I have a stepped volume control in a tube pre-amp that recently started to popped loudly, the popping is intermittent, There is a faint tick every time I change volume. The pre-amp KIT worked flawlessly for a year before the problem started. I read on this forum that there could be DC leaking into the pot. How do I checked for this? If there is DC, what could have caused this and how do I solve this?
Just test the input tag on the volume control with a multimeter set at DC low voltage or if auto ranging just DC one leg to earth.
Your stepped volume control could have bad contacts .
If not one of the above you could have a touch of instability.
Your stepped volume control could have bad contacts .
If not one of the above you could have a touch of instability.
A multimeter measuring Dc millivolts from the input of the volume control to ground. If there is more than a few millivolts across the attenuator you have a problem with a leaking coupling capacitor (if used) or a problem with DC offset in the volume control driving stage.
Just disconnect the (leaking?) source and try again, ideally with a shorting plug in the input socket.
No DC, replaced with an ALPS blue pot and sound deteriorated, but popping is gone. Stepped attenuator goes back in, reflowed suspected solder points. No more popping sound when changing volumes EXCEPT for the first click. I think it is the pot that has a problem, I will just stay away from zero volume and leave at 1 click 🙂
"Replaced with an ALPS blue pot and sound deteriorated" .
Good as they are even ALPS admit they are -quote - "liable to potentiometer sliding noise expressed as a voltage/ resistance " .
Just shows you stepped volume controls ( quality ones ) although more costly present a superior fidelity of sound reproduction.
Good as they are even ALPS admit they are -quote - "liable to potentiometer sliding noise expressed as a voltage/ resistance " .
Just shows you stepped volume controls ( quality ones ) although more costly present a superior fidelity of sound reproduction.
How so? Stepped volume controls guarantee there will be transients generated when the control is stepped with signal going through.
The transient causes an often audible click even if the signal going through the stepped attenuator is not audible, say 40kHz or 1Hz.
This is because a step level change in any signal causes a transient pulse which has an energy spectra from DC to blue light.
A potentiometer in reality has dozens (hundreds?) of tiny steps when the control is moved a few dB, but the steps are are tiny so the energy in the transients is corresponding small and normally below audibility, unless there is enough DC or RF across the potentiometer.
Qguy the biggest dB step level transition is the first step from zero, so the click will be most audible on that first step. If you hear a click with no signal (no music playing) there must be some out of band signal going through the attenuator, maybe something is unstable in the amplifier.
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Of course there will be minute transients but once the level is set a high quality stepped potentiometer will be superior in sound quality even ALPS admit to noise on their blue potentiometers as I posted above .
OTOH which potentiometer with a slider can compete with these -
http://www.vishaypg.com/docs/63140/var.pdf
current noise =0.010 uV/TCR +/- 0.05 ppm/C
OTOH which potentiometer with a slider can compete with these -
http://www.vishaypg.com/docs/63140/var.pdf
current noise =0.010 uV/TCR +/- 0.05 ppm/C
The thread is about popping aka clicks and scratchiness when the control is moving, and my answer is about the same.
If you can't hear the transients when you move a stepped attenuator you are not listening. If you need to learn what it sounds like, put a low frequency sine-wave test tone through the preamp and step the attenuator while listening to the tone.
In any case when listening to music one can keep one's hands off the volume knob; problem solved.
As far as the need for such precision in level control, I suspect the blood pulsing in the neck arteries near the ears will introduce significantly more timing and level errors at the eardrums than any potentiometer, stepped or otherwise, though I'm happy to be disproven on that.
If you can't hear the transients when you move a stepped attenuator you are not listening. If you need to learn what it sounds like, put a low frequency sine-wave test tone through the preamp and step the attenuator while listening to the tone.
In any case when listening to music one can keep one's hands off the volume knob; problem solved.
As far as the need for such precision in level control, I suspect the blood pulsing in the neck arteries near the ears will introduce significantly more timing and level errors at the eardrums than any potentiometer, stepped or otherwise, though I'm happy to be disproven on that.
My google must be broken, I don't get any hits on that quote. I suspect Alps mean "in the presence of DC or out of band noise on the pot". Of course this phenomena affects stepped attenuators as well in a stepped way, rather than in a sliding way. They are both resistive ladders after all!
"Quote-You don't get any hits" that's because you use Google I have zero Google on my Linux PC,s and that includes all the apps including Wine , I have blocked Google network ports , yes I lose some "entertainment etc " but my small open source search engines reach places that Google doesn't earn money from.
Big issue in the UK at this very moment due to Google prominently putting scammer websites like --"we do your UK driving license or road tax " --sure they do while skimming £79 out of your bank account for the "privilege " --1000,s of very angry UK citizens because Google gets a cut --and yes I get daily emails from my old website with citizens cursing it upside down.
You can "suspect " as much as you want but what I said in post #6 does not include DC , they are admitting the Truth which to me is refreshing and doesn't put me off ALPS as they are quoting an engineering fact unlike some others who leave out such things in their abbreviated specifications .
Big issue in the UK at this very moment due to Google prominently putting scammer websites like --"we do your UK driving license or road tax " --sure they do while skimming £79 out of your bank account for the "privilege " --1000,s of very angry UK citizens because Google gets a cut --and yes I get daily emails from my old website with citizens cursing it upside down.
