Ultrasimple mm/mc RIAA preamp 2 - Page 19

jah_zoldat · 16th November 2009, 03:30 PM

Hello! I did not found 2sk170 too, as well as J110. I made a simulation according to Wrenchone's advise, using BF244A with 15 ohm source resistors and 100uF bypass caps (voltage is 30V). THD is about 2.2 with huge 2nd and 8nd harmonics! I had an idea to build something simple with "pleasant distortion"..just for grins)) but i'm in doubt now.

Riaa curve is not changed, good at least.

Just noticed that with inverse RIAA connected to the ground 8th harmonic disappeared and THD is ~0.6 now. How to measure it properly? I'm novice in Microcap.

Salas · 16th November 2009, 03:42 PM

R4 3.3k, V2 24V. No C5,C6, you need some degeneration to lower THD. Do you have 2SK170BL model? So to compare what you may check for BF244 to match THD with original.

jah_zoldat · 17th November 2009, 12:28 PM

Thank you very much! Now THD is about 0.3 at 44 dB gain, almost entirely 2nd harmonic (I think I can deal with it

). BF244 mutual conductance is not so linear as 2sk170 at low gate-source voltage. i think I'll build it, maybe change jfets to 2sk170 when will find them.

Salas · 17th November 2009, 01:48 PM

Up the Rs resistors to 27R, aim for 7-8V Vd, no less than 40dB gain, by adjusting the drain load resistors, if you are going to use 5mV MM. THD will go lower. For 2SK170 available look in http://www.hifituning24.de/0000009b2...a415/index.php

sakdi · 18th November 2009, 04:08 AM

Hello

I can't find 2sk170. Is it possible to replace this jfet with j310?
Could you please help and suggest?

Regards

Salas · 19th November 2009, 12:15 AM

J310 has enough more noise in comparison. Better with BF244A, adequate enough for MM cartridges.

ra7 · 19th November 2009, 12:28 AM

Can I run these simulations on LTSpice? What simulator would you guys recommend?
I want to learn one.

Salas,
I'm planning to make a pcb for the one you suggested, hence taking more time!

Thanks guys!

sakdi · 20th November 2009, 07:05 AM

Thank you.

ra7 · 26th November 2009, 06:50 AM

Salas,
read all your posts for my problem in this thread.
One question I left unanswered was the cartridge...
ADC QLM 34 III... 7.8 mV.

taught myself some spice. Simulated the circuit and
am getting the same results as you. I can't get the
THD numbers to make any sense. Dug up some old
threads here and found that it is pretty unreliable
for measuring THD and harmonics. Also, I'm not sure
if I'm using the software correctly.

Anyway, I'm etching PCBs right now (for the first time)
for the circuit you posted. Its tough going... but
hopefully I'll get there.

Salas · 26th November 2009, 06:58 AM

Good luck with your PCB. THD is going to be good enough, better than in the Pacific. When you got results, let us know.

17th November 2009, 12:28 PM	#183
jah_zoldat diyAudio Member Join Date: Apr 2009	Thank you very much! Now THD is about 0.3 at 44 dB gain, almost entirely 2nd harmonic (I think I can deal with it). BF244 mutual conductance is not so linear as 2sk170 at low gate-source voltage. i think I'll build it, maybe change jfets to 2sk170 when will find them.

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16th November 2009, 03:30 PM	#181
jah_zoldat diyAudio Member Join Date: Apr 2009	Hello! I did not found 2sk170 too, as well as J110. I made a simulation according to Wrenchone's advise, using BF244A with 15 ohm source resistors and 100uF bypass caps (voltage is 30V). THD is about 2.2 with huge 2nd and 8nd harmonics! I had an idea to build something simple with "pleasant distortion"..just for grins)) but i'm in doubt now. Riaa curve is not changed, good at least. Just noticed that with inverse RIAA connected to the ground 8th harmonic disappeared and THD is ~0.6 now. How to measure it properly? I'm novice in Microcap.

16th November 2009, 03:42 PM	#182
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	R4 3.3k, V2 24V. No C5,C6, you need some degeneration to lower THD. Do you have 2SK170BL model? So to compare what you may check for BF244 to match THD with original.

17th November 2009, 01:48 PM	#184
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Up the Rs resistors to 27R, aim for 7-8V Vd, no less than 40dB gain, by adjusting the drain load resistors, if you are going to use 5mV MM. THD will go lower. For 2SK170 available look in http://www.hifituning24.de/0000009b2...a415/index.php

18th November 2009, 04:08 AM	#185
sakdi diyAudio Member Join Date: Jul 2007	Hello I can't find 2sk170. Is it possible to replace this jfet with j310? Could you please help and suggest? Regards

19th November 2009, 12:15 AM	#186
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	J310 has enough more noise in comparison. Better with BF244A, adequate enough for MM cartridges.

19th November 2009, 12:28 AM	#187
ra7 diyAudio Member Join Date: Feb 2009 Blog Entries: 1	Can I run these simulations on LTSpice? What simulator would you guys recommend? I want to learn one. Salas, I'm planning to make a pcb for the one you suggested, hence taking more time! Thanks guys!

20th November 2009, 07:05 AM	#188
sakdi diyAudio Member Join Date: Jul 2007	Thank you.

26th November 2009, 06:50 AM	#189
ra7 diyAudio Member Join Date: Feb 2009 Blog Entries: 1	Salas, read all your posts for my problem in this thread. One question I left unanswered was the cartridge... ADC QLM 34 III... 7.8 mV. taught myself some spice. Simulated the circuit and am getting the same results as you. I can't get the THD numbers to make any sense. Dug up some old threads here and found that it is pretty unreliable for measuring THD and harmonics. Also, I'm not sure if I'm using the software correctly. Anyway, I'm etching PCBs right now (for the first time) for the circuit you posted. Its tough going... but hopefully I'll get there.

26th November 2009, 06:58 AM	#190
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Good luck with your PCB. THD is going to be good enough, better than in the Pacific. When you got results, let us know.

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