Is There A Dimebag Darrell Wah Schematic? (DB-02)

[Paul Marossy]

I've got a malfunctioning Dime DB-02 wah on my bench. It is semi-functional, but you have to really hit the strings hard before any sound comes out and then what does come out sound like a misbiased transistor or opamp. It has SMT components on it, and there is two transistors and two opamps on the PCB.

Does anyone know if a schematic exists for this model? It sure would be helpful! I want to try and fix it if I can before I cannibalize it... 

[cd]

FYI DB-01 is here:

http://forum.musikding.de/gallery/displayimage.php?album=8&pos=1

[Paul Marossy]

Bummer. That DB-01 circuit is quite different than the DB-02 circuit. 

Looking at the DB-01 schematic is of some help, though. 

[kusi]

hi paul,

the db02 is a db01 with fixed pot-values, right?
the basic-circuit should be similary to the db01.

if you want, i send you the orginal factory schematic.


greetings, kusi

[Paul Marossy]

the db02 is a db01 with fixed pot-values, right?
the basic-circuit should be similary to the db01.

I guess so...

EDIT: The DB-02 does not have the LED circuit(s), the sweep cap selector switch, or the "Q" control. That's the most obvious differences that I can see right off the bat.

if you want, i send you the orginal factory schematic.

That would be great! You can send it to: psalmist AT att.net

[Paul Marossy]

OK, I got a factory schematic for the DB-01, but I am still needing a schemo for the DB-02... 

And before anyone asks, no, I am not going to share it - per the request of the individual that sent it to me.

[kusi]

if you want, i send you the orginal factory schematic.

That would be great! You can send it to: psalmist AT att.net

sorry, i talked about the 01

could you post some big pictures? maybe we could analyse the differences...

best greetings,
kusi

[Paul Marossy]

could you post some big pictures? maybe we could analyse the differences...

I can try to take some pictures of it. My camera isn't the highest quality, though. With everything being SMT components, with no markings on the PCB for individual components, it's hard to follow what's going on. It would be hard to capture all of this in pictures. But I'll see what I can do.

I do know that the LED switching system is absent (because there are no LEDs), there is no 1K Q control and the 6-way rotary switch that selects the different sweep caps is not present. From what I can see on the PCB, there is an opamp input buffer, the usual pair of transistors and there appears to be an opamp output buffer as well. Except everything is SMT components.

[Paul Marossy]

OK, here are some pictures - not super high-quality, but it gives the general idea.

The opamps are marked 33178 2ADWM
The transistors are marked 1R with something following it that looks like a U or a C lying on its side.

[kusi]

hello paul,

thanks for the pictures! i drawn a new schematic for the DB02 - but it could have errors. the basic-circuit should be correctly.

IC1a is the input-buffer, IC1b is the impedance-converter for Uref.
IC2a is the output-buffer, IC2b is the boost-stage after the Wah-circuit (not used as booster)
the MC33178 is a normal dualOP, in SMD-package.
the both transistors are MMBT5089, this is the SMD-verison of the 2N5089. this is a high-gain NPN-transistor. (search the datasheet for pinout)

first, check the incomming voltage at the Z-Diode. it should be around 9V. then, check the voltage at IC1b pin7. this is Uref, 4.5V if these are correctly, you have to analyse the signal-flow with an osciloscopeand a sinewave-generator. and tell us the voltages at the collector, base and emitter of Q1 and 2!


maybe you can correct my schematic? SMD-PCBs are easy to analyse, they look only complicated.  i work with SMDs every day.

i think, that one of the Transistors has a defect.


best greetings,
markus

[kusi]

here a link to the DB02 schematic:
http://forum.musikding.de/gallery/displayimage.php?album=8&pos=2

here a link to the datasheet of the MMBT5089 / 2n5089:
http://www.ee.washington.edu/stores/DataSheets/transistors/2n5088.pdf

here a link to the datasheet of the MC33178:
http://www.onsemi.com/pub/Collateral/MC33178-D.PDF

[Paul Marossy]

Thanks kusi! I will go thru that schematic and compare it to my own schematic that I am working on right now. I also have a feeling that it's a bad transistor. I will check thiose voltages and report back. 

[Paul Marossy]

Well, I couldn't get the blasted thing to work, so I just parted it out. 

For the record, I'll share my findings. I replaced both 2N5089s with some regular ones (not SMD types), and that was a pain but I did it. Anyhow, it was somewhat improved, but the signal was still lost if the guitar volume was anything less than full on and then the sound was very distorted. So I measured the voltages on the transistors, and here is what I found:

Q1
E = 0.09V
B = 0.63V
C = 4.39V

Q2
E = 3.62V
B = 2.90V
C = 8.17V

The battery voltage was 9.42V and the voltage at the input to the zener diode was 8.54V, which is the lower end of the ranges that the 1N5293s fall in. I forgot to measure Uref voltage, though. 

Does anything sound funky? I think it may have been one of those opamps, which is why I decided to trash the circuit board - just too difficut to work with SMD opamps (translation: I don't have the patience for that!).