Series MOSFET regulator better with just voltage ref on gate or with error amp? - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th January 2007, 02:15 PM   #11
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Jack, my info came from the Errol Dietz EDN paper reprinted in Pease's "Troubleshooting." He shows the effect of bypassing the reference resistor and the output on noise and source impedance.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 15th January 2007, 04:35 PM   #12
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
i think you have to take a look at the charts in 2/95 Audio Amateur -- at any rate, here are some bandwidth limited results integrated over 10 seconds -- using a 5223A storage scope and a 5a22n differential amplifier -- it's a much lower noise setup than my TDS3012B -- (edit) I also use the Jim Williams "cookie tin" isolation method and zero out the charge on the preamp before each measurement:

Click the image to open in full size.

Click the image to open in full size.

BASELINE:

Click the image to open in full size.
  Reply With Quote
Old 15th January 2007, 07:56 PM   #13
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
From my experience: simple source follower is enough for grids of output toobs and pre powering.
I used an one transistor error amp in the power supply with positive feedback by current that applies voltage to tubes when they are hot and start consuming current.
I can repost the schematic if you want.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 15th January 2007, 08:44 PM   #14
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Jack, I don't mean to be greedy but... could you do this with both an output and reference bypass? And a little higher current- 5mA is less than the chip needs to regulate properly, or at least is on the hairy edge.

I'll try to scan some of Dietz's results.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 16th January 2007, 01:59 AM   #15
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Jack, I am totally wrong here. On reviewing the Dietz paper, he shows noise voltage versus frequency, which is in the microvolt range. But without knowing his measurement bandwidth, it's likely that the rms value is pretty high as you're seeing.

The interesting thing about his results is that the value of the output bypass controls that noise spectrum because of the interaction with the source resistance and inductance of the 317.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 16th January 2007, 10:59 PM   #16
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Hi, Wavebourn.

I am encouraged by your comments, as well those from SY.
Quote:
I can repost the schematic if you want.
Yes, that would be interesting, thanks.

Hi, SY,

Could an LM317 be used effectively as a current source, to develop a fixed voltage across a resistor to apply to the gate of a MOSFET series regulator, do you think? It would avoid having a string of high-voltage zeners, which I don't like the idea of, or a string of VR tubes, which would be unwieldy and take up space.
  Reply With Quote
Old 17th January 2007, 12:56 AM   #17
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally posted by ray_moth
Hi, Wavebourn.


Yes, that would be interesting, thanks.

Here you go:

Click the image to open in full size.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 17th January 2007, 01:48 AM   #18
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
A first, it starts softly, raising a voltage up slowly, waiting for tubes to warm up and to start consuming a current. As the result of a current, due to a positive feedback it more quickly increases output voltage up to a regulated value, after that a positive feedback stops working, but a negative feedback starts to dominate, stabilizing output voltage on a given level, and decreasing a ripple level, without a costly and heavy chokes, without vacuum tubes to regulate output voltage.

Please be advised that no one polarity of a rectifier and filter cap must be grounded!
Also, it produces a negative bias voltage that may be used for good, otherwise leave it as is (it is a positive feedback loop for soft starting).

Vout=12V*(R5/(R6+R7)) so you may vary output voltage.
Minimum input voltage should be no less than 5V + ripple + Vout + 12V.

However, you may use it for another voltages. For example, 36V zener may be used for a bias stabilizer (it is a shunt regulator that takes the current from the entire amp), and resistors in feedback recalculated for 350V output (however, make sure that selected transistors and electrolytics can work on such voltages), to power 6L6 amp. 400V rectified in such case would be enough.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 17th January 2007, 02:08 AM   #19
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Now how do I fit this into my tube amp ?
Attached Images
File Type: jpg maida.jpg (46.7 KB, 866 views)
__________________
AM
  Reply With Quote
Old 17th January 2007, 08:48 AM   #20
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Hi Wavebourn,

Thanks for putting up the schematic and the explanation. I must be a bit slow, I can't see a positive FB loop nor what would cause a soft start nor how it senses the amp starting to draw current. Could you please give me a clue?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
mosfet gate voltage question carpenter Pass Labs 6 22nd July 2009 02:34 AM
tube voltage regulator error amp nhuwar Tubes / Valves 14 20th May 2008 10:38 PM
Do I have to match voltage Gate-Source of mosfet in SMPS? Charoenchai Car Audio 5 17th November 2006 09:28 PM
MOSFET gate voltage xplod1236 Parts 17 4th December 2004 03:23 PM
Where to buy a low gate voltage p channel MOSFET or make an alternative? Corn-Picker Everything Else 6 16th December 2003 10:15 PM


New To Site? Need Help?

All times are GMT. The time now is 06:50 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2