Input voltage range for lm3886 amp

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srinath

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Joined 2010
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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ChrisA

Member
Joined 2008
srinath said:
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.
Click to expand...

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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nightanole

Member
Joined 2009
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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ChrisA

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Joined 2008
godfrey said:
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
Click to expand...

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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srinath

Member
Joined 2010
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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srinath

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Joined 2010
The wiring is like this for that transformer.
1 and 2 are input - 110 VAC. 3 is ground on the input side.
4-5 is 28.2 VAC.
6-7 is 9VAC.
8 is output ground.

The fuses etc seem to all be on the 110V side, and not the output side.
I have found 7.2 V between 4 and 8, not 8 and ground as I mentioned earlier. There is a tube pre amp buffer in this thing which needs 6.3-8VAC for warming it.

I guess I better get one more of these and connect them and check it before connecting the amp. Thanks much.
Cool.
Srinath.
 
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