Finished capacitance multiplier - Page 42 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 14th September 2013, 02:09 PM   #411
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
Quote:
Originally Posted by AndrewT View Post

I always try to use close rated fusing. That requires all transformers bigger than 50VA to have a soft start.
AndrewT,

There are millions of amps produced by the famous companies that use transformers much bigger than 50VA and does not have soft start circuit.

Ideally, all amps should have soft start but considering added complexity and very small possibility of problems, this advice seems like exaggeration. We do not need paranoia among diy-ers. How many amps you know that failed because they did not used close rated fusing and soft start? If there is some problem no fuse will prevent amp failure. The fuses are extremely unreliable components. As far as fire hazard is concerned I always presume that we build amps with metal enclosures, not wooden. Also, I hope that we all keep electrical home installation in good condition, with sufficient cross section of conductors, etc.

Last edited by ivanlukic; 14th September 2013 at 02:15 PM.
  Reply With Quote
Old 14th September 2013, 07:10 PM   #412
diyAudio Member
 
Join Date: Apr 2013
Quote:
Originally Posted by ivanlukic View Post
There are millions of amps produced by the famous companies that use transformers much bigger than 50VA and does not have soft start circuit.
I bought two broken amps from Ebay last week to salvage the cases and heatsinks. Not high end units just "run of the mill" stuff you find in average households. Both had small 170W transformers and both had soft start circuitry comprising thermistor and bypass relay.

But what really surprised me was when I disassembled my wife's old "mini system". Despite the fact that it it had a tiny transformer and cheap parts, it still had the soft start circuitry on the power supply board.
  Reply With Quote
Old 14th September 2013, 09:30 PM   #413
quan is online now quan  Australia
diyAudio Member
 
Join Date: Feb 2007
Location: sydney
Hi guys, i 've tried 2Amp slow blow fuse and it blew straight away after switching on. Does this means a soft start is in order as per AT?. It sounds then ideally each individual transformer should have its own primary fuse to avoid overating total fuse value ?.
Quan
  Reply With Quote
Old 14th September 2013, 11:26 PM   #414
diyAudio Member
 
Join Date: Apr 2013
Hi Quan

Andrew (and others) have advocated seperate fusing in other threads. It gives better protection in case one transformer has a problem but not the other. Its pretty unlikely both would fail simultaneously.

If the only reason you use a soft starter is to stop the main breaker tripping, you can get away without it until >300VA. Rod Elliott says as much on his pages. I guess if you had 2x 300VA you could implement some sort of stagger start circuit (better yet just use a soft starter).

The argument AndrewT successfully makes is that a fuse can pass current far greater than its rating for very long periods of time. For short periods it can pass enormous currents that far exceed its rating. In the interests of safety (a fuse is a safety device, if we aren't concerned about safety why even use one?) then the fuse should be close rated.

I guess the eye opener for me was pulling apart these old broken amps. All were obviously built to a price with cheap components, small filter caps, flimsy heatsink, etc. But all of them had a soft start circuit comprising small dedicated board mounted transformer, thermistor, bypass relay and trigger logic. If it wasn't an important safety feature then I have no doubt the penny pinching engineers and accountants would have omitted it from the design.
  Reply With Quote
Old 15th September 2013, 12:42 AM   #415
PMI is offline PMI  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Milwaukee, Wisconsin
Quote:
Originally Posted by Ranchu32 View Post
I guess the eye opener for me was pulling apart these old broken amps...
What size were the fuses? If the fuse is small, relative to the size of the transformer and the expected inrush current, you have your answer. If the fuse is large, then it was there for another reason, such as protecting a weak component against a peak current at startup, etc. (UL, CSA, and their equivalents mandate some interesting tests for home electronics.) Or it could be there to eliminate startup noise from the speakers, from a poorly designed circuit. It would be interesting to know what happens when you bypass one of those commercial soft-start circuits...
  Reply With Quote
Old 15th September 2013, 05:13 AM   #416
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
What I wanted to say is that fuses are not great protection in the first place. Fuses will blow for no apparent reason and will pass destructive currents that will cause malfunction of amp. Nobody can predict how particular fuse that you put in your amp will behave.

It seems that mains fuse is there not to protect the amp itself but to prevent fire hazard according to direction for each country. Therefore, I doubt the usefulness of mains fuses for the protection of amps. HT fuses are somewhat better protection for the transformer secondaries but also unpredictable and therefore not really that good protection. Some kind of (magnetic) circuit breaker would be much better than fuse, in my opinion.

