382 watts into 8 ohms @ +-68 volts

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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.
 
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??
 
p400 addition example.
 

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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

R.I.P
2001-02-04 4:23 am
USA
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,

Thanks for your encouragement to build the Leach Amp. And thanks everyone else for your valueable comments so far.

Let me briefly explain my current set up for PA. 2 Bass Horns on each of two sides with 18" EV drivers. One Mid-Horn on each side with 12" Drivers. Highs are Hornloaded as well. I would like to add one more Bass Horn to each side making it a load of 2.6 ohms that can handle 1200watts continuous. I would also like to add a midhorn to each side. Currently I do not have anything covering the near-field but will shortly be addid 12" 2 way x 3Nos. topboxes to each side in a flying arrangement.

I drive the Bass Horns with Dynacord S1200 amp which can deliver 380w - 8ohms, 600w - 4ohms and 800w - 2ohms. It is a reasonably good sounding amplifier and absolutely reliable and bullet proof. German Engineering!! However, the definition of the bass is not to my liking. The micro-dynamics are too smeared.

I have three options before me:

1) Build a souped up Leach SuperAmp and get about 1200 watts into 2 ohms; so it would be safe for 2.6 ohms.

2) Build the Elektor Titan 2000 amplifier. Current feedback topology that delivers 300w - 8ohms, 500w - 4ohms or 800w - 2 ohms and is 1.5ohms stable. Delivers 1.6kw into 2ohms bridged!!

3) Randy Slone's OPTIMOS with double die Lateral Mosfets that deliver 400w - 8ohms and start current limiting into 4 and 2 ohms loads. Eventually I would require to build 6 of these beasts for the bass bins alone.

An outside choice is to bridge Anthony Holton's N-channel amp for each bass bin requiring 12 amps to be constructed.

In this event, what would be the best choice in terms of performance (approaching High Fidelity resolution) and reliability?

Hope to resolve the issue and keep the Dynacord S1200 as a stand-by amplifier.
 
PA-hifi ?

Generally a PA system is meant to reproduce very loud sound with the least possible audible distortion. In the process they also try to keep the bandwidth as wide as possible at high volume levels.
To make a PA system "HI-FI" as we understand it will be quite difficult. Another factor to note is that horns are the most efficient transducers that we have today- which is why they are used in PA systems.
Unfortunately they are not the best sounding ones. Even some of the most popular "HI-FI Horns" have a honkiness about them which is never eliminated even in the best designs. Horns have always be considered "honky". This does not mean that they are totally bad but cannot compete with the best direct radiator speakers. We have some very famous names making horns and I have heard a few of them. Interesting is all that I can say !
Note that if you start feeding the drivers in the horns with very very high levels , it will cause other forms of compression due to heating up of the voice coil. Playing at very high power levels is not a simple matter of adding a super brute power amp. Reliability is of utmost importance in a PA system and I hope all that will be taken care of. IMO home brew amplifiers at such high power levels in a PA system is a NO NO !
 

djk

R.I.P
2001-02-04 4:23 am
USA
"Fantastic", I'm sure you believe what you're saying, and in the limited context of your experience, I'm sure you're right. But I don't want you discouraging anyone from DIY.
"IMO home brew amplifiers at such high power levels in a PA system is a NO NO !"
Maybe YOU are not capable of building a high power amplifier, but most people with a little help can.
"Horns have always be considered "honky". This does not mean that they are totally bad but cannot compete with the best direct radiator speakers. "
Horns that sound 'honky' are either designed improperly or used improperly. Inexpensive properly designed horn systems can not only compete, but can sound BETTER than ridiculously expensive direct radiator speakers.
"Note that if you start feeding the drivers in the horns with very very high levels , it will cause other forms of compression due to heating up of the voice coil. "
So, what kind of problems am I going to have with my 4" voice coil compression driver that is 110dB/W when I am pushing in 400W (+26dB) and it is playing 106dB peak at 100 ft? I've driven them at these kind of levels for 20 years now, do you think I might be having problems anytime soon? How come 1" hi-fi direct radiator tweeters only play 90dB/W, and when you try and run 20W continuous through them for a couple of hours they won't play over 100dB and then their voice coils turn black and they burn up?
Twenty five years ago I ran sound for touring bands. I used hi-fi amps I modified and kit built units as well. I built my electronic crossovers and equalizers and a 1/3 oct measuring system. My speakers used $5 piezo tweeters, $34 Atlas paging horn midrange drivers (a step DOWN from the one Klipsch uses), and some woofers I had made for $23 each (his factory was in his barn). My system sounded better and was more reliable than factory built rigs costing 10X as much as mine cost.
If there is something I should know about this stuff, please tell me now. I am currently building a project for the military that is supposed to have a twenty year service life, and I'd hate to make a mistake!
 
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