Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Volume pot question
New Posts  All Forums:Forum Nav:

Volume pot question

post #1 of 4
6/6/10 at 11:45am
Thread Starter 

I have a question about something that seems like it should work intuitively but want to be sure before I try it.  I'm finding that when listening to amps I'm building through my 325is' I never rotate the volume pot beyond 9:30.  I keep reading that pots sound best when in the 12-2 position.  Both of the amps I've built have 50k ohm pots.  What would happen if I swapped out a 50k pot (I assume this means 50k resistance per channel) for a 25k pot with a 25k ohm resistor before the pot on each channel?  It would seem like doing this would allow me to use more of the "sweet spot" of the pot.  Is this correct?

 

Thanks in advance.

Reply
post #2 of 4
6/6/10 at 11:53am

I don't know about the actual specs, but you are right about wanting as wide a sweet spot as possible, where the amp is driving the headphones with enough power to make all of the detail and dynamics clear, but there is no distortion.

 

In the past I have used attenuators to help widen that sweet spot, Google Rothwell and Golden Jacks and see if they will fit into your system. Attenuation stops the source from 'overloading' the amp and matches the voltage. 

 

I have also found that different interconnects can widen or narrow the sweet spot as they present different resistances between amp and DAC or source.

Reply
post #3 of 4
6/6/10 at 12:20pm

Changing the value of the pot actually doesn't change its attenuation at all.  Instead you could try putting a resistor in front of the pot which basically always attenuates the signal some before you even adjust it.

 

Also interconnects should never affect the volume unless there is something very wrong.  A wire will have an impedance less than an ohm for any reasonable gauge and length.  Volume pots have at least a 10,000 ohm impedance.

Reply
post #4 of 4
6/7/10 at 7:32am
Thread Starter 

After doing some number crunching I found the following:

 

- A standard 50k pot has a Zin of 50k ohms and a max Zout of 12.5k ohms

 

- Adding a 50k resistor before the pot raises the Zin to 100k ohms and has a max Zout of 25k ohms.  This should yield around 6dB of attenuation

 

- Adding a 100k resistor before the pot raises the Zin to 150k ohms and has a max Zout of 33k ohms.  This should yield around 9.5 dB of attenuation

 

- Putting a 40k resistor before a 10k pot keeps the Zin in the same at 50k ohms and gives a Zout of 8k ohms.  This should yield around 14dB of attenuation

 

 

So, if I simply add a resistor in front of the existing pot I am potentially placing a greater load on the amplifier and only getting 6-10dB of attenuation.  By swapping out the pot and putting a large resistor in front I'm getting 14dB of attenuation and putting less of a load on the amplifier.  Is this a better alternative?

 

Thanks

Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Volume pot question