Understanding stepped attenuator choices

[dobbykins]

I've been hoping to upgrade the stock pot in my SEX to a stepped attenuator, and have been struggling to understand the different types of attenuators, as well as decide which is appropriate for my purposes.  To illustrate, I've found several dale-stuffed ebay attenuators, seemingly based on similar switches.

First, I believe this is a series type:  http://www.ebay.com/itm/2P-23-Step-DALE-Attenuator-Volume-Pot-Stereo-100K-Y-/260857417997?pt=LH_DefaultDomain_0&hash=item3cbc50510d#ht_1481wt_905

This one has about the same number of resistors, but notes it is a shunt type:  http://www.ebay.com/itm/4P-24-Step-DALE-Attenuator-Volume-Pot-Stereo-100K-Y-/250896216491?pt=LH_DefaultDomain_0&hash=item3a6a9471ab#ht_1443wt_1163

And this one is a ladder type, with twice as many resistors (though from a different seller): http://www.ebay.com/itm/Assembled-Dale-23-Step-Attenuator-Volume-Control-100k-/270311271326?pt=LH_DefaultDomain_0&hash=item3eefceab9e#ht_707wt_1163

Part of my confusion lies in the number of poles listed for the first two.  Why does a series say two pole, while a shunt type is four pole?  Perhaps I'm misunderstanding what a pole actually is, but from my research, each of these types only needs to have one switch for each channel, correct?

Secondly, it seems a given that the shunt and ladder types will offer higher sound quality than the series type.  The shunt will have two resistors and one switch in the signal path, while the ladder will have two resistors and two switches.  The downside to the shunt type is that it presents a varying input resistance to the source driving the amp.  For a 100k attenuator, when would this be an issue?  I run a Seduction into my SEX, and it seems that the input resistance will always be "ok", but is it likely to be enough of a concern to go with the ladder type, despite it adding an extra switch in the path and costing more due to the doubled resistors?

I'd really appreciate anyone confirming my theories here, and feel free to point and laugh, if it's appropriate.    Thanks very much in advance for helping me get my thoughts straight!

- Guy

 

[Paul Birkeland]

I don't understand the 4 pole designation on the shunt control, the picture may not be accurate?  But this is maybe not the best option for you.

The ladder is the nicest option for you IMO, it provides a constant impedance for you and only two resistors in the signal path, but ladders are somewhat pricey.

The series type is conceptually the closest to the original controls, a string of resistors instead of a carbon trace, with contacts at each junction for your steps.  This control will also present a constant input impedance, but there are more parts in the signal path.  This is not really the doomsday scenario that many make it out to be, these are still great controls.

The shunt control you linked to is a little mysterious.  Generally, you will have a fixed resistor from the input jacks to the input of the switch, then the switch will select different resistors to place between your fixed resistor and ground.  This is an outstanding option for a sensitive circuit or a piece of equipment with lots of gain, but I'm not sure it's the best idea for a SEX amp. 

I hope this helps!

-PB

 

[Grainger49]

Look on VoltSecond's site:

http://www.siteswithstyle.com/VoltSecond/12_posistion_shunt/12_Position_Pure_Shunt.html

There are all kinds of ways to control volume and most of them are discussed on the page above.

If I have it right, the series puts all the resistors in the signal path till you cut them out, increasing the volume.  The shunt can put just two resistors in the signal path but has a varying impedance.  The dual series, double the number of resistors, keeps the same impedance and only puts two resistors in the signal path at a time.

But a good read or two of VoltSecond's page will give you a better understanding.

 

[4krow]

Wow, thanks you guys for the 'lesson'. Man, sometimes even changing a light bulb ends up with an opened can of worms-"so what kelvin temperature do you need?' "how many lumens?' "will that be incandescent or led or florescent?' "is that Mogul base or minature?' Seems like every time I ass-u-me something....

 

[dobbykins]

Thanks very much for the information, guys.  VoltSecond's site is certainly a great resource. 

In the end, I decided that due to the prices involved, I might as well spend the extra $20 (up to a whopping $50) and get a ladder attenuator with Dale resistors.  I will definitely post back with my impressions once it arrives.

 

[VoltSecond]

Vishay Dale makes all kinds of resistors from "Cheap" to "Inexpensive" to "Oh My."  Find out what series "DALE" resistors are used in your attenuator and look up their performance.

I put the 25 ppm/C and 50ppm/C Vishay/Dale CMF resistors in the "Inexpensive" and "Good Value" group. The CMF line specifies a low voltage coefficient and they specify a low voltage noise coefficient. I.E. they are quiet and they are linear.  More importantly, Vishay Dale actually specifies these parameters instead of just saying they have good performance.

http://www.vishay.com/docs/31018/cmfind.pdf

 

[4krow]

'Will that be modern, or Edison style sir?'

