Simplistic NJFET RIAA - Page 254

disco · 12:23 AM

Ricardo,

In general:

The regulator needs a minimal input of 28.1 + 5.7 + 2V margin for unexpected drop = 36 volt. Don't go much higher for dissipation reasons.

If you know the current you can calculate the resistance value needed to drop any voltage you like to your needs. Terminate with a decent cap (1 milli Farad) and connect your regulator.

If you're unlucky (count on it) the bench supply makes your reg oscillate. Why don't you use the intended supply for your phono?

edit: Whoops, mustard after the meal

RCruz · 28th October 2009, 12:48 AM

R1 as 15r... low heat.... +50vin.... max 27.2vout... no good.

I can not go on today.... tomorrow I will keep going

Salas · 28th October 2009, 01:08 AM

You are determined to solve it I see. Never backing away.

ikoflexer · 28th October 2009, 01:08 AM

Hey, it's better, get a good night sleep and attack it with fresh forces next time. I'm sorry to see you taste some of this; to move from v1 to v1.5 and v2, all those versions in between, lots of failures, oscillation, and so on, I've tasted quite a bit of this. But you will prevail!

A solution will be found.

RCruz · 28th October 2009, 10:43 AM

Before I spend more in a new TX, I need to know If the lower input voltage might be responsible by the oscilation.

I am currently using a 25v TX + full wave rectifier + cap and should get +35v (I am reading 34,5v).

Next possibility would be a 30v TX that would provide +45vout.

I can not find a TX in between.

Is there a possibility that a low Vin should create oscilation ?

Salas · 28th October 2009, 11:33 AM

We can't put the finger. Beyond that we use buffers successfully, and the one that breaks your errr, nerves, works in 3-4 builds, we can know nothing more in a specific build that we can not physically examine. It surely can give some additional performance, but I suggest you go for remote sensing instead, in your case. Maybe it will compensate subjectively to enough degree for a notch better without the head busting part.

massimo · 28th October 2009, 11:53 AM

I'm trying to design a suitable pcb.... one question: should I refer Q7 & R8 in the same Vref loop? In particular, should I connect Q7 collector + Q2 drain + R 7 togheter, then to V+ and R8 + R5 + Q3 emitter togheter and then to the gnd point (star)?
I would like to prearrange the pcb for remote sensing if needed.

Salas · 28th October 2009, 12:05 PM

It ''belongs'' to the output loop. See it and arrange it as a compound with the shunt Mosfet.

P.S. Don't design anything unless you know it works for you in p2p first. My 2c.

AndrewT · 28th October 2009, 12:29 PM

Quote:

Originally Posted by RCruz

I am currently using a 25v TX + full wave rectifier + cap and should get +35v (I am reading 34,5v).

34.5Vdc @ what mains input voltage?
What are the minimum and maximum DC PSU voltages when mains supply is at minimum and at maximum?

massimo · 28th October 2009, 12:53 PM

Quote:

Originally Posted by Salas

It ''belongs'' to the output loop. See it and arrange it as a compound with the shunt Mosfet.

P.S. Don't design anything unless you know it works for you in p2p first. My 2c.

Ok, thank you.
That was my first idea... and my pcb design, then a doubt arose.....

P2P: While I can draw nice pcbs (even for "porfessional") I'm a disaster with P2P....
My pcb design is based on "working examples" such as the drawings developed by James and Disco.... I'll cross my finger anyway!

28th October 2009, 12:18 AM	#2531
disco diyAudio Member Join Date: Apr 2006 Location: Holland	Ricardo, In general: The regulator needs a minimal input of 28.1 + 5.7 + 2V margin for unexpected drop = 36 volt. Don't go much higher for dissipation reasons. If you know the current you can calculate the resistance value needed to drop any voltage you like to your needs. Terminate with a decent cap (1 milli Farad) and connect your regulator. If you're unlucky (count on it) the bench supply makes your reg oscillate. Why don't you use the intended supply for your phono? edit: Whoops, mustard after the meal __________________ jaap Last edited by disco; 28th October 2009 at 12:23 AM.

28th October 2009, 11:53 AM	#2537
massimo diyAudio Member Join Date: Dec 2002 Location: Milan, Italy	Universal Phono Shunt (aka v1.1) pcb I'm trying to design a suitable pcb.... one question: should I refer Q7 & R8 in the same Vref loop? In particular, should I connect Q7 collector + Q2 drain + R 7 togheter, then to V+ and R8 + R5 + Q3 emitter togheter and then to the gnd point (star)? I would like to prearrange the pcb for remote sensing if needed.

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28th October 2009, 12:48 AM	#2532
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	R1 as 15r... low heat.... +50vin.... max 27.2vout... no good. I can not go on today.... tomorrow I will keep going

28th October 2009, 01:08 AM	#2533
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	You are determined to solve it I see. Never backing away.

28th October 2009, 01:08 AM	#2534
ikoflexer diyAudio Moderator Join Date: May 2008 Location: Toronto	Hey, it's better, get a good night sleep and attack it with fresh forces next time. I'm sorry to see you taste some of this; to move from v1 to v1.5 and v2, all those versions in between, lots of failures, oscillation, and so on, I've tasted quite a bit of this. But you will prevail! A solution will be found.

28th October 2009, 10:43 AM	#2535
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	Before I spend more in a new TX, I need to know If the lower input voltage might be responsible by the oscilation. I am currently using a 25v TX + full wave rectifier + cap and should get +35v (I am reading 34,5v). Next possibility would be a 30v TX that would provide +45vout. I can not find a TX in between. Is there a possibility that a low Vin should create oscilation ?

28th October 2009, 11:33 AM	#2536
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	We can't put the finger. Beyond that we use buffers successfully, and the one that breaks your errr, nerves, works in 3-4 builds, we can know nothing more in a specific build that we can not physically examine. It surely can give some additional performance, but I suggest you go for remote sensing instead, in your case. Maybe it will compensate subjectively to enough degree for a notch better without the head busting part.

28th October 2009, 12:05 PM	#2538
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	It ''belongs'' to the output loop. See it and arrange it as a compound with the shunt Mosfet. P.S. Don't design anything unless you know it works for you in p2p first. My 2c.

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