From a lin to a log

[stumted2]

Hi all,

I have just found a 1meg dual pot for my Pye Black Box, the only problem is that they are lin not log. (they should be log)

Does any kind member know the best way of changing the law of the pot to approximate the mimic of from lin to log, and if so, the value of caps or resistors across the legs of the pot.

Keeping my fingers crossed that some kind member maybe able to assist.

Cheers,
Ted

[Ambientnoise]

Try this article/site

https://sound-au.com/project01.htm

Ken

[ms660]

http://www.learnabout-electronics.or...istors_09a.php

http://www.geofex.com/article_folder...s/potscret.htm

Basically a resistor from the wiper to the bottom end (chassis end) of the pot that's of a value that's approx. 1/4 to 1/5th of the pots value.

Lawrence.

[snowman_al]

deleted

[stumted2]

Hi Ken,

Many thanks for your very kind help, it's very much appreciated.

Hi Lawrence,

Many thanks to you also Lawrence, it's very kind of you to let me know, so the resistor value should be around 250-300k if I am understand this correctly? Just a thought, will this affect the value of the 1 Meg pot?

Sorry to be a bit dim, but just thought I would ask. All help is very much appreciated.

All my very kindest regards,
Ted

[Alistair D]

This is a link to a discussion on here back in 2017 https://www.vintage-radio.net/forum/...d.php?t=142531

Al

[Stockden]

See here

[ms660]

Originally Posted by stumted2

Many thanks to you also Lawrence, it's very kind of you to let me know, so the resistor value should be around 250-300k if I am understand this correctly? Just a thought, will this affect the value of the 1 Meg pot?

It won't affect the resistance value of the track inside the pot but the resistance across the track that's presented to the input will vary as the volume control is advanced, ie: with a 270k taper resistor connected and the volume set to minimum the resistance across the pots track will be 1 meg (the tracks resistance) When the volume is set to maximum the resistance across the pots track will consist of the resistance of the track (1 meg) in parallel with the 270k resistor which equates to approx. 212k, that's the resistance that will be presented to the input at maximum volume.

So, in effect you end up with a 212k "log" pot.

That will affect the output from the signal source as the volume is advanced, the usual potential divider rules apply...eg: source impedance and load impedance = a potential divider so therefore the lower the load impedance the lower the signal output from the source will be.

That's for one section of the control, yours is a dual pot and they are in effect connected together, section A wiper to section B's track according to a schematic I'm looking at.

You can but try it and see how it performs.

Lawrence.

[stumted2]

Hi Ken, Al, and Stockden,

Many thanks for your very much appreciated kind help, it's very much appreciated.

H Lawrence,

Wow, many thanks for your very much appreciated kind help and advice. I am now wondering should I use my 500k dual log pot in my Pye Black box, or go for the modified 1 Meg lin to log option. Your thoughts and views would be very much appreciated, in other words, what option would you go for? (I forgot to mention that this is the Black Box volume control.)

So sorry to be a pain, but am completely stuck on what to do. All help is very, very much appreciated.

All my warmest and kindest regards
Ted (Alias Puzzled and stuck.)

[ms660]

Originally Posted by stumted2

I am now wondering should I use my 500k dual log pot in my Pye Black box, or go for the modified 1 Meg lin to log option. Your thoughts and views would be very much appreciated, in other words, what option would you go for? (I forgot to mention that this is the Black Box volume control.)

The dual 500k log pot would be my choice.

Lawrence.

[stumted2]

Hi Lawrence,

Many thanks for your very kind help, I will take your advice and go for the 500k log pot.

Many thanks once again for your very kind help.

All my kindest regards
Ted.

[Herald1360]

If you have plenty of "spare" volume, a series resistor at the top end of each pot of 220k-470k will improve the bass response with the 500k option.

[stumted2]

Hi Herald 1360,

Many thanks again for your very kind help, I tried to find my last post with your very helpful advice , but it has been deleted.

I will now follow your advice, and fit the 500K log pot with as you advised fitting 470K resistors fitted at the top end of each pot. (Have just ordered some 470K 1% resistors)

Many, many thanks once again for all your very much appreciated kind help.

All my very best and kindest regards,
Ted.

[Techman]

Originally Posted by stumted2

I tried to find my last post with your very helpful advice , but it has been deleted.

Are you sure it's been deleted?

There was a thread where a kind member offered you a pot free of charge, which you declined as you'd already got fixed up, so the thread got closed. Why not ask that member about that particular pot as it could be what you're looking for to save all this messing about.

The thread's here - two pages of it, and the link to it is below, good luck.
https://www.vintage-radio.net/forum/...d.php?t=159522

[AC/HL]

There was briefly a post by snowman al in this thread, but he deleted it himself.

[stumted2]

Hi Techman

Many thanks for your message, it's very kind of you to find the thread for me, I did search for my original thread, but couldn't find it. (I'm not the brightest star in the sky)

I have taken some very kind advice from forum members, and will replace the pot with a 500K dual log pot with added resistors. I do have a 1meg dual pot, but it is lin.

Many thanks once again for all your very kind help.

All my very best and kindest regards,
Ted