382 watts into 8 ohms @ +-68 volts

[Samuel Jayaraj]

The amplifier in the following link http://www.ptt.yu/korisnici/s/r/srmarkovic/poweramp.htm is rated at 382 watts into 8 ohms and is specified as stable down to 2 ohms loads. With only two MJ15003/15004 (total Pd of 500w) will the amplifier be able to withstand a 2 ohm load or will the VI limiters kick in by then, greatly reducing the output power? Would it be possible to parallel the output devices and modify the limiting circuitry to obtain quadrupled power into 2 ohm loads?

Any comments are welcome and thanks in advance.

[Duo]

To achieve greater current capability for 2 ohms or even lower maybe, you just need to add more parallel output transistors.
If you leave the protection circuit as it is and just add mroe pairs of transistors with their emitter just going to the output with .39 ohm resistors you'll be fine. Since the original protection circuit is only connected to the emitters of the original transistors, it won't kick in until those individual transistors are overloaded. The current will now be divided into all the output transistors so you won't have to change the protection resistors at all.


Here's an example, does this help you??

[Duo]

p400 addition example.

[schizeckinosy]

If that amp was 100% efficient, it would produce 289 wpc. Realistically, it's probably about a 160 wpc amp. Note that Prof. Leach uses the same output complement at +/- 58V and rates his amp at 120 wpc.

I would be afraid to use this amp at 2ohms with 68v rails.

Cheers, Dan

[Duo]

Their ratings for 382 watts are obviousely peak power which is quite possible in that arrangement. RMS power would be about 160 to 200 watts at max. With the additional transistors it should be able to drive a 2 ohm load to about 800 watts but I would suggest even more transistors added to the circuit. The original design will work just fine into 2 ohms but the protection circuit will be working all the time and you won't get much power.

EDIT: For 800 watts into 2 ohms you'd want at least 5 sets of output trannies so the protection wouldn't cut in all the time.
You'd be better off running it into 4 or 8 ohms, then you'd easily be fine with 3 or 4 sets.

[djk]

That thing is a disaster, build a Leach. The TIP41C has a secondary breakdown curve that starts folding back at 30V. Besides, they are only rated at 100V and +/- 68V needs 150V parts. Use MJ21193/21194 outputs and MJE15030/15031 drivers. The second voltage amplifiers are only running at 2.3mA, not enough to drive a dual darlington output stage. The input off-set trim is a mess too. I have a Leach that runs on +/- 65V from a 90VCT 1KVA transformer. It will do 160W/8R or 300W/4R and has three pair of MJ15011/15012 outputs with MJE15030/15031 drivers 2N3440/5415 pre drivers and 2nd voltage amps, MPSA06/A56 for diff pairs.

[djk]

If you really need 400W/8R this is what it takes:
http://www.mif.pg.gda.pl/homepages/t...es/usa1310.gif
The current version uses MJ21193/94 for the outputs.

[Duo]

And just what kind of joke is this??? If the output trannis try to conduct, they'll be conducting the rails right to ground, how on earth will this produce audio????

[Geoff]

djk

That schematic looks remarkably like the QSC Series One 1700 amplifier :-)

Duo

The circuit works and has been discussed previously in this forum. Unfortunately I cannot remember in which thread.

Edit: I've just found the relevant thread:

What?!

Geoff

[Duo]

Okay, I see what's happening. You mean that the CT on the PSU trannie is where you connect the speaker??? I see how that would work.