Vintage Ibanez inductor EQ need help choosing the right pots.

[Vyvyan]

Hi I'm building a clone of this 70s Ibanez EQ it calls for G20k pots (originally fader with center detent)

I have plenty of center detent G50k pots but no 20k.

Can I use the 50k pot without any poof effects on the circuit?

Any recommendations on tweaking the circuit to better accommodate 50k pots?

Thanks!

 

[Script]

Lin pots, I guess.

If 5 X 50k Lin in circuit, I'd probably expect a change in overall gain (R14), maybe also changes on the LC filters... Yet, I'd say try.

Bourns have 20KB at Mouser. Not sure about centre detent though.

And some old Behringer units (MDX2000, I think) use 20KB with many detents.

 

[dai h.]

couple places (U.S., Europe, Japan) sell 20k'W' (I understand this to be the same half audio/half reverse audio as 'G') for Tube Screamer tone control replacements :

https://smallbear-electronics.mybigcommerce.com/alpha-single-gang-16mm-solder-lug/

https://www.musikding.de/Alpha-pot-angled-pc-mount-20k-W

https://www.banzaimusic.com/ibanez-8vrc3003.html

https://www.sakurayadenkiten.com/eshopdo/refer/vidalphapot001_A13-16.html

(my novice understanding) is that if you use a linear where you ideally want to use a G/W, you have good control near zero but once you move higher (or lower) beyond a certain point (where it should curve and slow the change of resistance with rotation) you won't have as good a control over the change. I also recall reading from someone (on the Gearwhatever forum) who was apparently involved with development of an API graphic EQ that some of them used a slide pot with more sections, so some G/W tapers may be better than others (as with audio pots that have more sections on the resistive track besides the minimum of two).

(edit: okay, found the link with the post about the taper: )

There is another change that I have never seen mentioned, that is more
important than it might seem at first. Both the 560 and 560A use
special S-taper controls. The resistance curve has an "S" shape. It
is symmetric but is steeper in the middle, and relatively slow at the
ends. If it used linear pots, the control would be all scrunched toward the ends. The use of the S taper also allowed a higher resistance, resulting in lower noise and the "proportional-Q". The 560 used Alps pots. The 560A used Noble pots. The Alps pots were not available in the small quantities we needed. The taper is a little different, but the same at the calibration points. The Alps taper really looks like an "S". It is all curved. The Noble taper looks more like piecewise linear with rounded corners. This was not a conscious decision, and was considered to be a negative at the time, but we really didn't have a choice. It points out an issue that is often overlooked in products like EQ's ... A production change beyond the control of anyone who should know can significantly affect the sound.

source:

https://gearspace.com/board/so-much-gear-so-little-time/71012-api-graphic-eq-560-560a-560b.html

 

[Script]

This one? S-curve


Could stick five resistors of 20K in place of the pots (CCW to CW) first to measure unity gain.

 

[capacitorless]

I'm kind of in the same boat except I'm assessing whether to try converting a 50k W-taper pot to 10k.

These are found in the 4-band eq section of a Yamaha PM2000 channel strip (first/top page, right half of schematic).

Edit: I'm not at all 100% in on this (may wire up a JLM-type inductor eq into each of the 2 mid sections and call it a day) but I'm interested to see if this can be done. G taper is log on one side of the center detent; W taper is log on both sides.

 

[dai h.]

yeah, that's the one. So (variously described as) 'G', 'W', or 'S' apparently.

This one? S-curve

View attachment 146300
Could stick five resistors of 20K in place of the pots (CCW to CW) first to measure unity gain.

in this chart '4B' is described as 'W':



additionally, it looks like 'G' can also refer to a 5% audio taper (possible source of confusion) :


here is a related discussion (check out post #3 about adding the tapering (slugging) resistors to a linear pot--maybe that will work?) :

https://groupdiy.com/threads/w-type-potentiometer.56985/

 

[Script]

Had found the S-curve graph here:
https://electronics.stackexchange.com/questions/76313/does-anyone-have-a-g-pot-graph#76328

Says it's from a Panasonic document -- and that Alps call it a W curve. But there is S curve and inverted S (inverse S).

Adding resistors to a pot (slugging) can create "inverted S" curve but not "S" curve, I think.

With rotaries, any curve is possible. But rotaries on an FX pedal?

 

[dai h.]

Adding resistors to a pot (slugging) can create "inverted S" curve but not "S" curve, I think.

so would that end up as if you mistakenly wired a pot backwards? I've never tried it myself but there are some web articles outlining this technique, such as this one:

https://electro-music.com/forum/phpbb-files/pot_taper_amz_168.pdf

With rotaries, any curve is possible. But rotaries on an FX pedal?

the original Ibanez "Renometer" (IIRC) is just a graphic EQ with inductors (instead of the later more typical "gyrators" made with op amps) and uses slide pots, so I suppose it could be weird. The OP will have to work out if it makes sense or not. Oh wait, maybe you meant a rotary switch? This is the cheapest (switching/make before break) one I know that has lots of positions (23)--USD$14.37 at today's exchange rate :
(has phenolic wafers instead of glass epoxy or ceramic)

http://www.monta-musen.com/shop/products/detail.php?product_id=403

Unless there's something really special, seems much cheaper to buy a used Boss GE or whatever suits your fancy.