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Old 12th December 2011, 01:15 PM   #1
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Default DIY Chip Amp From Old Plate Amp Parts?

I have a few Klipsch subwoofer plate amps collecting dust. 2 of them I plan to rebuild into full range amps. The other 3 I can't do much with as they have seperate power supplies/chip amps. The chip amps use alot of smd and small components and that's a mess I would rather not get into.

However these amps have smps power supplies that I would like to make use of. The amps are rated for 150W continuous and 350W peak. The power supplies have a regulated +-15V 1A and a DC output. I am not home to measure the output but as a guess its 24-60V.

Looking at datasheets most chip amps call for a +- supply. Is it acceptable to reference the -V to ground or do they require a bi-polar supply? I would like to make some small 120-150W amps to make use of these nice supplies. NXP has some nice higher power chip amps with relatively low THD that I am looking at in hopes I can use them. IF these supplies are not acceptable for a chip amp can someone recomend a topology that would beneit from these supplies?
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Old 12th December 2011, 01:38 PM   #2
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Sure just look at page 6 but it sure gets more complicated to use a single supply.


http://www.national.com/ds/LM/LM3886.pdf
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Old 12th December 2011, 02:11 PM   #3
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Quote:
Originally Posted by crazifunguy View Post
The power supplies have a regulated +-15V 1A and a DC output. I am not home to measure the output but as a guess its 24-60V.
More information is needed.
How many power supplies of what voltage and current capacity are available?
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Old 12th December 2011, 03:03 PM   #4
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Imformation required

1 The actual votage and current rating of the psu.
2 The impedance of the speaker you intend to drive.
I suspect the amplifiers these PSU where powering are class d. If that is the case i suggest you go for a class d chip. this will also mean a small heatsink wich will enable you to build a small amplifier.

Regards Ian
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Old 12th December 2011, 03:15 PM   #5
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I will measure the output voltage when I get home...Assuming 150WRMS I will be able to make a good guess output current.

I really like the NXP TDA8950 but I can't find information on a single supply.
The ST 7575B is my second choice.

More to come after I find the output voltage.

Here is a picture of the amp and power supply.
Click the image to open in full size.
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Last edited by crazifunguy; 12th December 2011 at 03:26 PM.
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Old 13th December 2011, 12:20 AM   #6
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I measured the voltages. The main output is 48VDC with a +-9V secondary supply. The current is im guessing around 4-8A(150-350W). Expected speaker Z 4-8ohms. I am not sure what mode the SMPS runs in there is no feedback that I can easily see. The output is 5 wires. +42V GND -9V GND +9V. It may have some sort of current sensing, I'd have to look up the data sheets on the controller IC's.

The chip amplifier part of the amp is very "HIGH TECH" it uses this IC for who knows what. Seems a little over-complicated for a sub amp but I must say the thing does sound pretty crisp.
http://www.st.com/internet/com/TECHN...CD00169555.pdf

Its a shame that modifying the crossover on the amp is so complicated. It will be much simpler and way more fun to build a custom chip amp and just steal the SMPS.

Last edited by crazifunguy; 13th December 2011 at 12:38 AM.
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Old 13th December 2011, 10:36 AM   #7
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The LM1875 chip will run on that 48v or 42v single rail just fine. This can get you about 24 watts of hi-fi. Remember that a speaker that just 3db more efficient makes up the difference between a 25 watt amp and a 50 watt amp.

If you'd like more power, select a stereo chip, such as one of ST's and bridge it. There's quite a few that call for 48v or +-24 and most of them have bridge options demonstrated in the datasheet. This can get you about 40 watts.

If I remember correctly, there is a Tripath kit that was specified for 48vdc, and it is possibly a bridged kit. This can also get you about 40 watts.
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Old 13th December 2011, 12:12 PM   #8
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Quote:
Originally Posted by crazifunguy View Post
I have a few Klipsch subwoofer plate amps collecting dust. 2 of them I plan to rebuild into full range amps.
Are they not functional the way they are?

Quote:
Originally Posted by crazifunguy View Post
I measured the voltages. The main output is 48VDC with a +-9V secondary supply. [...]The output is 5 wires. +42V GND -9V GND +9V.
42 V marked and 48 V measured? That is quite a big regulation for an SMPS. For your plan of 150 W, you will need 4 Ohm speakers and to use chip amps in (paralleled) BTL mode on single supply. That is about as complicated as it can get with chip amps.
Or sou could try to make a split supply from two of those SMPS, and then choose a chip amp that can work from 48 V rails, like the TDA7293.

Quote:
Originally Posted by crazifunguy View Post
The chip amplifier part of the amp is very "HIGH TECH" it uses this IC for who knows what.
That is the crossover. You won't need it for full-range amps.
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Old 13th December 2011, 06:00 PM   #9
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Quote:
Originally Posted by pacificblue View Post
Are they not functional the way they are?

42 V marked and 48 V measured? That is quite a big regulation for an SMPS. For your plan of 150 W, you will need 4 Ohm speakers and to use chip amps in (paralleled) BTL mode on single supply. That is about as complicated as it can get with chip amps.
Or sou could try to make a split supply from two of those SMPS, and then choose a chip amp that can work from 48 V rails, like the TDA7293.


That is the crossover. You won't need it for full-range amps.
The 2 Sub-12 plate amps I have are in pretty bad shape and not fixable the way they are. I am in the process of making a schematic and PCB. They run in class G with a linear full bridge amp.

48V marked and 42.5V measured loaded and unloaded. The SMPS boards are rather nice compact and covered in component glue. I would prefer to not modify them at the expense of having a more complicated chip amp. More challenge=more fun.

The SW-350 amps with these smps's are full digital chip amps. They use an a/d converter digital filtering and amplification. Down the road that might be a fun project to venture into but as my first real amp build I will stick with analog for now.

The chip I have selected to use is the LM 4780 basically the 2 channel version of the LM 3886.....Let the fun begin!
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Old 13th December 2011, 10:43 PM   #10
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WOW!! You weren't joking about single supply being a pain. Bridged is out of the question for right now. I made my first schematic of this setup following the data sheet. Have a look and let me know if any of my values are no good. The data sheets states to use poly film caps in the signal path for better response.

Click the image to open in full size.
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