audio log as reverse log

[buschfsu]

iv read up on this and if im correct as long as one side goes to ground and the audio is taken off of the wiper i should be able to reverse the connections ( cw and ccw) and be ok? i need it for the eisen audio diy500 and reverse log clarostats are impossible to find.

thanks for any help
http://www.eisenaudio.com/diy500/schematic.jpg

 

[bcarso]

But you have the wrong sense with respect to rotation then.

A trick to make the connection swap work is to put the markings on the knob skirt instead of the panel.

 

[Svart]

there is no way to make a "log" pot become a "reverse log".


BUT, there are tricks you can play with a linear pot to make it *sort of* like a reverse log. I've done it plenty of times and you can't really tell with your ears.

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

 

[edanderson]

i believe john hardy has helped out DIYers in the past, as he stocks this part for his preamps.

ed

 

[MikoKensington]

Why does it have to be a Clarostat? Have you looked into Spectrol, Bourns or Alphastat?

Does it need to be PC mount? Have you looked into a different value? By most accounts you won't notice a difference between a 25K rev log and a 50K rev log in an API style circuit. I use 50K reverse logs with my Melcor/MAP preamps. Work just fine and you can get them from any Fender amp part supplier for peanuts.

 

[SSLtech]

[quote author="Svart"]there is no way to make a "log" pot become a "reverse log".


BUT, there are tricks you can play with a linear pot to make it *sort of* like a reverse log. I've done it plenty of times and you can't really tell with your ears.

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm[/quote]

This link keeps getting re-cycled, and EVERY time, I feel compelled to point out the following:

A LINEAR POT CAN NEVER BE MADE TO WORK AS -OR EVEN REMOTELY LIKE- A REVERSE LOG 2-TERMINAL VARIABLE RESISTANCE.

Prove me wrong a win a million dollars.

By the way, Both log and reverse log variable resistances have 10% resistance at 50% rotation.

Achieve that by externally 'bending' a linear pot, and I'll give anyone a million dollars.

Keith

 

[12afael]

there is no way to make a "log" pot become a "reverse log".

mmm I disagree :green:

http://www.gyraf.dk/gy_pd/calreq/magnus_j/index.htm
http://www.gyraf.dk/gy_pd/calreq/magnus_j/rebuilding_pot.htm

 

[Curtis]

If you can live with installing a double gang pot, with some styles of log pots you can swap the outer and inner wafers and end up with a dual gang reverse log pot. I've done it several times with Alpha-style 16mm pots and it works well.

I think there's a link on Gyraf's site, on his DIY Calrec parametric EQ pages that describes how to do it.

 

[Crusty2]

...or just buy a reverse log pot from Digikey:

http://dkc3.digikey.com/PDF/T081/1828-1829.pdf ("KB" series, last page)

 

[pstamler]

There is another way to turn a log pot into a reverse log pot.

Gears.

Peace,
Paul

 

[syn]

[quote author="12afael"]

there is no way to make a "log" pot become a "reverse log".

mmm I disagree :green:

http://www.gyraf.dk/gy_pd/calreq/magnus_j/index.htm
http://www.gyraf.dk/gy_pd/calreq/magnus_j/rebuilding_pot.htm[/quote]

The only draw back to the above is that one can not use any log pot. It has to be mechanically suitable as well (pot).

 

[Svart]

A LINEAR POT CAN NEVER BE MADE TO WORK AS -OR EVEN REMOTELY LIKE- A REVERSE LOG 2-TERMINAL VARIABLE RESISTANCE.

Don't tempt me young man.

I will wave my finger violently at you.

(ah yes but I didn't actually read that he meant a rheostat.. sorry Keef! )

 

[SSLtech]

Yeah... I know! :green:

That's usually the misunderstanding that triggers confusion, so I feel obligated to point it out.

As a 3-terminal device a linear control can be persuaded to approach reverse-log behaviour... certainly less objectionable than an un-'bent' linear at least- but as a 2-terminal device it can't be done, and all attempts to try produce WORSE results than straight linear.

Keith

 

[Svart]

IF he can't find the right pot, a rotary switch is the next best thing.. plenty of schemos around here for those in a value that will suit his needs. Since I finally looked at the schematic link, take a look at the schematic for Fabio's 312 board or this link:

http://www.groupdiy.com/index.php?topic=246&highlight=fabio+312

 

[buschfsu]

thanks guys,
problem is it has to fit the 1/2inch square pcb mount footprint of the eisen diy500 board. im game for anything that will be acceptable in the 512 type circuit.

 

[edanderson]

right, you want either the clarostat 3x8 series or a bourns 51 series. to get either one in single piece qtys you are probably going to have to find someone who already uses them. so contact jens at eisen or john hardy. you could also try contacting state electronics, the vendor that both almost certainly use for clarostat, but they may be reluctant to sell just one piece.

ed

 

[babyhead]

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=KB2531S28-ND

It may not work for a cartridge chassis, but if you are putting it in a rack, you can just jumper this to the PCB. Pricey, but well worth it.

 

[babyhead]

To me, putting components like these into our projects is the key. Just look at them... We can spend more on better parts than a mass produced product because we have no price point to match. Unless you want to spend top dollar, we can make it better. I am using PECs everywhere... guitars and basses, tube amp repairs, mic pres, etc. I like trowing money at DIY...

 

[EisenAudio]

Indeed, the DIY500 PCB, versions 1-4, used Clarostat 388 series. We've discontinued the part and no longer have any in stock. I've never seen any 388 in catalogs, and State Electronics rarely has them in single/small quantities from stock. However, Clarostat 308 should fit the same foot print, and you might be able to find log in stock at State. 1/8" shaft, though.

DIY500mkII (coming June) is going to use a Bourns 51 series reverse log. 1/8" shaft. Again, this is not something you can buy single/small quantities of from stock... but that's what it takes to get a good reverse long conductive plastic pot (several hundred at a time). Will we be selling them individually? Probably not. Will it fit the DIY500 v1-4 PCB (and front panel)? Definitely not.

 

[buschfsu]

wohoo! very excited that there will be a diy500 mkII. i have a jensen, cinemag, and a 2520 with no home.

i think ive found a suitable replacement 10k rev log conductive plastic from slenderchap audiomaintenance.com. I was ordering some carnhills and he has dual ganged pots that i can remove the rear gang.

thanks all