I'm not sure how many of you are familiar with anti-log or inverse log pots.
But they seem to be what most (or all) balanced microphone ICs seem to need, if you want to set gain with a pot.
Many people prefer to use a multiposition switch and select the different resistor values.
I didn't try this, but I wonder what would happen if I invert a log pot when connecting it, which normally would work anti-clockwise then.
What I wonder is if it would work to set the gain as with an anti-log pot, or what would happen.
Is it possible to recreate an "anti-log fake resistor" using a linear pot?
But they seem to be what most (or all) balanced microphone ICs seem to need, if you want to set gain with a pot.
Many people prefer to use a multiposition switch and select the different resistor values.
I didn't try this, but I wonder what would happen if I invert a log pot when connecting it, which normally would work anti-clockwise then.
What I wonder is if it would work to set the gain as with an anti-log pot, or what would happen.
Is it possible to recreate an "anti-log fake resistor" using a linear pot?
In the old days, we had Linear, Log and anti Log.
It meant that the "action" was either linear at the begining or at the end of the travel.
Cheaper than using Fet input Op Amps I surpose, as we didn't have them then.
Log pots have the difference of resistance in the middle of the range and anti log have the difference at the begining, then at the end.
It meant that the "action" was either linear at the begining or at the end of the travel.
Cheaper than using Fet input Op Amps I surpose, as we didn't have them then.
Log pots have the difference of resistance in the middle of the range and anti log have the difference at the begining, then at the end.
From Bing image search:
~Tom
An externally hosted image should be here but it was not working when we last tested it.
~Tom
Hi,
An anti log pot is just a log pot wired differently.
Yes you can create a fake log using a linear pot,
and wire it to to produce an antilog characteristic.
Though one has to be careful about defining ins
and outs, and what it does, I'm pretty sure in
mic preamps in the end you get log volume.
Anti log pots work the same way as log, except
they work anti clockwise as opposed to clockwise.
Log faking linear pots can be wired either way.
(Typically 100K with 15K wired wiper to either
of the ends for an ~ 10K log or anti log pot,
1M with 150K for an ~ 100K fake log pot)
rgds, sreten.
FWIW dual linears used as fake log generally have far
better channel matching than dual logs, especially
at low levels when used as volume controls.
An anti log pot is just a log pot wired differently.
Yes you can create a fake log using a linear pot,
and wire it to to produce an antilog characteristic.
Though one has to be careful about defining ins
and outs, and what it does, I'm pretty sure in
mic preamps in the end you get log volume.
Anti log pots work the same way as log, except
they work anti clockwise as opposed to clockwise.
Log faking linear pots can be wired either way.
(Typically 100K with 15K wired wiper to either
of the ends for an ~ 10K log or anti log pot,
1M with 150K for an ~ 100K fake log pot)
rgds, sreten.
FWIW dual linears used as fake log generally have far
better channel matching than dual logs, especially
at low levels when used as volume controls.
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What I'm trying to achieve, if I can, is a use a dual 10K log, wiring one log side as close as possible to anti-log (anti-clockwise?), and the other normally clockwise.
The anti-log would control the gain of the IC and the log would control the output level of the chip.
But I'm not sure if it would work or how it would work.
It's for a small batch of mic preamps, so I can't afford ordering an anti-log+log combo from Alps, which would be the right thing to do.
The anti-log would control the gain of the IC and the log would control the output level of the chip.
But I'm not sure if it would work or how it would work.
It's for a small batch of mic preamps, so I can't afford ordering an anti-log+log combo from Alps, which would be the right thing to do.
Are you familiar with configuration "A" in the link below? You can adjust the resistor values to yield varying levels of gain and relative gain offset. The basic configuration yields an attenuation which is linear in db using a linear taper pot.
Also, the configuration results in essentially zero current through the potentiometer, which is a nice advantage.
Active Filters
Suitable for your application?
Dave.
Unfortunately not really.
What I'm trying to do is replace a three position gain switch, which sets three "gain groups", for a pot, and the pot has to handle gain and level.
The first problem is one of the stages of the dual pot has to be anti-log, the second problem is it has to be around 1K. The second problem I could try to solve by adding a resistor in parallel with the pot, but that doesn't work too precisely. Now the third problem, and the reason for this thread, is if I can get close to an anti-log behavior by inverting the pin wiring.
I did try the pot option several years ago, and it was very satisfactory in many aspects. But I don't remember if it was a log or linear type. At the time I probably didn't care how gain changed if moving clock or anticlockwise. But it probably was a 1K pot or something.
What I'm trying to do is replace a three position gain switch, which sets three "gain groups", for a pot, and the pot has to handle gain and level.
The first problem is one of the stages of the dual pot has to be anti-log, the second problem is it has to be around 1K. The second problem I could try to solve by adding a resistor in parallel with the pot, but that doesn't work too precisely. Now the third problem, and the reason for this thread, is if I can get close to an anti-log behavior by inverting the pin wiring.
