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Old 4th February 2003, 11:12 PM   #1
OliverD is offline OliverD  Germany
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Default Easy-to-build 600W Power Amp

There have been several requests for a simple and cheap high power amp for DJing or PA recently.

The circuit below is the Elektor PA 300 in a high power version. You can easily bridge it to deliver more than 1kW RMS into 8 Ohms.

Have fun!
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Old 4th February 2003, 11:33 PM   #2
halojoy is offline halojoy  Sweden
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Default Re: Easy-to-build 600W Power Amp

Quote:
Originally posted by AMT-freak
There have been several requests for a simple and cheap high power amp for DJing or PA recently.

The circuit below is the Elektor PA 300 in a high power version. You can easily bridge it (swap inverting and non-inverting input of the opamp in one channel) to deliver more than 1kW RMS into 8 Ohms.

Have fun!
Yes, there has been seveal questions for real power full amps.
And we have had some diffilculties to give a good answer.
Sometimes you can need something extra.

I am a long time, 20 years, prescriptor of Elektor.
So I have that article of PA300.
It is a tremendous Amp. not only for PA,
but for Hifi.

I wouldn't say it is easy to build. No beginners project.
But it is well documented and tested. With some figures!
In bridge version it should be a real KILLER.

halo - not in need for a kill - but who knows ...
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Old 4th February 2003, 11:38 PM   #3
OliverD is offline OliverD  Germany
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Ooops, I've just editet my post to remove a stupid mistake, and now everyone can see it because Halo quoted me

Swapping inverting and non-inverting input of the opamp for bridging two channels will NOT work as it is within the feedback loop. Use an external phase splitter instead.

Halo, you are right of course. It is not as easy to build as, say, an LED flasher, but certainly one of the most simple amplifiers with that much output power. Definitely not a beginner's project, though.

/AMT-Freak - likes peace as much as halo
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Old 5th February 2003, 12:13 AM   #4
halojoy is offline halojoy  Sweden
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Quote:
Originally posted by AMT-freak
Halo, you are right of course. It is not as easy to build as, say, an LED flasher, but certainly one of the most simple amplifiers with that much output power. Definitely not a beginner's project, though.

/AMT-Freak - likes peace as much as halo
I am too quick t post.

Yes, it is simple for so much power.
But the difficulty is more in the practical building
of the amplifier. With so much power you have to be
careful with small details. Much current will flow!
At high voltage supply.
-----------------------------------------------------

The heart of the amp is the good old NE5534 OPamp.
It shows that this OP have data enough to get
HiFi in a PowerAmp.

halo - Loves NE5534 - Don't you say no bad about it!
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File Type: gif pa300b.gif (15.4 KB, 6113 views)
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Old 5th February 2003, 03:55 AM   #5
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Oliver/AMT-freak,

Thanks for the schematic. Yes, I have built the PA-300. It is a good but not a great amplifier.

First, a suggestion: I have used TLE2141 in place of the NE5534 and found the resolution of the amp to be much better. The mid-frequencies come forward with the replaced chip. Also the voltage to the input stage can be increased to +-20volts for more headroom and dynamic range than the more normal +-15volts required for the NE5534. (Other opamps like OP27, OPA604 did not sound as good in this position).

Secondly, some questions:

1. If you have heard/built the Leach Low TIM Amp/Leach SuperAmp, how would you compare the sound of the PA600 to this?

2. Is this design, as is, capable of driving 2ohm loads continuously?

3. By today's standards, won't replacement of the output stage with MJ21193/21194 be a better choice?

4. Would it be possible to post a rough idea of the original PCB design?

Thanks,
__________________
Sam
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Old 5th February 2003, 09:41 AM   #6
yugaaa is offline yugaaa  India
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Default hi

if you want to replace the transistors with mj21194 and 93 ,due to the operating frequency change i think additional compensation is required.
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Old 5th February 2003, 10:07 AM   #7
OliverD is offline OliverD  Germany
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Hi Samuel,

I agree to your suggestions. I also tried different opamps and found them to have more influence on sound than I expected. I posted the schematic mostly for DJing or use as a subwoofer amplifier. The amps I'm currently using in my PA system are fully discrete designs and much more complicated.

1. I haven't heard the "Leach SuperAmp"

2. No. 2 Ohm is really low. To be able to drive full rated power continously into 2 Ohms, you'll need a bigger power supply and you have to add some more complementary pairs to be on the safe side.

3. The design is from 1990, so yes, you could improve things by updating some of the components. You might have to modify the compensation capacitors in the feedback network, as Yugaaa mentioned.

4. The original design was a small PCB, containing only the driver circuit. An extra board contained the protection circuit. The rest (power supply & output stage) was wired p2p. On the original PCB, T102 and T104..T107 were mounted to a common small heatsink for better thermal stability. Signal and power ground were separated. Component placement was - as you would expect - close to the schematic. I did a similar design, but my older PCB files got lost at the last computer crash, sorry...

"djk" mentioned in the original thread that even the article in "Elrad" from 1990 wasn't the origin of the circuit. Interestingly, it seems to have been available commercially. Read his post here:

http://www.diyaudio.com/forums/showt...662#post123662
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Old 5th February 2003, 07:18 PM   #8
SlaitH is offline SlaitH  Sweden
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Crap that you lost youre PCB:s in the crash I would have loved them with the new design on the safety circuits. I've built the PA300 som years ago and it just doesn't have enough for bigger woofers it goes into clipping way too soon.

Crap I would have loved to build that amp.

Thanks for schematic anyway very helpful

Patrik
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Old 5th February 2003, 07:36 PM   #9
OliverD is offline OliverD  Germany
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I won't build any more of these, so motivation to re-make a PCB layout is somewhat limited... And I wouldn't have time until April anyway. If you don't want to wait that long, hm, maybe someone else volunteers? I know there are great PCB experts here

SlaitH, do you have a 8 Ohm sub? Have you tried bridging two PA300 channels? Then you'd have around 500W instead of 160W...
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Old 6th February 2003, 05:51 AM   #10
SlaitH is offline SlaitH  Sweden
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Yep did that and it worked just fine actually.

I made my own op based inverter with a realy for switching the output. Works just fine, but at this time i've got the thing in a 19" rack box, but i think i'm gonna redo it and put the transformer, rectifier, capacitors and softstart in a separate box.
Maybe not for the sound so much as the more simple thing to carry At this time it's weight is about 19 Kilos. And i'm gonna redo a little with the passive cooling, new cables stuff like that. Just got to get around to it.

Been looking for Passive Coolers for a nice price but I just can't find any good ones here.

Not building them anymore eh?? ...Found a better solution??

Thanks anyway

/Patrik
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