Lorlin wiring for a 312(newbie here)

[Cosmonaut]

After some days looking for the correct 22k rev log for my mitsos 312...I've decided to use the lorlin rotary switch 1 pol 12 positions.

http://es.mouser.com/Search/ProductDetail.aspx?R=CK1454_6.35X20.7MM_FLAT_SHAFTvirtualkey12200000virtualkey10WA364

But I have some newbie doubts:

First at all, I´m looking for the right resistor values, but the stepped atennuator calculator provided by Gyraf is hosted by really bad website  
(I can't open it correctly), any other calculator?

Secondly, a rev log is simply put the resistors in the other way?from 11 to 1?

Thirdly, normally a pot wiring has 3 terminals, CW, center y CCW. In this case with the switch I have only two terminals, one in the center of the switch and other in the final pin, in this case number , where is the third terminal?

Some help with this??
I have been looking the thread about "Lorlin wiring in the greenpre"...but I'm still having this doubts.

 

[Rybow]

Bob Schwenkler has a nice stepped pot calculator on his site. You can grab that here www.bicyclerecordings.com/312. Its an excel spreadsheet. Works quite well.

If you reversed your resistor values, you would be turning down the gain by turning it clockwise, and turning it up by turning it counter clockwise. So all you would be doing is changing the direction on the control, not the taper. Taper refers to how much attenuation/gain is applied with each step in the control. Rev logs will apply most of their gain in the first 1/2 of their travel or so, with finer gain control later on. Log pots are the opposite offering finer gain control in the first half of their travel with big jumps near the end. If I am wrong on this, please correct me.

You have a couple options for wiring up the switch, but the best one for noise is to do it in a ladder configuration. This allows you to switch in one resistor at a time separately as opposed to adding them together. Do a search for wiring stepped attenuators, and you should come up with lots of info. Sorry I can't be really specific here.

 

[Cosmonaut]

Thanks!

The stepped gain calculator is so complete...but I need schematic from mitsos board to identify Rf and Ri, equally I'm still a little confused...how to wire a rotary switch as pot, this one should be one of those things only asked by a newbie...


(this year I begin studying electronics at my 28 years old...I hope to learn these things!)

 

[mitsos]

bob's spreadsheet is very good and gives a lot of info.  But, IIRC, there is one caveat since it is made for his boards, which means it gives you distinct resistor values for each gain step, not values that will mimic a rev log pot.  What this means is you connect one end of each resistor to the switch, then connect all the other ends together. Solder one wire to the "connected-together" ends of the resistors and another to the pole of the switch.  

If you notice on the 312 PCBs, 2 of the pot pads are connected. Treat those as one pad (so pretend there are only 2 pads for the pot/switch). One wire of the switch goes to one pad, the other goes to the other. It shouldn't matter which goes to which, just make sure the largest resistor is in circuit when the switch is in the counterclockwise position, and that they get progressively smaller going clockwise.

HTH! cheers!

EDIT: oops, forgot this: On my PCBs,
Rf = R17
Ri = R18

 

[Cosmonaut]

Thanks a lot Mitsos, so much clearer now...about connecting the Lorlin, equally I would like to know how to calculate the resistors values that will mimic a rev log pot.

Thanks again,

I'm preparing the materials, as soon as I have the boards I'll tell you how is going for a total newbie making a 312.