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Old 4th May 2004, 01:37 AM   #1
RX5 is offline RX5  Philippines
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Question ohms for amps

hi all,


ive got a 100W amp +35/-35 @4A...got it from a local mag here in the philippines.... its output impedance should be 8 ohms..... been using it for a while now... until i used it in a 4ohm 300W subwoofer....

sometimes i hear as if the subwoofer cone is about to "pop out" looks like it isnt stable at 4ohms??... but when i connect it to an 8 ohm subwoofer speaker, it sound just fine ... so i SHOULD use 8 oms and not 4 ohms.... bummer!!!

how do you know(at first glance) if the amp scheme is stable at 4ohms/2ohms?? any tehniquies to modify those 8 ohm amps to handle/be stable with 2ohms/8ohms ?? or any good amps that could hanlde those low impedances???

thanks.....
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Old 4th May 2004, 05:38 AM   #2
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Hard to make a comment unless you post the schematic.
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Old 4th May 2004, 09:02 AM   #3
djQUAN is offline djQUAN  Philippines
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first of all, kabayan!



aahh yes. I think you're talking about EE's 100 watt "incredible amplifier" using only one MJ15015 / 016 output devices per channel with +/-50V PSU.

it already had built in overload/overcurrent protection so it doesn't make sense (and is probably not worth it) to modify it for lower impedances. doing so calls for major upgrades and a bigger supply transformer.

IMO, I'd say look for a better schematic like rod's P68 amp and use it instead.

regarding your question to how to know if the amp can handle low impedances, they usually have two or more pairs of high current output devices per channel even if it has a low voltage PSU.
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Old 4th May 2004, 10:55 PM   #4
RX5 is offline RX5  Philippines
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@ Bill Fitzpatrick

ill try to scan it if i got time

@djQUAN
kabayan

yup twas EE's incredi-amp" 100W.... ill try rod's P68...


meanwhile, im still busy trying to make an SMPS.... still waiting for that LM3525 to arrive in my place (tacloban city) .... toroid imm using is about 1inch outer dia.. found in PC PSU.. dunno how many AMPS(current) it could handle.... my pri was 4x4 and sec was 16x16.... and im gonna use IRFZ40 (50A,50V,.022ohms RDSon) in parrallel (per side)...

laters..
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Old 5th May 2004, 10:39 AM   #5
Alcaid is offline Alcaid  Norway
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Quote:
Originally posted by RX5

...
.... toroid imm using is about 1inch outer dia.. found in PC PSU.. dunno how many AMPS(current) it could handle.... my pri was 4x4 and sec was 16x16.... and im gonna use IRFZ40 (50A,50V,.022ohms RDSon) in parrallel (per side)...

laters..

The toroid is too small!

If you read http://www.sound.westhost.com/project89.htm then you'll find this:
"Another possibility is using a toroid. You can extract it from a BIG power inductor. As a guide, a 4cm diameter toroid with a section of about 1cm2 can be used for a > 250W SMPS. Winding is a little bit more complicated than with ETD cores but with a little practice is not too difficult either."
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Old 6th May 2004, 08:04 AM   #6
djQUAN is offline djQUAN  Philippines
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I have three big toroids. you could have a look in this thread in the ESP forum....

those are the types that you need to build a SMPS.

http://www.instantboard.com/users/ro...opic.php?t=852

they are big and will handle enough power for most amps.

the toroid from a PC PSU is powdered iron and you need ferrites. it will not work (or worse, blow up. based on experience).
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Old 12th May 2004, 07:45 AM   #7
RX5 is offline RX5  Philippines
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Thumbs up nice

oh ic.. now im clarified... hehehe

i think i can distinguish a ferrite material from an iron powder... well i know a flyback transformes IS a ferrite (or is it???) could i possibly use that type od core????U core)


@ djQUAN

can i as k for your addy?? or maybe ull mail me: beamrx5@yahoo.com ... need to ask some info bout where u get your parts locally..... tnx
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Old 12th May 2004, 12:01 PM   #8
RX5 is offline RX5  Philippines
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Question need another clarification

hi guys,

anyone could comment on what type of circuit configuration is the BEST for SMPS????

based on the SG3525, what type would it be, using this chip with "feedback" type regulation using 4N35 ??

or simply using it to do 50% duty cycle (without line regulation)????

im just confused w/c type of circuit config to use...

tnx for any comment/info/help
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Old 17th May 2004, 04:44 PM   #9
djQUAN is offline djQUAN  Philippines
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use the non regulated types with the 50% duty cycle. they are usually more efficient and simpler to build.

I get my parts locally in "raon" near chinatown. cheapest electronics paradise.

although I got my toroid cores (and big toroidal trannys) in hongkong when I last went there since I can't find any available locally.
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