Confusing or what?

[ruffrecords]

I have recently been  banging my head against the 'which pot to use' question. To put it into context, I am designing a twin line channel module. basically two line input channels with EQ, Pan and AUX sends. There is a main board on which one channel of EQ and routing and all the amplifiers are contained and a daughter board on which the other EQ and routing is contained. The problem revolves around trying to get both sets of controls lined up in the same way and roughly dispersed about the centre line of the module. To cut a long story short, the EQ is not a problem but the pan and AUX pots are. To cut an even longer story short, I decided upon ALPS 9mm pots as this gave the best overall layout. Took me a while and a lot of going back and forth but in the end it looks quite goo.

So, next the easy bit - order a few of the pots. These are the RK09 series from ALPS and really only available from RS in the UK (Rapid do a very limited sub-set). I needed a dual 50K LIN for the pan pot and some 50K logs for the AUX sends. RS has both but when I go to order then, one has only a littl;e stock and the other in on back ordr. So I back order them (After searching all over the place for somewhere else to buy them from - OK mouser had them but for the few I wanted the shipping woulf be more than the cost of the parts). Then I get an email from RS saying they are discontinued parts. Blast! After taking all that time to dind the right physical part, to then find it is discontinued is a royal PITA. So I contact RS and ask for alternatives. There is no direct alternative but they give a list of possibilities with slightly different mechanical properties like shaft length. I find two parts that will do the job but the manufacturer part number they give does not appear on the data sheets they point to on the web site so I cannot check product details. I enter the part numbers into the ALPS web site only to find they do not exist!!!  getting frustrated now. Contact RS and they get an engineer to call me back. Very helpful guy called Paul gives me the low down. ALPS has changed the part numbers and he tells me the new ones. Ah, this starts to make sense as these appear on the data sheet the RS web site points to but there is absolutely no way of knowing which part on the RS web site corresponds with which item in the data sheets. So, I pick the parts I really want and give Paul a call. I tell the ones I want and he tells me the corresponding RS part numbers. Turns out they don't do the whole range but they do at least do the ones I want. I suggest to Paul that RS needs to update its web site. He agrees. I check the RS web site and behold, they are in stock! I place an order and the next day they arrive and are just what I need - except the shaft is 25mm long rather than the 15mm I would have preferred but I can work with that. Interestingly, the parts are in the usual individual RS plastic packs and each one has the OLD part number printed on it - the same one used on the web site - the one that ALPS no longer recognises.

I then go searching  for the NEW part numbers to see who else does them. I come across an ALPS catalogue that lists them and includes the same data sheet shown on the RS web site. On the second page of the catalogue is this statement?

"The publication of ALPS ELECTRIC EUROPA GmbH shows only a selection of the complete ALPS product line. Please note that the used order no. system is only valid for the European market."

What???? Special part numbers just for the European market??? Why??? What is going on?? At least I know how to get the pots I want but to say the least I am utterly confused.

Cheers

Ian

 

[okgb]

Because they are charging you differently ? there is another distributor who has an exclusive deal or territory ?

 

[JohnRoberts]

I don't know if alps have become more DIY friendly but back when I bought pots from Alps I had to buy 5,000 of a specific part and they were all semi-custom assembled from a recipe of different bushings, shafts, etc.

JR

 

[ruffrecords]

Because they are charging you differently ? there is another distributor who has an exclusive deal or territory ?

I don't think so. I cannot find any other distributors. There are many standard parts of the RK09 series stocked by both RS and Mouser and RS is consistently cheaper. It is just this special range that is only available in Europe. I'll give you and example.

There European part number for a dual 50K LIn 25mm shaft with no ident is  STRK0971

The ALPS part number printed on the packet is RK097121009N

The RS part number is 249-9193 and if you search for this you get the follwoing RS web page:

http://uk.rs-online.com/web/p/potentiometers/2499193/

Search for RK097121009N at alps.com and you get 0 results. Search for it on the web and you get lots of pointers to various RS web sites.

Very odd.

Cheers

Ian

 

[thermionic]

I'm pretty sure that TW Alpha makes (or made - it's a while ago when I saw them) a 9mm pot which is interchangeable with the RK09. TLA used to implement both in their designs.

BTW - from what I've witnessed, the track lube in the RK09 dries out and the pots wear very quickly if they're used near items that are hot, i.e. valves / vregs etc. Although I'm a fan of Alps in general (the RK27 is fantastic for what it costs), I've always had mixed experiences with RK09 regarding durability.

Example of TW part (wrong value, I know): http://www.mouser.in/ProductDetail/Alpha-Taiwan/RD901F-20-15R1-B14/?qs=hsxrNzhi17BKEVSoOHNBLw==

 

[ruffrecords]

I looked at TW Alpha but I cannot find the values in dual pots that I need anywhere. I have used them before so I know they are OK although my experience has been mainly with their 16mm pots.

