stopping stepped attenuator pop
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JMS

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My fake ALPS stepped attenuator makes the speakers/headphones pop when turning. Sounds like it's a break-before-make type. Can I stop this pop by wiring a resistor (say 500Kohm) in parallel, and would there be any bad side effects from doing this?
 
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zbuddah

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wouldn't a resistor in parrallel affect the overall volume also? like... say that 500k reistor and whatever resistance the pot is set at say 25k so overall volume would be really be at 1/25k + 1/500K = 1/R. R being 23.8k? at 5k on the pot total resistance would be 4.95k with the pot at 50k total resistance would be 45.5k hmmm it might work but you'll get less volume not much though, I think. yeah I think it would work maybe someone else can say so.

I've grounded the pot and made sure i've gotten good solders to the 1/8" jack and rca jacks... and that reduced a whole lot of noise from the hum on the pot if you touched the metal knob to the pops everytime you turn it. Its still there but I barely notice it at all unless i turn real slow and stop half way then one channel will cut out heh.
I used to have the pot ungrounded and the hook up wire tied to the jacks with no solder... the pops could have made you deaf I swear.
 
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aeberbach

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You can't do anything about it. Some attenuators just pop by design and that's all there is to it.

This site has a good description of the various types and why some pop and others don't:

http://www.goldpt.com/compare.html

I bought a DACT (cheaper and made with surface mount resistors) and it pops. You learn to live with it. In fact it's a nice audible notification that you are changing to volume, it can be all too easy to unconsciously creep it up until you are listening way too loud.
 
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Tomo

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Hello,

Bypassing a LINEAR pot with a resistor of "proper" value will give you LOG pot.

Now if you use LOG pot, things are little more interesting. Given some value, it will decay faster. If you use compartively larger value of resistor to bypass, the effect is minimal.

However, I think having a bypassing resistor would change anything at all. "Why bother?" is what I think.

This uses rotary switch so it comes with mechanical issues. So like aeberbach says, you can't do anything. (to change the nature of the component.)

Or you can simply use plastic layer pots. I use them in my little weirdly rigged up passive preamp. Depending on designs, they can be good. (Muhaha! tainting the purist ideals!
)

Tomo
 
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Dev

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Hi, Tomo!

What does it look like? Pot + parallel resistos after him (like pot + R2 in CMoy amp project) of nominal as such as pot nominal (100k for example)?

I'm about log pot made through linear one...
 
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Tomo

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Hello,

It is pretty easy. Imagine a voltage divider with 2 resistors connected in series. Now you replace the bottom one with a pot. However, note that it has attenuation even at max volume so do not use if your setup is poor on voltage swing.

This gives you logarithmic attenuation if you graph it. (YOU MUST GRAPH!)

This curvature is determined by the value of resistors you use for the top resistor. This should be close to the value of the pot at max attenuation, according to my calculation. However, you must grraph yourself for confirmation.

I had 50kohm Nobels, so I used 50kohms. You can pick larger value of the top resistors, but note that frequency response suffers if too large. Keep it at reasonable value.

The quality of the sound is determined by the quality of the top resistors. This resistor can range from wirewound, metal film, metal oxide, tantalum, carbon, to plate resistors. This is because the parasitic characteristics aren't so critical here. You get to fiddle around for your favorites!! Yey! (I picked non-inductive wirewound. That's my fav.)

Note the coolest part of all these. You can tweek the volume control very easily while keeping the many of the good things of stepping attenuator. If you want to swap the resistor, it takes 5 mins. If you want to swap the pot it takes 5 mins. It is very very easy to tweek this volume control.

Imagine doing that with stepping attenuator. Who in the right mind would swap resistors after spending hours soldering 46 resistors? So I usually never end up upgrading my steppers once I build them.

Tomo (the Tainter of the Purist Ideals!!
)

P.S. Note Linear pots should be used for this.
 
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Dev

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Tomo, thanks a lot for your description!

Hmm, volume regulator you described looks like L-type volume attenuator I've construct yesterday
.

Sheme of this:


It uses linear 100k pot and have 200k series resistor because lower vaules is way to much loud sound for me. I think good way of tweak this is change 100k pot to 10k or 50k and reduce 200k resistors value.

And I got one deleterious question. My audio system is cdp -> volume_att -> power_amp (well, I upholding your opinion of shortest signal way is best signal way, e.g. no preamp
). Connections shown as "->" is interconnect cables...
And interesting quest is: how volume att. influencing to volume_att->power_amp cord? Have it "output impedance" type influence?
Well, this question hunts my mind
.
 
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Tomo

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Dev -

I would keep the wire short as possible. Yeah.

And use less total impedance across the volume control. I think your current set up has too high a resistance. You do not want to have high value resistors directly in the path of signal. lower value pot should allow lower value of top resistors.

My cables have reasonably low capacitance and are easy to drive. However, if you are using coax etc which have inherently high capacitance, it is probably bad. In such case, I would implement the volume control in the power amp. This is a better idea.

