Voltage divider instead of expensive volume pot or stepped attenuator. - diyAudio
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Old 19th September 2010, 04:20 AM   #1
Brit01 is offline Brit01  United Kingdom
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Default Voltage divider instead of expensive volume pot or stepped attenuator.

Economical volume pots that don't degrade the sound are hard to come by. I use the alps but still are 15 USD each with shipping.

I've just tried a simple voltage divider with a pot.

The input signal only goes through 1 resistor (I use a Allen Bradleyor Holco), and the bottom pot wired to earth is used to vary the voltage signal.

First impressions are very good. It's getting late, tomorrow I'll test more.

But this means I can use any old cheap pot to vary the voltage on the divider to adjust the volume as the signal only goes through the 1 good quality resistor.

Any drawbacks of this? Experiences?
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Old 19th September 2010, 04:39 AM   #2
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You can wire a fair linear twin pot, each section one by one, and get a second order function that is still fine to regulate volume, but quality is much better than you can get from log pots.
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Old 19th September 2010, 04:42 AM   #3
Brit01 is offline Brit01  United Kingdom
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Quote:
get a second order function
Hi wavebourn.

not sure what you mean by this.

Do you have a diagram handy?
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Old 19th September 2010, 05:09 AM   #4
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Originally Posted by Brit01 View Post
Any drawbacks of this? Experiences?
only drawback I can see is that it goes full volume input if you have an open section of track on your pot.

Possibly best used with speaker protection...
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Old 19th September 2010, 06:54 AM   #5
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Quote:
Originally Posted by Brit01 View Post
Hi wavebourn.

not sure what you mean by this.

Do you have a diagram handy?
Like pictured.

The drawback is, on full volume it's input resistance is twice higher than on zero volume. But I used this feature for a ton-compensation, when used excess of power to extend bass. A cap before it was selected appropriately, and the amp had slight boost on bottom.
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Last edited by Wavebourn; 19th September 2010 at 06:56 AM.
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Old 19th September 2010, 05:38 PM   #6
DF96 is offline DF96  England
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Your cheap pot is shunting the signal. Thus it will have exactly the same effect as a normal pot arrangement. There is nothing magicly different about a component the signal goes "through" and a component the signal goes past. If it touches the signal, it affects it. Not everyone seems to realise this. You could argue that your arrangement is worse in this respect as the signal current is forced to go through the worst possible contact - wiper to track. A conventional volume pot feeding a high impedance stage simply picks off a voltage from a reliable potential divider - the wiper-track contact has to deteriorate quite badly before it affects the signal.

Your arrangement has the disadvantage that near maximum volume the output impedance remains high so it is less able to drive capacitive loads. Near minimum volume the input impedance reduces which could increase distortion in the previous stage. And when the slider lifts off the track?
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Old 19th September 2010, 07:39 PM   #7
piano3 is offline piano3  United Kingdom
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Hi Brit01,

Why don't you find a couple of multi-position switches and make yourself a stepped attenuator-it is easy once you have matched the resistors. It is really worth the effort!

Regards, N.A.
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Old 19th September 2010, 09:40 PM   #8
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Why don't you find a couple of multi-position switches and make yourself a stepped attenuator
Tried this with a dual six pole switch from an old noise gate kit from Maplins, it was certainly a lot of effort getting the values of the middle switch settings to reflect my listening levels - and IIRC got quite complicated as each switch setting consisted of a sequence of resistors forming a potential divider adding up to 47k ( the value of the pot it was replacing ) I had access at the time to a large stock of resistors so was able to match the resistors closely. I measured my volume pot at my lowest and highest listening level and that defined the resistance range of the switch.

In the end I couldn't hear any difference between the pot and the switch, maybe when I get better speakers I will

p.s.

Now that I think about it my first experiment was to measure the resistance of my volume pot at my favourite listening level, then I replaced the pot with the equivalent circuit consisting of just two pairs of resistors. I dont recall hearing any improvement

Last edited by Soonerorlater; 19th September 2010 at 10:09 PM.
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Old 19th September 2010, 10:25 PM   #9
Brit01 is offline Brit01  United Kingdom
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Good comments and thanks for the drawbacks I was unaware of.

Certainly a couple of home made stepped attenuators could be attempted to avoid the drawbacks mentioned of the pot.

I used the alps as the bottom divider and certainly heard an improvement of the signal directly through the alps.
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Old 20th September 2010, 12:19 AM   #10
piano3 is offline piano3  United Kingdom
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Pay particular attention to the second paragraph of DF96's post which implies that a shunt volume control should be loaded with a low capacitance stage-don't stick a D3A pentode triode wired after it!-and then you can use a higher value of series resistance so that the previous stage is not unfavourably loaded.Of course,if you do build a stepped attenuator you may have no reason to make it a shunt one unless you want to minimize the number of resistors/switch wafers and the number of solder joints in the signal path. Alex Djubuk in the Ukraine has fantastic switches at a good price.He is 100% reliable and 100% a gentleman.
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