Shallco t-pad schematic?

I admit I don't understand what's going on here, but I took apart a shallco 21 step attentuator and drawed a drawing. The Com to Out terminals read almost constant 600 ohms DC throughout the attentuator range , but the IN to Com starts at 600 dcr then drops to 400 for two steps then sticks around 600 for most of the steps, then rises to 900 dcr by the last step. So I think I have a 600ohm t-pad on my hands but I wondering if anything weird about this guy or if adjustments need to be made. The resistors don't look like they have been altered. The bottom and top ranges of this attenuator will probably never be used but still. I would like to understand how to replicate scheme for other load values. Does the scheme look right?

The scheme looks right. I don't know why we would question Shalco's design. A single-gang attenuator can NOT be "matched" at all settings (that's why ladders and bridge-Tees exist; and cost more). 400-900 Ohms sounds pretty good. This will not bother most "600" audio interfaces. For other nominal impedances, just multiply.

burdoto said:

I think I have a 600ohm t-pad on my hands   

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you have a ladder.

burdoto said:

Does the scheme look right? 

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yes.

Yeah, ladder.  Find some old texts, tons of old electronics magazine downloads out there that give formula and sometimes recipe charts.  Audio Cyclopedia, RDH4, etc.  Much easier than taking these things apart!