But, in the diy context building soft start circuit just to be able to choose close rated fuse is not very practical. So much complexity just to suit an fuse, component that is unreliable in the first place. You need space to put such circuit, you have problem to place additional conductors, etc. Is not it much simpler to choose slow blow fuse of sufficient rating? Think for the moment about vacuum cleaners. How big is inrush that 1500W motor produces?
  Reply With Quote
Old 15th September 2013, 06:29 AM   #417
diyAudio Member
 
Join Date: Feb 2005
Just want to add 'a something' to the above posts (talking 'bout fuses) that I've come across over the years -

Firstly, as Andrew has mentioned above, they're not the most accurate item regarding designed power failure/burn tolerances and as most of the commercially available ones are built for ac power use, they're designed for mains 110, 120, 220 Hz use, not dc rails that we're looking at here.

Then, they do NOT age gracefully, without failing - a generally accepted procedure by most tech's with a unit in for repair is to initially replace the fuses. Also, in a number of amps and preamps, when replacing the mains fuse, even tho it's not blown, sometimes produces an improvement in the sound - not a significant 'thing' like those expensive fuses, for example, but more of a 'good procedure' (I've not noticed any improvement in any equipment with those expensive fuses, but assume it's my lack, as other people seem to have good results).

Low power Circuit Breakers seem to have similar characteristics as fuses, IMO - the electronic Fet switches set up as over current limiters are about the best way of doing things but they're not simple things, (or cheap either), and there are plenty of threads here over the years to look them up.

In Peter/Miles design here, the fuses are after the main filtering caps so don't have to suffer the high current charging pulses and it also acts as a soft start for the following circuits but it's still good practice to use an initial current limiting 'soft start' cct for the primary windings, particularly with the Torroidal transformers.
I generally use the simple Thermistor 10 Ohm ones in series with the primary windings for power amps and the 40 - 100 Ohm ones for lower power ccts, plus the usual input line filters, dc traps, snubbers, etc (this is just my particular way of doing things, not any 'rule' or anything!)

... my 2 cents, to a particularly useful project - my thanks to Peter, Miles and everyone.
__________________
... jh
  Reply With Quote
Old 15th September 2013, 06:38 AM   #418
diyAudio Member
 
Join Date: Feb 2005
Oh, forgot to mention this piece of essential 'feel good' circuitry, even tho it's a bit off the subject -

It's called a dc protection cct - even with CMx in power supplies, sometimes things 'go wrong' and that 'dreaded dc' appears on the speaker terminals with unpleasant results - I only leave these simple protection devices out with single rail amps that have a dc blocking capacitor (hey, they work for me quite well!) or the electronic current sense/limiting circuits on the power rails to the o/p stages.
__________________
... jh
  Reply With Quote
Old 15th September 2013, 03:46 PM   #419
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by ivanlukic View Post
AndrewT,

There are millions of amps produced by the famous companies that use transformers much bigger than 50VA and does not have soft start circuit.

Ideally, all amps should have soft start but considering added complexity and very small possibility of problems, this advice seems like exaggeration. We do not need paranoia among diy-ers. How many amps you know that failed because they did not used close rated fusing and soft start? If there is some problem no fuse will prevent amp failure. The fuses are extremely unreliable components. .......................... Also, I hope that we all keep electrical home installation in good condition, with sufficient cross section of conductors, etc.
Ivan,
you barking up the wrong tree.
It seems you are not reading what I have said.

I never said anywhere, nor at any time, that fuses prevent failures.

Fuses are there to help prevent you setting fire to your house.
They are a Safety feature and as such act "after an incident".
__________________
regards Andrew T.
  Reply With Quote
Old 15th September 2013, 08:03 PM   #420
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
AndrewT,

I admit that I misunderstood your post. Now it's clear what we are talking about. We certainly need some kind of protection against fire hazard but I am not sure what is the best method. I think that we need a separate thread about safety in audio amps, including user safety, not only home safety. There was some comments by Ian Finch regarding the use of open SMPS modules recommended by Lazy Cat. It is my impression that user safety is somehow neglected aspect of general safety topic.

Is there an official safety directive for audio products available on the net?
  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
Capacitance Multiplier PSU Ted205 Chip Amps 3 2nd March 2009 01:27 PM
Capacitance Multiplier Kinnja Solid State 2 13th January 2008 08:12 PM
Capacitance Multiplier for A5? siouxiebuff Pass Labs 3 21st January 2006 04:27 PM


New To Site? Need Help?

All times are GMT. The time now is 10:33 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