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
 
demogorgon said:
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. :)
 
Unwind

demogorgon said:
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.:idea:


demogorgon said:
eagery awaiting your reply.

Done.:D
 
Re: Unwind

neutron7 said:
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..

leadbelly said:


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 :D

planet10 said:
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..

pinkmouse said:
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? :eek:

carlosfm said:


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.:idea:




Done.:D

ooohh... that actually sounds like a good plan..
I'l try it if the amp blows on me. :hot:
 
I_Forgot said:
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.
 
demogorgon said:
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
Why don't you build an amp which actually can take +- 50 volts?

You could also add two windings (approx. 0.3 volt/turn) and let them counteract. (-x+ +x-) Try to loose 3-4 volts => 10-13 turns
 

XELB

Member
2004-12-07 11:26 pm
Lisboa
Re: Re: Unwind

demogorgon said:



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?




A friend of mine have tested the LM3886 at ~50V(35V trafo), now is going to 60V :eek:
Is using a massive heatsink :bigeyes:

Is testing the chip in different conditions and comparing the sound quality.



Ps: At 50V he said that it plays very well ;)
 

XELB

Member
2004-12-07 11:26 pm
Lisboa
He's testing the chip to know is behavior in different conditions.
Since he have free :bawling: LM3886 chips, burning is not a problem for him :p

I will follow is work with attention, than, I will post some data ;)




At this moment, I think my amp will run at 30V(based in the new Carlos regulated PSU).

Do you guys use big heatsinks at this voltage ?
 
just to kill the thread, it worked well, at leat for some time, then i managed to make a fool of myself and short something while unplugging a phono plug, and pow, the magic smoke escaped from one of the lm3886.
I would guess that you didn't 'short something' while unplugging the RCA. Your amp was very likely unstable (or only stable under certain conditions if you prefer), and disconnecting the input source was enough to send it into oscillations. That, combined with the ungodly power supply voltage, promptly destroyed the chip.
 
If you run an amplifier at voltage higher than its design limit, what will you learn? What knowledge is to be gained besides "gee, if I run it at 2X the maximum rated voltage it blows up". You can learn that by looking at the data sheet. Even if you know nothing about electronics and all those other numbers don't mean anything to you, ANYONE can understand what ABSOLUTE MAXIMUM RATINGS means.

You can run an IC at its maximum rated voltage, but its reliability will decrease. A blown up amplifier definitely won't drive your speakers very well, but I guess that won't matter much if the amp takes your speakers with it to "the other side"...

Good luck!

I_F
 
macboy said:

I would guess that you didn't 'short something' while unplugging the RCA. Your amp was very likely unstable (or only stable under certain conditions if you prefer), and disconnecting the input source was enough to send it into oscillations. That, combined with the ungodly power supply voltage, promptly destroyed the chip.

That sounds like a probable case scenario, i couldn't under stand what i could possibly have shorted.

well, i guess i'l have to think of something to hinder oscilliations at the input, maby a lowpass filter..

nothing is impossible, it just takes a while longer.

I_Forgot said:
If you run an amplifier at voltage higher than its design limit, what will you learn? What knowledge is to be gained besides "gee, if I run it at 2X the maximum rated voltage it blows up". You can learn that by looking at the data sheet. Even if you know nothing about electronics and all those other numbers don't mean anything to you, ANYONE can understand what ABSOLUTE MAXIMUM RATINGS means.

You can run an IC at its maximum rated voltage, but its reliability will decrease. A blown up amplifier definitely won't drive your speakers very well, but I guess that won't matter much if the amp takes your speakers with it to "the other side"...

Good luck!

I_F


Well, anyone can read a datasheet as you say, at least the maks voltage input part, but I wasn't looking for a datasheet answer, i wanted real life resoults, of which i got, so i'm satesfied. (and 10bucks poorer..)

I gained the knowledge that if the lm3886 is to be used outside it's maks ratings, some precautions have to be taken.

-Marius