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Old 9th January 2014, 06:28 AM   #31
yd1cvj is offline yd1cvj  Indonesia
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I want to continue assemble this amp. I got a nice box . But after I check there is not enough space for adequate transformer. I wll put in 4 x LM3886 as stereo, each channel has parallel of 2 pcs.

I'm thinking to use phase inverter (sorry I'm not sure this is the right termination) in order to get efficiency of psu. Does anybody have experience with phase inverter ?
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Old 11th January 2014, 01:43 PM   #32
yd1cvj is offline yd1cvj  Indonesia
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Click the image to open in full size.




Click the image to open in full size.


The height of box is limited factor for big transformer. I can't find big wattage toroid with low voltage here, most of them up to +/- 24 -55 volt. So maybe I use 400 watt smps to supply this chip.
Now I have 1 transformer +/- 25 volt only 6 A can fit into this casing, or 400 watt smps.

Any suggest which one should I use ?
If use transformer I plan use phase inverting.(?! )
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Old 11th January 2014, 02:45 PM   #33
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by yd1cvj View Post
.........The height of box is limited factor for big transformer. .................
Now I have 1 transformer +/- 25 volt only 6 A can fit into this casing, ...........
That's a 300VA transformer.
It can power a group of chipamps up to a total of 300W of maximum output power.
For better performance you may find that limiting the maximum total output power to 200W sounds a little bit better.
Some builders will claim that 150W of total maximum output should be the limit for high quality performance.

The maximum power from an lm3886 working with a 25+25Vac transformer is ~50W.
That allows 1 to 6 of these chipamps to be powered by your 300VA transformer.

Why is your chassis height a problem?
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Old 11th January 2014, 03:31 PM   #34
yd1cvj is offline yd1cvj  Indonesia
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Thank you Andrew. I will use normal tranformer rather than smps. Sorry the transformer 5A only, yes actually it is sufficient.
The chassis head room about 7.8 . So I must use transformer max 7.8 cm height, and this is what I got 5A +/- 25V.
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Old 11th January 2014, 03:33 PM   #35
AndrewT is offline AndrewT  Scotland
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5A @ 25+25Vac is 250VA.
That can power 1 to 5 lm3886.
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Old 14th January 2014, 06:06 AM   #36
yd1cvj is offline yd1cvj  Indonesia
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For power supply I have Elco Elna Gold 12000 microF/50volt = 4 pcs and 2 LM338 for regulator. I tried LM338 this morning (in my country is holiday) , but unfortunatelly the IC just blew . Eventhough I bought it from well known electronic component shop . Only this shop sells LM338 and LT1083. It looks I got the fake one.
From data sheet : pin1=ajust; pin2=out; pin3=in

Click the image to open in full size.Click the image to open in full size.

I will not buy it again , maybe I will parallel 5-6 pcs of LM337 , LM317 ; or use 2N3005 or without regulator.
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Old 14th January 2014, 10:58 AM   #37
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The boards you are using are ok up to around +/- 35vdc and you should NOT use any regulators, h
Just a 25A 400V bridge and some good filter caps and bypass with 0.1uF across the diodes and filter caps (snuberised) with maybe a 10-50uF electro as well. This should give you around 33-35vdc for the amps
Run all your grounds to one point at the caps grounds in the transformer ct
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Old 15th January 2014, 02:06 AM   #38
yd1cvj is offline yd1cvj  Indonesia
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@wizardofoz: thank you for advise and I agree.
The idea why I want to use regulator, to avoid big voltage swing and from some comment at others thread, with supply >+/-28 volt is too hot for chip.
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Old 16th January 2014, 08:45 AM   #39
AndrewT is offline AndrewT  Scotland
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the chipamp specification is <=+-42Vdc with signal present.

The chipamp heats more with a load connected.

As the load resistance or impedance goes down, the current being delivered goes up. This results in a 4ohm chipamp running hotter than an 8ohm chipamp and both will be hotter than a 16ohm chipamp.

For heating and reliability reasons the recommended supply voltage is changed for different load impedances.
+-40Vdc for 8ohms and +-30Vdc for 4ohms.
These voltages droop considerably when delivering maximum power for longer than a few milliseconds, typically by 2V to 5V. This supply rail droop helps to reduce the temperature that the chipamp operates at.
The reduced supply voltages below the specified +-42Vdc is a reliability issue.
Generally one requires the amplifiers to run with the highest supply voltage they can accept and remain reliable. That higher supply voltage reduces the amount of time that the signal is being distorted by clipping of the output.
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Old 16th January 2014, 02:44 PM   #40
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[QUOTE=yd1cvj;3777209]For power supply I have Elco Elna Gold 12000 microF/50volt = 4 pcs and 2 LM338 for regulator. I tried LM338 this morning (in my country is holiday) , but unfortunatelly the IC just blew . Eventhough I bought it from well known electronic component shop . Only this shop sells LM338 and LT1083. It looks I got the fake one.
From data sheet : pin1=ajust; pin2=out; pin3=in

Did you place any of these caps after the regulators? LM338 is 5A max.
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