Simplistic NJFET RIAA - Page 667

RCruz · 25th July 2011, 05:17 PM

Just replaced Q1 and Q3 on both channels.

Q1 = 8.5mA Idss
Q3 = 700 hFe

Sound is now even in both channels.

I will let it burn for a while and report back with results.

1st impression is very positive

Salas · 25th July 2011, 05:22 PM

Now its like in the PDF version and sorted out.

RCruz · 25th July 2011, 08:45 PM

Almost.... In reality, to get 10v on Q2 Drain to GND, I must set it´s Rs to 45 ohm.

I noticed improvements when moving from the previous 9.7v to 10v on Q2D. More explicit highs and more "air".

Lowering second stage gain by increasing it´s Rs seems to lower miller effect (that adds to the 15n cap in the riaa filter).
There is no perceptible increase of noise when doing so.

What should happen to THD when we increase Rs in this jfet ?

PS: I am starting to enjoy the FT-1

Salas · 26th July 2011, 01:33 AM

Will lower 2nd and bring up 3rd harmonic a bit in FFT. The total will be lower due to more local feedback.

RCruz · 26th July 2011, 07:01 PM

What should be the 2nd and 3rd harmonic distortion values with Rs = 45r for a 28v psu ?

Rload is 4k7 for Q2. How can I determine the best relation between Rload and Rs in this case ?

Salas · 26th July 2011, 07:16 PM

I used to have such a 28V ~43dB build, I don't have it anymore to measure THD in FFT and to show you exactly. It donated parts when I moved from the DL160 to the DL103R.

What I remember is it was about 0.03% THD for 300mV with second like 2&1/2 times higher visually than 3rd and no further overtones. Noise floor was something like -110dB @ 20Hz ref 1V out 0dB scale. Don't think that the Miller gets much different for about same second stage gain and say 10R difference in Rs. Having 9-10V on drain is a good balance between B+, Load, gain & Rs in 2nd stage as far as I recall.

RCruz · 28th July 2011, 08:17 PM

Finally found the error.

Left channel 15.3nF FT-1 is faulty... When I first measured it I found that the DMM oscilated between 15.3 and 9.7nF... I did not think about it and was convinced the problem was due to tarnished wires on the cap... I just cleaned it and soldered it in place.

Now I found that it still oscilates during measuring soldered in place.

I will replace it and report back.

merlin el mago · 29th July 2011, 09:44 AM

Bad news about FT-1

, I still don't soldered any cap but I will measure again to see if oscillate before to solder, thanks for advice Ricardo

eliaselias_0 · 30th July 2011, 12:30 PM

Hallo Salas.
I have the Grado Statement Master (0.4 mV, 47K, Mooving Iron) cartridge.
What sircuit is the best for this cartridge.
I read about the Grado Prestige Gold, but it is 4mV (high output).
My Master is low output. Only 0.4mV.
Do I must use 1% resistors and 5% capasitors?
In what watt are the resistors?
Thank you.

Salas · 30th July 2011, 02:44 PM

All your questions are covered in the pdf guide linked from post#1. Read it.

25th July 2011, 05:17 PM	#6661
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	Just replaced Q1 and Q3 on both channels. Q1 = 8.5mA Idss Q3 = 700 hFe Sound is now even in both channels. I will let it burn for a while and report back with results. 1st impression is very positive __________________ RC

25th July 2011, 08:45 PM	#6663
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	Almost.... In reality, to get 10v on Q2 Drain to GND, I must set it´s Rs to 45 ohm. I noticed improvements when moving from the previous 9.7v to 10v on Q2D. More explicit highs and more "air". Lowering second stage gain by increasing it´s Rs seems to lower miller effect (that adds to the 15n cap in the riaa filter). There is no perceptible increase of noise when doing so. What should happen to THD when we increase Rs in this jfet ? PS: I am starting to enjoy the FT-1 __________________ RC

26th July 2011, 07:01 PM	#6665
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	What should be the 2nd and 3rd harmonic distortion values with Rs = 45r for a 28v psu ? Rload is 4k7 for Q2. How can I determine the best relation between Rload and Rs in this case ? __________________ RC

28th July 2011, 08:17 PM	#6667
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	Finally found the error. Left channel 15.3nF FT-1 is faulty... When I first measured it I found that the DMM oscilated between 15.3 and 9.7nF... I did not think about it and was convinced the problem was due to tarnished wires on the cap... I just cleaned it and soldered it in place. Now I found that it still oscilates during measuring soldered in place. I will replace it and report back. __________________ RC

29th July 2011, 09:44 AM	#6668
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	Bad news about FT-1, I still don't soldered any cap but I will measure again to see if oscillate before to solder, thanks for advice Ricardo


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25th July 2011, 05:22 PM	#6662
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Now its like in the PDF version and sorted out.

26th July 2011, 01:33 AM	#6664
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Will lower 2nd and bring up 3rd harmonic a bit in FFT. The total will be lower due to more local feedback.

26th July 2011, 07:16 PM	#6666
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	I used to have such a 28V ~43dB build, I don't have it anymore to measure THD in FFT and to show you exactly. It donated parts when I moved from the DL160 to the DL103R. What I remember is it was about 0.03% THD for 300mV with second like 2&1/2 times higher visually than 3rd and no further overtones. Noise floor was something like -110dB @ 20Hz ref 1V out 0dB scale. Don't think that the Miller gets much different for about same second stage gain and say 10R difference in Rs. Having 9-10V on drain is a good balance between B+, Load, gain & Rs in 2nd stage as far as I recall.

30th July 2011, 12:30 PM	#6669
eliaselias_0 diyAudio Member Join Date: Feb 2009	Hallo Salas. I have the Grado Statement Master (0.4 mV, 47K, Mooving Iron) cartridge. What sircuit is the best for this cartridge. I read about the Grado Prestige Gold, but it is 4mV (high output). My Master is low output. Only 0.4mV. Do I must use 1% resistors and 5% capasitors? In what watt are the resistors? Thank you.

30th July 2011, 02:44 PM	#6670
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	All your questions are covered in the pdf guide linked from post#1. Read it.

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