expand...

Another question on the 1Meg res value, Rush, if you don't mind.

Given the "rule of thumb" which says that Zout of one component (or gain stage) should be <1/10th - and preferably <1/20th - of the Zin of the following gain stage ... if we assume Zin for a JFET is ~15Meg then using a Gate resistor of 1Meg gets us much closer to the low-end limit than 500K does (1/15th as against 1/30th).

Is this a problem? 😕

Thanks,

Andy
 
#8,207
Salas said:
For that with MPF103 fets one or you made a simplistic also?
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Hi Salas - you mean the circuit using MPF102s that I posted a Q about, last year? 🙂 (You have a good memory.)

No, I haven't built a Simplistic ... I have made substantial modifications to that initial circuit over the past 3 years, so that it retains the basic construct (2 x JFET gain stages with a passive composite RIAA network in between) but everything about the gain stages is different! 🙄 (Including changing to 2SK170s, to get me more gain.)


Regards,

Andy
 
#8,210
andyr said:
Another question on the 1Meg res value, Rush, if you don't mind.

Given the "rule of thumb" which says that Zout of one component (or gain stage) should be <1/10th - and preferably <1/20th - of the Zin of the following gain stage ... if we assume Zin for a JFET is ~15Meg then using a Gate resistor of 1Meg gets us much closer to the low-end limit than 500K does (1/15th as against 1/30th).

Is this a problem? 😕

Thanks,

Andy
Click to expand...

I am not the master of JFET knowledge, I leave that up to Salas.
You can pick what ever size output cap you have or want and figure the resistor backwards within reason, 1 meg being the highest value resistor.
The roll off frequency should be less than 2 Hz.
The phono sounds the best it has after this mod, due to .... who knows why? I'm going with better coupling caps as the reason.

Rush
 
#8,213
Rush said:
You can pick what ever size output cap you have or want and figure the resistor backwards within reason, 1 meg being the highest value resistor.

The roll off frequency should be less than 2 Hz.

Rush
Click to expand...

Sure, Rush, I understand:
a) the inverse relation between resistor value and cap value, and
b) the far higher cost of good caps - so it's cheaper to use a 0.1uF cap than a 0.2uF cap! 😉

I was simply wondering if 1Meg was pushing it a bit high! 😕

Rush said:
I am not the master of JFET knowledge, I leave that up to Salas.
Click to expand...

So, Salas ... can you advise? 🙂

Q1: Is it a problem to use a 1Meg resistor on the Gate of a JFET?
Q2: Would it be better to use 500K?

Thanks a lot,

Andy
 
#8,214
Depends on Jfet type and its gate leakage current spec IGXS-VDS. The way we bias them in the simplistic they won't leak more than 100pA, so no problems with up to one meg. I had cranked them up further even and could not see any sudden rise for noise floor in FFT.
 
#8,216
kstlfido said:
Hi John- Please feel free to emulate away!

How does it sound? Great! I only have a Mitsubishi Integra preamp to compare it to. My Salas RIAA build has more dynamics and life. Very happy with it's sound. Of course there are many variables and subjectivity. I'm also using a lab supply to power the shunts as I've been too distracted/busy to build a transformer/CLC power supply.

It doesn't have quite as much gain as the Integra but plenty loud enough. Possibly the latest ideas on this thread will address that. Still good to go. I hope I can get into in a box for Burning Amp in October! 😀

-Kent
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Sorry for some reason I missed seeing your reply Kent. Very encouraging to hear about your results. I'm still getting the parts together, but hope to start building next month sometime 🙂

Glad it's being enjoyed - does seem to be a universally well-liked and highly praised design. I'm really looking forward to giving it a whirl.

John.
 
#8,218
No, the second line comment is about the experimental phono. The little line amp will be with some gain, simple symmetric Fet John Curl style cheap to make solution. I had given him a B1 from mid summer now not to be without music, but he has to have some gain, his ARC amp needs that even from a CDP as source.
 
#8,219
Now with a much better matched k170 at 8mA idss, I get 12v sharp on the output of the cascode.

Using 1k4 to power the buffer (also with 8mA fets) I get 23.7v for Vd on the top fet....

Wondefull... Allready have one board populated... soon to be news about experimental wallis simplistic 🙂
 
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