Mono blocks using National LME49830

[binspaul]

Hi,

I am planning to start a new mono blocks project using the National LME49830 chips. The circuit employed will be from the application note available at: http://www.national.com/an/AN/AN-1850.pdf. I am having almost all the components readily available with me.

Some of the parameters/requirements are:
1. Each mono block should be able to generate an output power of 150W RMS
2. the speaker load will be 8 Ohms.
3. Extremely silent power supply.

I was not able to find a simple and cost effective supply for this project. I am not so interested in the power supply application note that is available from National as it is a bit bulky and costly. Also, some of the components are not easy to find. But, I am interested in taking the delay and mute sections from that note.

Can someone help me ?

Best regards,
Bins.

[h_a]

With the exception of ClassA monsters, the power supply is not the source of humm and hiss and therefore does not have to be extremely silent. The cause for this is then grounding, cabling, distance of the VAS to transformer etc. So I think - especially as these ICs usually have huge PSRR - that you will be happy with a classic linear supply (transformer+ caps).

Or am I missing something? By the way I couldn't find a schematic for a PSU in the referenced application note or anything else that would suggest something special?

Have fun, Hannes

[AndrewT]

Hi,
a dual secondary 40+40Vac transformer will give ~58 to 59Vdc.
With good smoothing and a well built amp you can easily achieve 150W into 8r0.

If you want to have the ability to drive a 4ohm load then you will need to double the smoothing capacitance and double the VA rating of the transformer.

For 150W into 8r0, a 300VA with +-20mF will do.

My 230:40+40Vac gives +-58.5Vdc when fed with 240Vac and the amp bias is 220mA. It gives 170W into 8r0 from a 3pair output stage.

[wahab]

to feed a monoblock, you ll need a 2 x 50V ac transformer,
a 400V/20A rectifier bridge and at least 10 000 uF/ 90 to 100 v caps
per rail....this is the minimum requirements..

[binspaul]

Hello Hannes,

The power supply application note is available at http://www.national.com/an/AN/AN-1849.pdf

Best regards,
Bins.

[binspaul]

Hi,

1. Which class does the amplifier illustrated in the original application note (http://www.national.com/an/AN/AN-1850.pdf) belongs to ?

2. The recommended power supply rating is around 60 - 70V.

Best regards,
Bins.

[MJL21193]

Originally Posted by binspaul

Hi,

1. Which class does the amplifier illustrated in the original application note (http://www.national.com/an/AN/AN-1850.pdf) belongs to ?

2. The recommended power supply rating is around 60 - 70V.

Best regards,
Bins.

1. Class AB
2. 60-70 volts will get you the 150 watts you want. See AndrewT's post.

[binspaul]

Hi,

Does anyone have the schematics for a similar supply ? The inrush control and the mute control sections seems very much suited for the amplifier.

Best regards,
Bins.

[h_a]

Hi Bins,

build the right half of the PSU in the app-note (Fig.1) and instead of all the soft-start/relay fun, put a thermistor, CL60, in series with the primary leads of the transformer.

Works very well.

Have fun, Hannes

PS: by the way, I'm not sure you need soft-start for 2x20000uF at all.

[binspaul]

Hi ,

Had a brief look at the thermistors and their application in current limiting. The CL-60 solution seems good. How can we provide the mute control if we take off the soft start section ?

Can I reduce the 20,000uF supply reservoir to a lower value around 10,000uF without affecting the amp performance ? What is the main purpose of this ?

Best regards,
Bins.