300watt in to 8ohm amps

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i have a 8 ohm sub and i am trying to find some schematics and plans for amps that will produce 350 watt in to this 8ohm speaker.

What amps are there to build?

Super leech ? i have seen leachs site, it seems quite complex amp but people say that it is very good.

something of holdens? these are genally classic AB type designs that are very proven

how many output transistors will i need on these 'cos it will be about 700 watts in to 4 ohms and almost a 1.2kw at lower impedence (but i don't plan to drive less then 4 ohms)

I guess i need rails at around 75volt or more

what else is there ?

Seeeing as at the moment i olny have 1 sub it might be worth making a over-engineered monoblock, rather then trying to squeeze a dual channel in to a case (and my budget :))

any comments are most welcome!

Another tack you might take is to build a balanced bridge amp. If you're only driving a single or dual sub drivers, you can take a circuit with supply voltages that's more appropriate for 150-200 watts at 8 ohms, beef up the output stage and power supply, and in balanced bridge you'll see very high output power with more manageable stress on the output transistors. Remember, bipolar output transistors handle current pretty well, but because of second breakdown, don't like high voltage (over 50V or so) all that much. ;)

As an example, consider the Aragon Palladium, which is basically an 8008BB with the inputs wired to a single XLR (for the standard version) or to a bridging differential amp (for the single ended version) (For a simple very high grade bridging op amp, see the TI Differential Op Amps, like the THS4131, which is very low noise and distortion with true differential outputs.)

The Palladium, while biased to operate class A to 125 watts, clips at about 600 watts at 8 ohms and nearly 1000 watts at four. Your requirements are less demanding, but even with 60-65 volts on the rails, fairly high power can be managed with a balanced bridge circuit. There's lots of designs to borrow and build on in that voltage range.


OK i have decided what to do.

I think i will build the AV-800 watt am of athony holden


I think i will run the rails at around 80volts ish (depends on transformer) and use a 1Kva tranny and twin rects on each amp.
With twin power supplys do they ALL share on star ground? i guess so

a few qestions i am currently thinking is....

two 0.5k/w heatsinks bolted together make a 0.25 k/w heatsink, correct or not? this should be enough i think at 80 volt rails especially once the heatsinks are attached to a big case.

The diagram has two diodes 1N4936 on the output and says they are optional. I guess the are there to catch back EMFs? and what are there pros and cons? whats wrong with the diodes built in to the FET's?

Hopefully i should fit two including there trannies in a 3U case, with about 40,000uf per amp (i shoud really put on more i guess).

I could bridge them (8 ohm load only) for 700 watts in to 8 ohm.

It says the bandwidth is 10hz upwards, is this OK for big subwoofer use. I think so

The inputs are balanced, to connected unbalanced input i just connect the signal ('hot') to the non-inverting and the ground of the RCA to the inverting input correct or not?

Is this thing stable? i don't want to see the biggest most expensive flash of light (second only to edinburgh newyear fireworks :)).

Protection - I will fit a couple of relays on the output. It should have DC protection, Temp protection and soa protection (for soa, is it ok to detect the voltage across one of the 0.22 source resistors?)

I don't like the idea of rail fuses, cos if one goes for no good reason, the thing will latch to a rail then the output stage blows up :rolleyes: . What about inrush limit the mains then put a smallish mains fuse, so at least the house won't burn down.

I have seen thePCB design on the website and i don't like it, but i appreciate is very difficalt to do complex output stagesonly only using one plane (single sided). My not liking is about the FET outputs/speaker connection/feedback track. Actually i can't see the output for the speaker but the feedback is at the bottom, i always thought, from D Self's advice that it is important to get the feedback from where the N and P channels join and go off to the speaker because of resistive losses in the tracks and hence not fully balanced feedback.

any other high power amp circuits i should think of?

