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Old 15th February 2009, 10:07 PM   #1
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Default Yamaha Surgery

Well, this Yamaha baby cost just about nothing -- has a nice transformer and a heat sink radiator like those base-board heaters -- doesn't sound bad, but it is a mess cosmetically and soon to become "Franken-Receiver A-10".

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THD% For 1W

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THD% For 20W

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Flatness -- you can't eliminate the tone controls:

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Slew Rate:

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Old 15th February 2009, 10:18 PM   #2
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Anyone think that an LM4702 could be fit in here:

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I already cleaned up the output connectors -- who the heck needs an

A/B speaker switch anyway?

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Old 4th March 2009, 01:15 AM   #3
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Changing the filter caps from 6,800 uF to 10,000 uF resulted in a 1.4V increase in the rail voltages. The old caps didn't even have to be desoldered -- just twisting a bit and they popped out. They were really dried out as well.
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Old 4th March 2009, 07:27 PM   #4
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Well, this thing is going to run HOT!!! The rail voltage is now close to 44V each, but this receiver is only rated (I think) at 50 WPC -- here's a shot of the new driver board installed -- for the moment we are dispensing with the tone and loudness controls. The CD4066 analog switches are also going to have to stay for a while as I can't find an adequate replacement.

I've used this LM4702 driver in about 6 mods so far.

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Old 7th March 2009, 09:37 PM   #5
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I am using Troy Huebner's method for determining the value of the gate resistors on the lateral MOSFETs. A pair of 1K trimpots set at center rotation. With a square wave, crank the amplifier up to where it sweats and adjust the trimpots until the rise and fall patterns are identical:

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Old 15th July 2009, 05:12 PM   #6
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Oh well, forget the lateral MOSFETs -- the distances are too great so I am using bipolars.

Here's the new controller which will use Silonex LDR's -- the Yamaha has 4 inputs and a switchable loop -- so there are 2 loops in the code to read the button port -- I don't know if one resistor pack is going to work with the LED's.

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