Real brute power amplifier

[ostie01]

I'm planning to build a huge power amplifier, would like it to be very powerful, preferably dual mono or two mono block. Would like to get about 400w RMS design on 2 toroidal transformer and about 60000uF per channel.I'm on the market right now to buy heat sink and transformers. Will need a pre-amp board too.would like to keep it as simple as possible with minimal parts.Would like to know what you think about it.

Thanks

[AndrewT]

Hi,
have a read of the ESP site.
For 400W + 400W into 8r ClassAB you will need a transformer of about 1200VA, dual secondary 65Vac + 65Vac or a pair of 625VA.

Peak current into your 8ohm load will be about 10Apk and requires about +- 20mF to +-30mF per channel.
You will need soft start and maybe DC blocking as well.

Although the Leach Lo Tim is only 130W into 8r the design article is an excellent guide, which you should read and re-read until you have commited the design process to memory. He also gives a double barrel design that may just stretch to 400W using modern high voltage, high power devices in the output stage (two or three sets of quads should do).

Alternatively, consider putting a dedicated amplifier onto each driver. Initially keeping the passive crossover (passive bi-amping/tri-amping).
You may find you need less power in each amplifier for the same SPL. If you were to extend this to fully active as a later project you would definitely need less power (possibly less than third power but more likely half power).

[ostie01]

HI, thanks for the reply, My speakers are active , no passive crossover inside.I tought using at least 12 X 150w, 200v transistors per side (6npn - 6pnp), maybe more. At least 60000uF for some headroom.As I want to keep as simple as possible, will need a small preamp board.
My goal is maybe not really 400w rms but I want a very high current power amplifier.

[quasi]

Active speakers generally means speakers with ampifiers built into the boxes. Is this what you mean i.e, will you build amplifiers into the boxes? Or are you going to use an active crossover connected to seperate amplifiers running into band-type boxes?

Cheers
Quasi

[ostie01]

No , my speaker are 4 way active speaker with one amplifier per speaker. Would like to build one by myself by pleasure and in a learning process. I have everything needed in term of electronic components. I have an Adcom power amplifier with a blown transformer, maybe I could use the preamp board in it.

[AndrewT]

Hi Sono,

At least 60000uF for some headroom

capacitance does not give you headroom. What, I think, it does give you is the ability to maintain good current flow when high demands are placed on the PSU.

Headroom is the difference between the output signal and the peak ability of the amplifier. This is a voltage drive requirement.
Many cheaply produced amplifiers quote a high headroom figure, but this actually tells you how badly designed the PSU/output stage is.

A low headroom indicates the ability to maintain close to peak voltage into the rated load for a sustained period.

An example using your 400W proposal.

This will need +-Vrails ~=+-95V.
A short term pulse signal with low duty cycle will manage about 85Vpk into your 8ohm load indicating 452W into 8r.
Now apply this same input signal for a sustained period @ 1kHz and the drive voltage will drop possibly to 80Vpk into 8r. This is 400W. The input signal will need slight attenuation to eliminate the clipping that becomes evident on sustained sine wave signals.
Reduce the frequency to 20Hz and the voltage just prior to clipping will now be about 75Vpk indicating 352W.

This 352W to 452W shows a headroom of 1.1db. A bad amplifier could have a headroom of 2db to 3db in these circumstances.
A very good amplifier may have just 0.5db headroom. i.e. 452W short term power and 402W into 8r @ 20Hz.
The low headroom amplifer is better than the high headroom amplifier.

Your choice of capacitance will more likely give you low headroom (good) if the rest of the design is optimised to achieve good power delivery. Good power delivery is often associated with strong and controlled bass. Not necessarily good for treble where delicacy seems to be the requirement.

There is another use to the headroom definition.
How far above the normal signal level your systenm can go before excessive distortion sets in. This difference between normal and peak allows for reproduction of transients and interference with minimal clipping.
Clipping sounds bad and must be avoided, it matters not whether it is transient signal or interference.

A 4way active with 400W on one of the drivers. Wow, are you a PA supplier?

[ostie01]

HI, Thanks for the explanation, When I used the word headroom, I was thinking about the power supply, but I learn a lot from your reply, Thanks so much

[rpapps]

I thought Max Headroom was in the order of 2.4

[AndrewT]

Hi Sono,
you do realise that working with +-rails approaching 100V is past the point of getting dangerous.

200V will not give you a shock. It will kill you.

[ostie01]

Ya, I know, I'm use to play in those kind of power amplifier from 100 to 300w RMS