 

[mcandmar]

Just to confirm this, with the ladder type attenuator (3rd link in original post) with the switch between positions do you get full attenuation of 100k, or only the value of the first pair of resistors?    Basically i am trying to understand what happens to the volume level if you slowly move from position to position.

If you are still around dobbykins can you share your experience with that ladder attenuator?

Thanks,

Mark

 

[Paul Birkeland]

Basically i am trying to understand what happens to the volume level if you slowly move from position to position.

For each position, there is a resistor from signal in to signal out, and a resistor from signal out to ground.  When the level is all the way down, the resistor from signal out to ground will be a piece of wire.  When the level is all the way up, the resistor from signal in to signal out will be a piece of wire. 

This type of attenuator most mimics the performance of a potentiometer.

 

[mcandmar]

Thanks Paul, i understood that part, my query is in relation to the gaps in between positions. I'm assuming it cant instantaneously switch from one pair of resistors to then next, surly there is a dead spot in the middle of each position.  So my question is what happens there, does it go open circuit or short the signal to ground?  I guess my real question is do you hear anything while switching, and is it healthy for the amp/headphones.

 

[Paul Birkeland]

Ah, now you're onto something.  When you go switch shopping, you'll see a given switch labelled as shorting or non-shorting.  A shorting switch will not let go of the previous contact before it has engaged the next contact, so there is no gap in the switching.

A non-shoring switch will have a "gap" so to speak. 

There is an incredible variety of quality levels in shorting switches.

 

[mcandmar]

Gotcha.  That $50 one is a "smooth transition design" apparently whatever that means. I can only assume they mean shorting.

Its seems too cheap to be true, especially vs the Goldpoint and Elna versions that are almost four times the price for a blank without resistors.

Decisions, decisions. I should have just ordered an alps pot and quit while i was ahead.

 

[Paul Birkeland]

I do have a couple of those cheapie blue Chinese stepped attenuators floating around.  While all the shiny metal on them is super rusty, they do still seem to work properly, though they are nowhere near as nice as Goldpoints or the Switches we use in the Submissive.

 

[4krow]

As I recall from many years ago, the shorting switches were called 'make before break' switches. At least that was the term used by Bell System.

 

[Grainger49]

Greg,

That would have been my response.  It used to be the phrase, shorting and non-shorting is used today.

 

[mcandmar]

Make-before-break is a term i have seen looking at various options.

I am leaning towards the Goldpoint from a quality/tactility point of view even though they no longer offer a ladder style, series only.

I priced up dale resistors from Mouser to populate a Goldpoint and they are ~

 

[Paul Birkeland]

1/4W resistors are totally overkill.  1/100W resistors would be more than sufficient, and they are much easier to install on the switches.

 

[4krow]

I have used Goldpoint and just have nothing but good to say about them. I do believe that there a few others out the that are quite good. Wish I could think of the brand that I saw a while back. It just blew me away. It was up there with GP.

 

[mcandmar]

After reading good reviews on various sites i cheeped out and went for the $42 ebay kit.  I also opted for the DIY version as i'm a sucker for punishment  :  I'm more curious to hand measure/match the resistors more than anything.

I have yet to assemble and fully test it but the quality seems alright, doesnt feel that flimsy and all the resistors look like the real deal vs the stock of Dales i have on hand.  Amazing really as i couldn't have bought the resistors alone for $42 shipped. Its also much smaller than i was expecting, it looks coke can size in the photos, but in reality if more like those little cans you find in mini-bars. We will see how positive i am after i've soldered 90 odd resistors to it...

http://www.ebay.com/itm/DIY-kit-Dale-23-Step-Attenuator-for-Volume-Control-100k-/280321499342?pt=US_Amplifier_Parts_Components&hash=item414476a0ce

 

[mcandmar]

If anybody is interested i have attached a list of the supplied resistors plotting the input impedance and resistance curves. It aint the best but i'm working on smoothing things out by swapping out a few resistors.

I also pulled it apart to look at the mechanism and its just regular plated steel contacts, time will tell how well it lasts.  I also advise you buy the ready assembled version as it took forever to build and can be rather tedious. The instructions (which are a bit vague) can be found here http://kikitronic.blogspot.ie/search/label/Attenuator%20for%20volume%20control

/edit: Added in the resistor values / charts as used in the Goldpoint ladder attenuator kits.