# Replacing transistors in pedals?



## devnulljp (Mar 18, 2008)

So, can I just throw some random BC109Cs into a wah (or fuzz?) pedal in place of the trannies that are already in there and hope it will work better?
What does biasing and matching actually consist of from a practical perspective (_i.e._, what do you actually do)?

Can anyone explain non-polarized/ non-electrolytic vs. polarized electrolytic caps? And how to find the latter? 

Resistors are resistors right? No different types, and they're not polarised right? 

Thanks


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## Guest (Dec 1, 2008)

All start. But wait for mhammer. He can probably explain it better than I can. :smile:



devnulljp said:


> So, can I just throw some random BC109Cs into a wah (or fuzz?) pedal in place of the trannies that are already in there and hope it will work better?


Does the wah in question have BC109s in it already? Otherwise: probably not. Some transistors can be used as functional equivalents of others though. Depends. What's in there now?



> What does biasing and matching actually consist of from a practical perspective (_i.e._, what do you actually do)?


Where should I start -- do you understand the basic premise of an NPN type transistor? Collector, base, emitter? Typically a current flows from the collector to the emitter if a current is made to flow between the base and the emitter. If you ignore leakage the current flow between emitter and collector is equal to the current flow between the base and the emitter multiplied by the hfe value of the transistor. The bias generally refers to the voltage you need at base to effect a collector current you have in mind. It's the practice of setting the operation of the transistor to meet the needs of your design.



> Can anyone explain non-polarized/ non-electrolytic vs. polarized electrolytic caps? And how to find the latter?


All capacitors store and release energy. The capacitance tells you how much energy it can store before it gets released. A polarized capacitor has two distinct operating poles: +'ve and -'ve. Charge can only be stored and released from and to the appropriate pole. As such you have to place it in your circuit correctly. A non-polarized capacitor can operate in both directions. Electrolytic refers to the materials used to construct the capacitor. The material choice changes the operating conditions of the capacitor. Electrolytic capacitors, for example, can be had in much higher capacitance values than non-electrolytics.



> Resistors are resistors right? No different types, and they're not polarised right?


They have no polarity, that is correct. But they do have tolerances. And power ratings. For most pedal applications the 5% tolerance and 1/4W power rating are sufficient.


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## greco (Jul 15, 2007)

devnulljp said:


> So, can I just throw some random BC109Cs into a wah (or fuzz?) pedal in place of the trannies that are already in there and hope it will work better?
> 
> What does biasing and matching actually consist of from a practical perspective (_i.e._, what do you actually do)?
> 
> ...


Trannies is usually the short version for Transformers AFAIK

I don't think you can do this "randomly" as the transistors would have to have similar/same specs for replacement.

"biasing" is part of the circuit design and "matching" refers to what I wrote above 

...again.. AFAIK. 

I'm just learning about electronics myself.

Polarized caps MUST be soldered into the circuit using the correct polarity. Other caps ar not polarized and therefore can be soldered with either leg to negative or positive.

Resistors are not polarized, but there are many types.

Does this help at all?

Others will give you more detailed information..I just don't have the confidence to get into long descriptions.

Cheers

Dave

Ian C. and I were typing at the same time...his post was far superior to mine !!


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## devnulljp (Mar 18, 2008)

Thanks guys. I have alot of homework to do, obviously.
I was reading a thing about modding to Clyde specs, and I have an old Dunlop Crybaby sitting here doing nothing interesting so I thought it might make a good project. 

This page http://fuzzcentral.ssguitar.com/mccoy.php talks about using BC109Cs in there...and they're easy enough to come by. Ijust don't knowwhatto actually _do_ with them. Dumb, I know. 

BTW, I used to live in Chiang Mai in Thailand, and a _trannie_ was something else entirely


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## greco (Jul 15, 2007)

devnulljp said:


> Thanks guys. I have alot of homework to do, obviously.
> I was reading a thing about modding to Clyde specs, and I have an old Dunlop Crybaby sitting here doing nothing interesting so I thought it might make a good project.
> 
> This page http://fuzzcentral.ssguitar.com/mccoy.php talks about using BC109Cs in there...and they're easy enough to come by. Ijust don't knowwhatto actually _do_ with them. Dumb, I know.
> ...


