Alpha Pots - A vs B

[Siegfried Meier]

Hey guys,

In speaking about output pots (in this case, a 1290), I have a question regarding the A vs B alpha pots.  A is Audio or Logarithmic, I think, while B is Linear - am I correct there?

I had put the B's in some other pres of ours and the taper feels odd and not smooth in the output volume.  It would make sense to me to use the A or Log, as that mimics what a normal console fader is like.  Any thoughts on this?  I have both here, and am building up another pair of 1290's so just wanted to know what would normally be used here.

I do know that Brent Averill uses B pots in their Neve output sections (that's where we bought our first batch), but they just don't sound right to my ear.  Also, most guitar volume pots are Log so this seems to go against common convention.

Any info would be much appreciated.

Thanks!
Sig

 

[okgb]

A=log
B=Linear
c=Reverse log

Log so called audio taper are often used for control where you need finer degree of change
at the start of rotation

 

[Harpo]

...regarding the A vs B alpha pots.  A is Audio or Logarithmic, I think, while B is Linear - am I correct there?

seems correct for both manufacturers Alpha and Alpha (Taiwan).
'A' might as well be linear taper for other manufacturers (FI Vishay/Sfernice/Spectrol,Piher).
When in doubt, measure resistance at different rotation angles or look up the parts datasheet.

 

[joaquins]

...regarding the A vs B alpha pots.  A is Audio or Logarithmic, I think, while B is Linear - am I correct there?

seems correct for both manufacturers Alpha and Alpha (Taiwan).
'A' might as well be linear taper for other manufacturers (FI Vishay/Sfernice/Spectrol,Piher).
When in doubt, measure resistance at different rotation angles or look up the parts datasheet.

measuring at mid point should be enought to determine A, B or C... if other tapers are in game like log-antilog more points are needed.

JS

 

[gyraf]

Pot curves  - two different traditions:

Japanese tradition - Letter first, e.g. A10K: A=Log, B=Lin, C=Neg.log

European tradition - Number first, e.g. 10KA: A=Lin, B=Log, C=Neg.log

Jakob E.

 

[Siegfried Meier]

Hmmmmm - Alphas are Japanese you say then?

What is the general consensus on what I need for the output fader then?  Me thinks log, yes?

 

[abbey road d enfer]

Hmmmmm - Alphas are Japanese you say then?

Asian. They have adopted the Japanese nomenclature because they were the primary customers.

What is the general consensus on what I need for the output fader then?  Me thinks log, yes?

What type of equipment? Is it a preamp? Depends what you want to do. If you want to fine trim the output, a linear pot gives better resolution. If you want to mix with the fader, Log gives you more control.

 

[plimousse]

Hi,
Please, see attached file.
Regards,
Pascal

 

[ruffrecords]

A=log
B=Linear
c=Reverse log

Log so called audio taper are often used for control where you need finer degree of change
at the start of rotation

True for most Far Eastern manufacturers but OMEG in the UK use:

A - LIN
B- LOG
C- Anti LOG

The only way t be certain is to check the manufacturers data sheet.

Cheers

Ian

 

[Jidis]

Japanese tradition - Letter first

Much thanks for that! I've had to look the tapers up numerous times, but unless I've forgotten, most people make no mention of being able to tell which set they're using by where the letter is placed.

George

 

[Siegfried Meier]

What type of equipment? Is it a preamp? Depends what you want to do. If you want to fine trim the output, a linear pot gives better resolution. If you want to mix with the fader, Log gives you more control.
[/quote]

It is for a preamp, and I've always been told that a linear gives better resolution, but it didn't seem to sound that way in actual use.  However, I'll play around and see - I have both here, and will measure to see which to use.

Thanks guys!
Sig

 

[abbey road d enfer]

It is for a preamp, and I've always been told that a linear gives better resolution, but it didn't seem to sound that way in actual use.  However, I'll play around and see - I have both here, and will measure to see which to use.

Let's be clear. A linear pot has an excellent resolution over 2/3rds ot its rotation, with a span of about 10dB spread on 180°. The first 1/3 has worse resolution. In particular, the first 15° of rotation cover -infinity to -20dB, which makes fades extremely difficult.
Log pots are in fact made out of two linear portions of different resistivity; they cover about 20dB between mid-position (which makes trimming a tad more delicate) and full CW and -infinity to -20 in the first half-rotation, which makes fades a little easier.

For trimming, infinite attenuation is not needed. It is relatively easy to twist the taper with resistors to make a nice +/-10 or +/-15dB range with remarkably consistent control.