stepped attenuator pop - Page 2

Nuuk · 18th July 2008, 08:57 AM

Ted, your 10K attenuator will have 24 voltage dividers that consist of two resistors, one in series, and one to ground that divide the signal and shunt the unwanted part to ground.

The total value of the resistors in each pair will add up to the value of the attenuator - 10K (10,000 ohms) in your case.

If one of the resistor values is 100K as Peter points out from the picture of your attenuator, then the attenuator cannot be 10K.

Ted205 · 18th July 2008, 09:39 AM

sorry i should have said, the picture is just a representation not the actual pot.

I have put a 1vp-p signal at 1kHz though the amp with the attenuator. The 'middle' steps really do almost nothing

Ted205 · 18th July 2008, 10:24 AM

Putting the scope across the stepper just by itself is not much better either.

It must be a duff attenuator ?

artquake · 18th July 2008, 10:48 AM

just take some rest ... then ... seat down ... then ... measure each restistance for each step ... then enter the values into excel and compare both channels with the resulting graph ... this all takes about 10 minutes to get an oversight about what you are holding in your hands ... and it let's you avoid troubles before you solder a part into a circuit

Ted205 · 18th July 2008, 11:39 AM

here is a graph of the output resistance. As you can see steps 16-24 are wasted.

The sound is an improvement over a 'normal' pot so I will have to look out for another stepper

AndrewT · 19th July 2008, 11:44 AM

Hi,
you have the attenuator wired up wrong.

The return side should be common to both the input and output.
I think you have wired it up as a variable resistor instead of an attenuator.

Peter Daniel · 19th July 2008, 01:21 PM

Quote:

Originally posted by Ted205
here is a graph of the output resistance. As you can see steps 16-24 are wasted.

Quote:

Originally posted by AndrewT
Hi,
you have the attenuator wired up wrong.

The return side should be common to both the input and output.
I think you have wired it up as a variable resistor instead of an attenuator.

It looks like input and output connections from attenuator are mixed up.

Attached is a graph showing proper way to a wire a pot. You can see that at lowest setting, the output resistance is zero and then goes up and the input resistance is fixed, equal to pot value.

If you wire your attenuator this way, it should work fine.

Ted205 · 21st July 2008, 02:10 PM

i'm not sure its the wiring.

Steps 16->23 can be either 0ohms or 10ohms depending which way i put the input/GND as the only measurable varying resistance is the wiper (output)

18th July 2008, 08:57 AM	#11
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Ted, your 10K attenuator will have 24 voltage dividers that consist of two resistors, one in series, and one to ground that divide the signal and shunt the unwanted part to ground. The total value of the resistors in each pair will add up to the value of the attenuator - 10K (10,000 ohms) in your case. If one of the resistor values is 100K as Peter points out from the picture of your attenuator, then the attenuator cannot be 10K. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

18th July 2008, 10:48 AM	#14
artquake diyAudio Member Join Date: Mar 2005	just take some rest ... then ... seat down ... then ... measure each restistance for each step ... then enter the values into excel and compare both channels with the resulting graph ... this all takes about 10 minutes to get an oversight about what you are holding in your hands ... and it let's you avoid troubles before you solder a part into a circuit __________________ the truth is somewere

19th July 2008, 11:44 AM	#16
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, you have the attenuator wired up wrong. The return side should be common to both the input and output. I think you have wired it up as a variable resistor instead of an attenuator. __________________ regards Andrew T.

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18th July 2008, 09:39 AM	#12
Ted205 diyAudio Member Join Date: Jun 2008	sorry i should have said, the picture is just a representation not the actual pot. I have put a 1vp-p signal at 1kHz though the amp with the attenuator. The 'middle' steps really do almost nothing

18th July 2008, 10:24 AM	#13
Ted205 diyAudio Member Join Date: Jun 2008	Putting the scope across the stepper just by itself is not much better either. It must be a duff attenuator ?

21st July 2008, 02:10 PM	#18
Ted205 diyAudio Member Join Date: Jun 2008	i'm not sure its the wiring. Steps 16->23 can be either 0ohms or 10ohms depending which way i put the input/GND as the only measurable varying resistance is the wiper (output)

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