[KillingTime]

Hi,

I'm building another headphone amp, and am looking for a linear alps 10k stereo pot.

Farnell and RS (in the UK) only seem to sell the LOG pots.
HiFi collective only does the LOG pots too.

I've found a guy on ebay (familygate) who is selling linear RK27112's but the pdf spec sheet says they're indented mid way.

I don't want a volume control thats indented mid way round, but I'm unsure as to whether I've misread the spec sheet.

Does anyone have this pot?
Is rotation smooth all the way round, or does it have an indent?

Thanks.

 

[n_maher]

a) You want a log taper pot generally speaking for audio applications. A linear pot will not give linear results regarding attenuation.

b) I've never heard of a center detented pot except for balance pots where you want to be able to find the middle. But I looked at the pdf and I don't see what you're talking about.

 

[luvdunhill]

why not use a linear pot with a parallel resistor to make it into a log pot?

 

[KillingTime]

Hi,

The pdf on the guys webpage is:

avpg2.homepage.t-online.de/PDF/RK27112_LIN_LINCC.PDF

On the second page of the pdf, it lists the detent position as 150 deg +- 3 deg.

I've tried log before, and I always end up using the second half of the rotation span because the first half is too quiet. Seems to be a waste of the 1st half.

On my Rotel RA02 (integrated amp with headphone output), it's a linear pot, and I use most of the rotation angle.

 

[amb]

If you're not achieving adequate levels with a log pot, then your amp's gain is too low.

 

[nikongod]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif why not use a linear pot with a parallel resistor to make it into a log pot?

It is supremely "un-logarithmic". It works well if you can use it at roughly the midpoint of its travel, but at the limits of the pots travel you are not anywhere near as well off as a real log pot.

It also represents a varying load to the source. Generally not a problem, but worth mention for cases which are very dependent on load for proper operation.
Quote:

Originally Posted by amb /img/forum/go_quote.gif If you're not achieving adequate levels with a log pot, then your amp's gain is too low.

You rock!111

It should be noted that this includes the area beyond 1/2 rotation... the trend to build amps with way-a-lot of gain of 10 or so has lead may people to avoid this section of the potentiometer.
Quote:

Originally Posted by KillingTime /img/forum/go_quote.gif I've tried log before, and I always end up using the second half of the rotation span because the first half is too quiet. Seems to be a waste of the 1st half.

I would generaly say build your gear to use the pot right smack in the middle of its rotation. This accounts for both "hot-mixed crap discs" and well mixed and cut media.
Quote:

On my Rotel RA02 (integrated amp with headphone output), it's a linear pot, and I use most of the rotation angle.

Do you mean linear as in the sound increases linearly with rotating the pot: getting continually louder as you rotate the knob up and up? thats good, its a log pot then which coincides with the (approximately) logarithmic response of the human ear.

when you use a linear pot in an audio-signal app, you get about 5-10min (on a clock face) of adjustment and then very little change between there and the limit of travel.

 

[KillingTime]

The owner \ manager of 'familygate' has replied to my question, and for the benefit of anyone else reading this, his linear apls pots listed as 10KBx2 do not have an indent at 150deg.

He does sell linear pots with an indent at 150deg, but for simplicity, uses the pdf for these pots to show the electrical characteristics of the ones without the indent. This is where my confusion originally arose.

With regards to lin v's log, I have to say I'm new to building amps, so I will try both and see which I like best.

Thank you for all your responses.

 

[MrMajestic2]

Quote:

Originally Posted by KillingTime /img/forum/go_quote.gif The owner \ manager of 'familygate' has replied to my question, and for the benefit of anyone else reading this, his linear apls pots listed as 10KBx2 do not have an indent at 150deg. He does sell linear pots with an indent at 150deg, but for simplicity, uses the pdf for these pots to show the electrical characteristics of the ones without the indent. This is where my confusion originally arose. With regards to lin v's log, I have to say I'm new to building amps, so I will try both and see which I like best. Thank you for all your responses.

I bought a 10k linear RK27 from family gate to use with my Joshua Tree attenuator. Worked great.

 

[luvdunhill]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif It is supremely "un-logarithmic". It works well if you can use it at roughly the midpoint of its travel, but at the limits of the pots travel you are not anywhere near as well off as a real log pot. It also represents a varying load to the source. Generally not a problem, but worth mention for cases which are very dependent on load for proper operation.

meh, works in a pinch. Perhaps KillingTime can try it as well and report back...