1kW MOSFET amplifier

[Aussieamps]

the figures quoted are result of real world measurements across the load.
The only explanation would be supply regulation, as the DC voltage on the supply caps drops to about 85 volts under load...

The way Crown achieve power o/p approching 4 times the power o/p is because they use tightly regulated SMPS...

[Michel]

check out www.accuphase.com and www.krellonline.com for some serious constant voltage amps!!

[AudioFreak]

Originally posted by Aussieamps
OK

Bridging works like this in theory.

You have an amplifier which has say a 2kw power supply.
Its power o/p into 8 Ohms is 100 watts RMS (28.4 VAC @ 3.55 Amperes RMS= 100.82 watts RMS)
If you bridge this same amplifier into an 8 Ohm load in theory you should get twice the voltage across the 8 Ohm load (56.8 VAC RMS @ 7.1 Amperes RMS = 403.28 Watts RMS)
Or 4 times the power o/p

If you then half the impedance or load on this bridged amplifier to say 4 Ohms. In theory you should get twice the o/p power again.
(56.8 VAC @ 14.2 amperes = 806.56 Watts RMS)
Which is 8 times the power o/p into 8 Ohms on an non-bridged amplifier or 4 times power o/p @ the same impedance of 4 Ohms.

Now this is assuming ideal amplifiers and power supplies with no losses what so ever

In practice this doesn't happen....

If you look at any commercial amplifier which operates in bridge mode, they only ever double their power o/p into any given load equal to the non bridged load...

My AV800 amplifier produces over 870 watts rms into 4 Ohms non bridged. In bridge mode it produce about 1600 watts rms into 4 Ohms with a 2KVA transformer. Into 8 Ohms bridged it produces about 870 watts. which is about double its power o/p into 8 Ohms of 450 watts RMS.

The only commercial amplifier that could possibly come close to 4 times the o/p power would be Crown amplifiers. Which use Grounded Bridge Technology and even then they a subject to power losses and produce 4 times the power o/p or greater by driving into impedances of 2 Ohms or less...
Another amplifier would be Krell and not even Nelson Pass amplifiers x1000 can produce 4 times the power o/p in bridge mode using just two single module amplifiers into 8 Ohms...

I am willing to be corrected here, But I just don't see it...

regards

Anthony Holton

I agree with the 1st part of that post but i would suggest you check your facts .... Pass X-1000 is a bridged monoblock before you start also 2 such units are indeed very capable of producing 4000W into 8ohms .... that is 4x the output power of a single X-1000 into the same 8ohm load also the professional yamaha amps produce twice the power into twice the load in bridged configuration but are unable to produce 4 times the output into the original load because the power supply is current limited.

[Kilowatt]

Also, here's an example that proves that more than 2x the power is attainable using bridge mode (and it's not class D). This is the power ouput of Alpine's MRV-1507:

450W x 2 (4 Ohm Stereo) 1500 x 1 (Bridged 4 Ohm)
This is the max power, RMS is (they claim) 225W/900W respectively, which also proves the point, even if that 900W figure is a slight exaggeration.

Perhaps it is all in the power supply, an Anthony has suggested.

[AudioFreak]

I agree it is hugely dependent on the capabities of the power supply .... also most the specs for car amps are voltage limited not current limited .... mind you, if your bridging 2 amps to achieve 4 times the power then each of them must supply only double that of their normal output.... with a BIG power supply and plenty of o/p devices, this shouldnt be too much to ask.... after all, this is the equivalent of running the amp into half the impedance ... upto a point, this is quite doable.

[Michel]

Hi aussiamps,

If you use electronicsworkbench, and/or Multisim, i would like to send you a conceptual bridging schematic for your consideration...and comment?!?

[Aussieamps]

Ok

you can email me @ aeholton@utas.edu.au

regards

Anthony

[AudioFreak]

Originally posted by Aussieamps
My AV800 amplifier produces over 870 watts rms into 4 Ohms non bridged. In bridge mode it produce about 1600 watts rms into 4 Ohms with a 2KVA transformer. Into 8 Ohms bridged it produces about 870 watts. which is about double its power o/p into 8 Ohms of 450 watts RMS.

regards

Anthony Holton

it appears we have misunderstood each other.... you say your AV800 can do 450W into 8ohms and 870W into 4ohms .... well if you bridge these amps into an 8ohm load then each will see the equivalent of 4ohms .... so each will produce 870W into the load ... giving a total of 1740W into the 8ohm load between the 2 amps .... this is almost 4 times the power of a single amp into 8ohms so it works quite nicely with theory ... sure i am willing to concede 30W loss per amp ... i just dont know how one of us didnt pick up on this earlier.... when bridging you'll have a minimum of 2 amps ...assuming 2 amps.... each produces the same voltage as they would have in non bridge config ... but because when one amp is + the other is - the voltage between them is double that of what a single amp would have produced on it's own.... so they are called upon to deliver twice the normal current ... which is the equivalent of running each amp into 1/2 the original load... now each amp has produced twice it's normal power but the voltage across the speaker terminals is doubled and so has the current so the speaker will get 4 times the power.... no bridging theory states that each single amp should have to produce 4 times the power into the same load .... only twice the power .... it is the total power into the speaker that goes up 4 fold compared to a single amp so if you have an amp rated for 2 x 100W into 8ohms, 2 x 200W into 4ohms then it should be rated 1 x 400W into 8ohms bridged ... sure, in practice it'll be a little less but that about does it.

So i stand by my earlier post ....

Originally posted by AudioFreak
it wouldnt be such a bad idea to make 2 smaller amps of say 300W in 8ohms based on this amp then run them bridged into an 8ohm speaker.... you should get around 1200W into that 8ohm load and it would give a much bigger safety margin on the o/p devices..... i'd just run each amp with say 16 o/p devices (8 x IRFP240 and 8 x IRFP9240) with a big power supply. All said and done this should be enough given that this is a low bias Class AB design.

in the above example, each amp is rated @ 300W into 8ohms so will give probably just less than 600W into 4ohms....now you have 2 such amps... if you bridge these into an 8ohm speaker then each will effectively see 4ohms and so produce just under 600W ... now each amp is making 600W into that load so there is 1200W into the load.... just like i originally stated it.

[Kilowatt]

I thought we were talking about the total power of the two amps all along. I guess not.

[AudioFreak]

Well kilowatt.... you and i were but it appears Anthony was not.