Simplistic NJFET RIAA

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Hi Salas

A learning tech question for you.

Imagine I would like to lower input noise and use 4 x k170 there.

This would double Id current so I would need to increase Vdd to around 60V in order to have enough curren over R4 right ?

This is only a suposition, but using the same R13 (1500r) I would also increase gain to around 47dB right ?
 
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Hi,

What are the voltage and current demands for the folded simplistic?
I need two bib´s to be one of the cool guys, right? And they are both positive?


Thanks!

The demands are monopole +35V @ 30-35mA per channel. We usually set the SSLV regulator much higher for it to work its MOSFETS better. Usually at 150-300mA CCS per channel depending on how much sinking you are prepared to use.
 
diyAudio Chief Moderator
Joined 2002
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Hi Salas

A learning tech question for you.

Imagine I would like to lower input noise and use 4 x k170 there.

This would double Id current so I would need to increase Vdd to around 60V in order to have enough curren over R4 right ?

This is only a suposition, but using the same R13 (1500r) I would also increase gain to around 47dB right ?

To increase the current you don't need to increase the voltage also. Its a matter of redesigning for proper current biases around the input stage. Buzz uses 2XK170BL @ ~60dB gain with 0.5mV cartridge and he is reporting OK for noise though. Are you going for LMC? There is the 2X369BL 63dB example there already that Merlin has in mind.
 
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To increase the current you don't need to increase the voltage also. Its a matter of redesigning for proper current biases around the input stage. Buzz uses 2XK170BL @ ~60dB gain with 0.5mV cartridge and he is reporting OK for noise though. Are you going for LMC? There is the 2X369BL 63dB example there already that Merlin has in mind.

No, I am just trying to understand the 1st stage biasing.

I found your post here: http://www.diyaudio.com/forums/analogue-source/129126-simplistic-njfet-riaa-790.html#post3141205

Just do not know how you determined the 12r for k170 Rs
 
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4 Rs in parallel amount to 1/4 the value, its just we use one each for better current sharing, auto matching by local feedback in other words. So we get a total current in a single virtual "super transconductance'" JFET device with lower noise, more gain, more gate capacitance. Then the CCS resistor (1K in that example) steals that current from the PSU node just shy of what we need left for the PNP cascoding BJT to run through its resistive load folded to ground (2K2) for centering it voltage wise so we get a symmetrically clipping sinewave at max input drive.
 
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So if you used only one common Rs for the four k170, it would have to be 3r to generate the same Vgs right ?

Now I did not think of the 1k resistor as a CCS.... that explains a lot. That resistor must be correctly dimensioned to let go only the right amount of current so if it runs on the fets and also on the folded load resistor.

If we decrease the CCS resistor, more current will flow and as the current through the fets is fixed by Rs, there is more current through the folded load resistor and so more Vdrop there. That is how the trimmer works :):):)

Thank you again for your cristal clear explanation.
 
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Now in the double K369 schematic you used the same 2r2 as in the single K369 schematic (Not 4r4).... The difference in this case is in the CCS resistor that is smaller (1k2 instead of 2k2)

So your choice of Rs does not follow a strict trend... It must come from your simulation and experience.
 
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Even 3R each. Depends on what cart I want to use it for, how much mS I want from a particular JFET in single or more -given a stash- how much additional Johnson from resistive elementsI find excusable as a stability and capacitance trade off. And I judge it in use for small tunings.
 
Hi Salas,:D
I built this one from the first pages ,It's almost ready ,waiting on some parts to get here,I made 2 power supply boards so each board could have it's own power source,What do you recommend to feed the power supply boards? I am using the MM cartridge 47k load, I got out my old techniques sl 230 turn table and cleaned it up ,it's ready to go ,I realized I didn't have anything to plug it into,so I built your layout !:):):)
Thanks,
NS:wave2s:
 

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diyAudio Chief Moderator
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Compact and following the schematic lines will do. Do I see leds light down the Nichicons on photo#2? Powered already with own psu or just a lab psu test? Feed the power boards with 0.47R 1W to 4700uF RC after some soft recovery bridge.

P.S. Keep the Tx+bridge+main lytics at a distance or even in another box.
 
The demands are monopole +35V @ 30-35mA per channel. We usually set the SSLV regulator much higher for it to work its MOSFETS better. Usually at 150-300mA CCS per channel depending on how much sinking you are prepared to use.

I just needed the ratings to have the right resistor for adjusting it. I plan to have plenty of overhead current.

Thanks a lot for the reply! I have been reading threads here for years. I´ll let you know how my ears like the design later. ;)
 
Hi Salas,:D
I wish they were LED's burning but no must be a reflection,Thanks for the info on the supply ,I am waiting on fet's for the PS board ,I can be patient,lol.
I have the transformers,bridge .47R and some caps(10,000-4700-1000-470-100,10uf-and a .1) to run the supply boards ,and hope that's good enought,The box can be moved if it's LOF interfers!
Happy Listening!:)
NS
 
Last edited:
Hi Salas ,
Got the parts today and got the the shunt regs working fine They adjust from 18 to 30 volts,I will check for a 30 volt or better xformer tomorrow,I used a 24 vac,was in the junk box.
Got a problem ,I checked the layout and still don't see what I have done wrong,the last fet Q3 at the output isn't working,I have signal on the base of Q2 ,I have the PS at 30 vdc and get 18 v on Q3,Do I need to adjust R10,
It's bed time,,,, I will work on it tomorrow,,,,and get 'er done,lol.
Thanks for anyone help!
NS
 
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You should have about 4mA running through R10. Whatever voltage in respect to ground that resistor's drop imposes on Q2's drain gets to Q3's source minus little something. Your R9 value should allow double that voltage on its drain. Check those conditions. Trim R9 accordingly if Q3 is healthy. R10 changes the gain, better don't go there first.