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Old 27th February 2007, 06:20 PM   #1
beerman is offline beerman  United States
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Default I want to start small, have a question about a toroid

I decided I want to build a small chip amp for my PC using a single LM1876.

This unit from digikey is called a "mini". It is a 50va with 12v secondaries.

Will that suffice for a small 15w per channel stereo amplifier?
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Old 27th February 2007, 08:07 PM   #2
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Just about, a bit on the small side but probably a lot better than most of the PC systems advertised as 60W or more...
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Old 28th February 2007, 01:15 AM   #3
Leolabs is offline Leolabs  Malaysia
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Yes,with something like the LM1875.
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Old 28th February 2007, 02:55 AM   #4
beerman is offline beerman  United States
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Originally posted by Leolabs
Yes,with something like the LM1875.
If I recall, the 1876 is two 1875s in a single chip?
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Old 28th February 2007, 03:26 AM   #5
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I think you'd be better off with a chia-yu xformer from apexjr for 12.50

http://www.apexjr.com/miscellaneous.html#Toroids

12V will be on the low side
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Old 28th February 2007, 05:33 AM   #6
beerman is offline beerman  United States
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Originally posted by twitchie
I think you'd be better off with a chia-yu xformer from apexjr for 12.50

http://www.apexjr.com/miscellaneous.html#Toroids

12V will be on the low side
I'll admit to being a newbie on this subject.

I'm trying to stay "safe". I will want to run 4ohm drivers with this amplifier at one point or another.

Correct me if I'm wrong: if the drivers are low impedance, shouldn't the PSU send lower voltage to the chip? (I don't remember the reason, I'm no engineer, but I do remember reading it somewhere.)

But that is a decent deal.
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Old 28th February 2007, 09:38 AM   #7
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Quote:
Originally posted by beerman


I'll admit to being a newbie on this subject.

I'm trying to stay "safe". I will want to run 4ohm drivers with this amplifier at one point or another.

Correct me if I'm wrong: if the drivers are low impedance, shouldn't the PSU send lower voltage to the chip? (I don't remember the reason, I'm no engineer, but I do remember reading it somewhere.)

But that is a decent deal.
Yes, that's right.

The required voltage into a given impedance speaker for a given power is V = sqrt(PR) where sqrt is 'square root'. So you need less V into 4 compared to 8. You could keep the supply high, but you'd increase the power dissipated in the amp chip.

So for 15W in 4 ohm you need 7.5V RMS = 11V peak. Add a few (or look at the data sheet) volts for losses in the amp, so it looks like 15V rails will do the job. A 12V transformer will give about 15V after rectification, so there you go.
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