You can use a cable driver to drive the cable also. I was thinking about it because output impedance varies with volume position. However, neither was necessary for my short interconnects. (The effects were minimal.)

By the way, your design isn't L-Type. It is called Shunt-Type. L-Type is short for Ladder-Type and it isn't Ladder-Type. (At least in my mind.)

As crazy as I am, I would remove input coupling capacitor. Nothing can burn out in the volume control. So I would depend on the power amp to isolate on its own. What is point of having interstage coupling capacitors if you don't need them, right?

Tomo
 
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Dev

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I use microphone cable of twisted pair wires, its about 0.5 metre (after att. I mean). I guess capacitance and inductivity of it low, but I still doubt in influencing of signal...

My choice is dilemma between having cable driver after att. (so, hmm, preamp
) and nothing after attenuator. I knew what making active driver (opamp) is not a problem and I may use my own CMoy amp, but I just don't want a "unnecessary" elements in my audio system...

Ladder-Type seems like my att. but with stepped (discrete) pot instead of solid type pot...

And about cap in my sheme. I post piece of full curcuit, and this 0.47u polypropylene capacitor uses to DC leaving because my cdp is hard tweaked and have DC-output
. Leaving this cap and dropping DC to the att. causes bad symptoms, well...
 
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Tomo

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Hello,

Mine is about 0.5 meters TOTAL. CDP -> Vol -> Amp. 0.25 meters each.

CMOY amp isn't optimum solution. You will have to decrease the gain and if you are going to do that, might as well use BUF04. (BUF634 require feedback, BUF04 has inline feedback. So it is preferable if you are going to use it by itself.) But I have a feeling you don't need to. If you are that concerned might as well implement the volume control inside the amp, problem solved.

I use microphone cable of twisted pair wires, its about 0.5 metre (after att. I mean). I guess capacitance and inductivity of it low, but I still doubt in influencing of signal...

My choice is dilemma between having cable driver after att. (so, hmm, preamp ) and nothing after attenuator. I knew what making active driver (opamp) is not a problem and I may use my own CMoy amp, but I just don't want a "unnecessary" elements in my audio system...

"Ladder-Type seems like my att. but with stepped (discrete) pot instead of solid type pot..."

There is no pot equivalent of Ladder Attenuator. It is only possible option if you are building stepped attenuator. It doesn't matter if your pot is stepped or not. (FAKE ALPS is SERIES-Type stepped attenuator.)

http://www.goldpt.com/compare.html

That's yo reading assignment
Note the difference between THREE different types of stepped attenuator. Notice that TWO out of THREE have pot-equvalents designs.

You have DC from your CDP? You better fix that. What kind of modification did you do? If I were you, I would fix it before I accidentally plug into some powerful poweramp and blow it to the satellite orbits. It is well worth it too. Nothing beats having one less "unnecessary" coupling caps. (Well it is a bit of overstatement, but it is somewhat true.)

Tomo
 
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Dev

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My CDP -> Vol cable is Nordost Black Knight (flatline, very quality cable). And after Vol is DIY cable... I think good idea is to trade places of cables. But Nordost is not shielded cable (as far as I knew and it looks like) and way of 2nd cable is near of loudspeaker cables and AC power cord. Maybe I'll try this change...

Volume control inside amp? Well, it's mightily
. But its need to carve amp chassis... Now my volume in chassis of my CMoy amp.

Yeah, buffer is good. I may to use EL200x buffers also, I think...

Thanks for the link.

You may see scheme of my cdp-vol system: http://dev.azz.ru/pic/dev_sys211.gif
I have Sony cdp-ce335 as cdp and Rotel RB971 as power amp. All Ok of DC
.
 
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Tomo

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Hello,

Shielding on cables doesn't do anything particularly interesting unless you are dealing with minute signals. You should have no problem with your Nordost cables.

The primary noise pick up comes from the connector. So I always pick shielded connectors. Otherwise, I use unshielded cables. I have no pick up problems.

I still think you should go and fix the offset problems. I see no reason why you would want to keep it. And I see far too many reasons why you should fix. ... I dunno.

Tomo
 
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Dev

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Thus, I try cables change. My shielded DIY before Volume and Nordost unshielded after it. I get the "humm"!

Just a reverse of change clear away this effect...

Maybe reason of "humm" is what Nordost is directed cable (one source end grounded and other is in air, I think) and my DIY is just wired by ground terminal... So, I would fix it and test again. But I'm totaly not understand how Volume will work without ground
.

I'm listen music through this "uncorrect" connection - nothing particularly, maybe bit a clear sound.

I could not understand what you meaning when you talking about DC offset and offer to fix it. Look at scheme - DC of DAC decoupling at 0.47uF series cap and in power amp I have 10uF Black Gate (yeah, great!) series cap at it input. I have no DC at Volume regulator...
 
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Tomo

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Hello,

Lookie this, this is closest your passive preamps can get to your power amps!! LOL!




Tomo
 
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Dev

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