Using Log Pot instead of RevLog (simple question)

I'm trying to find dual gang 50K RevLog pot but i can't.Only 50K Log.

So...

If i solder pot reversed,can i get RevLog pot? Or it will change only CW and CCW?

Like this...



Or how about if i use linear or log pot instead of rev log as eq frequency?

Thanks.

Or can i use fake reverse log pot? 100K linear pot with 10K resistor and i will get 50K reverse?

Yes, you can wire it reversed and it will work. However it will also work backwards. So, if full gain with a rev log was fully clockwise it will now be fully anti clockwise.

Cheers

ian

ruffrecords said:

Yes, you can wire it reversed and it will work. However it will also work backwards. So, if full gain with a rev log was fully clockwise it will now be fully anti clockwise.

Cheers

ian

Click to expand...

Thanks for reply.

If i wire like this,when i turn to right,it will decrease.So it's not usable.

Which one i should instead of rev log for eq frequecny?Which one is close?Linear or log?

And is there any place to buy dual gang 50k reverse log? I can't find.

ForthMonkey said:

ruffrecords said:

Yes, you can wire it reversed and it will work. However it will also work backwards. So, if full gain with a rev log was fully clockwise it will now be fully anti clockwise.

Cheers

ian

Click to expand...

Thanks for reply.

If i wire like this,when i turn to right,it will decrease.So it's not usable.

Click to expand...

Not if you turn it upside down. Imagine a pointer knob (chicken head type) . Normally you fit it so the pointer is on the bottom left when the pot is fully anticlockwise and as you rotate the knob from left to right, the pointer goes over the TOP of the control. However, if you fit the knob so that when it is fully clockwise, the knob points to the top left, you still rotate it from right to left but the pointer goes UNDER the pot.

Cheers

ian

ForthMonkey said:

Which one i should instead of rev log for eq frequecny?Which one is close?Linear or log?

Click to expand...

You may use linear instead of revLog, but the end of travel will be cramped. If you use Log instead of revLog it will be even more cramped.
Some dual potentiometers use two wafers facing each other; by opening the pot and switching the two wafers you get a dual revLog.
But I would suggest you buy revLog pots from AudioMaintenance in the UK.

ruffrecords said:

ForthMonkey said:

ruffrecords said:

Yes, you can wire it reversed and it will work. However it will also work backwards. So, if full gain with a rev log was fully clockwise it will now be fully anti clockwise.

Cheers

ian

Click to expand...

Thanks for reply.

If i wire like this,when i turn to right,it will decrease.So it's not usable.

Click to expand...

Not if you turn it upside down. Imagine a pointer knob (chicken head type) . Normally you fit it so the pointer is on the bottom left when the pot is fully anticlockwise and as you rotate the knob from left to right, the pointer goes over the TOP of the control. However, if you fit the knob so that when it is fully clockwise, the knob points to the top left, you still rotate it from right to left but the pointer goes UNDER the pot.

Cheers

ian

Click to expand...

Sorry but i can't understand correctly because of my English.

If i wire log pot as i said,i will get rev log pot.And when i turn to clockwise,it will increase.Am i right? Or it will work backwards? So useless?

abbey road d enfer said:

ForthMonkey said:

Which one i should instead of rev log for eq frequecny?Which one is close?Linear or log?

Click to expand...

You may use linear instead of revLog, but the end of travel will be cramped. If you use Log instead of revLog it will be even more cramped.
Some dual potentiometers use two wafers facing each other; by opening the pot and switching the two wafers you get a dual revLog.
But I would suggest you buy revLog pots from AudioMaintenance in the UK.

Click to expand...

I'm looking for cheaper option and i need 2-3 pieces for prototype.But AudioMaintenance little bir expensive for now.

And their dual gang 16 mm pot same as Alpha pots?Same footprint and same pin dimension?

Quick search at Digikey

http://www.digikey.es/product-search/en/potentiometers-variable-resistors/rotary-potentiometers-rheostats/263488?k=&pv1092=4&pv1=574&pv1849=3&FV=fff40004%2Cfff80540&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Hope it helps...if it's just for prototypes you can use single gang 50k revlog from Musikding:

https://www.banzaimusic.com/search.php?mode=search&page=1&keep_https=yes

hazel said:

Quick search at Digikey

http://www.digikey.es/product-search/en/potentiometers-variable-resistors/rotary-potentiometers-rheostats/263488?k=&pv1092=4&pv1=574&pv1849=3&FV=fff40004%2Cfff80540&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Hope it helps...if it's just for prototypes you can use single gang 50k revlog from Musikding:

https://www.banzaimusic.com/search.php?mode=search&page=1&keep_https=yes

Click to expand...

Thanks but Digikey's shipping cost really high for me.I never use it.

And unfortunately i need dual gang.

ForthMonkey said:

ruffrecords said:

Not if you turn it upside down. Imagine a pointer knob (chicken head type) . Normally you fit it so the pointer is on the bottom left when the pot is fully anticlockwise and as you rotate the knob from left to right, the pointer goes over the TOP of the control. However, if you fit the knob so that when it is fully clockwise, the knob points to the top left, you still rotate it from right to left but the pointer goes UNDER the pot.

Cheers

ian

Click to expand...

Sorry but i can't understand correctly because of my English.

Click to expand...