Cheers

Ian

 

[sahib]

Ian,

We use the RK09 (and dual 50kC) on our EQ ONE.  The distributor is AVNET. I'll e-mail you my contact.

 

[ddt]

Ian, why not have Omeg make them to your spec?

 

[ruffrecords]

Ian, why not have Omeg make them to your spec?

I normally use OMEG pots and all the values and combinations I need are in stock at CPC here in the UK. They are my standard go to pots. BUT, they are 16mm pots and the centre of the pot shaft is 12.5mm above the PCB surface. Try as I might I cannot get a good front panel layout for my twin channel module using them. The ALPS pots have the shaft centre just 6.5mm above the PCB surface and with them I can get an acceptable layout. As far as I am aware, OMEG does not have a 9mm product.

Cheers

Ian

 

[sodderboy]

You can order all linear, and slug those that need to be log 
I ended up doing this for a Melcor repair because I did not find a 20K rev-log small shaft pot of any quality.
Mike

 

[ruffrecords]

You can order all linear, and slug those that need to be log 
I ended up doing this for a Melcor repair because I did not find a 20K rev-log small shaft pot of any quality.
Mike

Unfortunately it is the linear ones I cannot get !!! These are for pan pots which I slug to get the required law.

I recently looked at using a linear pot to make a REV LOG pot for a mic pre gain control using a slugged linear pot but unfortunately it cannot be done.

Cheers

Ian

 

[joaquins]

Unfortunately it is the linear ones I cannot get !!! These are for pan pots which I slug to get the required law.

I recently looked at using a linear pot to make a REV LOG pot for a mic pre gain control using a slugged linear pot but unfortunately it cannot be done.

Cheers

Ian

You can't do that because you can't get the linear pots or why?
Usually the mic pre use rheostat rather than a pot, log rheostats can't be made, but there's no problem to do an anti log rheostat. The curve isn't perfect and may have some problems at the ends, but in the most used range it should be good. As usual when the max gain is wanted some problems appears, and may be a good idea to have a "high gain" switch to set it closer, as John Hardy's M1 for example.

JS

 

[JohnRoberts]

Unfortunately it is the linear ones I cannot get !!! These are for pan pots which I slug to get the required law.

I recently looked at using a linear pot to make a REV LOG pot for a mic pre gain control using a slugged linear pot but unfortunately it cannot be done.

Cheers

Ian

You can't do that because you can't get the linear pots or why?
Usually the mic pre use rheostat rather than a pot, log rheostats can't be made, but there's no problem to do an anti log rheostat. The curve isn't perfect and may have some problems at the ends, but in the most used range it should be good. As usual when the max gain is wanted some problems appears, and may be a good idea to have a "high gain" switch to set it closer, as John Hardy's M1 for example.

JS

The difficulty in sourcing a good gain pot for popular mic preamp topology is that you want good adjustment resolution down at the high gain end where it could be single digit ohms resistance, while at the low gain end you want a couple tens of K ohms so preamp can handle hot input levels.

At Peavey we made custom pots with IIRC as many as 4 different screened resistive ink steps overlaid, so the resistance change was smooth from hop off low ohms to low gain tens of K. These pots cost us $0.10 to $0.20 more per, but we used so many it was worth tooling up the special parts to keep the customers happy.

JR

 

[ruffrecords]

Unfortunately it is the linear ones I cannot get !!! These are for pan pots which I slug to get the required law.

I recently looked at using a linear pot to make a REV LOG pot for a mic pre gain control using a slugged linear pot but unfortunately it cannot be done.

Cheers

Ian

It is a rheostat in my mic pre application, What I am saying is you cannot do a rev log rheostat with a slugged linear pot.

Cheers

Ian
You can't do that because you can't get the linear pots or why?
Usually the mic pre use rheostat rather than a pot, log rheostats can't be made, but there's no problem to do an anti log rheostat. The curve isn't perfect and may have some problems at the ends, but in the most used range it should be good. As usual when the max gain is wanted some problems appears, and may be a good idea to have a "high gain" switch to set it closer, as John Hardy's M1 for example.

JS

 

[sodderboy]

Who bought all of the Clarokit assets at the fire sale?  That's the person to schmooz.
Mike

 

[ruffrecords]

Unfortunately it is the linear ones I cannot get !!! These are for pan pots which I slug to get the required law.

I recently looked at using a linear pot to make a REV LOG pot for a mic pre gain control using a slugged linear pot but unfortunately it cannot be done.

Cheers

Ian

You can't do that because you can't get the linear pots or why?
Usually the mic pre use rheostat rather than a pot, log rheostats can't be made, but there's no problem to do an anti log rheostat.

JS

I can get linear pots. It cannot be done because their is no way to slug a linear pot to get  anywhere close to a rev log rheostat. I need it to have the following properties:

1. 47K resistance when fully anti-clockwise
2. 4K7 resistance at the mid point
3. Close to zero ohms resistance when fully clockwise. Does not have to be exactly zero because there will be a 430 ohm resistor in series with it to set the maximum gain.

