Axtman 8/30/2016 7:39 PM
Ibanez preamp

I am looking for a schematic for an Ibanez 3eq1cvm3 "Vari Mid" 5 band onboard preamp for a BTB bass guitar. Any ideas where I can find one?

oc disorder 9/1/2016 1:20 PM
Hi Axtman, bit thin on the ground but only reference is on the "chat" site at Elektrotanya
to a Ibanez 3000 bass eq with some hand drawn sketches corrected?

and corrected?

Whole link here

IBANEZ SR3000 aktív gitár
IBANEZ SR3000 aktív gitár el?er?sít? kiakad tápfeszre--MEGOLDVA | ElektroTanya | Service manuals and repair tips for electronics experts

Translated from Hungarian

IBANEZ SR3000 active preamp guitar

Picture of your board and pots that looks like may be available as a drop in replacement?

That's all I could find.
Axtman 9/2/2016 3:06 PM
Thanks OC,

Here is an actual picture of my board. Notice the missing surface mounted component.

Axtman 9/2/2016 3:08 PM
Here is the wiring diagram.

oc disorder 9/4/2016 5:36 PM
'Bout the best I can do without having the board.
Looks like the mystery component goes between the wiper and the inside leg of the bass control.
J M Fahey 9/4/2016 7:06 PM
WHICH missing component?
Please circle it in your board because I find none.

Also: what is the actual problem you are trying to fix?
What are its symptoms?

Enzo 9/4/2016 7:32 PM
Top row of components, sixth position from left I see pads where a part was. Or if you prefer, I see three groups of connector pins, and the missing part is immediately below the left-most pin of the center grouping.

I am assuming that is the one...
J M Fahey 9/4/2016 10:56 PM
I also saw that but am not 100% convinced there is a missing part there, meaning Factory might have decided it´s not needed, I see that all the time, PCBs with unfilled holes, "parts missing", yet revised schematics state NF (not fit) or similar warnings.

And if missing, not sure how; legged parts can flex and crack them, not so legless ones. Somebody messed with that board?
Not forgetting that for an amateur it´s hard to pull SMT parts, even on purpose ... unless he crushes them with pliers and then desolders ends one by one.

And even so, remaining solder should solidify rounded like a half drop, because of capillarity.

In fact, way more questions and doubts than certainties.

That´s why I want to know what seems to be the actual problem, which was never mentioned.

Was the Bass working and malfunctioned in the middle of a song?

Did it roll down stairs?

Was it used to smash a Zombie head?
MarkusBass 9/5/2016 5:22 AM
Quote Originally Posted by oc disorder View Post
'Bout the best I can do without having the board.
Looks like the mystery component goes between the wiper and the inside leg of the bass control.
I think that you are right. Two 6k8 resistors are in series with the Bass pot and there are (were - one is missing) two capacitors from the wiper to outer legs of the pot. There is a big chance that the missing capacitor is the same as the one that is to the left of the first 6k8 resistor. Can you desolder it and measure it's capacity?
Here is similar tone control circuit (with different values):


Axtman 9/5/2016 10:13 AM
Thanks everyone for their help.

Here's the story. I was helping a luthier friend of mine move his workshop. As "payment" he gave me (or I took) stuff that was headed for the dumpster. I got a bunch of broken crap but I did get this nice bass. We were pulling cases out of his basement and opening them up. Sometimes he would say, "Oh this is ______'s guitar. Put a tag on it with his name. I will call him and tell him to pick up his stuff." Sometimes we would open up a box and find a cheap acoustic guitar in 5 million pieces. That immediately went into the dumpster. My friend pulled out a box and opened it up to reveal an Ibanez BTB 405QM five string bass in very good condition. My friend said a guitar store gave it to him 12 years ago (when he moved into the facility he is moving out of). Since they never bugged him about it, he gave it to me. Score! This bass listed for a grand!

I took the bass (and my small pile of crap home). I plugged in the bass to an amp and got no sound. I checked the battery compartment and the batteries were dead (12 year old batteries duh!). One of the battery leads was broken. So I opened up the back panel and soldered in a new cable. To my horror I saw extremely rusted potentiometers. I mean like it must have been stored under a dock! As I was taking the wiring assembly out wires would break off due to corrosion. How did it get so rusty when the parts on the outside of the bass look brand new?

After a few dips in the ultrasonic pen cleaner and a wire brush I just decided that I was wasting my youth and beauty. It would be so much easier to just buy a new wiring harness and preamp. Well that's why I THOUGHT! So far I have had no such luck finding one. I though for sure that a big guitar maker (Ibanez) with a bass that has been in production for over 20 years would have spare parts. Nope. I tried Googling, Ebay, Reverb, etc. with no luck. So it is back to repairing.

I'm going to lubricate the pots and hook everything back up. Maybe the damn thing will actually work. My friend Mark Black recommended that I just solder a 0.1 ceramic cap across where the surface mounted component is missing.

