Phase 90 fet's, zener and pot questions

[JebemMajke]

Yeah, not working here. There is almost no difference until 12 o clock and difference between 3 and 4 o'clock is enormous. :/
Would log pot work better.

[Govmnt_Lacky]

I believe a log pot will work however, you will need to wire it in reverse AND the rate will DECREASE as you turn the pot CW. You will get the desired travel though 

You really should get a rev log pot.

[JebemMajke]

Not an easy task in my country. And i have no intention of ordering rev log from small bear or any other place because with shipping it will cost me more than all other parts combined.

I guess i ll go with log.

[JebemMajke]

How about 50k log?

[samhay]

50k will work, but you will not get as much of a variation in speed. This may be a good thing depending on what you want. You could add a Hi/Lo switch that switches in e.g. a 50k resistor in series to increase the range a bit. 
Either way, you will probably have to tune the value of the 15u cap so that you get the speed you want in the middle of your range.
If you have a 1M pot and the taper with a 1M resistor is not to your liking, you could try adding smaller resistors until you find a good compromise between range and feel.

Govmnt_Lacky - My suggestion to put a 1M R across a B1M pot will work. Read the bottom of RGs secret life of pots (after the section of voltage dividers), which is about variable resistors.

[Govmnt_Lacky]

@samhay

I went through this to great extent when I built my Echoflanger. No matter what taper resistors I threw at the liner pot I had (5M) I could get the resistance down to the required 2M but, I could not get the right travel as I turned the pot. I finally ended up doubling the charging caps in the LFO and halving the rate pot to a more available 1MC pot. Worked out great!

[samhay]

Govment_Lacky - Fair enough and I can relate. Finding the right taper for this type of a LFO is a real PITA.
RG's correct in the sense that you can make a reverse log taper variable resistor. However, my guess is that your 1MC pot worked better is because it doesn't have a proper reverse log taper but rather a taper like the reverse of (3) below. However, did you ever try putting a 1M across your 5M pot to see how close to the stock 1MC you could get? The smaller the resistor (relative to the pot), the steeper the taper will be.

[JebemMajke]

My suggestion to put a 1M R across a B1M pot will work. Read the bottom of RGs secret life of pots (after the section of voltage dividers), which is about variable resistors.

Dude, this is in my device at the moment, and i dont like it. Difference between 3 and 4 o'clock is extreme.

My personal setting of speed on this pedal would be
https://www.youtube.com/watch?v=UkQOT0mZ9ZI
I am aware that he is using pandora's phaser, but it's possible on phase 90. It somewhere between 3,2 and 3,3 o'clock, with this pot. So yeah, rev log is a must here :/

[samhay]

JebemMajke - sorry, let me clarify. My suggestion will work in the sense that it will make the pot a little bit reverse taper. It will probably not work in the sense that it will make it do exactly what you want.
If you want it to behave like a stock Phase 90, then you will need the same type of pot as the schem shows (500kC?). You MIGHT be able to fake one of these with a 5M pot and a 500k resistor, but I'm guessing that a 5M pot isn't that easy for you to find either.
IF the range of the speed pot between 3 and 4 o'clock is sufficient for you, measure the resistance at each end and use a log/rev log pot of this size with a series resistor of the appropriate size.

[JebemMajke]

I've used 500k log, wired ccw. Works great. And I don't mind that its in reverse. Kinda cool
Thanks for the help guys.

[samhay]

Excellent - glad it worked out.

[duck_arse]

So what you are saying that i can not mix b,a and c in phaser? Even if they are matched?

JebemMajke, I'm not saying you can't, but by marking them a b or c, the manufacturer is saying "don't bother trying, they almost certainly won't match". they are selected by their Vgs into the three different ranges, and you'd be lucky to get some a's at the high end of their range and some b's at the low end of their range, for example, in the same handful on your bench. if you manage to measure an "a" to match a "b" in the matcher, go for it.

[JebemMajke]

That's some useful info. Thnx