B1 Buffer Preamp - Page 362

AndrewT · 11th October 2012, 12:25 PM

I note you have used 150kHz sq from a 3MHz gen, just as you described for your 20:1 ratio.

Could you add a 1us filter in between the gen and the B1 so that we can see the difference in the sq shape?

Salas · 11th October 2012, 12:33 PM

I just fully dismantled it to bits and back to parts bins, sorry. I used the higher Ciss 2SK170V to give it its worse spec possible for RC with gate stopper though. You may spot them in the first macro picture.

Salas · 11th October 2012, 02:32 PM

...Still later on the bug got me, and I put it back together once again.

So here it is with 1K grid stopper and 1nF gate to ground capacitor.

José Humberto · 15th October 2012, 07:49 AM

Quote:

Originally Posted by AndrewT

I do not like the 317 regulator sending noise back into the input of the FET buffer.

I think the 317 should take it's supply from the 18Vdc line.
The 317 also needs it's stability caps on the input and output.

The 317's performance improves significantly if a cap is added in parallel to VR1. Without these caps, it cannot match the performance of a 7805.

Hello Andrew and alls.
I´m thinking put this PSU for my B1 (I´m waitting for the parts at this moment).
Do you think I´ll have problem with the noise? Will the rippe enoght low?
Thank you very much
Jose

KatieandDad · 15th October 2012, 08:52 AM

I used a similar regulator with a 30VA transformer and it was silent.

The B1 isn't super sensitive to PSU choice. I used 4700uF + 2R2 + 4700uF CRC into the LM317.

José Humberto · 09:29 AM

Quote:

Originally Posted by KatieandDad

I used a similar regulator with a 30VA transformer and it was silent.

The B1 isn't super sensitive to PSU choice. I used 4700uF + 2R2 + 4700uF CRC into the LM317.

Thanks you very much for your reply KatieanDad.
Sorry a lot but I´m no sure understand exactly your schematic.
where did you put 4700uF + 2R2 + 4700uF CRC? In the place of 1.0 uF capacitor? Replacement 1000 uF and putting 2r2+4700 uF at the end?
Regards

wintermute · 15th October 2012, 11:46 AM

It will be in place of the 1000uF cap. For a demonstration of what this does see my blog post

http://www.diyaudio.com/forums/blogs...-progress.html look at pics 1, 2 and 3 which show the ripple accross the first cap, 2nd cap and third cap. The caps in this test were overkill and I ended up going with 4700-3r3-4700-3r3-1000 (which is probably also overkill) but it substantially reduces the ripple before the regulator, and since the regulator only reduces the ripple (doesn't eliminate it) making it smaller before makes it smaller after

The other thing I found was that having 5V difference input to output voltage resulted in the lowest noise on the output. Increasing over 5V in - out differential didn't make any further improvement.

Note that using a resistor in between the caps does drop the voltage, and that drop is proportional to current draw, so the more current your circuit pulls the bigger the drop, a standard B1 won't draw much current though

Tony.

AndrewT · 15th October 2012, 11:55 AM

the other big advantage of rCRC is that the second filter is more effective at attenuating the HF stuff that gets past the transformer and then gets past the rC.

The 3pin IC regulators have poor performance at HF and the system usually benefits from all the help you give the PSU to sound quiet (= clean DC).

tinitus · 15th October 2012, 12:54 PM

Im using a simple regulated supply with relatively small 500-1000uf caps
feeds directly into a 3300uf, then 1R, followed by another 3300uf
bleeder and LED is placed on the first
seems to work ok

José Humberto · 15th October 2012, 01:07 PM

Thank you guys.
Then, I´ll try put crc after. At the beginer I´ll try it with 1000 uF I have a handful of this. I think C1 lower the ripple too.
I´ll read your link Tony, I played changed cups with Duncan´s PSU desingers some years ago, but I´v not patient to learn use pspice or other sophisticated
software.

15th October 2012, 11:46 AM	#3617
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	It will be in place of the 1000uF cap. For a demonstration of what this does see my blog post http://www.diyaudio.com/forums/blogs...-progress.html look at pics 1, 2 and 3 which show the ripple accross the first cap, 2nd cap and third cap. The caps in this test were overkill and I ended up going with 4700-3r3-4700-3r3-1000 (which is probably also overkill) but it substantially reduces the ripple before the regulator, and since the regulator only reduces the ripple (doesn't eliminate it) making it smaller before makes it smaller after The other thing I found was that having 5V difference input to output voltage resulted in the lowest noise on the output. Increasing over 5V in - out differential didn't make any further improvement. Note that using a resistor in between the caps does drop the voltage, and that drop is proportional to current draw, so the more current your circuit pulls the bigger the drop, a standard B1 won't draw much current though Tony. __________________ Any intelligence I may appear to have is purely artificial! Some of my photos

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11th October 2012, 12:25 PM	#3611
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I note you have used 150kHz sq from a 3MHz gen, just as you described for your 20:1 ratio. Could you add a 1us filter in between the gen and the B1 so that we can see the difference in the sq shape?

11th October 2012, 12:33 PM	#3612
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	I just fully dismantled it to bits and back to parts bins, sorry. I used the higher Ciss 2SK170V to give it its worse spec possible for RC with gate stopper though. You may spot them in the first macro picture.

15th October 2012, 08:52 AM	#3615
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	I used a similar regulator with a 30VA transformer and it was silent. The B1 isn't super sensitive to PSU choice. I used 4700uF + 2R2 + 4700uF CRC into the LM317.

15th October 2012, 11:55 AM	#3618
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	the other big advantage of rCRC is that the second filter is more effective at attenuating the HF stuff that gets past the transformer and then gets past the rC. The 3pin IC regulators have poor performance at HF and the system usually benefits from all the help you give the PSU to sound quiet (= clean DC).

15th October 2012, 01:07 PM	#3620
José Humberto diyAudio Member Join Date: Nov 2004 Location: Canary Islands	Thank you guys. Then, I´ll try put crc after. At the beginer I´ll try it with 1000 uF I have a handful of this. I think C1 lower the ripple too. I´ll read your link Tony, I played changed cups with Duncan´s PSU desingers some years ago, but I´v not patient to learn use pspice or other sophisticated software.