B+ power supply - 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 December 2003, 09:05 AM   #1
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
Default B+ power supply

I'm going to rebuild my headphones amp and I'd need some advice on the power supply.

Currently, the amp is using a very simple supply : a 250VAC xformer and a 220uF cap. That's it, and that's for both channel. No need to say that ripple measures are awful in psud.

The amp is class A and its total consumption is 40W. B+ is around 320VDC. Am I right assuming I've to work on psud with a current of 150mA (both channels, 150mA * 320 = 48W) ?

As it is class A, is it necessary to use seperate power supplies, for each channel ?

Here are the two options giving me the best results in psud :

For a single supply :

Click the image to open in full size.

Click the image to open in full size.




For seperate supllies :

Click the image to open in full size.

Click the image to open in full size.

If someone has better ideas, I'll gladly take them Just don't ask for more iron please. Costs are already high enough .
  Reply With Quote
Old 15th December 2003, 11:13 AM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
A couple of comments:

First, and most important, you have to consider the circuit being driven as well as the supply. What's the PSRR of the amplifier? Can that be improved? Remember, every 20dB increase in PSRR is like reducing the ripple by an order of magnitude.

Second, the supply can be reconfigured to give you a cap input, then a pi section. This should smooth things out quite well. Careful bypassing at the output will take care of higher frequency crosstalk and coupling between stages.

Third, if you really want the supply rail to be DC and nothing but DC, an active regulator is absolutely the best way to go.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th December 2003, 12:18 PM   #3
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
Thx for the comments.

The amp is an old kit, which evolved into a commercial product, the Audiovalve RKV mkII. According to the website, the circuit is strictly the same. Evolutions are at first sight : use of a toroidal xformer, dual mono power supply and a bunch of bypass caps. However, they still use a basic power supply, with only one big cap and perhaps a resistor. So I suppose the PSRR is quite good, considering the amp is 1000$ and is among the best of its category.

A pi filter is ruled out : no money for a big choke sadly.

Is a 0.006V ripple as I got in the first case not good enough? Would the advantages of a dual supply justify the increase to a 0.26V ripple ?
  Reply With Quote
Old 15th December 2003, 12:33 PM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
First question: do you currently hear hum?
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th December 2003, 01:49 PM   #5
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
there's a low background noise but in an amp with : a shitty old pot, 20years olds big output caps and a noisy xformer located at 2 inch of the circuit, without shielded wires, it'd be a miracle if I didn't have noise Actually, the background noise is really low.

All of the above issues will be fixed of course.
  Reply With Quote
Old 15th December 2003, 02:03 PM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Honestly, it sounds like you've got some other issues to address before you go crazy with ripple reduction.

Nonetheless, I'd strongly consider some regulation- you can use a simple three-pin adjustable floated with a HV pass transistor in this application. If you're nervous about using a chip, use the reg as a preregulator to get rid of the ripple, then use a simple R->C to your circuit.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th December 2003, 06:02 PM   #7
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
Quote:
Originally posted by SY
Honestly, it sounds like you've got some other issues to address before you go crazy with ripple reduction.
More than you think

but I've already ordered a stepped attenuator, shielded wires, I've a nice big transformer and lots of caps to change.

In fact, I've now to order metal sheets to make a new box (I didn't tell you that it was needed too ? ) and the layout and thus the size of the box depends a bit of what I take for PS. As i have those 4 big caps, I'd just want to know the best way to do it.

It's not just a lifting, more like a rebuild as you can see.
  Reply With Quote
Old 15th December 2003, 08:24 PM   #8
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Sorry to put cold water over ideas.....OF Using all those caps.
Why not dispense with most except one/two and use a cap multiplier or basic mosfet stabiliser which will give you easily 30dB ripple rejection, a far lower output impedance and noise and you can connect A+B together without intermodulation effects between channels. I use it in my amps.
Look under Steve Bench's pages in Triode electronics site to get a crack what's involved.. There is a whole section about stabilised PSu's. It's a big site and the simplest circuit using SS works wonders on tube circuits.

You shouldn't have to use sep supplies for each channel If you you a SS regie-.

As SY mentions.......it's all up to your ability.

rich
  Reply With Quote
Old 16th December 2003, 02:51 PM   #9
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
using a floating lm317 wouldn't be a problem for me, beside the fact that I read the worse things you could imagine on chip regulation. I found some schematics of mosfet regulators but then it becomes clearly more complicated.
  Reply With Quote
Old 16th December 2003, 08:12 PM   #10
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
It isn't more complicated........The thing to remember about using chip reggies on H.V applications above their intended application voltage i.e lifting the reference term way higher than ground potentials is to put plenty of protection between adj and o/p and IN terminals....With MOSFEts, a15V zener between gate and source and feed... gate via resistor of a few hundred ohms. Often I fit a low ohm in the drain as well.
We aren't looking for perfect regulation as these SS devices have a much faster slew rate when compared to the old circuits using OA2's etc.
Linear technology appls note AN2 <<performance enhancing techniques for three terminal regulators>> gives a practical overview of using 317 types with lifted adj term.

I regulary use IRF840's in 450V supplies, but don't ignore gate protection w.r.t source. No protection = No working device.

hope this helps

rich
  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
Split Voltage Switching Power Supply for Power Amp vectorplane Swap Meet 2 23rd April 2011 11:48 PM
LTspice tool for power amp power supply component evaluation andy_c Software Tools 2 23rd August 2009 05:10 PM
Can i use a computer power supply to power audio amplifiers? destroyer X Solid State 91 25th September 2006 04:36 AM
selling high current power supply for power amps. ericpeters Swap Meet 0 14th January 2005 02:21 PM
heater supply (xformer specs are 6.3V 2.5A) as supply for a power LED? jarthel Tubes / Valves 10 21st July 2003 01:30 PM


New To Site? Need Help?

All times are GMT. The time now is 11:23 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