Volume Pot vs Stepped Attenuater

I'm curious to get some opinions on choosing a volume pot or stepped attenuator. I'm looking at an Alps 100k "Blue Velvet" for about $20. I imagine that a stepped attenuator, even if cheap would probably exceed the sound quality of any standard pot. Any thoughts?

If so, where are some good sources for affordable stepped attenuators?

Thanks!
 

kvk

Member
2008-01-25 4:37 pm
You can get one on Ebay from Hong Kong for $9 plus $5 shipping and you'll have it in a couple weeks. But, you have to put it together which means solder in 48 little resisters. I bought one but haven't put it together yet. When I get a change I will. It's a test. If I'm not sink over soldering after that, then I'll buy the stuff to build and amp.
 

aerius

Member
2006-09-10 4:53 pm
I need adjustments in really fine increments so a stepped attenuator would likely need somewhere around 100 steps so that I can always get the perfect volume. Unfortunately, that's going to be pretty darn big and expensive so I go with a standard pot and take a possible hit in sound quality. A drop in sound quality bugs me a heck of a lot less than never being able to get the volume right.
 
I have myself gone to the DACT stepped attenuator, having tried Alps Blue and Black, and TKD pots. This is for two reasons:

They are slightly more transparent.

They have far better channel-to-channel balance at low volume settings than any pot.  Part of the finishing up of any client piece is testing for gain, hum+noise, bandwidth of the circuit, and part of this is generally done at fairly low signal levels, to avoid nonlinearity.  It's more practical to do the level adjustment with the volume control in the gear than the dollar pot in the generator.  I was shocked (shocked!) at the channel-to-channel imbalance in even the best pots at low volume settings; typically around 20%!  The DACT (and Goldpoint) are specced at less than 1%.

I have had myself no problem with the step spacing of the DACT at any volume level, but that's each geek's choice.

Aloha,

Poinz
 
aerius said:
I need adjustments in really fine increments so a stepped attenuator would likely need somewhere around 100 steps so that I can always get the perfect volume. Unfortunately, that's going to be pretty darn big and expensive ...

Not necessarily true. Check out the units offered by John Broskie of Tubecad Journal fame:

http://www.tubecad.com/2007/04/blog0102.htm

Enjoy,

-- josé k.
 

sharpi31

Member
2005-10-20 12:57 pm
I have used a few different stepped attenuators from Ebay including:

SMD type

and also the vishay/dale ladder type:

vishay dale ladder type

The SMD one is a series attenuator; the vishay dale is ladder type. In all honesty I think I prefer the SMD although both are excellent and I'm not confident I could tell the difference in a blind test.

I don't see why anyone would buy a potentiometer when stepped attenuators can be had for so little money. I absolutely agree that the balance at low volume levels is a serious advantage, aside from the increased transparency.
 
Call me a "party pooper". My preference is the use of individual PEC hot molded Carbon controls in each channel, instead of ganged, stereo, volume and balance units. The PEC Carbon parts sound better than metal film resistors plus switches and they cost less. :D

The PEC controls are milspec and built better than the proverbial brick outhouse. DigiKey carries PEC and the catalog page is here. A PEC data sheet is here.
 
These PEC controls look like copies of the Allen Bradley and Clarastat 2 watt controls that I've been using for years. But some time ago I bought this Vishay stepped attenuator from a fee-bay seller in Hong Kong. I just haven't had the ambition to try it in something yet.

Victor
 

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sharpi31

Member
2005-10-20 12:57 pm
I've used the PEC pots but only a 1Meg linear in fake law configuration (with a 39Kohm kiwame resistor).

The tracking balance at low volumes was the worst I've ever encountered - one channel kicked in about 10degrees before the other. Ok, maybe my pot was a poor example - I'm sure others could be fine.

Aside from this I found the pot really good but definitely warm at the expense of fine detail. This could be great in a cold sounding system...

Horses for courses :)
 
These PEC controls look like copies of the Allen Bradley and Clarastat 2 watt controls that I've been using for years.

I don't know what the vintage controls look like, inside. PEC uses a block of Carbon stuff as the wiper contact. The worn tracks people describe in vintage amps, such as Fisher, will not happen. :)

Horses for courses :)

AGREED! Pick your spots, carefully.

The tracking balance at low volumes was the worst I've ever encountered - one channel kicked in about 10degrees before the other.

I can see that sort of problem with molded composition construction. That is the primary reason why I suggest individual, rather than ganged, controls. Channel tracking is more or less consistently tricky.
 
Eli Duttman said:


I don't know what the vintage controls look like, inside. PEC uses a block of Carbon stuff as the wiper contact. The worn tracks people describe in vintage amps, such as Fisher, will not happen. :)




That's what AB and Clarastat did. Carbon against carbon. Nothing new. Many vintage amps did use the cheaper pots with a springy metal wiper against the carbon track.
 
Psychobiker said:
Would it not hypothetically be better to separate the channels and have two individual stepped attenuators...

Yes, many people feel this way. Especially if you're using continuously variably controls that may not be closely matched. However with stepped controls, it's the value of the individual resistors that provide the tracking accuracy. Assuming they are correct, having them on a common shaft gives you the convenience of having only one knob to turn.

This assumes that both channels otherwise have equal gain. If there is something else that is upsetting the gain balance, then fixing that, or using seperate controls is necessary.