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A DIY series stepped attenuator (1)

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Stepped attenuators are ready available and come in two different kinds:

Series stepped attenuator.
Here are the resistors mounted in series. In using a switch a postition between these resistors is chosen which determines the total attenuation. Disadvantage is that all resistors used are "in signal" (to ground).

Ladder stepped attenuator.
This one owes his name to the schematic as drawn: looks like a ladder... Here for each step of attenuation a voltage divider is chosen consisting of 2 resistors, so only 2 resistors in "signal". Disadvantage of the "ladder" is it's size: 4 decks, each 24 steps and thus requiring twice the amount of resistors.

I've built both of them and my conclusion is that sonical differences between them are minimal. The BIG improvement is upgrading from a "normal pot" to a stepped attenuator, no matter if the pot is Noble or Alps aso.. Is only the best good enough, and space is no problem, then I recommend building a ladder right from the start. This to spare you the materials end efforts if you are not sure which one to choose. There is one thing a ladder and series have in common: they're expensive!! I hope to spare you some money in showing how one is easily made yourself!

I picked the series because of the lack of space since it is to be mounted in my nearly finished headphone amplifier. The switches being used are bought at a ham-radio flea-market. They are second-hand, but are made out of good materials and if cleaned up, can be as good or maybe better than Elna's. This because of the higher pressure being made by the switch selector. I you cannot find such switches, Elna may be the way to go...

Click here to see the schematic and resistor values. By the way, this is the same schematic as in "Tips and Tricks".

The switches. The one on the left is already cleaned up. It will ease up mounting the resistors as the eye-lets are clean and open. Remove all old solder and clean up the residuals from soldering (black spots).
Two decks. Dirty? Probably... some switches have special grease on them, which is not to be removed (like Daven). If you are not sure: Clean it up! I use aceton, ethanol will also do fine.
The switch selector has to be cleaned up also. As you can see, not the whole construction is the conductor, only the little contact in the foreground... Don't forget to use a spray like Contact to grease and protect your clean contacts!
This picture clearly shows the type of switch to be used: the upcoming contact should be made before the previous is broken. IMPORTANT!
The actual mechanism. By stretching the spring the switch will rotate much easier thus preventing any audible clicks on the chassis and, worse, clicks audible in the line stage (microphonics).

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