Rotary pot vs blend pot

[rangermaster]

Hi there. I'm going to build a texas ranger soon but i have some questions.

1. Can i use a normal pot instead of the rotary pot? And can i wire it like the photo in the attachement? Will this do the same thing? And what value pot is best for this ?

2. Should the transistor bias be set on +7v like a rangemaster ? (BC547 NPN pedal negative ground)

Thanks.

[antonis]

1. Can i use a normal pot instead of the rotary pot?

Unfortunatelly, No..!! 

Rotary switch selects between different values series caps (posistions) where a "normal" pot acts as resistive voltage divider..

On ther other hand, a pot (wired as variable resistor) could act as part of input HPF (DC isolated from bias configuration) but you'll have to take into account bias configuration and BJT input impedance, also..

P.S.
If you don't have a 3 position rotary switch, you can implement a SPDT (on-off-on) by wiring series/shunt caps respectively..

[GGBB]

You can also use an SP3T - or DPDT on-on-on - toggle switch in place of a 3-position rotary switch:

[abc1234]

Uhh, I don't know what the others are on about—yes, you can use a pot.

However, a better version is to use it in series with the high value cap as a variable resistor:

• On max the resistance will attenuate the signal coming through the higher cap so it can't be heard at all/much.
• On min. there's no resistance so you'll get the increased low end and volume.
• In between the two extremes you'll obviously be able to increase and decrease the low end and volume.

The way it's wired in your drawing it'll work as above at the extremes, but in between you'd have resistance added to both caps, which seems unnecessary and could result in making the input quieter as you sweep between caps.

One thing to bear in mind—there's a difference in volume between a 4.7nf and a 100nf, so you might want to use a high value pot to ensure the signal coming through the 100nf can't be heard on min.

I've used the setup I recommend with a 10nf and a 1uf, and found I needed a 1M pot, and even then on min. there's slightly more low end coming through than without the 1uf on the input. (It sounded like the 10nf was maybe a 20nf, which wasn't a big deal for my circuit.)

If you also have this issue, try putting a resistor between the signal and the 100nf.

And obviously breadboard before soldering. 

[GGBB]

Uhh, I don't know what the others are on about—yes, you can use a pot.

Would you kindly share the specifics - can you provide a schematic?

EDIT: Never mind - for some reason I originally didn't see the first diagram.

As Antonis stated - and you repeated and elaborated - that is far from ideal. His variable resistor suggestion - same as your "better version" - would be far better if using a pot in place of a switch.

So I think we are all "on about" the same thing here. 

[antonis]

I suppose abc1234 talks about something like "caps blender", like below:



It could be a solution but, IMHO, it's rather complicated due to R1/R2 involvement in signal transfer function in conjunction with following stage input impedance..

Unless, of course, he means something like "resistively variable equivalent capacitor"..
(which can't be obtained without the implementation of general impendance converter..)

[rangermaster]

Thanks for all the replies ! Really helpful.

I think i'll use a rotary switch pot for this build and experiment later with a pot to hear what the differences are.

In the attachment you can see the rotary switches i have.. i also have some spdt switches that i can use maybe ?

If there's anyone that can draw me a layout on how to wire 3 caps on a rotary or spdt switch ? I'm totally new with these kind switches.

Thanks!

[antonis]

Can't say for first rotary switch but the second one (black plastic shaft) seems to me like a 3 pole - 3 toggle one..
(3 X 1 input -> 3 outputs..)

Of course you can use it for 3 different series caps..
(although the other 2 X 3 setting will be unused..)

P.S.
SPDT switch can also be used if only is a ON-OFF-ON type..
In the mean of there will be a cap permanently wired on middle lug, which cap will be set in series when switch is OFF..
For either ON toggle setting, that cap should be set in parallel with each individual cap resulting into respective equivalent capacitance..)

[ElectricDruid]

Can't say for first rotary switch but the second one (black plastic shaft) seems to me like a 3 pole - 3 toggle one..
(3 X 1 input -> 3 outputs..)

It might be, but those Lorlin rotary switches are available in a bewildering array of options, so it might be 3x4 instead. Three middle pin and 12 outside pins makes me think that's likely.

https://lorlinelectronics.co.uk/catalogue?filter_switch-category=rotary-switches

[antonis]

and 12 outside pins

Very true and correct..!!

P.S.
Where "toggle" put "throw" above..
(late night here..)

[abc1234]

I suppose abc1234 talks about something like "caps blender", like below:



It could be a solution but, IMHO, it's rather complicated due to R1/R2 involvement in signal transfer function in conjunction with following stage input impedance..

Unless, of course, he means something like "resistively variable equivalent capacitor"..
(which can't be obtained without the implementation of general impendance converter..)

Using your image, make C1 the lower value cap and remove the resistor. Make C2 the higher value cap and replace the resistor with a pot wired as a variable resistor.

I used this set up for a circuit based on the Fuzz Factory 7 instead of using a rotary switch—far less "complicated" and time-consuming than wiring a rotary; much more sonic variety; no issues.

Like I wrote, instead of worrying about what might happen, breadboard ideas and discover what actually occurs.

[rangermaster]

Thanks for the replies. I am going to use a 4 position switch now and want to use 4 caps to choose.

In the attachment is a photo of a switch i have. Can anyone draw me a diagram on how to wire it? I can't find any useful layouts.

4 tone caps, input and output wire.

Thanks

[BJM]

I didn't see an attachment but I suppose it's the picture of the Lorlin switch you posted earlier (3P4T rotary)?

Here's a quick drawing (sorry, I don't have any fancy software for this).



Just noticed I forgot to number the pins... 1 to 12 and A to C from left to right.

Btw I don't think you'll need a 3P4T, unless you want add some leds..... You could also use a 2P4T, as in this link:

https://www.musikding.de/Rotary-switch-2P4T-print

This switch is a lot smaller than the Lorlin switch so it can save some space in your build 

[rangermaster]

Here it is sorry. 3 pole 4 positions

[BJM]

No problem .

I 'm not familiar with this type of switch ( I don't know how the pin's connect ) but the schematic should work also,

[antonis]

[rangermaster]

Thanks for the help! I'll try that!

[BJM]

Ah, OK Antonis! I didn't notice it was supposed to tie the ends of the capacitors together.

[GGBB]

If you don't like a bulging bunch of leads soldered together like me, you can use the unused terminals of the switch to keep things a bit neater and less prone to breaking from moving around:



Whatever floats your boat.

[rangermaster]

If you don't like a bulging bunch of leads soldered together like me, you can use the unused terminals of the switch to keep things a bit neater and less prone to breaking from moving around:



Whatever floats your boat.

Awesome thanks !