Author Topic: Overdrive circuit mod help with JRC4558  (Read 865 times)

crafter57

Overdrive circuit mod help with JRC4558
« on: February 02, 2018, 11:14:45 PM »
Hi Folks, I'd like to ask for advice or suggestions on how to modify my Hammond x5 organ circuit to include an overdrive circuit like on the Korg CX3 analog version. I would like to modify either the "brilliance pot" taking it to overdrive or if possible adding it to the "EXT in" Q4 amp portion or switching from "brilliance" to "overdrive". I'm not sure if the jrc4558 from the CX3 uses a bipolar supply or not but +/-15v is available from the X5 circuit.
Any help will be greatly appreciated, thank you in advance



antonis

Re: Overdrive circuit mod help with JRC4558
« Reply #1 on: February 06, 2018, 12:10:10 PM »
I'm not sure if the jrc4558 from the CX3 uses a bipolar supply or not
Considering its bias supply, it uses single 12V..

Of course you can feed it with bipolar +/- 15V as far as you connect its non-inverting input to GND..
(instead of +6V..)
« Last Edit: February 06, 2018, 12:11:51 PM by antonis »
Can't follow your signature changes, Stephen..!!

crafter57

Re: Overdrive circuit mod help with JRC4558
« Reply #2 on: February 08, 2018, 12:54:33 AM »
I wasn't sure how to connect it. I will try with pin3 to Gnd. Do you think this overdrive will work inserted somewhere in the other circuit? I'm trying to get away from buying a pedal when with a few components I can get some overdrive, but I'm confused in doing this mod.

anyways, thank you

antonis

Re: Overdrive circuit mod help with JRC4558
« Reply #3 on: February 08, 2018, 07:16:05 AM »
Of course it could be substitute Q4 circuitry (eliminating also the need for Q5 buffer) but I'd suggest to first determine/find "unkown" resistor value (from what impedance is driven..) and listen it as stand-alone overdrive..
(you may not like it's asymmetrical clipping and/or want to replace/shunt D1 with a small value cap to create a low pass filter - a high pass one should already been formed from C14 & unkown resistor combination..)

edit: I've just noticed you actually have +15/-14 supply so you should need some ground off-set for pin 3 if you don't want asymmetrical clipping of negative signal peaks on high gain settings..

P.S.
For that kind of project I'd suggest a more "plain" overdrive.. :icon_wink:
(like replacing R26 with a pot, tweaking R25 value and by-passing it with a cap.. - exact values are depended on your taste of added gain..)
« Last Edit: February 08, 2018, 07:19:59 AM by antonis »
Can't follow your signature changes, Stephen..!!

Hatredman

Re: Overdrive circuit mod help with JRC4558
« Reply #4 on: February 09, 2018, 05:56:30 PM »
Why not an external overdrive pedal?

.sig goes here.

Kirk Hammet invented the Burst Box.

crafter57

Re: Overdrive circuit mod help with JRC4558
« Reply #5 on: February 13, 2018, 06:02:38 AM »
Fellas, I've looked at this circuit but I'm not really well versed at modding circuits. I've built the muff fuzz op amp version and tried  connecting that circuit various ways in the original but it also doesn't work well, not even at the output.
so maybe an external pedal will have to do. probably a EHX tube overdrive, nothing harsh..

any other comments or ideas will be appreciated.
thanks