Stepped attenuators

Hello all,

I currently use a Blue Alps pot' with a shunt mod. I have been looking at the Stepped attenuator article in HFW but this unit is just too big for my pre. Having a quick look on ebay brought this up:

http://cgi.ebay.co.uk/Blue-Valvet-re...QQcmdZViewItem

Its from the same seller as the Vishay Dale stepped attenuator.

It looks like a Blue Alps pot but what has he done to it and how does it work?? I hope someone will have an idea!

[KTea88]

Stu, what is the shunt mod on a alps pot?

[Richard]

I think he's just showing it with the back off, 2 corner screws and similar case to the Blue pot. I notice the shaft is splined too which suggests it is a stepped switch.

Classic Sounds in Leics were advertising a Leak pre which they'd converted to passive and described as using an Alps Blue stepped attenuator. I looked at it and thought it looked like a Blue pot but possibly Alps really do this as a stepped attenuator. A new line?

Rich

[Richard]

OK, here we go, I've not read to the end,

http://www6.head-fi.org/forums/showt...threadid=11704

Rich

Originally Posted by KTea88

Stu, what is the shunt mod on a alps pot?

The shunt mod is probably the simplest, cheapest and best tweak you can make to a standard pot like the alps. Rather than going into details I'll find the thread on the WAD forum and post it on here.

Richard, I was wondering if it was a standard blue Alps with the cover off but I couldnt work out what he's done. Now that you've mentioned the stepped switch it maked sense that its a stepped switch from Alps. Im attracted by the compactness of it all. For the cash I may just order one.

Here is one of the original threads on the subject:

http://www.worldaudiodesign.com/foru...ad.php?t=18784

Richard, thats quite an interesting discussion you found there, it reads like he didnt even realise he was buying a stepped attenuator!

Think I'll order one.

[Richard]

Here's another thread that had many of us trying different circuits,

http://www.worldaudiodesign.com/foru...ad.php?t=18861

My own is wired "D", note the pot is inverted with signal in going to the end that would normally have been earth connection. There was a difference in sound and I've one or two ideas why but would be interested to hear others opinions.

Mine is wired D too.

Ive just ordered one of those attenuators, I'll add it to the already large collection of odds 'n' sods if its no better!

[Richard]

Be interesting to hear what you make of it; whether it looks like a real Alps and if it sounds any good.

Rich

[Greg.]

Looking at the photo, if it's a stereo pot, it may only have about 6 positions. Depending on design, I doubt it would have more than 12. Most quality steppers are 23 position or more. It is worth thinking hard on this one. I have a shunt attenuator I built with Elma switch and Welwyn RC55Y resistors. I also have a ladder style fitted with Dale resistors. Both 23 position and sound equally good, but neither of them shine over my Alps blue Pseudo shunt in 'D' wiring using a pair of Rikens in the signal path. My view is that if you already have a reasonable quality pot, use the pseudo shunt method. If you're seriously into tweaked volume controls, explore the muti-tap Tx options.

Best wishes,

Greg