BF862 Preamp - Page 12 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 18th January 2010, 01:06 PM   #111
diyAudio Member
 
Join Date: Apr 2009
Send a message via MSN to chchyong89
Quote:
Originally Posted by njepitt View Post

...that a 2A trafo would likely have been enough...

Nigel
woah, tat's a big load of this preamp.
__________________
~.~
  Reply With Quote
Old 18th January 2010, 01:13 PM   #112
njepitt is offline njepitt  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
Location: Maine
Quote:
Originally Posted by chchyong89 View Post
woah, tat's a big load of this preamp.
Yes, 18 copies of it, more or less...
  Reply With Quote
Old 18th January 2010, 02:12 PM   #113
juma is offline juma  Germany
diyAudio Member
 
juma's Avatar
 
Join Date: Nov 2005
Location: Berlin
Quote:
Originally Posted by chchyong89 View Post
can i ask a stupid question? whats the VAC rating of the transformer used. ~.~
Stereo version of this preamp draws 40ma from +24V side and 20ma from -4.6V side. It's a bit over 1W, total. Allow times 5 for different loses, shunt regulation etc. and give times 2 margin on top of that => 10VA or so is more than enough.
  Reply With Quote
Old 18th January 2010, 03:42 PM   #114
brianco is offline brianco  Ireland
diyAudio Member
 
brianco's Avatar
 
Join Date: Aug 2005
Location: Scottish Borders - Kelso; on the famous Tweed River!
Quote:
Originally Posted by njepitt View Post
Whoooaaaa.... I know it's OT, but tell us more!!
Well - it's your thread so I hold you responsible!

Two, the old early 1960s 3500GT model, were non-starters - so I totally rebuilt the engines. The third was a rather rare 4 litre Mistrale which had been badly treated and allowed to go downhill; the requirement was a head-off revalve, timing chain etc. Sold them all not long after their repairs were completed. This was back in the early 70s when - poor examples - were easy to find at well under 800.00. Even nice examples running properly made less than 1500.00 without a full Maserati service record. But their great grace was that they were perfectly balanced quite fast tourers which were more pleasure to drive than almost any other car I have had. I would have kept one except for a divorce at that time made it impossible.
  Reply With Quote
Old 18th January 2010, 03:55 PM   #115
njepitt is offline njepitt  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
Location: Maine
Quote:
Originally Posted by brianco View Post
Well - it's your thread so I hold you responsible!
Actually, it's not my thread, although I have posted a fair bit. Both thread and preamp design are juma's. Sorry from taking things OT, juma!!!

(The cars sound like they were sweet...)
  Reply With Quote
Old 18th January 2010, 10:31 PM   #116
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
10VA 24+24Vac allows a maximum of about 50mA of constant current draw.
That is not enough for a circuit requiring 40mA from a shunt regulator.
__________________
regards Andrew T.
  Reply With Quote
Old 19th January 2010, 12:27 AM   #117
diyAudio Member
 
Join Date: Apr 2009
Send a message via MSN to chchyong89
Quote:
Originally Posted by AndrewT View Post
10VA 24+24Vac allows a maximum of about 50mA of constant current draw.
That is not enough for a circuit requiring 40mA from a shunt regulator.
what is the single transformer VA's recommendation to power up a shunt stereo version?
__________________
~.~
  Reply With Quote
Old 19th January 2010, 07:54 AM   #118
juma is offline juma  Germany
diyAudio Member
 
juma's Avatar
 
Join Date: Nov 2005
Location: Berlin
Quote:
Originally Posted by AndrewT View Post
10VA 24+24Vac allows a maximum of about 50mA of constant current draw.
That is not enough for a circuit requiring 40mA from a shunt regulator.
10VA / 48V = 0.2083 A => 100ma draw easily

BTW, I was talking about 24V AC + 9V AC 10VA transformer (post #28 - final preamp's schematic)

Last edited by juma; 19th January 2010 at 07:56 AM.
  Reply With Quote
Old 19th January 2010, 09:16 AM   #119
njepitt is offline njepitt  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
Location: Maine
Quote:
Originally Posted by juma View Post
200mW per one BF862 is OK, and here you won't have more than 130mW (especially when you don't have to worry about thermal drift).
I prefer to keep small signal circuits as compact as possible and this way Gates are too exposed for my taste. OTOH those are line level signals and there shouldn't be much of a problem. Let's see how it works - you have a nice box and shielded transformer, I guess it'll be all right.
Hi juma,

I'm considering redoing the boards for the output buffers - the ones you remarked on in this post. Reasons are: 1. I'm going to have a problem with space on the board for the rest of the project, so making these smaller would help 2. The little test setup I posted in the crossover thread proves that you were right and the big surfaces are unnecessary 3. I've been thinking about the part of your post I put in boldface, and while there doesn't appear to be any major problem the way I've done it is somehow inelegant, so you are right.

So, a couple of questions.

1. How hot do your original adaptor boards from post #2 get? They appear to be about 1/4 sq. cm., and have about 8 sq.mm. or so of copper on the gate. Is that about right? This would help in estimating a minimum size for boards.

2. You mention above "no problem with thermal drift". If my boards were smaller, and therefore hotter, might this become a problem?

3. It may be a bit optimistic to put three jfets on a DIP-8 board without heatsinking it, but a DIP-16 board should certainly be possible. This might allow for bypass caps C12, C13, C19, C20 to be on the board, helping with the space problem, and except for the output caps (which people like me tinker with anyhow) would put the whole preamp on a plugin board, like EUVL did with his "turbo B1". Does this sound to you like a good way to do it?

As always, much obliged for any help

Cheers

Nigel
  Reply With Quote
Old 19th January 2010, 09:35 AM   #120
diyAudio Member
 
stormsonic's Avatar
 
Join Date: Aug 2008
@juma
set shunt current to 200-250mA for each supply line, MOSFET's transconductance is higher. Then calculate transformer power with this currents. Quadruple result to avoid transformer overheating.
  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
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps MartyM Tubes / Valves 3 16th October 2008 04:52 AM
twisted pear Preamp/other suggestions for Preamp kit LukeDuke Chip Amps 1 1st February 2008 09:57 PM
Electret mic preamp - will phono preamp work? darthmullet Analogue Source 6 12th October 2007 07:32 AM
wiring preamp outs on a preamp bonsai171 Solid State 4 22nd March 2004 10:13 PM


New To Site? Need Help?

All times are GMT. The time now is 08:53 AM.


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