Simplistic NJFET RIAA - Page 69

es44 · 21st January 2009, 02:43 PM

Quote:

Originally posted by salas
Did you notice any better turntable replay with what you already have?

P.S. There are really cheap MM out there, considered very good. Like Audio-Technica CN5625AL.

It's too early to make any statement, but i do think i hear more details on good records. Was disappointed first, when i heard "Wish You Were Here", but it is a record i just bought, and it's in a bad shape i guess.
Different story when i put Miss B, Haven on. ( Danish female rockband ), it came to life like i didn't hear before.

Must have a new cartridge, but as said, have to wait a little. I did hovever look around, and found a lot of sellers, mostly from Usa, and the costums here will kill the good deal

Best regards
Ebbe

iko · 21st January 2009, 08:09 PM

Hi salas, guys,

I don't know if people would be interested in a pcb layout I worked out for a version of the shunt regulator. I will attach the image of the slightly modified schematic I have, and if there is any interest I will provide a link to the pcb layout. The reason I modified the schematic a bit is to use parts I had on hand, and also to test the effect of pre-regulating the input with a LM317 the way Walt Jung has done on his super regulator. In simulation it gets rid almost entirely of any output ripple. It is very easy to jumper-out the LM317 and simply not use it. In any case, details can be provided if you guys are interested.

Salas · 21st January 2009, 08:38 PM

Its a nice version, I like the use of a JFET CCS creating a resistor Vdrop voltage reference for the CCS Mosfet. It has to be measured for Idss. I would avoid to wrap a non feedback shunt in a series high feedback IC though. It defies its purpose. By jumper bypass you can test its subjective impression on sonics. But ripple is already vanishingly low so a pre reg is just for curiosity IMO. PCBs are always welcome to be posted.

iko · 21st January 2009, 08:59 PM

I forgot to mention that I replaced the three LEDs with a resistor, the reason being that I don't really see the advantage of three LEDs. I'm in agreement with you that the vreg is in there because of my curiosity, and it can be easily bypassed with a piece of wire. I suppose I can just take it out, then I'll post the pcb file.

Salas · 21st January 2009, 09:07 PM

The LEDS are Vref on their own with very low noise. The 2SK170 I use under them locks their current too, and it is maybe the lowest Jfet for noise. 3 Leds maybe contribute as much noise as a 60-150 Ohm resistor. A 1600 Ohm contributes more and it will drift along with the Idss thermal cycle of the Jfet, which in your version isn't the best there is for self noise. But those are little things to compare. Both versions are good.

iko · 21st January 2009, 10:27 PM

Let's just say I have a bad tendency to use parts I have at hand, but it's not always a good idea. I will put together a pcb using the LEDs and 2sk170. Do you recommend any particular LEDs?

nicoch58 · 21st January 2009, 10:33 PM

led

http://search.digikey.com/scripts/Dk...ame=67-1122-ND

Salas · 22nd January 2009, 02:29 AM

Quote:

Originally posted by ikoflexer
Let's just say I have a bad tendency to use parts I have at hand, but it's not always a good idea. I will put together a pcb using the LEDs and 2sk170. Do you recommend any particular LEDs?

I recommend experimentation. Use your ideas and parts, listen and compare. I have some certain reasons for choosing some topologies and parts, based on technical and subjective stuff that I evaluate in my own way. Not carved in stone. It only takes time. I just wanted to reply my reasoning behind the LEDS, that is all. LEDS must be 1.7V for the circuit to give the stated current, with the stated R1. If you find them in green they usually come closer to each other statistically. In other color they spread a bit, so you may need sample more. One way is just to string 3 of them together using 1k resistor at their one string end, use a 9V battery, and measure the total drop across them 3. You can subtract 3.4V (Mosfet VGS) from what you measured . What is left will give you the wanted set current for the CCS if you divide it by an adequate resistor. So you can make do with what LEDS you may already have.

iko · 22nd January 2009, 02:32 AM

Thanks nicoch46!

Here's the pcb image for perusal; one can use either LEDs, or the resistor with this layout. Also, one can use either BF245A or 2SK170 JFETs on the same pcb (they have different pinouts). Interesting that in simulation the bf245a show less noise.

iko · 22nd January 2009, 02:34 AM

For part numbering reference, here's the schematic that corresponds to the pcb layout.

21st January 2009, 10:33 PM	#687
nicoch58 diyAudio Member Join Date: Oct 2004	led http://search.digikey.com/scripts/Dk...ame=67-1122-ND __________________ Sic58

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21st January 2009, 08:38 PM	#683
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Its a nice version, I like the use of a JFET CCS creating a resistor Vdrop voltage reference for the CCS Mosfet. It has to be measured for Idss. I would avoid to wrap a non feedback shunt in a series high feedback IC though. It defies its purpose. By jumper bypass you can test its subjective impression on sonics. But ripple is already vanishingly low so a pre reg is just for curiosity IMO. PCBs are always welcome to be posted.

21st January 2009, 08:59 PM	#684
iko diyAudio Moderator Join Date: May 2008 Location: Toronto	I forgot to mention that I replaced the three LEDs with a resistor, the reason being that I don't really see the advantage of three LEDs. I'm in agreement with you that the vreg is in there because of my curiosity, and it can be easily bypassed with a piece of wire. I suppose I can just take it out, then I'll post the pcb file.

21st January 2009, 09:07 PM	#685
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	The LEDS are Vref on their own with very low noise. The 2SK170 I use under them locks their current too, and it is maybe the lowest Jfet for noise. 3 Leds maybe contribute as much noise as a 60-150 Ohm resistor. A 1600 Ohm contributes more and it will drift along with the Idss thermal cycle of the Jfet, which in your version isn't the best there is for self noise. But those are little things to compare. Both versions are good.

21st January 2009, 10:27 PM	#686
iko diyAudio Moderator Join Date: May 2008 Location: Toronto	Let's just say I have a bad tendency to use parts I have at hand, but it's not always a good idea. I will put together a pcb using the LEDs and 2sk170. Do you recommend any particular LEDs?