You can "suspect " as much as you want but what I said in post #6 does not include DC , they are admitting the Truth which to me is refreshing and doesn't put me off ALPS as they are quoting an engineering fact unlike some others who leave out such things in their abbreviated specifications .
A stepped attenuator constructed with MBB switch contacts will never pop unless there is DC between the input and output, or a set of dirty contacts.
It is not usual for a stepped attenuator to have contact failure early in life, last significantly longer than rotary plastic or carbon pots. However the switch does need maintenance, and often 'favorite' listening spots will allow dust build-up that can cause (very minor) transients.
A small amount of isopropyl on the contact surfaces will usually clean it right up, and if you don't have any on hand, briskly moving the control between both its end stops a few times will reduce the issue somewhat, maybe even eliminate it.
When built with a BBM switch, it will always have transients.
It is not usual for a stepped attenuator to have contact failure early in life, last significantly longer than rotary plastic or carbon pots. However the switch does need maintenance, and often 'favorite' listening spots will allow dust build-up that can cause (very minor) transients.
A small amount of isopropyl on the contact surfaces will usually clean it right up, and if you don't have any on hand, briskly moving the control between both its end stops a few times will reduce the issue somewhat, maybe even eliminate it.
When built with a BBM switch, it will always have transients.
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Why so sensitive? I did not say Alps was wrong, they are not. I said I couldn't find the Alps statement, which I tried to find to understand the context the statement was made in. Perhaps you could provide a link...
I said stepped attenuators cause non-musical noises on changing taps. They do. Play a low frequency tone through a stepped attenuator and listen to the clicks when you change the taps. It's a consequence of physics, not quality of the components used to make the attenuator.
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"stepped attenuators cause non-musical noises on changing taps"
This is just not true if you get REAL ones:
The Daven Company Balanced, T and H audio attenuators for preamps and line level HiFi Audio vintage 1950s
This is just not true if you get REAL ones:
The Daven Company Balanced, T and H audio attenuators for preamps and line level HiFi Audio vintage 1950s
Please explain the 'physics' behind this 'phenomenon'.
MBB attenuators do have two ladders in parallel between clicks. Proper system design eliminates this issue completely.
If you have questionable system design, you can create all sorts of issues that do not actually exist.
The name says it all : STEPPED attenuator !!!!
Then again it can be more smooth if you use "make BEFORE break" ones.
Then again it can be more smooth if you use "make BEFORE break" ones.
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When the contact in a stepped attenuator moves from one level to the next, the signal also steps up or down in level. Imagine a graph of sine-wave at a constant level. Then switch up a 2dB step at the attenuator. The sine-wave is now bigger.
The transition could happen at any point in the sine-wave curve. How can the new sine-wave join to the original sine-wave? There needs to be a straight vertical jump in the signal (AKA transient) to join the before and after wave magnitudes. This is the tick or click that can be heard because it has nothing to do with the musical content of the signal going through.
Although it may be counter intuitive, even if the step transition occurred at zero volts as the signal passes through 0, there will stell be a transient generated. A signal cannot start, stop, or change in level suddenly without the generation of a transient. This is pure physics.
This transient by definition contains energy from DC to blue light. This energy is not related harmonically to the signal going through the attenuator, and if not masked by the audio signal it will be heard for what it is, a characteristic transient tick or a click.
If the steps are very small, say ½dB, the transisents will be nearly inaudible. If the steps occur during during a constant low frequency tone, there is very little masking the the clicks will stand out like proverbial dogs b...
The only way to prevent the clicks is to ramp the voltage transition between steps. This can and is done in active attenuator circuits, but there is not means to effect a ramp up or down between steps in a mechanical switch, irrespective of MBB or BBM. Obviously a BBM switch introduces two transients for each step - the 'off' and then the 'on', both of them much bigger than a the transients generated by a MBB switch.
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Alps measure sliding noise noise with 20 volts DC across the potentiometer as detailed in their Test and Measurement documentation.
〔Sliding Noise〕
Measured by connecting the resistor to an amplifier having frequency characteristics specified in JIS C 6443, applying DC voltage of 20V between the terminals 1 and 3 (if rated voltage is 20V or less, this voltage shall be applied) and by rotating (moving) the shaft (lever) at a speed of about 30 cycles per minute.
Measured by connecting the resistor to an amplifier having frequency characteristics specified in JIS C 6443, applying DC voltage of 20V between the terminals 1 and 3 (if rated voltage is 20V or less, this voltage shall be applied) and by rotating (moving) the shaft (lever) at a speed of about 30 cycles per minute.
https://tech.alpsalpine.com/prod/e/pdf/potentiometer/measurement.pdf
Sliding noise is the slight electrical noise generated as the wiper moves over the resistive element thats the standard definition if somebody want to use DC as a method of testing it all well and good but its not the original definition of it .
The use of DC is to advertise how low their noise factor is but its not the default for the definition.
See -
Potentiometers – What Are They?
scroll down.
The use of DC is to advertise how low their noise factor is but its not the default for the definition.
See -
Potentiometers – What Are They?
scroll down.