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Old 6th May 2005, 11:40 PM   #1
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Default running the lm3886 at +-50V

Now, i have been looking through the forums for an answer to this a for a long time, but to no availe, so i figure i'd just open a new thread.

the question is simple, how will the lm3886 respond to 50V rails?

I recon one of three things will happen:
1: the chip's protection sircut will shut the chip down.
2: The thing will pop instantly
3: the chip wil work, but very hot, and not very happy with low impedans loads.

i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice.
alas, when i power it up i read 35.4V pr. secondary. this should mount to DC voltages close to, if not over 50V pr. rail, so..

eagery awaiting your reply.
-Marius
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Old 7th May 2005, 02:21 AM   #2
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you could use LM338 regulator circuit and bring the voltage down to more reasonable level like say 35 volts. regulator max in>out difference is 40 volts so you could try various voltages if you wanted.
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Old 7th May 2005, 03:14 AM   #3
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Default Re: running the lm3886 at +-50V

Quote:
Originally posted by demogorgon
i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice.
I know everybody in this forum just regurgitates the same gainclone voltage guidelines over and over again ad nauseum, so I thought I would make a point just for fun. Sitting a couple of feet away from me is a commercial PCB set for a Line6 guitar amp that powers the LM3886TF with a 60VCT transformer. So go ahead.
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Old 7th May 2005, 07:31 AM   #4
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30-0-30 puts you right at the official limit about 42V... BrianGT has a bud running one at something like 46V.

You can try it... you'll likely find out pretty quick if the smoke stays in.

I like stable into low/complex impedances so i'd regulate or maybe try a CRC (or even CLC) to drop a bit of V.

dave
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Old 7th May 2005, 08:28 AM   #5
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Use much bigger heatsinks, and give up the idea of driving low impedance/ difficult loads, and you can get by on 45v rails. That's as high as I got...
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Old 7th May 2005, 10:51 AM   #6
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Lightbulb Unwind

Quote:
Originally posted by demogorgon
i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice.
alas, when i power it up i read 35.4V pr. secondary. this should mount to DC voltages close to, if not over 50V pr. rail, so..
Marius, more important than if it will work is: will it sound decent?
A guitar amp doesn't need to amplify low frequencies, and the chip may work at it's max. voltage.
But you are not making a guitar amp, and you are passing the max. voltage.

Instead of fiddling with the whole bazooka making it play and stopping it's protection from kickin' in, I can't think of an easier route than unwinding some turns of wire from the trafo's secondaries.


Quote:
Originally posted by demogorgon
eagery awaiting your reply.
Done.
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Old 7th May 2005, 02:21 PM   #7
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Default Re: Unwind

Quote:
Originally posted by neutron7
you could use LM338 regulator circuit and bring the voltage down to more reasonable level like say 35 volts. regulator max in>out difference is 40 volts so you could try various voltages if you wanted.
nah, to much work, and besides, they cost like 12dollars a piece here up north. thats almost as much as the rest of the amp cost me..

Quote:
Originally posted by leadbelly


I know everybody in this forum just regurgitates the same gainclone voltage guidelines over and over again ad nauseum, so I thought I would make a point just for fun. Sitting a couple of feet away from me is a commercial PCB set for a Line6 guitar amp that powers the LM3886TF with a 60VCT transformer. So go ahead.
I just might do that

Quote:
Originally posted by planet10
30-0-30 puts you right at the official limit about 42V... BrianGT has a bud running one at something like 46V.

You can try it... you'll likely find out pretty quick if the smoke stays in.

I like stable into low/complex impedances so i'd regulate or maybe try a CRC (or even CLC) to drop a bit of V.

dave
well, i hooked the xformer to the psu board, and measured 48.5V rails, so.. if i'm not mistaking, isn't the max voltage suply for the lm3886 96V unloaded?

time to test..

Quote:
Originally posted by pinkmouse
Use much bigger heatsinks, and give up the idea of driving low impedance/ difficult loads, and you can get by on 45v rails. That's as high as I got...
my heatsink is fairly beefy, so i figure.. wait, you got to 45V, then what?

Quote:
Originally posted by carlosfm


Marius, more important than if it will work is: will it sound decent?
A guitar amp doesn't need to amplify low frequencies, and the chip may work at it's max. voltage.
But you are not making a guitar amp, and you are passing the max. voltage.

Instead of fiddling with the whole bazooka making it play and stopping it's protection from kickin' in, I can't think of an easier route than unwinding some turns of wire from the trafo's secondaries.




Done.
ooohh... that actually sounds like a good plan..
I'l try it if the amp blows on me.
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Old 7th May 2005, 02:45 PM   #8
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Carlos,

How successful can a person unwind trafo secondaries to your opinion. Is there any chances that you might screwed up the trafo because overlapping of sec. winding? I mean stuck halfway..

Toni
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Old 7th May 2005, 03:38 PM   #9
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If the transformer is a toroid you can lower the voltage by ADDING a few turns of wire around the core, but wound in the opposite direction as the existing windings. No need to take the transformer apart...

I_F
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Old 7th May 2005, 04:21 PM   #10
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Quote:
Originally posted by I_Forgot
If the transformer is a toroid you can lower the voltage by ADDING a few turns of wire around the core, but wound in the opposite direction as the existing windings. No need to take the transformer apart...

I_F
Yes, that's one of the options.

Guys, a toroid is not so complicated inside...
If you don't feel like doing it, wind in the opposite direction.
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