running the lm3886 at +-50V

[demogorgon]

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

[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.

[leadbelly]

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.

[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

[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...

[carlosfm]

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.

Originally posted by demogorgon
eagery awaiting your reply.

Done.

[demogorgon]

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..

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

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..

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?

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.

[tonitze]

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

[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

[carlosfm]

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.