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Old 7th July 2007, 03:55 PM   #1
Pery is offline Pery  Brazil
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Default Using +/-70V on a LM 3886

Hi there !!

I have a very good power supply of +/- 70 Volts.

Could I use it to make an audio amplifier for 8 ohms speaker using LM3886 chip ?

I wonder if anyone has experience in this project. I would like to get around 60 watts RMS or so.

Thanks for any help.

Pery
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Old 7th July 2007, 04:15 PM   #2
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+/-70v is way too much for an LM3886. You should be looking more around the +/-30v mark. Unless you mean 70v from rail to rail, which would be +/-35v? That would be OK for an 8 ohm load according to the datasheet, and would give about 50W.
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Old 7th July 2007, 08:12 PM   #3
pchw is offline pchw  United States
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I have 2 salvage toroids from Radio Shack's Accurian. Each is 28.5x2 at 2A, that should make it a 110VA rating. Will it be enough to drive one channel of BrianGT's LM3886 kit? My speaker is rated at 6ohm. As you can see that I am trying to fit the kit into the Accurian :-)

Thanks,
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Old 7th July 2007, 10:53 PM   #4
Arx is offline Arx  Canada
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Quote:
Originally posted by pchw
I have 2 salvage toroids from Radio Shack's Accurian. Each is 28.5x2 at 2A, that should make it a 110VA rating. Will it be enough to drive one channel of BrianGT's LM3886 kit? My speaker is rated at 6ohm. As you can see that I am trying to fit the kit into the Accurian :-)

Thanks,
That voltage is probably a bit on the high side, and power is probably a bit too low. It would probably work, but maybe not well, depending how much power you're hoping for.

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Old 8th July 2007, 01:07 AM   #5
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Quote:
Originally posted by pchw
I have 2 salvage toroids from Radio Shack's Accurian. Each is 28.5x2 at 2A, that should make it a 110VA rating. Will it be enough to drive one channel of BrianGT's LM3886 kit? My speaker is rated at 6ohm. As you can see that I am trying to fit the kit into the Accurian :-)

Thanks,
This is from Brain's user guide page 16

"Many have successfully used 160VA transformers, while the 220VA range seems to be adequate for almost all stereo implementations, not straining the transformer. The price point between 220VA and 330VA, however might lead one to purchase the larger of the two. Anything above this could be considered frivolous for a stereo pair, unless one happens to be on the shelf or in a surplus vendors stock"
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Old 8th July 2007, 01:55 AM   #6
pchw is offline pchw  United States
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Yup, I read the manual and saw this paragraph.
From the VA rating's perspective, 2 of these toroids will be equivalent to 220VA. The Accurian is only rated rms 25wpc at 50-20KHz, the chipamp should be a big improvement regardless I just need to be careful and don't get too excited and crank up the volumne
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Old 8th July 2007, 02:09 AM   #7
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Default What do you have to lose.

I think that either the voltage needs to be lower, or the current higher though. The 2A current is a real limit. 5 amps would be much better.
The 28 volts AC would be perfect for a paralleled LM3886 amplifier and 8 ohm loading. You might get 80 watts or so with a higher current transformer.


George
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Old 8th July 2007, 02:23 AM   #8
pchw is offline pchw  United States
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I must apologize to Pery for threadjacking.
If your xformer is indeed 70VAC x 2, then it will be too high. What voltage is yout country?
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Old 10th July 2007, 04:09 AM   #9
Pery is offline Pery  Brazil
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Default LM 3886 using +/-70Volts.

Hi,

I was reading the LM 3886 specs and is not possible to use this voltage of +70V, 0 Volts, - 70V !!

In my country , Brazil, Rio de Janeiro , the voltage is 117V AC 60Hz (wall outlet).
I was wondering to make a mono amp using a power supply of an old Marantz 300DC.. together LM 3886. I see now that this is not possible. The appropriate voltage is +/- 25V to 35V.

Question solved .

Thanks
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Old 10th July 2007, 04:55 AM   #10
pchw is offline pchw  United States
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Hi Perry,

So, it is like US, 117V 60hz. Now, second question, does your transformer have dual primaries (120 and 240). If so, you can wire it to use the 240 primary. That way the secondary's voltage will effectively cut in halves, i.e. 35VAC x 2. Then you use input choke instead of input cap. That way you should be able to use your tranny, just some thoughts, see whether this will work.
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