Stand by for future episodes.
MarkusBass 9/5/2016 11:13 AM
As I said before, you can easily measure the other capacitor and it seems to me that this should be rather in 22-47 nF range.

oc disorder 9/5/2016 11:16 AM
"My friend Mark Black recommended that I just solder a 0.1 ceramic cap across where the surface mounted component is missing."
Well to make it easier why not simply solder a greencap across the pot? I assume that those smd caps are 0.1 ... commonly used
for decoupling? .. not sure if the color orange/brown? means anything ...some gaps in my smt knowledge.

Surprised Ibanez don't have replacements although I haven't been keeping up with the (whoever it is now... Smiths?)!

I suspected some corrosion , hopefully there's not any other faults... the board/pu should work without that cap anyhow.

Good find ! Someone has to do it although I was hoping it was my turn !
J M Fahey 9/5/2016 3:48 PM
Internal corrosion must have been caused by 12 y.o. dead batteries.

Try to repair it; absolute worst case there are generic potted active bass preamps available as spares, get one which matches your current pickups and needs 5 pots (or whatever yours has).

Or you can build your own if you dare.
Jazz P Bass 9/5/2016 6:09 PM
My feeling is there never was a component there.
g1 9/5/2016 7:17 PM
To me, the upper pad looks like there was something there. However, it could have been removed at the factory (or later) for a reason.
Mark Black 9/10/2016 2:41 PM
As has been said, the preamp should likely still work to some extent even if there is indeed a missing cap.

I think there are bigger problems going on: the corrosion visible in the photo immediately reminds me of other surface mount automotive PCB's I have worked on which had numerous discontinuities everywhere. I think if the solder mask is scraped off the darkened areas of the traces the true extent of the horror will be revealed, and it probably exists underneath components as well as at the interfaces between the traces and solder pads. Indeed some of the components on the automotive boards were separated by corrosion from the solder blobs at the ends and the parts only held in place by the assembly adhesive dots underneath.

Could be a very deep rabbit hole indeed...
J M Fahey 9/10/2016 7:57 PM
Build this :

You can replace the inductor with a single transistor gyrator.

Or design your own: basically the blend pot and gain stage, and replace Bartolini 3 band EQ by a simplified Boss or MXR 6 or 7 band Grapic EQ chopped down to 3 bands.
Pick the 3 bands most useful to you.

EDIT: found this which makes it very doable.
With real inductors, of course:

didn´t check it wire by wire, might match this wiring diagram:
MarkusBass 9/11/2016 1:11 AM
The remark regarding the corrosion is very important. You can clearly see places on the board that look very suspected. Like this one:
If you fail to make the preamp working, I could make such a preamp for you (I mean the exact copy of the original preamp). But then you would need to send the preamp to Poland . I can see the schematic from your photo but some traces are under opamps and other components.
Is the MID frequency pot in good condition? It is very special potentiometer and I'm not sure whether it can be purchased. Everything else can be purchased without any problems.

MarkusBass 9/12/2016 2:11 PM
The Vari-mid part of the preamp looks like this:
I redrawn the Hungarian schematic posted previously. Once it is redrawn, you can clearly recognize typical topology of a parametric equalizer.
On your board just few components are different: you have 2k resistors instead of 2k2, 430R instead of 1k, 5k6 instead of 4k7. Nothing very complex.
And the BASS/TREBLE part looks like this:

One of the caps near the BASS pot is missing. I think it is exactly as the other capacitor - you can just measure it and solder exactly the same value in the place of the missing component.

MarkusBass 10/30/2017 5:59 AM
I wonder whether this preamp was ever fixed? It seemed to be an easy task .

Axtman 10/30/2017 12:19 PM
The preamp/controls/wiring had a lot of issues. Instead of spending the rest of my adult life repairing it, I installed a new preamp (I forget the exact model) that I ordered from Best Bass Gear. The new preamp had the exact control layout and configuration. I sold the Ibanez bass to a friend of mine for a very reasonable price (family discount). He LOVES the bass and it has become his main gigging instrument. So it was a Win-Win!
MarkusBass 10/31/2017 12:55 AM
Thanks for the info. But it's also a pity that you haven't try to fix the old one. I would say that it required just 1 hour of work (including missing components, wiring problems and corrosion problems).
Anyway, it's good that it's now fully operational and it's used on a daily basis.

Axtman 11/7/2017 5:33 PM
I'm the type of guy that will spend hours and many dollars trying to repair a part that I could order on line for less money.

This preamp was toast. It had a lot of problems. The wires kept breaking on it the more I handled it. I was not set up to do surface mount component repairs. The controls were rusted and one was frozen. I just decided it would be better to let it go and buy a new part. When my friend walked away with the bass, I wanted to feel confident that he would not call me up later to say that it was working.