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anders3408 7th December 2011 01:37 PM

High Power Amplifier
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i am working on an power amp in multisim that i need some help to. will it work as it is or ? i have an 1.3kW trafo that gives +- 58volt dc. i will then use 60.000 uF per rail and i have some BYV54-V200 Double Rectifier Diodes i want to use as the diodebridge. will the amp i had designed be stable at 2 ohm or as low as 1 ohm ? i am planning to build 2 of the amps and thinking on bridging the 2 pcb and drives it in 2 ohm bridge ? or elles i need to go 4 ohm per channel. but then i dont have as much power .Attachment 253608

sorry for myu bad english i am from denmark :)

moschfet 7th December 2011 05:13 PM

Hi anders,

will it work as it is or ?
Look at Q14... ;)

bear 7th December 2011 09:19 PM

The orientation of the output devices is puzzling - usually one expects the emitters to face the output line, or both collectors, given it is a complementary output.

To determine the output's capabilities look at the spec sheet for the devices, figure out the
current that will flow at full power (58v swing), then see what the SOA is per device, multiply x the number of devices per rail that will tell you if you are within bounds or where the limits are. Seems unlikely that this number of devices will handle a 1 ohm load.
In bridged configuration the power available increases by 4x, because the voltage swing is now +/- 2 x rail voltage (approximately).


a.wayne 7th December 2011 09:42 PM

Agree that's not enuff outputs for one ohm operation, well at that voltage. you may want to consider lowering the output voltage ...

amptech 7th December 2011 10:27 PM

Anders3408, that's one big transformer!
one question, why down to 1 ohm? most amplifiers are stable at 4 ohms and give plenty of out put power. Also bridging at 2 ohms is on the hairy edge and your amp may end up going up in smoke with it's limited o/p devices.

I've worked on many peavey's like the old work horse 'pv 1.3k' and this old monster was a 1000w per at 2 ohms and could be bridged at 4 ohms!
As I recall there was two large power stages with plenty of To-3's devices,the only this apart from weighting like a boat anchor the triac if fired would take most of the o/ps with it! I would remove this part and replace with a speaker protection relay system thus removing that turn on/off plop and giving a much better over system..

I noticed on your amp there's no cap after the 1k where it goes to ground, most designs within the feed back part have, say,27k or 33k etc.. then say 1k followed by 47uf or 100uf etc to ground.

anders3408 8th December 2011 12:16 AM

moscheft: what is wrong with Q14 ? :S

the low ohm is because i have an sub with two 4 ohms subs, and these are in parallel and i need to disamble the sub if it shall goes in 4 ohms. how many output devices is need for 1 ohm ? i had made one of these class ab amp before with +-40 volt rail and smaller output deviceses and i also just gave 65 watt whit low thd. but now i will try a bigger one. and because i have a serios transformer laying with many bigs caps and biig diode rectifier. i was building an class t amp , an amp 7 from but it played fm noise with an +-52 test rail, and my first time i mounted the 58+- rail it blows up, but it was because a lm317 was shorted so the 10 volt supply was 28 volt, all fets blows , the tripath ta3020 chip blows up and 5 caps blows up, i dont know if i try it again some time, but for now it is laying in the corner :(

amtech, what will the caps do diffrence ? are u meaning that i shall add a 47 uf cap or 100 uf between the resistor and ground ?

anders3408 8th December 2011 12:19 AM

if i can get enough power in 4 ohm per channel i am trying that, it is not so dangerous :D or 4 ohm bridge :D

whizgeek 8th December 2011 12:55 AM

The PNP output devices are drawn upside down.
what Amptech is saying it there is DC gain by omitting the feedback cap.
there is also a thread recently about this type of symmetrical input stage, ( or something similar, but I cant find it now) but seems to say that this type of design is not stable at DC.
If you have DC gain on top of that, then there will be trouble!

Tajzmaj 8th December 2011 05:35 AM

Everything prepared and board for each speaker so simple make stereo amp and feed each speaker separately. Nice and safe 4 ohm operation....
Best regards, Taj

moschfet 8th December 2011 07:11 AM


what is wrong with Q14 ? :S
If you don't see it, but Q14,20,21,22,23 are wrong wired. :)
The emitter must wired at positive voltage.

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