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Old 10th May 2010, 08:10 AM   #1
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Default Which chip amp for a +/- 48v supply?

I have several (4 in fact) +/- 48v power supplies. These seem to be just outside the maximum rated voltage of the LM3886.

Are there other chip amps that would be suitable? I'm not looking for the greatest sound quality, more cheap, simple and reliable. Application is general PA.

Thanks,

Simon.
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Old 10th May 2010, 09:22 AM   #2
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how about none ???? you may only be able to drive some chip that also has external tranistors
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Old 10th May 2010, 09:59 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
do the +-48Vdc supplies vary with mains voltage or temperature or other operating condition?
The MAX supply voltage for the 3886 is specified @ +-42Vdc (84V total)
to lose 15% is possible using a regulator. The regulator must be designed to never exceed 84Vdc under all operating conditions.

Alternatively use National's driver chip series lme49810/811/830 These are rated at upto 200Vdc
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Old 10th May 2010, 12:49 PM   #4
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Quote:
Originally Posted by sakis View Post
how about none ???? you may only be able to drive some chip that also has external tranistors
Please do suggest something. I am not an expert, but I can solder and follow instructions.

I do not know how to cross post to the solid sate forum, so I could start a parallel thread there.

Simon.
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Old 10th May 2010, 12:53 PM   #5
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Quote:
Originally Posted by AndrewT View Post
Hi,
do the +-48Vdc supplies vary with mains voltage or temperature or other operating condition?
The MAX supply voltage for the 3886 is specified @ +-42Vdc (84V total)
to lose 15% is possible using a regulator. The regulator must be designed to never exceed 84Vdc under all operating conditions.

Alternatively use National's driver chip series lme49810/811/830 These are rated at upto 200Vdc
Regarding stability, I dont really know. They consist of just a torroidal transformer, 4 diodes and 2 capacitors, so you probably have a better idea than I of how stable they might be.

Can you point me to any examples of kits/implementations of the lme49810/811/830 chips?

Thanks,

Simon.
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Old 10th May 2010, 01:35 PM   #6
riktw is offline riktw  Netherlands
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tda7294 can do max +50V -50V, should work
but dont forget to cool it really good then.
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Old 10th May 2010, 01:57 PM   #7
AndrewT is offline AndrewT  Scotland
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a standard and simple unregulated PSU, using transformer + rectifier + smoothing capacitors, has a variable output voltage that varies directly with the mains voltage.
Here in the UK our nominal voltage is 230Vac but we have not actually changed from our old 240Vac supply. All they did was widen the tolerance to make it look like our supply was the same as the EU 220/230/240Vac.

In the UK our range of normal voltage is from a low of 216Vac to a high of 254Vac.
Your 48Vdc supply will vary with this voltage.

In addition the voltage from the PSU has mains ripple.
At very low output current the ripple is almost zero volts peak to peak.
As output current rises the ripple rises.
You measure the average voltage. The ripple is superimposed on that average, roughly Vpk above average and Vpk below the average.

The highest [average voltage + Vpk] can never be more than the unloaded average Vdc.
The lowest can be anywhere between 100mV below the unloaded condition to 20V below the unloaded condition depending on the ratio of current demand to PSU current capability.

What is the worst case highest voltage your PSU can supply?
Your amplifier or regulator must be designed to survive this worst case voltage. It could easily be 2% to 30% above the nominal 48Vdc.

All these variations have nothing to do with stability. It's tolerances and the way they can stack up against the user.
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Last edited by AndrewT; 10th May 2010 at 02:01 PM.
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Old 10th May 2010, 02:12 PM   #8
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I have the same problem as you.
There are only four ways to go about this.
1.use regulating circuit
2.build a bridged or bridged parallel amplifier
3.build a semi disceret amplifier using 49xxx series chips
4.get another transformer


The data sheets show an absolute maximum no signal power supply voltage of +-50v for the TDA7294 and 94v for the LM3886.
I don't know if anyone has had any sucsess running these chips at thier absolute maximum voltages ,but it is not advisable.
May be some one can elaborate more on that subject. jer
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Old 11th May 2010, 04:03 AM   #9
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Default SANYO chip amps could work

I don't think that it would be a good idea to use the TDA729x chip amps with that voltage, since it is so close to the max Vcc. You can connect it, but as soon as you supply input, poof! The only way you could swing it would be to use two chip amps, each configured for single ended supply, between 0V and Vcc+ and another between -Vcc and 0V. You could do that with the LM3886 even I think...

You might want to take a look at some of the Sanyo chip amps. Many of them can operate from that Vcc no problem, and you can get some nice power. You are limited to 6ohm or 8ohm loads however. You can also find 2+ channel amps like this one:
STK4241; STK4241ii (120W x2) Power Amp IC - Buy Online @ AmpsLab
here is a link to the data sheet (also linked in the page above):
http://ampslab.com/Freewares/stk4241ii.pdf
This company is selling other Sanyo chip amps. Member "Michael Chua" has posted me about these chip amps before, and I think he is the owner. Contact him for more info. Here is their web site:
STK Chip Power Amp Series - Buy OnLine @ AmpsLab

-Charlie
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Old 12th May 2010, 04:06 PM   #10
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The LME49xxx chips look pretty interesting.

They’re all capable of massive power with a discrete output stage (300W and 500W into 8Ω) and have constant power dissipation for a given supply voltage.

The LME49810’s selling point seems to be the internal Baker Clamp and the comparatively low minimum stable gain (10).

The LME49811 has low drive current (9mA, versus 60mA for the 49810 and 56mA for the 49830), highest PSRR (115dB, compared to 110dB for the 49810 and 105dB for the 49830) and best THD+N (0.00035%, compared to 0.0007% for the 49810 and 0.0006% for the 49830).

Both the 49811 and 49830 have a minimum stable gain of 26dB, or just shy of 20.

I couldn’t identify a ‘selling point’ for the 49830 – any thoughts?

http://www.national.com/ds/LM/LME49830.pdf
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