It's not because of your English, it's because the suggestion comes from someone who drives on the wrong side of the road! 

http://m.aliexpress.com/item/32353509079.html?productId=32353509079&productSubject=Free-shipping-10PCS-stereo-sealing-potentiometer-C50K-15-mm-shaft-C503-6-Pins-WITH-NUTS-AND&tracelog=wwwdetail2mobilesitedetail

50k rev log... I used these pots in ssl4k EQ and work as they should

Other dimension and more expensive:

http://m.aliexpress.com/item/1391848105.html?productId=1391848105&productSubject=BELLA-Taiwan-Fu-Chinese-Type-16-double-potentiometer-C50K-10PCS-LOT&spm=2114.01010208.3.116.dYgqez&ws_ab_test=searchweb201556_1%2Csearchweb201602_2_10017_10005_10006_10034_10021_507_10022_10032_10020_10018_10019%2Csearchweb201603_7&btsid=9e28a7a4-9c46-4d9f-a5ef-907e640a80cd%3D&tracelog=wwwdetail2mobilesitedetail

abbey road d enfer said:

ForthMonkey said:

Sorry but i can't understand correctly because of my English.

Click to expand...

It's not because of your English, it's because the suggestion comes from someone who drives on the wrong side of the road! 

Click to expand...

LOL. The story goes that people meeting on the road used to keep to the left so that they had their sword hand close to the  person passing them and as most people are right handed that means passing on the left.

Either that, or we do it just to annoy the French.

Cheers

ian

ruffrecords said:

The story goes that people meeting on the road used to keep to the left so that they had their sword hand close to the  person passing them and as most people are right handed that means passing on the left.

Click to expand...

  And in their perfidy, the French decided to fight left-handed...

ForthMonkey, sorry for hijacking your thread.

You buy a straight audio taper, take it English roads, it becomes Reverse audio.

The knob rotation direction is LESS important than which side you carry your sword on when meeting road bandits.  There is no "right" way, just what we are used to. In the USA, radio volume knobs turn clock-wise (yes, most clocks are standard (but not all)) to get "more". However a kitchen gas stove knob turns counter-clockwise for "more". I can do both at the same time and never feel confused.

if i remember correctly its x5 and x1.25 ratio:
linear taper pot  x 5  and resistor x 1.25  across pin 2 and 3 = RevLog
in ur case:
50k x 5 = 250k
50k x 1.25 = 62.5k
you put a 62.5k resistor across pin 2 and 3 of a 250k pot. u got 50K revlog pot

experts will know better of course.

kambo said:

if i remember correctly its x5 and x1.25 ratio:
linear taper pot  x 5  and resistor x 1.25  across pin 2 and 3 = RevLog
in ur case:
50k x 5 = 250k
50k x 1.25 = 62.5k
you put a 62.5k resistor across pin 2 and 3 of a 250k pot. u got 50K revlog pot

experts will know better of course.

Click to expand...

This law-steering arrangement works ONLY when the pot is wired as a pot (3-terminal device); in a parametric EQ, the pots are often wired as rheostats (2-terminal).
To my knowledge, only the State Variable Filter (SVF) topology allows using potentiometers instead of rheostats.
The Wien-bridge topology works only with rheostats, so does not lend itself to law-steered potentiometers.

i guess i forgot ForthMonkey is the EQ guy

It's a  prototype,  just test it knowing you turn right to left.

Quote: "Yes, you can wire it reversed and it will work. However it will also work backwards. }" Unquote

abbey road d enfer said:

kambo said:

if i remember correctly its x5 and x1.25 ratio:
linear taper pot  x 5  and resistor x 1.25  across pin 2 and 3 = RevLog
in ur case:
50k x 5 = 250k
50k x 1.25 = 62.5k
you put a 62.5k resistor across pin 2 and 3 of a 250k pot. u got 50K revlog pot

experts will know better of course.

Click to expand...

This law-steering arrangement works ONLY when the pot is wired as a pot (3-terminal device); in a parametric EQ, the pots are often wired as rheostats (2-terminal).
To my knowledge, only the State Variable Filter (SVF) topology allows using potentiometers instead of rheostats.
The Wien-bridge topology works only with rheostats, so does not lend itself to law-steered potentiometers.

Click to expand...

This does works, for rheostats, only for the antilog version. The log version only works as a pot.

The thing is, you are making the center point to where you want it, relative to the end. So, you want a 100k antilog rheostat. 500k lin pot, 120k resistor. 97k at max, close enough. at mid point you get 250k//120k it's about 80k. That's a 80% law, you may prefer higher or lower, you could change the ratios, of course as the potentiometers choices are limited you can't get any value for any law, but you could work it around scaling other parts of the circuit.

This is just a second order approximation, the first is the value, the second is the taper. You don't get to choose the other points of the curve as some fancy brands do. It does works much better than the linear options for most of the range, the weak part is when the value get's to zero. If it's limited by a series resistor you get better results the bigger that gets, so you don't hit zero. (it could be inside the arrangement, is that any good?) Of course it depends on the circuit, one common application for this is mic preamps, or similar variable gain stages, where you need revlog pots to do the job smoothly. I've done it and the control was way more usable than with the linear pot but in the max gain it was quite touchy. I think that also happens with (cheap) antilog pots. JH used a combination with changed the pot to a smaller linear one for the higher gain range (10kC vs 500ΩB IIRC)

JS