Any help would be really cool, oh and don't worry i will not concider the 'transformer-less' idea:p

i think i need many ppl's 2cents;)
The Design of the AV800 PCB takes into account all of Douglas Self's Suggestions on PCB design.
I have read his book as well :)

This amplifier is very stable and delivers a very clean and detailed sound stage.
The design also lends it self well to bridging. With the right PSU your can expect up to 4 Times the power O/P at 8 Ohms.

Quite a few people now from all over the world have built this amplifier with great success and they are very happy with it...

Anthony Holton
www.aussieamplifiers.com :)
It Really depends on what power o/p you require.

But for 800 watts into 4 Ohms, Single channel. 1.2 KVA transformer min is required. for 2 channels 2KVA works well.
With the 2KVA Over 1600 Watts RMS into 4 Ohms can be achieved in bridge mode.

The DC filtering, I would recommend as much as you can afford.
However as little as 10,000uf per voltage rail has been used in some tests.
But as a starting point I would say 40,000uf per rail.

Higher power levels could be achieved by increasing the size of the power transformer....

I hope this helps...


Anthony Holton
"Go out and buy a DVD copy of "Attack of the Giant Leaches",
a Corman classic and an absolute must when plannng the
size of your amplifier."
Why did they pair "Attack of the Giant Leeches" with "Bucket of Blood"? I would have paired it with "Attack of the Giant Crab Monsters" instead.
I saw a dusk-to-dawn Roger Corwin/Vincent Price 5-bill at the drive-in. They burned the same castle (made of 2 X 4s) in three of the five films. It was great.
The Masque of the Red Death (1964)
The Haunted Palace (1963)
The Raven (1963)
Pit and the Pendulum (1961)
The Fall of the House of Usher (1960)
It may have been The Masque of the Red Death (1962) though, now that I think about it. (who else could have got away with making the same movie with the same star only a couple of years apart?)
Yes, this is vital information when planning the size of your amplifier.
Ahha, Anthony Holton, the man himself. Sorry for spelling your name wrong, I tried to recall it from memory.

Thanks for your replies; it’s always nice to hear from the designer himself! (One of the reasons I think highly of Nelson Pass)

I suppose you are right about the feedback thing, I couldn’t see the speaker output, so it’s unfair to judge.

Could you comment on the pros and cons of the two 1N4936 diodes?

Two more questions I have about the amp is…… would 0.25k/watt heatsinks be adequate on one amp module for normal use? And will 82 volt rails be OK for around 380watts in to 8 ohms without modification?

I saw your comment about the bridging of these modules, as I understand it two bridged AV-800 will power almost 2 KW in to a 4 ohm load but this would not be suggested as it will exceed the SOA limits on the output, because each amp is seeing a 2 ohm load, correct or not?

Thanks very much
The one and only
Joined 2001
Paid Member
My wife not only tolerates the incredible amount of
audio junk (none of it finished looking) but she also
arranged for me to have lunch with Roger Corman
two years ago. He is one of the smartest, nicest
people I've ever met, and when you consider that
most of Hollywood's best stars and directors owe
him their start, he needs an academy award.

I'm still waiting for Attack of the Crab Monsters, which
I'm hoping will be paired with It Conquered the World.

Your quite right of cause the SOA is exceeded at this power level.
Dropping the supply down to +-70 volts would help in bridge mode. Yes the AV800 would work fine without modification on 83 volt rails. Not so sure about the power o/p though. 380 watts might be expecting a bit to much.
You could expect about 320 watts.
The diodes on the o/p are there to simply to help swamp any Back EMF that might appear on the o/p from say a large driver or drivers or line transformer.

And Nelson what on earth are you going on about :) What's this Attack of the Crab Monsters?



Never in my life did i expect to read my Hero Mr. Nelson Pass talking about B-Movie sci-fi hahahahahah Rock On!!!

Someday i really want to take a visit out there to meet you and "See" & "Hear" all your audio "Junk" as you put it ahhahahaha TOYS!!!!!

Too Bad you dont still have those massive toob subwoofers still connected!!!!!

Zero :cool:
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