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Old 6th March 2009, 08:21 AM   #1
FlexQ is offline FlexQ  Denmark
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Default PA150 review

Hi Guys

I have made this little print, would anyone mind reviewing it?

It has been build around "shine7" BPA150 modules, however, i have got my hands on a pair of a 0.1uF Jensen caps, made for Tact audio . So they will be in the output.

I Might add that i use 3 lm 3876 and i have removed the "not Connected" pins at the IC. It makes the layout just a little bit easier .

But an TO220-11lead was not an component in my print layout program, so i made it myself. Thats why the three components in the top might look a bit strange.

The Schematic:

Click the image to open in full size.

And here is the 2 layer PCB:
Click the image to open in full size.

Click the image to open in full size.

The PCB images is in high-res here:

http://img7.imageshack.us/gal.php?g=tophighres.jpg


They will be handetched at my school, we have all the equip we need for doing that.

i know that it aint possible to make throughholes when handetching, but i will drill a lot of holes around many of the ground requiring components, and then connect the two goundplanes together. It is a rather slow process, but i think it will be worth the time.

Hope someone will look it through.

FlexQ
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Old 6th March 2009, 11:00 AM   #2
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Default Re: PA150 review

Quote:
Originally posted by FlexQ
It has been build around "shine7" BPA150 modules, however, i have got my hands on a pair of a 0.1uF Jensen caps, made for Tact audio . So they will be in the output.
There is no need for an output capacitor. You have a split power supply.

If you want to use it anyhow, be aware that a capacitor in series with the speaker will create a high-pass filter. With three ICs in parallel, you are probably driving 4 Ohm speakers, because that is the only reason to choose a parallel configuration. A 0,1 F cap in series with 4 Ohm will form a high-pass filter with ~400 kHz corner frequency. So you would effectively filter everything out that is in the audio range.

Use that Jensen cap in parallel with C1. It may improve the sound.

Any particular reason, why you chose the inverting application other than, because it was there?

Quote:
Originally posted by FlexQ
i know that it aint possible to make throughholes when handetching, but i will drill a lot of holes around many of the ground requiring components, and then connect the two goundplanes together. It is a rather slow process, but i think it will be worth the time.
Groundplanes are not the best choice for an audio amplifier. Have you built any other amplifiers before this? Or are you maybe taking the second step before the first with this project?
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Old 6th March 2009, 01:33 PM   #3
FlexQ is offline FlexQ  Denmark
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Default Re: Re: PA150 review

I have misunderstood some things, but that was why i asked for the review, the Jensen cap is ofcourse in the signal path.

Dont know what i was thinkin.

New pcb and sch will be up in a jiffy

Regarding the groundplane, i think i know what you are saying.

You would want me to seperate singal gnd and power/output-gnd, maybe with a .1R resistor?
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Old 6th March 2009, 05:02 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
the inverting topology adopted makes the input impedance of each amplifier = 10k.

Three amplifiers in parallel will have an effective input impedance of 3k3.

Take the 47k at the input filter and the net impedance seen by that 10uF is ~3k1

The bass will start to roll off @~50Hz and be 3dB down @~5Hz.


Either adopt a buffer to drive the 3k3 presented by the amplifier or use a very large electrolytic (220uF or 330uF Panasonic 16V bipolar) as the DC blocker.

If you don't know how a ground plane works and/or don't know how to design a ground plane, then DO NOT incorporate a ground plane.
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