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PostPosted: 22 Feb 2009, 21:14 
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Hi Stream, glad to hear the higher voltage is working better. I would still recommend a few more volts. If the supply is not regulated, you will know right away as you will get hum.

Adjust the pot until the voltage on the Source leg of the mosfet is one-half that of the supply voltage.
ie. If your supply is 12VDC on the Drain, you want 6VDC on the Source.

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PostPosted: 01 Jun 2010, 21:27 
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What modifications would be needed to power an 8ohm load? I have a few MOSFET's kicking around and was going to have a go at building one.


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PostPosted: 02 Jun 2010, 12:28 
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More current through the mosfet. Also, make sure you use a regulated power supply. Let us know how you make out.

Cheers

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PostPosted: 02 Jun 2010, 22:55 
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I have an old PSU from a computer somewhere. I believe it supplies 85ish watts at 12volt. Would that do it?


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PostPosted: 03 Jun 2010, 12:12 
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You would still need to regulate which will bring you down to the 9V range and then power is limited.

On a tight budget, I would think something along the lines of a 3 amp, 18V laptop/printer SMPS. Have one LM317 per channel to regulate the voltage to 15V and try the mosfets each at 1A.

This will be low power and have no gain.

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PostPosted: 04 Jun 2010, 21:29 
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Computer PSUs are regulated, so why would I have to regulate it again?


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PostPosted: 05 Jun 2010, 10:13 
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Also, would an ST Microelectronics P140NF55 (www.st.com/stonline/books/pdf/docs/11028.pdf) work as the Mosfet?


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PostPosted: 05 Jun 2010, 21:34 
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Computer power supplies are quite noisy and need lots of good filtering, you can see just how noisy they are by hooking up a pair of headphones to the output of the amplifier, you might be surprised. ;)

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PostPosted: 07 Jul 2010, 22:43 
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Gio

You mention connecting a cap and resistor to knock out hum between the signal ground and power ground connections. What kind of values are recommended? I am hoping this will not be required but want to be ready for the worst. My build will happen in the next week. For the supply I am using a regulated wall wart 15V with .40A output for starters, any thoughts on this?

Thanks


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PostPosted: 08 Jul 2010, 12:39 
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0.1 or 0.22uF X2 rated capacitor in parallel with ~100 ohm resistor. On the 5751/KT88 OddWatt amp a 0.1uF X2 capactior and 120R resistor are used.
Quote:
For the supply I am using a regulated wall wart 15V with .40A output for starters, any thoughts on this?

0.4A = 400mA That will likely be too small. The CCS in the circuit as shown is set at 250mA per mosfet. So the total draw is in the order of about 500-600mA.

Welcome to the forum.

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