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dustbro

Fairchild 662... where to add output control?
« on: October 20, 2007, 06:18:43 PM »
Can anyone take a shot at the best way to add an output mod to this Fairchild 662 amp?
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NewYorkDave

Fairchild 662... where to add output control?
« Reply #1 on: October 20, 2007, 07:04:20 PM »
Just slap a 600-ohm variable attenuator on the output terminals.
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dustbro

Fairchild 662... where to add output control?
« Reply #2 on: October 20, 2007, 08:49:25 PM »
Quote from: "NewYorkDave"
Just slap a 600-ohm variable attenuator on the output terminals.

Hey Dave,
Wouldn't that just allow me to decrease volume? So I would have to internally increase the total gain of the circuit, right?... and then use the attenuator on the output? Or am I missing the point of what a variable attenuator does?
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NewYorkDave

Fairchild 662... where to add output control?
« Reply #3 on: October 21, 2007, 03:11:56 AM »
Quote from: "dustbro"

Wouldn't that just allow me to decrease volume?


Is that not what you want?
If so, you'll have to explain what you mean, exactly, by "output control."
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NewYorkDave

Fairchild 662... where to add output control?
« Reply #4 on: October 21, 2007, 01:10:26 PM »
Oh, so he wanted a gain control. He shoulda said so :wink:.
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dustbro

Fairchild 662... where to add output control?
« Reply #5 on: October 22, 2007, 11:14:09 AM »
Quote from: "NewYorkDave"
Oh, so he wanted a gain control. He shoulda said so :wink:.

ha ha I guess I should have specified. But that brings up a good point... maybe I need Gain and Output control.
Thanks for the replies guys!
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dustbro

Fairchild 662... where to add output control?
« Reply #6 on: October 22, 2007, 11:21:09 AM »
Quote from: "kubi"

Anyway, you can use the pot R8 to control feedback and also gain. I guess without deeper calculations, it should give round about 20 to 55 dB of gain.

Isn't this the little trimpot on the front of the module? I think that only gave me a couple dB of gain each way.
I'll try to put a pot at R1 and see what happens.
thanks!
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SSLtech

Fairchild 662... where to add output control?
« Reply #7 on: October 22, 2007, 01:35:14 PM »
What about a higher value trim-pot for R8? Perhaps you'd get a little more gain trim range from that approach?

(I confess that I didn't spend long looking, so haven't thought it through, but I thought I might toss it out there to the better minds...)

Keith
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"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

dustbro

Fairchild 662... where to add output control?
« Reply #8 on: October 22, 2007, 10:47:13 PM »
Quote from: "SSLtech"
What about a higher value trim-pot for R8?

I dont know much about circuit design, but I would assume that when the trimpot that's already installed is wide open (no resistance) that this circuit is at it's maximum gain.. right? and when you start adding resistance, the gain goes down? Maybe someone can school me in this department
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