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A stupid question involving stepped attenuators

post #1 of 13
12/10/09 at 2:39am
Thread Starter 
If I buy a logarithmic stepped attenuator, than the highest gains per step are at the lower steps (i.e. the steps go something like 36dB, 30dB, 21dB, etc.)(yes, I know that is not logarithmic in nature).

However, I want the lower steps at the bottom. Is there any harm in wiring it backwards, so that the lower steps are first? Aside from having to counterintuitively turn it backwards to change volume, is this a problem?

Thanks,
Nkk
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post #2 of 13
12/10/09 at 4:17am
Good question, I'd first make sure you "can" wire the stepper "backwards" - not possible with a series type, not sure about ladder. Of course you can simply build your own and make the curve you want for yourself.
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post #3 of 13
12/10/09 at 4:26am
Thread Starter 
Which leads to the question of are there any good kits that are not SMD (I am not good enough to build a whole kit of SMD resistors, and this is not the project I want to learn on)?

-Nkk
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post #4 of 13
12/10/09 at 4:40am
Well, if you're planning to build your own curve, you'll have to pick resistors yourself. Grab a 24-step switch, resistors and get building.
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post #5 of 13
12/10/09 at 5:01am
Thread Starter 
Wait...where does one buy just the switch? I looked, but only found full kits.

Thanks,
Nkk
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post #6 of 13
12/10/09 at 5:06am
Quote:
Which leads to the question of are there any good kits that are not SMD (I am not good enough to build a whole kit of SMD resistors, and this is not the project I want to learn on)?
Goldpoint?

http://www.goldpt.com/prices.html

Stepped Attenuator Resistor String Calculator - Neville Roberts
SDS Labs Java Stepped Attenuator Constructor's Page
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post #7 of 13
12/10/09 at 5:47am
VT4C has some cheaper ones.

I can't really vouch for their quality though.
I'm gussing they're "OK", but I'm sure they'll fall short of higher quality (and higher priced) brands.
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post #8 of 13
12/10/09 at 6:36am
I'm not sure either about wiring the series attenuator backwards.

I would highly recommend builidng your own attenuator. Get one of the blue 4-deck 24-step switches from ebay and order your favorite resistors from digikey or mouser. Here is a link to an awesome calculator for a ladder style attenuator. Stepped Attenuator Resistor String Calculator - Neville Roberts

You can choose what you want the total impedance to be (ie. 100k 25k etc...) then you can choose what attenutation you want for EACH step. Make your own totally custom taper. You can even use ultra high end resistors in the positions you use most often. That way you don't have to spend a fortune on upgrading all 96 resistors.

I used this calculator myself with one of the blue switches and vishay CMF resistors. The results were more transparent than the DACT CT2 I had been using. My guess is that ladder style attenuators will usually be less obtrusive because they only have 2 resistors in the signal path no matter what level you are using. In a series style like the DACT there will be a whole string of resistors and solder joints in the path depending on what level you are listening at.

I guess Mr. X already posted that link. Here is a link to the switch $18 shipped.
Selector switch 4 pole 24-step DIY Attenuator/Pot NEW - eBay (item 270487302791 end time Dec-18-09 11:40:00 PST)
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post #9 of 13
12/10/09 at 7:19am
Thread Starter 
So is Goldpoint the only source for a balanced one? I would really like to avoid having two volume controls.
Actually...I could wire it so that L- and R- go through one, so that the volume on each channel is kept the same. The other could have L+ and R+. I may have to think about that to save a lot of money.

Thanks,
Nkk
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post #10 of 13
12/10/09 at 8:05am
Quote:
Originally Posted by nkk View Post
So is Goldpoint the only source for a balanced one? I would really like to avoid having two volume controls.
Actually...I could wire it so that L- and R- go through one, so that the volume on each channel is kept the same. The other could have L+ and R+. I may have to think about that to save a lot of money.

Thanks,
Nkk
I think the goldpoint balanced stereo switch is just a regular stacked 4 pole switch. The switch I linked to is a 4 pole as well. You could buy a blank switch and build it as a balanced stereo. It would have to be a series style attenuator not a ladder style. The ladder style attenuator uses 2 poles per channel. So I guess if you wanted a balanced ladder style you would need an 8 pole switch.

I bet if you asked the seller they would make it as a stereo balanced control.
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post #11 of 13
12/13/09 at 7:11am
Thread Starter 
For future reference:

The seller linked does not make them, and the factory he sources them from does not make 4 channel ones.

I am going to do the following:
Use 2 of the 2 ch one, with one being R+ and L+, and the other attenuating R- and L-. In this way, I never have to match channels with 2 controls. I will probably want to match them anyway, but while adjusting there will never be a time where one channel is louder than the other.

-Nkk
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post #12 of 13
12/14/09 at 9:41am
Quote:
Originally Posted by nkk View Post
...
Use 2 of the 2 ch one, with one being R+ and L+, and the other attenuating R- and L-. In this way, I never have to match channels with 2 controls. I will probably want to match them anyway, but while adjusting there will never be a time where one channel is louder than the other.
Not a good thing to do -- while you won't have channel imbalance issues this way, you throw the common-mode balance out the window. Why even bother with balanced interconnects and amp when you do this?
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post #13 of 13
12/14/09 at 2:45pm
Quote:
Originally Posted by amb View Post
Not a good thing to do -- while you won't have channel imbalance issues this way, you throw the common-mode balance out the window. Why even bother with balanced interconnects and amp when you do this?
If the "balanced" amp is just bridged, then common-mode balance is irrelevant.

se
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