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Old 1st April 2010, 03:43 PM   #1
srinath is offline srinath  United States
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Default Input voltage range for lm3886 amp

What would be the input voltage range of a lm3886 amp.

I have one that asks for a 28V-0 -28V AC - so just a transformer needed. Now sadly that costs 45 bucks and ship.
I am finding 24V center tap as well as 36V very cheap. Like 10-20 bucks.

Would either of those work ?

Thanks in advance.
Cool.
Srinath.
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Old 1st April 2010, 04:04 PM   #2
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by srinath View Post
What would be the input voltage range of a lm3886 amp.

I have one that asks for a 28V-0 -28V AC - so just a transformer needed. Now sadly that costs 45 bucks and ship.
I am finding 24V center tap as well as 36V very cheap. Like 10-20 bucks.

Would either of those work ?

Thanks in advance.
Cool.
Srinath.
Think of a 36V center tapped transformer as being 18-0-18 and the 24V CT as 12-0-12.

Yes they can work it the curent rating is what you need but you will get a lot less power from the amp if yo run at the lower voltages
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Old 1st April 2010, 04:14 PM   #3
srinath is offline srinath  United States
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I meant to say 24v - 0 -24v. So center tapped 48 I guess.

Now 24V I can get with good amperage ... up to 5-6 amp easy. Would that work.

Cool.
Srinath.

Last edited by srinath; 1st April 2010 at 04:17 PM. Reason: Forgot to put it.
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Old 1st April 2010, 04:45 PM   #4
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Generally you want 200va or higher for a stereo lm3886 setup. If its stable at 5 amps they would work and be about 200va. You would need 2 identical 24vac transformers at 5amps each.
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Old 1st April 2010, 04:58 PM   #5
srinath is offline srinath  United States
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So a center tapped 48V and atleast 5 amps will work ? K I'll check it, I am sure I can find it. Is 36V - 0 -36V likely to be too much ? I could get a smaller amp rated transformer with 36 ? but am I likely to burn up stuff wiht 36.
Thanks.
Srinath.
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Old 1st April 2010, 07:27 PM   #6
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Its a math game. You have to keep the output current within limits using your supply voltage. so your current limit is 10amps
Your power input limit is 85vdc rails. So 28vac secondaries is about the limit, which is 79vdc.

8ohm speakers 10amp limit is 80vdc rails or 28vac secondaries




The va for the transformer is for stability. Making it smaller doesnt help anything.
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Old 1st April 2010, 08:29 PM   #7
srinath is offline srinath  United States
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OK so ... well ... I'm confused here.
I should only stay with 28v-0 -28v. Not do 24v - 0 -24v ...

Cool.
Srinath.
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Old 1st April 2010, 09:05 PM   #8
godfrey is online now godfrey  South Africa
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Quote:
Originally Posted by srinath View Post
OK so ... well ... I'm confused here.
I should only stay with 28v-0 -28v. Not do 24v - 0 -24v ...
No, 24-0-24 is perfect.

Nightanole was just calculating that the biggest you can use is about 28-0-28 (so 36-0-36 is too much).

Regards - Godfrey

Last edited by godfrey; 1st April 2010 at 09:08 PM.
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Old 1st April 2010, 09:23 PM   #9
ChrisA is offline ChrisA  United States
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Originally Posted by godfrey View Post
No, 24-0-24 is perfect.

Nightanole was just calculating that the biggest you can use is about 28-0-28 (so 36-0-36 is too much).

Regards - Godfrey
Yes 24-0-24 will work.

But with some extra effort you could built a regulated power supply from the 36-0-36 transformer. The regulator would drop the voltage to exactly what's needed and improve the overall sound of the amp somewhat. But a regulator more than doubles the complexity of the power supply, creates heat and uses more power.
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Old 3rd April 2010, 03:47 AM   #10
srinath is offline srinath  United States
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Isn't this a kick in the pants. I found a 28.2V AC power supply. Its called a 00f3058 or ltps 3058. In many ways when I used to find bike parts I would generally not look for what it is, I would look for "what else" is it. I know its a handle bar master cyl holder for a savage suzuki - 1 inch bar, but a lot of car cam shafts have a 1 inch journal dia and many have the same bolt spacing. Hence I ran a car cam journal for my brake master cyl holder.

Anyway its got 28.2 between pin 4 and 5 and 7.2 V between pin 8 and ground.
I need 6.3 - 8 v ac for warming the tube. I can run that between 8 and ground right ?

Now for the 28 - 0 -28 can I run another one of these with a 4 from this, 5 and 4 of the 2 twisted together for the 0 and the 5 from the other one as the - 28 ?

I should put pics up but on this thing there are a few little fuse types on the input side and a capacitor about medium sized on the output side. What does that do, and do I have to cut them all out and just use the transformers ?

Cool.
Srinath.
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