Have you compared the Crybaby schematic to the Clyde schematic?...or are you going to build the Clyde board and use the Crybaby to house it?

as Jimi might have said "You dig?"

Dave


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## fairfield (Oct 12, 2008)

*Biasing* is indeed the action of setting the operating point of your amplifier. If the goal is to design for linear(ie. undistorted) gain, biasing will position your signal in a way to allow for maximum voltage swing on both sides (+ -). 

If you didn't bias(base at 0V) your NPN common emitter amplifier, you would only amplify signals above ~0.7V (forward voltage drop of the Base Emitter diode) and nothing below that.

Consider yourself doing jumping jacks with your shoulder against a wall. The results could be disastrous. If only you could move a few feet away, you could exercise in peace. This would be like biasing your body in the room.

*Matching* is usually taking 2 or more components of the same part number and trying to find similarities between them. This is necessary for balanced amplifiers, class AB and B amplifiers, stuff like that. Not really necessary here.

What were interested in is replacement. I quickly looked at the datasheets of BC109s and 2N3904s(assuming this is what's inside your Crybaby) and they look close enough. The characteristic you're interested in is hfe, this is the gain of the transistor.... ignore the rest for now.

Polarized caps can be purchased anywhere they sell electronic parts. There are 2 things to watch with polarized caps, voltage and polarity. Both of which can make them go PFFF, or POW if not respected. Loads of fun.

To answer your question, yes you can simply swap out the transistors in your Crybaby and hope it will work better. Just pull up the datasheets of both parts, and compare the pinout. They should be the same, but Murphy will pull out the ruler if you take it for granted.

The link you posted talks about more mods than just the NPNs. It seems the whole filter is tuned differently in both circuits. This has nothing or little to do with transistor selection. But you never know... sometimes, you can't explain why it sounds so damn good.


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## mhammer (Nov 30, 2007)

In a wah application, the actual gain is of minimal interest since the wah effect does not depend on how much gain. That being said, when I threw together a wah for myself a couple years ago, I was disappointed at the nature of the sweep. Admittedly the inductor was somewhat higher than typical (somewhere in the750-800mh range) but the resonance and width of sweep was very poor. Someone suggested that the gain of the first transistor in the circuit needed to be tweaked via the emitter resistor. So that's what I did. Lo and behold, the wah sprang to life and has a lovely throaty sound.

So, does transistor hfe and such matter when it comes to wahs? Perhaps only in so much as it would require adjustment of other components to bring the circuit to life.

In fuzzes, that can be another thing. It would also depend on the nature of the circuit. After all, "fuzz" is a pretty broad category. In a case like the Fuzz Face (see technology of fuzz face paper at www.geofex.com), or any of the its cousins (e.g., Tonebender, Fuzz Factory, et al), it is the *interaction* between the gains of two transistors that produces the qualities of the effect, so one needs to select for hfe, and possibly even other parameters carefully. In the case of something like a Big Muff, the stages operate independently. IN the case of something like a Superfuzz, Foxx Tone Machine, or any other octave-generating fuzz, there will be a pair in there whose hfe needs to be matched to achieve optimum octaving.


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## Ripper (Jul 1, 2006)

I took an old crybaby a couple of years ago and tried different trannies in it to see the effect and I wasn't impressed. I certainly didn't notice enough of a change to warrant the swapping. There are tons of mods for the wah that will do far more than swapping out the transistors.


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## mhammer (Nov 30, 2007)

Ripper said:


> I took an old crybaby a couple of years ago and tried different trannies in it to see the effect and I wasn't impressed. I certainly didn't notice enough of a change to warrant the swapping. There are tons of mods for the wah that will do far more than swapping out the transistors.


Mmm-hmmm. Again, I encourage one and all to read RG Keen's lovely and informative treatise on "The Technology of Wah Pedals". It will let you know exactly what each part of a conventional inductor-based wah does, and provide tons of ideas for tweaking. You will note that not a single mod is derived from transistor replacement.


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