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Old 12th November 2006, 06:57 PM   #1
skogs is offline skogs  Norway
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Default power supply for project 68

hi,
should i use a 50 or 28v+- transformer for the "Figure 1 - Basic Amplifier Schematic" setup?
would a 50v 300VA be too powerfull?
would a 28v 300VA be too weak?
http://sound.westhost.com/project68.htm
thanks
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Old 12th November 2006, 08:00 PM   #2
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Default psu

Hi there i would definately go for the +and_50 vdc supply
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Old 12th November 2006, 08:30 PM   #3
edl is offline edl  Hungary
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A 80V-CT (2*40V) 500VA transformer will do the job fine.
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Old 12th November 2006, 09:55 PM   #4
skogs is offline skogs  Norway
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the problem is that the site im ordering all my parts from doesn't have anything between 2*28v and 2*50v. are both of them so "unadvicable" (what can i say, im norwegian:P) that i should rather pay the extra bucks (shipping and stuff) for a for example 2*40v? i'm just wondering if the circuit can take 2*40v without overheating or anything.

thanks for the help
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Old 12th November 2006, 11:34 PM   #5
Minion is offline Minion  Canada
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What type of transformer can you get?? If you could get a 2 x 24v AC transformer you will get 28v DC or more after rectification and Voltage drop.....

If you can get Two 2X18v Transformers then you could wire them up so each Transformer gives you 36v AC which will give you your +/-40v DC after rectification.....


Just a couple work around options in case you can not get the exact transformer you need....

Cheers
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Old 13th November 2006, 12:13 AM   #6
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I am in the process of constructing a P68 using the 1 1/2 board ie. 500 watt and it requires the 50-0-50. I purchased a 50-0-50 @ 800VA off of ebay. Are you building the hipower version? The 1-board version has a recommended 40-0-40 @ 300VA or up to 50-0-50@at least 300VA and a big heatsink. Check out http://stores.ebay.com/Antek-inc_W0Q...QQftidZ2QQtZkm

I mean a BIG HEATSINK!
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Old 13th November 2006, 05:41 AM   #7
skogs is offline skogs  Norway
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i'm making the 300W version. so 50-0-50 will demand a much bigger heatsink than 40-0-40?
will 28-0-28 @ 300VA be insuffient?

and will a heatsink that offers 0.6C/W be enough?
thanks again for all the help
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Old 13th November 2006, 07:00 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi skogs,
28-0-28Vac will give about +-41Vdc on no load and fall a bit lower when the output stage is biassed to final level.

35-0-35 about +-50Vdc.

40-0-40 about +-58Vdc.

45-0-45 about +-66Vdc.

What voltage does your amp need to produce 300W into what load impedance?

Now you can just about get away with 300VA for a 300W amplifier but I recommend you adopt the usual 1.5times maximum output power 300W use 450VA.

What kind of music do you listen to?
How loud do you listen?
Do you ever host a party with loud music?
Would you loan out your amp for PA duty?
These will ALL affect the heatsink size.
The lower the duty the less heatsink you can get away with.
Ask it to produce close to full power all night and 0.6C/W will overheat.
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Old 13th November 2006, 07:47 PM   #9
skogs is offline skogs  Norway
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thanks a lot andrew!

the ting is that it's recommended a 40-0-40V @ 300VA transformatorer for about 250wrms into 4 ohms. i just wondered if the curcuit could handle 50-0-50V @ 300VA instead, without making any further improvements to it. or would this lead to overheat, distortion or anything?
the amp is going to be used for a subwoofer, 4 ohm. i will use it for HT and some varied music, from rammstein to bright eyes:P not very loud for long periods. so i'll just go for the 0,6C/W heatsink, and maybe mount a thermo-fan if the heatsink tends to get really hot.
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Old 13th November 2006, 08:09 PM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
50-0-50Vac is an enormous jump in voltage into an amplifier.
PSU rails @ +-73Vdc.

Your output stage will be very severely stressed trying to work with this supply voltage.
It is effectively a different amplifier, due to all the SOA calculations having to be redone.
The output power will jump to about 500W but the voltage from the transformer will collapse very quickly and then start clipping the bass signal, sounding absolutely terrible.

For a good bass amp the PSU should be very stiff to hold up while sustained high voltage signals are driven into the bass driver.
Have a rethink, or do the extensive calculations carefully.
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