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Old 14th February 2006, 07:45 AM   #1
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Default Amp Sensitivity, cap or resistor? Can I do this?

Below is the picture of the side of my amp. What I am wondering is, is the sensitivity controller a varaible capacitor? I tried measuring it for resistance but it came up with 0.00 as the reading(turned it to both extreme ends to test).

To make a long story short, im sodlering all the wires to the bottom of the amp directly to the circuitboard(except the power and ground wires) and the way my amp will be sitting, i wanted to see if i could buy the same value(as in ohms, or farads) device as is on the board now so i can make an external controller for that so i can mount it by the side of the amp(the way i will have it, it will be a BIG pain if i wanted to change those settings.

Click the image to open in full size.

Also, can anyone explain to me whats the difference of the sensitivity controller compared to a 'gain' controller.
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Old 14th February 2006, 08:18 AM   #2
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The sensitivity controller is simply a potentiometer (resistor with moveable wiper/tap), which controls how much the input signal is attenuated and passed to the amp itself. The reason you can't measure DC input resistance is because there is a DC blocking capacitor on the input of the pot, which is perfectly normal and good design.
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Old 14th February 2006, 09:55 AM   #3
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Default Re: Amp Sensitivity, cap or resistor? Can I do this?

Quote:
Originally posted by silentblackhat
Below is the picture of the side of my amp. What I am wondering is, is the sensitivity controller a varaible capacitor? I tried measuring it for resistance but it came up with 0.00 as the reading(turned it to both extreme ends to test).
[...]
Also, can anyone explain to me whats the difference of the sensitivity controller compared to a 'gain' controller.
Let me try some definitions:

Sensitivity: defined by the input signal voltage level that produces the maximum signal level at the output.

Gain: as it says, defines the gain for an amp to have a particular sensitivity. As far as I know, it is a fixed parameter for most amps (but not for yours !). For example, for an amp with feedback, it is generally related to the feedback factor.

VOlume Control: generally a resistive network (may be a potentiometer, a stepped attenuator) or a dedicated IC to attenuate de input signal, feeding the amp with a portion of your original input signal. No change in amp gain/sensitivity.

I don't know how gain is defined in your amp (wihthout schematics I can't try to say) but this "Sensitivity Setting" changes the gain of your amp, somehow. If this amp has global negative feedback, I would say this control changes feedback factor.

More experienced posters can correct me if I am wrong.

Best regards,

Joćo Pedro
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Old 14th February 2006, 10:38 AM   #4
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You are right with your definitions there, but no amp has variable gain because of stability reasons. Despite whether it's labelled volume or gain or sensitivity, it's exactly the same thing in this particular case, just the manufacturer being poor with their terminology.
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Old 14th February 2006, 11:09 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi Richie,
there are some exceptions.
Cambridge?
They use a linear pot in the input/feedback loop of an inverting amp.
The linear mimics a log type attenuator for the volume control.
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Old 14th February 2006, 11:38 AM   #6
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Quote:
Originally posted by AndrewT
Hi Richie,
there are some exceptions.
Cambridge?
They use a linear pot in the input/feedback loop of an inverting amp.
The linear mimics a log type attenuator for the volume control.
A potentiometer in power amp circuit is very unusal.

Even if this is not so common,
a potentiometer may be a part of OP-amp feedback
if there is such a preamp in an interegrated amp.
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Old 14th February 2006, 05:46 PM   #7
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Alright. I knew it was a pot(but thansk for maknig sure). im guessing how its wired up, i cant byass that one and make an external one?
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Old 14th February 2006, 07:02 PM   #8
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No, the possible noise and instability introduced by extending the pot a long way outside of the amp enclosure into a harsh environment, would not be worth it IMO. That's what head unit faders are for.
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Old 15th February 2006, 05:47 AM   #9
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alright just making sure. it wouldnt be a long ways away, it would just be about 1ft wire but, its probably(obviously) not to mess with it. i guess its not like i will want to chance the sensitivity every time i turn on my system. thanks fo the replies tho
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