Ibanez EQ Tone System

[Axldeziak]

This EQ/preamp was installed onboard certain Ibanez guitars (such as the AR500, MC500, ect.) between '78-'80. Later versions were different.

±6 dB Gain, 3-band ±15 dB active EQ (Bass, Mid, Treble)

[ibanez48]

Hey do you have the schematic for this thanks.

[fx-fidden]

I guess this is the schematic: https://www.talkbass.com/attachments/ibanez-3-band-eq-schematic-jpg.3032255/

It seems interesting.
Thanks!

[Axldeziak]

Yep, that's the one I used for the layout.

[ibanez48]

 Could you use this in a guitar I see it’s for bass guitar. Would you have to change any components for guitar.

[Axldeziak]

The EQ Tone system was installed in many different models. In addition to the two standard non-bass guitars I listed above (the AR500 and MC500) it was also used in others such as the 2622, AR3000, AR5000, MC400, MC550, ect.

[ibanez48]

Thanks man

[fx-fidden]

The 220uF should be 220nF.

My emulator says that the Bass frequency is really close to the Midrange frequency.

[Axldeziak]

Thanks for the correction. I updated the original layout in my first post.

Here's a link to an alternate schematic I found of the "old" circuit. The values on it are a bit different. (100nf on the input instead of 1uf, and the Bass cap is 4.7uf instead of 1uf.) It also has the schematic for the "new" circuit that was released later.

EQ Old and New

[fx-fidden]

Thanks.
The 4.7uF should be ok enough.

I'd like to build it, but I'm not going to build it soon. Anyway, I traced it and everything seems ok.

[ibanez48]

I guess I could build this put in a box use it as a pedal I don’t won’t to drill 3 new holes in my guitar. Or can I do this. Is there anything that has to hook up inside the guitar accept for the in and out.

[fx-fidden]

I'd do it in a box, too.
I'm trying to drawn the layout of the new and bigger schematic, but I'm not so good with the protoboard. I'l post it later.

The g-taper pot... I 'm not sure, but w-taper could be about the same, and the tape is very important in this schematic, else you will have almost no effect except at the extreme pot setting.

[Axldeziak]

The G versus W pot thing has been a source of confusion for years.

Electrosmash and Small Bear say they are the same:
https://www.electrosmash.com/tube-screamer-analysis
https://smallbear-electronics.mybigcommerce.com/product-faq/

while Pedal PCB, Panasonic, Bournes, and Alps seem to disagree:
https://wiki.pedalpcb.com/wiki/Potentiometers
https://web.archive.org/web/20100326180320/http://www.panasonic.com/industrial/components/pdf/AOK0000PE1.pdf
https://www.bourns.com/data/global/pdfs/ptv09.pdf
https://tech.alpsalpine.com/prod/e/pdf/potentiometer/taper.pdf

also take note that Panasonic labels them as G (4B), Bournes calls them 4B:B4, and Alps calls them W (4B) but their graph shows similarity to Panasonic and Bournes just for the added confusion.

In the end I don't think it matters.

[fx-fidden]

This is my layout of the new version. Unverified.


I really hope the w-taper will be ok.

[Axldeziak]

I drew up the 2nd old schematic layout with the changes.



Then I took a shot at the new schematic but with no standing resistors.



I was also able to find a '81 Ibanez catalog that shows the frequencies for standard and bass guitar (new).

             Standard          Bass
Bass     230Hz              88Hz
Mid       600Hz             500Hz
Treble     2kHz            1.4kHz

[fx-fidden]

Cool!
Standing resistors are not a problem for me if I need a smaller board.

I can confirm the frequency of the standard.

Waiting for someone verifying one of them!