I did try the pot option several years ago, and it was very satisfactory in many aspects. But I don't remember if it was a log or linear type. At the time I probably didn't care how gain changed if moving clock or anticlockwise. But it probably was a 1K pot or something.
The George Lightspeed uses a dual log pot to send variable current through the LEDs.
One side of the Log Pot is wired in reverse. It is effectively an "anti-log" pot.
Unfortunately it could not be applied to this project. It's cumbersome and expensive.
This is something I need to use on a 2-channel portable small sized mic amplifier. I am looking for ways to replace a toggle gain switch for a pot that works together with another one. So far the only option is to have them custom made, one anti-log and the other log, which would be very expensive because of the minimum quantities required.
This is something I need to use on a 2-channel portable small sized mic amplifier. I am looking for ways to replace a toggle gain switch for a pot that works together with another one. So far the only option is to have them custom made, one anti-log and the other log, which would be very expensive because of the minimum quantities required.
Potentiometer switch manufacturer, Omeg
They do user-specified custom parts, even really small qtys, starting from 10pcs (unless special tooling/processing is required), at reasonable cost. A long lead time, though.
They do user-specified custom parts, even really small qtys, starting from 10pcs (unless special tooling/processing is required), at reasonable cost. A long lead time, though.
For antilog pot, connect a shaft from back side of the log pot. Some shafts can be seen open from the back.
Gajanan Phadte
Gajanan Phadte
Faking a log/antilog pot with lower value parallel resistors is crude (horrible) way to do things.
There´s a reason why actual log and antilog pots are made, after all.
It depends on how the NFB gain control is set.
If the pot varies resistance from - input to ground, it must be an antilog ; if varying resistance from - input to output, it must be log.
And it´s a self defeating design, because since the same shaft moves both sections at the same time, si even if reverse wired, one of them will move "the wrong way" respect to the other.
What you need to do is yo have a log classic volume pot and if you wish, another pot controlling mic preamp gain .
You may use a standard log pot for that, wired normally (reverse wiring it will be even worse than using a linear one) , simply the gain scale as indicated on the dial will be backwards, no big deal.
As in: "0 to 10" will in fact be "10 to 0" (não, não estou falando do resultado Alemanha-Brasil no Mundial 😉 ) , somewhat counterintuitive but since it´s simply adjusted "once" (not like volume which is moved all the time), as I said no big deal.
An anti log pot has its carbon track made the exact opposite (or mirror image) to what a log one is.
Please check tomchr posted graph.
@ carlmart: if you need 100 or more custom dual log+antilog track pots you can order them in Argentina at Bisal/Vantronic for a reasonable price.
:::: Vantronic S.A ::::
If you go through their representative Taiyo they might order some small batch (say, 50).
Any friend travelling to Buenos Aires on holiday can carry that small package in his luggage.
Taiyo Electronica
What city are you from?
There´s a reason why actual log and antilog pots are made, after all.
¿¿¿???
It depends on how the NFB gain control is set.
If the pot varies resistance from - input to ground, it must be an antilog ; if varying resistance from - input to output, it must be log.
Why vary stage gain and output attenuation (what a standard volume control does) at the same time?
And it´s a self defeating design, because since the same shaft moves both sections at the same time, si even if reverse wired, one of them will move "the wrong way" respect to the other.
What you need to do is yo have a log classic volume pot and if you wish, another pot controlling mic preamp gain .
You may use a standard log pot for that, wired normally (reverse wiring it will be even worse than using a linear one) , simply the gain scale as indicated on the dial will be backwards, no big deal.
As in: "0 to 10" will in fact be "10 to 0" (não, não estou falando do resultado Alemanha-Brasil no Mundial 😉 ) , somewhat counterintuitive but since it´s simply adjusted "once" (not like volume which is moved all the time), as I said no big deal.
Sorry but no.
An anti log pot has its carbon track made the exact opposite (or mirror image) to what a log one is.
Please check tomchr posted graph.
@ carlmart: if you need 100 or more custom dual log+antilog track pots you can order them in Argentina at Bisal/Vantronic for a reasonable price.
:::: Vantronic S.A ::::
If you go through their representative Taiyo they might order some small batch (say, 50).
Any friend travelling to Buenos Aires on holiday can carry that small package in his luggage.
Taiyo Electronica
What city are you from?
Tom's post confirms that reversing the connections gives an anti-log transfer function. Just as the enquirer has already pointed out.
Hi!
Since I have a similar question I decided to post it here. I hope it's OK.
Is it possible to convert/rewire a dual log potentiometer to dual reverse log?
Since I have a similar question I decided to post it here. I hope it's OK.
Is it possible to convert/rewire a dual log potentiometer to dual reverse log?
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> convert/rewire a dual log potentiometer to dual reverse log?
Easy. Number the scale 10 to 0, and turn the knob backward.
"Fake reverse" is rarely fully satisfactory, and NOT possible in Rheostat connection (which was what the OP was doing, though he may not have known that).
Easy. Number the scale 10 to 0, and turn the knob backward.
"Fake reverse" is rarely fully satisfactory, and NOT possible in Rheostat connection (which was what the OP was doing, though he may not have known that).
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