If you can achieve these three points with a slugged linear pot I would be grateful to know how.

Cheers

Ian

 

[joaquins]

Unfortunately it is the linear ones I cannot get !!! These are for pan pots which I slug to get the required law.

I recently looked at using a linear pot to make a REV LOG pot for a mic pre gain control using a slugged linear pot but unfortunately it cannot be done.

Cheers

Ian

You can't do that because you can't get the linear pots or why?
Usually the mic pre use rheostat rather than a pot, log rheostats can't be made, but there's no problem to do an anti log rheostat.

JS

I can get linear pots. It cannot be done because their is no way to slug a linear pot to get  anywhere close to a rev log rheostat. I need it to have the following properties:

1. 47K resistance when fully anti-clockwise
2. 4K7 resistance at the mid point
3. Close to zero ohms resistance when fully clockwise. Does not have to be exactly zero because there will be a 430 ohm resistor in series with it to set the maximum gain.

If you can achieve these three points with a slugged linear pot I would be grateful to know how.

Cheers

Ian

Sorry, but that looks like what I know as log or audio. From the wiper to what we usually connect to ground when used as a fader, the expected response is something like that. If you are looking those to use as your faders in the poor men passive mixer log is what you are looking for and that's what's no way to make from a single linear trace and loading with a parallel resistor. It works as expected in the usual mic pre gain (linear pot and parallel resistor, usually the pot is 5 times higher and the resistor is 1.2 times higher, which gives a reasonable approach)

JS

PS: I forgot to mention, one of the nice things about Neve trick on that level control is about getting away with linear pots which tracks much better even over the same absolute error, but still the error of the attenuation is much lower. This is a really good thing in stereo tracks, like the monitor output where you expect to see lower drift between stereo channels, for mono applications using a regular log pot should be fine, and in your stereo tracks you could use the Neve trick to get better tracking and you don't need the pan so compromise wins there. With the Neve approach maybe the level range is bigger than the stated, but all this is to another topic you are running and I've assumed the log pot you want is for that.

 

[ricardo]

1. 47K resistance when fully anti-clockwise
2. 4K7 resistance at the mid point
3. Close to zero ohms resistance when fully clockwise. Does not have to be exactly zero because there will be a 430 ohm resistor in series with it to set the maximum gain.

Sorry, but that looks like what I know as log or audio.

Actually its a Reverse Log or Anti-log pot.  Usually from Ye Olde Unobtanium Shoppe  ;D

I forgot to mention, one of the nice things about Neve trick on that level control is about getting away with linear pots which tracks much better even over the same absolute error, but still the error of the attenuation is much lower.

Neve didn't invent this.  It's MUCH older than Neve's birth.

In the 1980's, I did a big investigation of this for Calrec but found the channel matching wasn't much better than a good log pot.

I concluded the most consistent log pots were the P&G faders .. and at a lower price, the better ALPS log pots.

IIRC, the best of the slugged Linears were the Bournes Conductive Plastic ones .. but still not as consistent as a good ALPS.

The application was 4-gang faders for the Calrec Soundfield Mk4.  In the end, we selected ALPS pots and trimmed them in production.

 

[joaquins]

1. 47K resistance when fully anti-clockwise
2. 4K7 resistance at the mid point
3. Close to zero ohms resistance when fully clockwise. Does not have to be exactly zero because there will be a 430 ohm resistor in series with it to set the maximum gain.

Sorry, but that looks like what I know as log or audio.

Actually its a Reverse Log or Anti-log pot.  Usually from Ye Olde Unobtanium Shoppe  ;D

Oh, you are right, it's what log usually do when used as rheostats, but in the other side of the pot. It can't be done loading the pot, it's true.

I forgot to mention, one of the nice things about Neve trick on that level control is about getting away with linear pots which tracks much better even over the same absolute error, but still the error of the attenuation is much lower.

Neve didn't invent this.  It's MUCH older than Neve's birth.

In the 1980's, I did a big investigation of this for Calrec but found the channel matching wasn't much better than a good log pot.

I concluded the most consistent log pots were the P&G faders .. and at a lower price, the better ALPS log pots.

IIRC, the best of the slugged Linears were the Bournes Conductive Plastic ones .. but still not as consistent as a good ALPS.

The application was 4-gang faders for the Calrec Soundfield Mk4.  In the end, we selected ALPS pots and trimmed them in production.
[/quote]

I thought that was the reason why Neve used that configuration, I have to take your word in this because I never made the test myself. What other reason may be?

JS

 

[CJ]

took me a whole day to find one pot for a Hartke bass amp,

DigiKey has about 20 million choices, split shaft, knurled shaft solid shaft, 1/4 inch, 6 mm shaft, center detent, on and on,

what about a rotary sw with your own custom resistor values?

probably more $$ and work i guess,