is this realy stupid? - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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
Closed Thread
 
Thread Tools Search this Thread
Old 20th December 2005, 11:05 PM   #1
bob123 is offline bob123  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: Southampton UK
Default is this realy stupid?

I am planning on building a very high power class d amp. Would it be plausible to rectify direct mains? i have got a 270w, 1ohm resistor to prevent a 100000000000A surge when you turn the power on. This could prevent the need for getting a massive transformer.

I live in england so have a 240v RMS power supply with 340v peaks. This would mean that the supply rails would be at +-170V.

A current regulator could also be used to prevent excessive current at turn on.



Rob
 
Old 20th December 2005, 11:35 PM   #2
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
Do you have a neutral?
 
Old 20th December 2005, 11:43 PM   #3
bob123 is offline bob123  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: Southampton UK
yes
 
Old 20th December 2005, 11:43 PM   #4
diyAudio Member
 
darkfenriz's Avatar
 
Join Date: Jun 2004
Location: Warsaw
Quote:
100000000000A
Hardly possible
if you have 340V rails than peak current at 'normal' operation (not hard-start) would be +-21A for 8ohms and +-40A for 4ohms. This may require 3-phase mains.

And Yes
putting 1ohm restricts 80% efficiency for 4ohm speaker. Except you will probably need a varactor and high current chokes for clean enough rails.

Quote:
+-170V.
For +-170 if your '0' has anything to do with physical earth or ground, than you're dead. A 'cold' wire in mains is often (in older hauses) the same as earthing. (I'm guessing you know about all these things better than me but many may read this thread). Bridge topology eith single rail may be a cure.

If you consider turn-on than it is absolutely OK to use soft start circuit. You may add a 10W transformer for it and a high current relay. That's not a problem. Problems are elsewhere. Fuses... protections... just think how hard it wll be isolate all these 'grounds' being 170V in your case.
 
Old 20th December 2005, 11:46 PM   #5
bob123 is offline bob123  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: Southampton UK
ive just realised that the supply would be at +- 340v not 170v as it is 340 above and below neutral. Thats a bit much and i dont think it is worth doing as i would need to be working with high voltage components.
 
Old 20th December 2005, 11:51 PM   #6
diyAudio Member
 
darkfenriz's Avatar
 
Join Date: Jun 2004
Location: Warsaw
It depends on rectification. If you use only one diode and a cap, than you have +340V, not +-
I assumed this.
 
Old 20th December 2005, 11:54 PM   #7
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
+/- 170V Rails would give you 1800 Watts into 8 Ohms... a little nuts I guess... potentially dangerous too.
 
Old 21st December 2005, 12:00 AM   #8
mzzj is offline mzzj  Finland
diyAudio Member
 
Join Date: Jul 2005
Location: 65N 25E
330v single rail is what you get. Then you better go with full-bridge. As my 4.5kW project...

Safety issues become quite serious but it is possible with amplifier integrated to sub casing and using 4kV isolation spec line-input transformers(lunhdall, spell?)

woofer element needs also some special attention, consider woofer chassis to be part of live circuitry, ie separate metal grille in front of it etc. Horn/bandbass box desings are probably easiest to design safe so that toughing to element is not possible.
 
Old 21st December 2005, 01:40 AM   #9
kartino is offline kartino  Indonesia
diyAudio Member
 
kartino's Avatar
 
Join Date: Feb 2005
Location: Gunungkidul Indonesia
Hi, actually I am an electrical engineer.

Basically you must protect electric shock as standard equipment. Even you use isolated transformer, leakage current for all equipment are to be considered. Of course if you care this issue.

Use current leakage protection to protect you. All metal shall be earthed. Live parts shall be isolated, including your amp input. Speaker including box that may be in wet must be grounded. Use speaker binding that prevent to be touched. Careful to charged capacitor.
 
Old 21st December 2005, 07:17 AM   #10
diyAudio Member
 
Join Date: Feb 2005
Location: Antwerp
I thought anything considering direct mains was a no-no on this forum?
 

Closed Thread


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
What is nested feedback, how it realy works and some examples... bogdan_borko Solid State 30 20th October 2014 11:02 AM
what poweramp is realy the best to build? prorms Solid State 60 13th February 2012 09:07 PM
Only for the people who realy likes BIG CHOKES :-) rintek Solid State 1 30th March 2005 01:44 PM
realy need help rulezzz Solid State 0 22nd January 2004 07:48 PM


New To Site? Need Help?

All times are GMT. The time now is 06:19 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