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Old 30th July 2009, 02:24 PM   #1
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Default 400 watts rms 8ohms audio amp design...help

I only got a 38-0-38 @ 8ampere transformer available,,,but the designed I got from the web required for about 50-0-50 @10 ampere can any one help me on the design to acquire the 400 watts rms.... if there is can anyone provide me also a PCB layout.....


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Old 30th July 2009, 04:32 PM   #2
AndrewT is offline AndrewT  Scotland
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I got 170W into 8r0 from a 230:40+40Vac transformer run on 240Vac.
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Old 30th July 2009, 05:46 PM   #3
taj is offline taj
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I would expect you to get 250-300 watts with a 4-ohm load using that transformer.

Just a hunch (without the arithmetic), but I don't think a 2-ohm load is advisable with that transformer, but it would probably provide 400 watts before it burst into flames.

..Todd
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Old 30th July 2009, 06:26 PM   #4
wg_ski is offline wg_ski  United States
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I would take about an hour to burst into flames. You'd notice the 'heat smell' long before that. And if there's a thermal cutout device installed it would trip before things got out of hand.

It's still a bigger trafo than what they usually get away with in store-bought amps.
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Old 31st July 2009, 06:41 AM   #5
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how about if I'll use the LM4702 together with a darlington pair output transformer using a 35-0-35 @ 8 amp. transformer how can I get the 400 watts output..Is it possible to attained the 400 watts rms @ 8 oms
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Old 31st July 2009, 07:25 AM   #6
AJT is offline AJT  Philippines
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Default Re: 400 watts rms 8ohms audio amp design...help

Quote:
Originally posted by darkwind_j
I only got a 38-0-38 @ 8ampere transformer available,,,but the designed I got from the web required for about 50-0-50 @10 ampere can any one help me on the design to acquire the 400 watts rms.... if there is can anyone provide me also a PCB layout.....


thankz and more power to all diyaudio member....
These are mere specs. you do not know the capability of the transformer until you measure it....

for starters, you can give the dimensions of your 30-0-38@8amps transformer, the wieght, what size core does it use and then we can judge...

what about dc resistance of the primary and secondary windings? can you measure them and report here?

these numbers that i mention will tell if what you have is sufficient or not...

from experience, there is not a world of difference between an 8 and a 10, for all we know, your 8amps traffo would probably suffice....
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Old 31st July 2009, 07:32 AM   #7
AJT is offline AJT  Philippines
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Quote:
Originally posted by darkwind_j
how about if I'll use the LM4702 together with a darlington pair output transformer using a 35-0-35 @ 8 amp. transformer how can I get the 400 watts output..Is it possible to attained the 400 watts rms @ 8 oms
100watts 8ohms, 200watts 4ohms, 400watts2ohms with that kind of transformer....assuming your rails can be kept constant...

the psu matters a lot, if you want the figures at 2ohms, you better have a power transformer that is robust and able to supply that power....
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Old 31st July 2009, 09:32 AM   #8
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Quote:
how about if I'll use the LM4702 together with a darlington pair output transformer using a 35-0-35 @ 8 amp. transformer how can I get the 400 watts output..Is it possible to attained the 400 watts rms @ 8 oms
darkwind_j
Please sit down and reconsider your projekt.........

From your posts here, I assume that you are not very experienced (Cheer up. We all had to start somewhere).

Building a power plant amplifier delivering 400W into 8ohms is not an easy task- even if you have a working circuit schematic and perhaps also the PCBs for it. There are so many things that can go wrong, and it could easily end up as a big

Your transformer will NEVER give you 400W into 8ohms!
For that you need +/-80VDC rail Voltages. Your transformer (one place you state 2x35VAC and next 2x38VAC) will only give you app. +/-50VDC rail Voltage = 150W into 8ohms.
You can reach 300W by making 2 identical amps and bridge them. But then you need two trafos + lots of uF in the PSU.
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Old 31st July 2009, 11:27 AM   #9
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Jan Dupont is absolutely right. Reconsider your project. Start with something smaller and simpler. Do not try to build an amplifier, if you do not know yet, how to calculate the achievable power from a voltage and impedance with Ohm's law.
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Old 31st July 2009, 11:50 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Jan Dupont
....... making 2 identical amps and bridge them. But then you need two trafos + lots of uF in the PSU.
we agree, but why do so many others not believe this?
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