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Author Topic: Power supply/ power amp question  (Read 188 times)

NPreston

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Power supply/ power amp question
« on: January 16, 2021, 09:42:00 AM »
Hi.  I am attempting to build an amp and learning as I go.  So I have built a simple power supply using a Hammond 166m72 transformer which is spec’d with output 72ct which I understand as 36-0-36 at full load..(correct me if I’m wrong). Anyways the supply after filtering with no load is 53-0-53.  Question is when designing the power amp to determine power dissipation of various parts do I use +/-53v in my calculations??  Not sure how much loading to expect once I actually hook something up and apply signals and loads. 
Thanks!

phatt

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Re: Power supply/ power amp question
« Reply #1 on: January 17, 2021, 09:17:24 PM »
Welcome,,
 If this is your first project I would suggest you do some reading first.
The power supply voltage you have is likely too high for a novice.
with 50VDC rails it's possible to end up dead,, the you accidentally touch both rails then it's 100Volts across your heart.  xP

You need a supply of around 35-0-35VDC would be a lot safer and far less chance of blowing up your circuit and dying as well. 8|

Working with anything over about 80Volts is a potential death trap. ???

Go here and do a lot of reading; https://sound-au.com/projects-0.htm#mus

Look at Project27; It's a 100Watt guitar amp running from a
SAFE 35-0-35VDC. You can even purchase a PCB from Rod which will save you a lot of blood and sweat trying to make your own.

This is by far one of the best places for those wanting to DIY an amplifier,, tons of stuff and written for folks like you who do not have the skill to go it alone.
Cheers Phil.

Enzo

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Re: Power supply/ power amp question
« Reply #2 on: January 17, 2021, 09:45:40 PM »
Transformers produce AC voltages, and those voltages are called RMS voltages.  SInce AC voltage changes all the time, we use an average.

36v AC, moves from zero up to a peak of About 51v, then back down through zero and out to -51v and back.   The average of that zero to 51v is 36v.  When you rectify and filter that, the caps charge up to the peak of 51vDC.   This is how it works.  You take the RMS AC voltage of the transformer, and multiply by 1.414 to get the peak voltage, which will be the rectified and filtered result.We might subtract a volt or two for losses in the rectifiers or some such, but that basic formula is close enough.

NPreston

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Re: Power supply/ power amp question
« Reply #3 on: January 18, 2021, 10:24:15 AM »
Hi..

Thanks for the replies.
I agree the voltages I have are nothing to take lightly.  Making a conscious effort to not touch anything with my left hand when working on this and ensuring caps are discharged enough before I go poking around.

when I ordered this transformer a couple years ago, I had expected to get a 36-0-36 supply, but I guess I missed the target on that one..

I've been reading and trying to understand how power amps/inside of opamps work and its starting to make sense..  I will definitely look into https://sound-au.com/projects-0.htm#mus for more understanding.

I've hacked together couple power amp circuits (albeit crude ones) at lower voltages with some success.. 
Trying to actually calculate things properly and really understand exactly what is happening where this time around.

Thanks