Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Class D Switching Power Amplifiers and Power D/A conversion

non-isolated amplifiers for active loudspeakers
non-isolated amplifiers for active loudspeakers
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 28th October 2008, 09:29 AM   #1
Davey T is offline Davey T  United Kingdom
diyAudio Member
Join Date: Jul 2007
Default non-isolated amplifiers for active loudspeakers

I was thinking...

You can rectify anf filter 240V AC to get a 320Vdc rail which could possible go straight into an half-bridge output stage to give you a nice 1-3k amplifier for a high power active PA subwoofer.

If this amplifier is (hermetically?) sealed INSIDE a loudspeaker, and there are no metal parts or connections to the outside world. AND the signal is electrically isolated too...AND the speaker is not visible (horn loaded) AND there is no user servicing or access...

Can you live without an isolating transformer? You would save on weight, cost and efficiency. Electrially its simple. but the big question here is health and safety.

dimmers and CLFs dont have transformers, neither do some old tvs. So what do you think?
Old 28th October 2008, 12:33 PM   #2
acid_k2 is offline acid_k2  Italy
diyAudio Member
Join Date: Oct 2006
hi Davey T

that amp is still really dangerous

how do you think to connect input signals?
how do you think to insulate the whole speaker? (do you imagine a fault on the voice coil?)

check this thread:
Old 28th October 2008, 01:27 PM   #3
richie00boy is offline richie00boy  United Kingdom
Did it Himself
diyAudio Member
richie00boy's Avatar
Join Date: Nov 2003
Location: Gloucestershire, England, UK
non-isolated amplifiers for active loudspeakers
He did say the signal would be isolated, presumably by a transformer would to mains isolation specifications (don't know if normal signal transformers are).

Yes I think it would be viable for a home use only if it is impossible to touch the drive unit. But just think about your own testing and electrical measurements of the unit. If it is for PA application I would not dare as you have lots of other people to think about and things get abused in the PA world, also some water or other liquid might get on/into the cabinet which could be touched.
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
Old 28th October 2008, 01:45 PM   #4
Eva is offline Eva  Spain
diyAudio Member
Eva's Avatar
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
This is a very demanding project and should not be considered DIY. I'm working on similar designs and all the development and testing has to be done isolated anyway.

The main problems are:

- Input signal must be mains-isolated with litttle or no degradation. This is quite a difficult task, particularly because a huge CMRR of 140dB or so is required in order to reject those 230V all the time across the isolation barrier and still get humm and buzz close to or below the noise floor. In my experience, neither analog optocouplers nor signal transformers provide satisfactory CMRR, at least not without going to complex application circuits. Input to output capacitance is really evil.

- The speaker driver and its mounting hardware should be designed and certified to provide mains isolation.

- Those 350V DC are way too high for any linear amplifier topology, and obtaining voltage taps for class G or class H would require a transformer anyway.

- Those 350V DC are quite on the high side for class D too. MOSFET with Vds ratings over 200V are not suitable for hard switching applications due to body diode charge storage. Losses in the output inductor at these voltage levels become a problem too, and in general, the higher voltage results in an high idle power consumption. Special solutions are required whose drawbacks may be higher conduction losses, higher distortion, higher propagation delays and losing the ability for full range operation.
I use to feel like the small child in The Emperor's New Clothes tale
Old 28th October 2008, 02:24 PM   #5
Davey T is offline Davey T  United Kingdom
diyAudio Member
Join Date: Jul 2007
Thanks for the replies

Ideally i would like to stream the signal wireless-ly. We're talking subwoofers so thats very low frequency and therefore low bitrate/bandwidth stuff. Failing that, digital IR would be the way to go perhaps.

The driver for my application is horn loaded sub so the driver would sit in the middle of the cab away from fingers. The front of the cab would have to have a grill and foam to avoid moisture/drinks inside.

Of course the output stage would be class-d. because the bandwidth is 200hz max, you can have a lower switching frequency and less switching losses with high voltage mosfets. Perhaps a PFC buck converter prior to the output stage to step down to 150vdc or something. In essence - the whole amp would be a 2-stage buck i guess.

As i said, electrically i think it can be done without too much difficulty. The issue is Health and Safety.

someone once told me that BOSE tried to do this but couldn't pass HSE due to moisture/condensation.

Any standards or literature you can point be towards regarding H&S and mains isolation?

Of course all testing/development will be done with an isolation transformer (1:1) prior to the unit. Only once its sealed up with that be removed.

OH, and i don't recommend anyone does this and i'm not planning to either. I'm just wanting to discuss whether it COULD be done with proper care taken.
Old 28th October 2008, 02:39 PM   #6
kASD is offline kASD
diyAudio Member
kASD's Avatar
Join Date: Dec 2004
Using new generation HI-voltage600V HI-speed IGBTs with inbuilt FRED, One can think for Class-D amplifier without any problem with SWFreq around 120kHz, if the application is dedicated towards Subwoofer or LF arena. One can also add PFC to regulate the DC voltage rail and get optimum effciency from mains.

Its would be nice powerpak arsenal of LF Thunderbolt, lets say 4 channels of 6KW each Class-D amps in 1U rack space. But norms would be a nightmare to pass, but imagination certainly has no limits.
Old 28th October 2008, 02:48 PM   #7
Pafi is offline Pafi  Hungary
diyAudio Member
Join Date: May 2004
Location: Budapest

This is the key:
losing the ability for full range operation
It is for low freq only, so you can use lower freq, and IGBT. It works perfectly. 10 W idle loss in a quite simple 1.2 kW amp, fsw=160 kHz. Efficiency is around 94 %.
Old 28th October 2008, 02:52 PM   #8
lumanauw is offline lumanauw  Indonesia
diyAudio Moderator Emeritus
lumanauw's Avatar
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Hi, Davey T,

We close threads about powering amps direct from live line. This is dangerous and lethal practice, so it is not discussable in here in DIYaudio.

Even if you don't get electric shock, if anything happen inside sealed loudspeaker box (Wood or MDF or plastic box), you are making a fire furnace from inside. ClassD and SMPS can make fire and smoke in miliseconds.

For now this thread is closed
Old 29th October 2008, 09:50 PM   #9
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
non-isolated amplifiers for active loudspeakers
Post Closed for good, gone soon

This is deadly dangerous. This practice is not to be encouraged ever, and so this thread is closed permanently.

Don't even consider building anything like this. You must use an isolation transformer of some kind. Switching power supply, or even a 1:1 mains isolation transformer would make this a safe project as long as there is complete isolation from the AC mains. Otherwise the shock hazard to too high.

One other thing to consider here. Your house insurance may be rendered null and void if they were to find out a DIY device like this existed on your premises.

All threads using a direct AC mains connection to circuitry will be removed. This is nothing new here. DO NOT attempt to continue this discussion anywhere here on this site.


"Just because you can, doesn't mean you should" my Wife

Closed Thread

non-isolated amplifiers for active loudspeakersHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Current Driven Loudspeakers and Tranconductance Amplifiers Tube_Dude Multi-Way 263 24th November 2010 07:21 PM
Amp for active loudspeakers Nm2285 Multi-Way 4 13th November 2007 08:43 PM
How to use (and switch) the same loudspeakers with two amplifiers spendorspain Solid State 4 21st October 2005 04:17 PM

New To Site? Need Help?

All times are GMT. The time now is 07:25 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio