Simplistic NJFET RIAA

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alexkosha

alexkosha

Member
Joined 2013
Yes, it's stared after some mishaps with RAW DC with K-Mults. It's stays even after worm-up process and I stars to heat it well when my volume is about 3/4 of max.
As I mentioned, they stays all the time.
I did not scoped FSP rail yet. But I'll test it today after work.


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ogromnii

Member
Joined 2016
some update for my project. comparison with my old preamp showed sound is too bright no matter with "lost constant" or not, although signal generator - inverse riaa - scope tests showed no deviation. decided that only obvious reason may be high input capacitance. thinkink how to check what's going on went to resonance search - connected through 560k resistor signal generator to phono out and scope also - and found well visible peak around 18k, but with capacitance of scope cable added. after that connected scope to preamp out and signal generator to input, with phono cable connected. again visible platеаu around 8K !! this means even cascoded version has something like 250-300 pf input cap :(
went back to not cascoded, and added emitter folower at the input. of course noise rised, but sounds incredible! also added 1k multiturn trimmers for "lost constant", used them for phase correction. simulation showed something like 140ohm, correct phase at 20K is around 100-110 , different at both channels.
will work at first stage a bit, and will update :)
 
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ogromnii

Member
Joined 2016
i was using your schematic from page 16 here, i'm not well educated in electronics, and dont know difference between folded and telescopic, and also dont know how to arrange it to minimise capacitance?
first stage source resistor is 50ohm.
is there simple way to measure input capacitance directly?
 
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Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
No not with an LCR or something direct, it does not work that way, it is inferred by measuring the -3dB HF frequency of a flat stage with 50 Ohm function generator source and then adding high resistance to the source and measuring the response again with the same known capacitance lab cable. So you know how many pF to subtract from the answer that comes from external cabling. Telescopic is like a Totem statue going up to the rail, folded is like in FSP when folding to the ground. Higher Rs like near 100R we use drops the pF by degeneration. In general when you got a high impedance (and inductance) MM cartridge the Rs will not add audible noise if it is enough times smaller than the cartridge's impedance. So use higher possible Rs for yours if its susceptible to HF audio band resonance and less pF TT wire type if possible. No C9 also.
 
alexkosha

alexkosha

Member
Joined 2013
alexkosha said:
Yes, it's stared after some mishaps with RAW DC with K-Mults. It's stays even after worm-up process and I stars to heat it well when my volume is about 3/4 of max.
As I mentioned, they stays all the time.
I did not scoped FSP rail yet. But I'll test it today after work.


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Click to expand...

Hi Nick,

I could't repeat the issue as soon as I opened FSP cover and connected my scope. I checked all connections and visually did not see any abnormality. All rail measurements are also good. I watched/listened several days and this is the reason why I did not report same day.
It is absolutely quite. Sorry for false alarm.

P.S. For guys who use DertyPCB KMs filters in Raw PSU: do not use that PCB as is. It is oscillating. Wait for Keatoken made PCB, or modify DertyPCB as advised on his forum.
 
alexkosha

alexkosha

Member
Joined 2013
Hi Nick,

I was too optimistic...
Clicking is back.
I went further and troubleshooted it from other direction.
I hope I found the source of that issue, but no resolution yet.

Interesting that FSP is absolutely quite when TT is disconnected or when I'm shorting the inputs.
I assumed that I have some pickup from cart.
So, disconnected it. No help?
These clicks appears when cable is connected on RCA side to FSP. At that pint, I tested the cable continually and/or cross-shorting.
No any evidence of problem.
Red ferule -> RCA Rch central pin;
Green ferule -> RCA Rch return (jacket);
White ferule -> RCA Lch central pin;
Blue ferule -> RCA Lch return (jacket);
None of them are shorted to GND screen and if my Fluke has 0.2R when leads are shorted, then I have 0.4R from RCAs to pins.

Can it be some cable capacitance issue or cable capacitance interaction with load resistor? Maybe some weird pickup on cable ..?
I'm out of ideas.
 
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Despearce

Member
Joined 2014
Before I go and spend £36 on 4 resistors (Charcroft naked Z foil as I can't easily get the Vishay version) as anyone tried other resistors in R1 and R14 with good results?

I'll be using an AT OC9ii/ml cartridge into a Puresound 2A3 amp and my homebrew Bastanis Wildhorn speakers, source is a replinthed Garrard 401 and Transfi Terminator T3 Pro tonearm.
 
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rtd

Member
Joined 2006
help :mad:, while measuring my probe slides and ... "catastrophe"
Dc in is ok, but rail + fails at 5v, tp1,tp2 at 5v too, D1..D4 don't light anymore (normal at 5v). all other led (in the regul) are ok (means are shining).

Any advice or other measure to detect the faulty component (before changing everything :rolleyes:)

edit : it works and sound well before what should have been the last measure
 
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