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Old 16th January 2006, 12:34 PM   #1
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Default Here is a small puzzle for you.

I am awaiting my chip amp kit and parts.

In order to practice soldering I have dug into an old Rotel reciever for fun.

What I have done so far....

Replaced AUX input wires with Cat5 for signal, ran directly into volume pot. After the Pot Cat5 is ran directly into amplication circuit posts.

Replaced AUX grounds with Cat5 ran directly into amplification circuit posts.

Next plan is to by-pass the headphone jack and run directly from the fuses into the speaker terminal tabs.

Ok now what is interesting.... The volume knob will no longer silence the input from my amplifier. It will adjust the sound to some degree. The Pot is a 100kohm. I figured I need more resistance so I put 150kohm resistors before the pot from the RCA's (5% tolerance from the trebel/bass/balance board removed) and consequently the amp is quieter to the laptop input but the 100kohm pot does next to nothing!

Well so what do I do?! I have only guessed to increase the resistance... There are some 470kohm resistors I could try. I however have no idea how the Pot will function if adding resistance kills this thing.... I am sure some one on here has some sort of idea.

On a side note the sound is certainly improved, my soldering skills are fresher, and I have one burn to remmeber it all by
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Old 16th January 2006, 12:48 PM   #2
SY is offline SY  United States
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Just guessing, but I'll wager that the end of the pot that is supposed to go to ground no longer does.

Voice of experience here!
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Old 16th January 2006, 01:08 PM   #3
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by SY
Just guessing, but I'll wager that the end of the pot that is supposed to go to ground no longer does.
Voice of experience here!
I second this guesstimation. Volume pot wired as a resistance in series.

It should be wired as a resistance in series and parallel with the input of the power amp.
That is signal in - one end of the track, signal out - wiper, other end of track ground.

/sreten.
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Old 16th January 2006, 01:12 PM   #4
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Old 16th January 2006, 01:38 PM   #5
lineup is offline lineup  Sweden
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Question is why you need more resistance?

100k is already a high resistance in input.

Is it lower volume you need, maybe?
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Old 16th January 2006, 01:46 PM   #6
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Quote:
Originally posted by lineup
Question is why you need more resistance?

100k is already a high resistance in input.

Is it lower volume you need, maybe?

It seems the volume is fine but the range of adjustment since the tweaks has been severely restricted....


BTW.... I also vote for the ground end of the pot no longer going to ground.
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Old 16th January 2006, 06:57 PM   #7
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There's probably a wiring error.
A volume control is effectively two resisiors with
one end of the resistors wired to the input, the junction of the as an output, and the other end as ground, thus splitting the voltage into two parts.

O____O____O
in out ground
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Old 16th January 2006, 10:10 PM   #8
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Funny thing is that the ground wire that comes in from the power cord is attached to nothing, there never was one! Also their is no evidence of grounds any where in this machine!

I will try grounding out the other side of the pot. I do have the wire and I do have a new three wire cord.
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Old 16th January 2006, 11:02 PM   #9
anatech is offline anatech  Canada
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Destroyer OS,
Not AC ground! They mean the RCA jack shields. Your signal common needs to go to the common (ground) of the control, then off to the circuits.

-Chris
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Old 16th January 2006, 11:09 PM   #10
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I have seen this film before...
A friend of mine internally bypassed the preamp seccion on a Nad amp, he wired the pot directly to the power amp.
Instead of leaving the ground alone, he cut the ground tracks near the pot and wired it to the power amp too.
The result?
A nice hummmm...
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