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Old 19th November 2006, 04:43 PM   #11
CarlosT is offline CarlosT  United States
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Most line receiver chips like the INA134 or the SSM2141 run on 15V+- or 18V+- max. How does one incorporate a little preamp/buffer like that into an LM3875 chipamp kit which runs at like 25V+-? Is it possible to share the same power supply and just use resistors to step down the voltage for just the preamp/buffer section? The LM3875 kit is powered through an unregulated bridge diode setup since I guess the LM3875 is OK with it. Would it be better to run everything off a lower voltage power supply?
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Old 19th November 2006, 04:47 PM   #12
Nordic is offline Nordic  South Africa
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LM337 and LM317 regulators should be able to step that down for you very nicely... look up the datasheets...

for higher voltage supplies yuo can use this prereg
http://sound.westhost.com/project102.htm

Click the image to open in full size. after which the regulators from the opening paragraphs would come..
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Old 20th November 2006, 04:47 AM   #13
CarlosT is offline CarlosT  United States
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Cool! I guess I would need 2 of these to handle each +/- side of the power supply.
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Old 20th November 2006, 06:16 AM   #14
Nordic is offline Nordic  South Africa
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That is correct, the lm317 is for positive rail.. and the rest follows from logic.
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Old 20th November 2006, 02:24 PM   #15
CarlosT is offline CarlosT  United States
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The fact that the power supply schema for the LM3875 is based on Carlos Felice's unregulated design, does that make any difference?
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Old 20th November 2006, 06:42 PM   #16
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Quote:
Originally posted by CarlosT
Most line receiver chips like the INA134 or the SSM2141 run on 15V+- or 18V+- max. How does one incorporate a little preamp/buffer like that into an LM3875 chipamp kit which runs at like 25V+-? Is it possible to share the same power supply and just use resistors to step down the voltage for just the preamp/buffer section? The LM3875 kit is powered through an unregulated bridge diode setup since I guess the LM3875 is OK with it. Would it be better to run everything off a lower voltage power supply?

The Power supply I use has a Regulated +/-15v and unregulated +/-24v useing the LM317/337 regulator chips.....

The supply was originally designed for Mic preamps but I changed the design so I could Run a LM3886 Chip amp and a Opamp Based +/-15v preamp from it, I just removed the Phantom power circuit and I modified it so I could have More PSU filter caps and just took the Power off the PSU before the regulators but after the Filter caps for the Unregulated 24v rails.....

I have a PCB and stuffing guide for this PSU if you want it?? Let me know and I"ll post it for you.....

Cheers

PS: I also designed a simple Preamp to use with the Chip amp that uses 2 Opamps (One dual and one single) all useing Inverted Topologies...It has Tone controlls (Bass,Treble,Mid) and Volume controlls and has a very High Gain.... I use if for Guitar and Bass but it could just as easilly be used for anything else....
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Old 20th November 2006, 08:33 PM   #17
CarlosT is offline CarlosT  United States
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Yeah...a simple, single tone control would be cool.

I just don't understand how they work in op amps.
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Old 20th November 2006, 11:24 PM   #18
Minion is offline Minion  Canada
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Well tone controlls work pretty much the same in Opamps as they do in any circuit....

All I did with this design was used a simple Tone Stack circuit and put it in between a couple Opamp gain stages with an Input buffer.....

For low impedance sources (Under say 100K) I would use a NE5532 on the input or some other Non fet input opamp but for High impedance sources a fet opamp is best....


Cheers
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Old 21st November 2006, 01:30 AM   #19
CarlosT is offline CarlosT  United States
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Somewhere in all this...a tone control is basically a potentiometer...right?
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Old 21st November 2006, 01:52 AM   #20
Minion is offline Minion  Canada
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Yes, a tone controll is a potentiometer,...

The Preamp I posted has a Treble, Bass and Mid controll...

If you want to have just a single knob for tone controll then you could drop the Mid range controll and use a Dual Ganged 250k Linear Pot and Connect the treble normally to one of the Gangs and connect the Bass to the other but in reverse then when you turned the Knob one way the Treble would increase at the same time the Bass decreases and the other way the treble decreases while the Bass increases.....

You would get better controll with the 3 Pots, or you could use Three Slider pots and have it set up like a 3 band EQ.....



Cheers
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